copyright header updated to 2026

ast.go

@@ -1,130 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// ast.go
-package expr
-
-import (
-	"strings"
-)
-
-//-------- ast
-
-type ast struct {
-	forest []*term
-	root   *term
-}
-
-func NewAst() *ast {
-	return &ast{}
-}
-
-func (expr *ast) TypeName() string {
-	return "Expression"
-}
-
-func (expr *ast) ToForest() {
-	if expr.root != nil {
-		if expr.forest == nil {
-			expr.forest = make([]*term, 0)
-		}
-		expr.forest = append(expr.forest, expr.root)
-		expr.root = nil
-	}
-}
-
-func (expr *ast) String() string {
-	var sb strings.Builder
-	if expr.root == nil {
-		sb.WriteString("(nil)")
-	} else {
-		expr.root.toString(&sb)
-	}
-	return sb.String()
-}
-
-func (expr *ast) addTokens(tokens ...*Token) (err error) {
-	for _, tk := range tokens {
-		if _, err = expr.addToken(tk); err != nil {
-			break
-		}
-	}
-	return
-}
-
-// func (expr *ast) addToken(tk *Token) (err error) {
-// 	_, err = expr.addToken2(tk)
-// 	return
-// }
-
-func (expr *ast) addToken(tk *Token) (t *term, err error) {
-	if t = newTerm(tk); t != nil {
-		err = expr.addTerm(t)
-	} else {
-		err = tk.Errorf("unexpected token %q", tk.String())
-	}
-	return
-}
-
-func (expr *ast) addTerm(node *term) (err error) {
-	if expr.root == nil {
-		expr.root = node
-	} else {
-		expr.root, err = expr.insert(expr.root, node)
-	}
-	return
-}
-
-func (expr *ast) insert(tree, node *term) (root *term, err error) {
-	if tree.getPriority() < node.getPriority() {
-		root = tree
-		if tree.isComplete() {
-			var subRoot *term
-			last := tree.removeLastChild()
-			if subRoot, err = expr.insert(last, node); err == nil {
-				subRoot.setParent(tree)
-			}
-		} else {
-			node.setParent(tree)
-		}
-	} else if !node.isLeaf() {
-		root = node
-		tree.setParent(node)
-	} else {
-		err = node.Errorf("two adjacent operators: %q and %q", tree, node)
-	}
-	return
-}
-
-func (expr *ast) Finish() {
-	if expr.root == nil && expr.forest != nil && len(expr.forest) >= 1 {
-		expr.root = expr.forest[len(expr.forest)-1]
-		expr.forest = expr.forest[0 : len(expr.forest)-1]
-	}
-}
-
-func (expr *ast) Eval(ctx ExprContext) (result any, err error) {
-	expr.Finish()
-
-	if expr.root != nil {
-		// initDefaultVars(ctx)
-		if expr.forest != nil {
-			for _, root := range expr.forest {
-				if result, err = root.compute(ctx); err == nil {
-					ctx.UnsafeSetVar(ControlLastResult, result)
-				} else {
-					//err = fmt.Errorf("error in expression nr %d: %v", i+1, err)
-					break
-				}
-			}
-		}
-		if err == nil {
-			if result, err = expr.root.compute(ctx); err == nil {
-				ctx.UnsafeSetVar(ControlLastResult, result)
-			}
-		}
-		// } else {
-		// 	err = errors.New("empty expression")
-	}
-	return
-}

bind-expr-functions.go

@@ -1,23 +1,27 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // function.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
 // ---- Linking with Expr functions
 type exprFunctor struct {
-	baseFunctor
-	params []ExprFuncParam
-	expr   Expr
-	defCtx ExprContext
+	kern.BaseFunctor
+	params []kern.ExprFuncParam
+	expr   kern.Expr
+	defCtx kern.ExprContext
 }
 
-func (functor *exprFunctor) GetParams() (params []ExprFuncParam) {
+func (functor *exprFunctor) GetParams() (params []kern.ExprFuncParam) {
 	return functor.params
 }
 
-func newExprFunctor(e Expr, params []ExprFuncParam, ctx ExprContext) *exprFunctor {
-	var defCtx ExprContext
+func newExprFunctor(e kern.Expr, params []kern.ExprFuncParam, ctx kern.ExprContext) *exprFunctor {
+	var defCtx kern.ExprContext
 	if ctx != nil {
 		defCtx = ctx
 	}
@@ -28,17 +32,17 @@ func (functor *exprFunctor) TypeName() string {
 	return "ExprFunctor"
 }
 
-func (functor *exprFunctor) GetDefinitionContext() ExprContext {
+func (functor *exprFunctor) GetDefinitionContext() kern.ExprContext {
 	return functor.defCtx
 }
 
-func (functor *exprFunctor) InvokeNamed(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func (functor *exprFunctor) InvokeNamed(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var missing []string
 	for _, p := range functor.params {
 		if arg, exists := args[p.Name()]; exists {
-			if funcArg, ok := arg.(Functor); ok {
+			if funcArg, ok := arg.(kern.Functor); ok {
 				paramSpecs := funcArg.GetParams()
-				ctx.RegisterFunc(p.Name(), funcArg, TypeAny, paramSpecs)
+				ctx.RegisterFunc(p.Name(), funcArg, kern.TypeAny, paramSpecs)
 			} else {
 				ctx.UnsafeSetVar(p.Name(), arg)
 			}
@@ -51,7 +55,7 @@ func (functor *exprFunctor) InvokeNamed(ctx ExprContext, name string, args map[s
 		}
 	}
 	if missing != nil {
-		err = ErrMissingParams(name, missing)
+		err = kern.ErrMissingParams(name, missing)
 	} else {
 		result, err = functor.expr.Eval(ctx)
 	}

bind-go-functions.go

@@ -1,23 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// bind-go-function.go
-package expr
-
-// ---- Linking with Go functions
-type golangFunctor struct {
-	baseFunctor
-	f FuncTemplate
-}
-
-func NewGolangFunctor(f FuncTemplate) *golangFunctor {
-	return &golangFunctor{f: f}
-}
-
-func (functor *golangFunctor) TypeName() string {
-	return "GoFunctor"
-}
-
-func (functor *golangFunctor) InvokeNamed(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	return functor.f(ctx, name, args)
-}

builtin-base.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-base.go
@@ -9,81 +9,84 @@ import (
 	"math"
 	"strconv"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 const (
 	ParamDenominator = "denominator"
 )
 
-func isNilFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = args[ParamValue] == nil
+func isNilFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = args[kern.ParamValue] == nil
 	return
 }
 
-func isIntFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsInteger(args[ParamValue])
+func isIntFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsInteger(args[kern.ParamValue])
 	return
 }
 
-func isFloatFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsFloat(args[ParamValue])
+func isFloatFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsFloat(args[kern.ParamValue])
 	return
 }
 
-func isBoolFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsBool(args[ParamValue])
+func isBoolFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsBool(args[kern.ParamValue])
 	return
 }
 
-func isStringFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsString(args[ParamValue])
+func isStringFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsString(args[kern.ParamValue])
 	return
 }
 
-func isFractionFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsFract(args[ParamValue])
+func isFractionFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsFraction(args[kern.ParamValue])
 	return
 }
 
-func isRationalFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsRational(args[ParamValue])
+func isRationalFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsRational(args[kern.ParamValue])
 	return
 }
 
-func isListFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsList(args[ParamValue])
+func isListFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsList(args[kern.ParamValue])
 	return
 }
 
-func isDictionaryFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	result = IsDict(args[ParamValue])
+func isDictionaryFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsDict(args[kern.ParamValue])
 	return
 }
 
-func boolFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	switch v := args[ParamValue].(type) {
+func boolFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = (v != 0)
-	case *FractionType:
-		result = v.num != 0
+	case *kern.FractionType:
+		result = v.N() != 0
 	case float64:
 		result = v != 0.0
 	case bool:
 		result = v
 	case string:
 		result = len(v) > 0
-	case *ListType:
+	case *kern.ListType:
 		result = len(*v) > 0
-	case *DictType:
+	case *kern.DictType:
 		result = len(*v) > 0
 	default:
-		err = ErrCantConvert(name, v, "bool")
+		err = kern.ErrCantConvert(name, v, "bool")
 	}
 	return
 }
 
-func intFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	switch v := args[ParamValue].(type) {
+func intFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = v
 	case float64:
@@ -99,16 +102,16 @@ func intFunc(ctx ExprContext, name string, args map[string]any) (result any, err
 		if i, err = strconv.Atoi(v); err == nil {
 			result = int64(i)
 		}
-	case *FractionType:
-		result = int64(v.num / v.den)
+	case *kern.FractionType:
+		result = int64(v.N() / v.D())
 	default:
-		err = ErrCantConvert(name, v, "int")
+		err = kern.ErrCantConvert(name, v, "int")
 	}
 	return
 }
 
-func decFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	switch v := args[ParamValue].(type) {
+func decFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = float64(v)
 	case float64:
@@ -124,16 +127,16 @@ func decFunc(ctx ExprContext, name string, args map[string]any) (result any, err
 		if f, err = strconv.ParseFloat(v, 64); err == nil {
 			result = f
 		}
-	case *FractionType:
-		result = v.toFloat()
+	case *kern.FractionType:
+		result = v.ToFloat()
 	default:
-		err = ErrCantConvert(name, v, "float")
+		err = kern.ErrCantConvert(name, v, "float")
 	}
 	return
 }
 
-func stringFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	switch v := args[ParamValue].(type) {
+func stringFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = strconv.FormatInt(v, 10)
 	case float64:
@@ -146,169 +149,169 @@ func stringFunc(ctx ExprContext, name string, args map[string]any) (result any,
 		}
 	case string:
 		result = v
-	case *FractionType:
+	case *kern.FractionType:
 		result = v.ToString(0)
-	case Formatter:
+	case kern.Formatter:
 		result = v.ToString(0)
 	case fmt.Stringer:
 		result = v.String()
 	default:
-		err = ErrCantConvert(name, v, "string")
+		err = kern.ErrCantConvert(name, v, "string")
 	}
 	return
 }
 
-func fractFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	switch v := args[ParamValue].(type) {
+func fractFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		var den int64 = 1
 
 		var ok bool
 		if den, ok = args[ParamDenominator].(int64); !ok {
-			err = ErrExpectedGot(name, "integer", args[ParamDenominator])
+			err = kern.ErrExpectedGot(name, "integer", args[ParamDenominator])
 		} else if den == 0 {
-			err = ErrFuncDivisionByZero(name)
+			err = kern.ErrFuncDivisionByZero(name)
 		}
 
 		if err == nil {
-			result = newFraction(v, den)
+			result = kern.NewFraction(v, den)
 		}
 	case float64:
-		result, err = float64ToFraction(v)
+		result, err = kern.Float64ToFraction(v)
 	case bool:
 		if v {
-			result = newFraction(1, 1)
+			result = kern.NewFraction(1, 1)
 		} else {
-			result = newFraction(0, 1)
+			result = kern.NewFraction(0, 1)
 		}
 	case string:
-		result, err = makeGeneratingFraction(v)
-	case *FractionType:
+		result, err = kern.MakeGeneratingFraction(v)
+	case *kern.FractionType:
 		result = v
 	default:
-		err = ErrCantConvert(name, v, "float")
+		err = kern.ErrCantConvert(name, v, "float")
 	}
 	return
 }
 
-// func iteratorFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+// func iteratorFunc(ctx expr.ExprContext, name string, args []any) (result any, err error) {
 // 	return
 // }
 
-func evalFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	if source, ok := args[ParamSource].(string); ok {
-		var expr Expr
+func evalFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if source, ok := args[kern.ParamSource].(string); ok {
+		var ast kern.Expr
 
 		parser := NewParser()
 		if ctx == nil {
-			ctx = NewSimpleStore()
+			ctx = NewSimpleStoreWithoutGlobalContext()
 		}
 
 		r := strings.NewReader(source)
-		scanner := NewScanner(r, DefaultTranslations())
+		scanner := scan.NewScanner(r, scan.DefaultTranslations())
 
-		if expr, err = parser.Parse(scanner); err == nil {
-			CtrlEnable(ctx, control_export_all)
-			result, err = expr.Eval(ctx)
+		if ast, err = parser.Parse(scanner); err == nil {
+			CtrlEnable(ctx, kern.ControlExportAll)
+			result, err = ast.Eval(ctx)
 		}
 	} else {
-		err = ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+		err = kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 	return
 }
 
-func varFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func varFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var varName string
 	var ok bool
 
-	if varName, ok = args[ParamName].(string); !ok {
-		return nil, ErrWrongParamType(name, ParamName, TypeString, args[ParamName])
+	if varName, ok = args[kern.ParamName].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
 	}
 
-	if result, ok = args[ParamValue]; ok && result != nil {
+	if result, ok = args[kern.ParamValue]; ok && result != nil {
 		ctx.GetParent().UnsafeSetVar(varName, result)
 		// } else {
-		// 	err = ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+		// 	err = expr.ErrWrongParamType(name, expr.ParamSource, expr.TypeString, args[expr.ParamSource])
 		// }
 	} else if result, ok = ctx.GetVar(varName); !ok {
-		err = ErrUnknownVar(name, varName)
+		err = kern.ErrUnknownVar(name, varName)
 	}
 	return
 }
 
-func setFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func setFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var varName string
 	var ok bool
 
-	if varName, ok = args[ParamName].(string); !ok {
-		return nil, ErrWrongParamType(name, ParamName, TypeString, args[ParamName])
+	if varName, ok = args[kern.ParamName].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
 	}
 
-	if result, ok = args[ParamValue]; ok {
+	if result, ok = args[kern.ParamValue]; ok {
 		ctx.GetParent().UnsafeSetVar(varName, result)
 	} else {
-		err = ErrWrongParamType(name, ParamValue, TypeAny, args[ParamValue])
+		err = kern.ErrWrongParamType(name, kern.ParamValue, kern.TypeAny, args[kern.ParamValue])
 	}
 	return
 }
 
-func unsetFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	var varName string
-	var ok bool
+// func unsetFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+// 	var varName string
+// 	var ok bool
 
-	if varName, ok = args[ParamName].(string); !ok {
-		return nil, ErrWrongParamType(name, ParamName, TypeString, args[ParamName])
-	} else {
-		ctx.GetParent().DeleteVar(varName)
-		result = nil
-	}
-	return
-}
+// 	if varName, ok = args[kern.ParamName].(string); !ok {
+// 		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
+// 	} else {
+// 		ctx.GetParent().DeleteVar(varName)
+// 		result = nil
+// 	}
+// 	return
+// }
 
 //// import
 
-func ImportBuiltinsFuncs(ctx ExprContext) {
-	anyParams := []ExprFuncParam{
-		NewFuncParam(ParamValue),
+func ImportBuiltinsFuncs(ctx kern.ExprContext) {
+	anyParams := []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamValue),
 	}
 
-	ctx.RegisterFunc("isNil", NewGolangFunctor(isNilFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isInt", NewGolangFunctor(isIntFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isFloat", NewGolangFunctor(isFloatFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isBool", NewGolangFunctor(isBoolFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isString", NewGolangFunctor(isStringFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isFract", NewGolangFunctor(isFractionFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isRational", NewGolangFunctor(isRationalFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isList", NewGolangFunctor(isListFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("isDict", NewGolangFunctor(isDictionaryFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isNil", kern.NewGolangFunctor(isNilFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isInt", kern.NewGolangFunctor(isIntFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isFloat", kern.NewGolangFunctor(isFloatFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isBool", kern.NewGolangFunctor(isBoolFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isString", kern.NewGolangFunctor(isStringFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isFract", kern.NewGolangFunctor(isFractionFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isRational", kern.NewGolangFunctor(isRationalFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isList", kern.NewGolangFunctor(isListFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isDict", kern.NewGolangFunctor(isDictionaryFunc), kern.TypeBoolean, anyParams)
 
-	ctx.RegisterFunc("bool", NewGolangFunctor(boolFunc), TypeBoolean, anyParams)
-	ctx.RegisterFunc("int", NewGolangFunctor(intFunc), TypeInt, anyParams)
-	ctx.RegisterFunc("dec", NewGolangFunctor(decFunc), TypeFloat, anyParams)
-	ctx.RegisterFunc("string", NewGolangFunctor(stringFunc), TypeString, anyParams)
-	ctx.RegisterFunc("fract", NewGolangFunctor(fractFunc), TypeFraction, []ExprFuncParam{
-		NewFuncParam(ParamValue),
-		NewFuncParamFlagDef(ParamDenominator, PfDefault, int64(1)),
+	ctx.RegisterFunc("bool", kern.NewGolangFunctor(boolFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("int", kern.NewGolangFunctor(intFunc), kern.TypeInt, anyParams)
+	ctx.RegisterFunc("dec", kern.NewGolangFunctor(decFunc), kern.TypeFloat, anyParams)
+	ctx.RegisterFunc("string", kern.NewGolangFunctor(stringFunc), kern.TypeString, anyParams)
+	ctx.RegisterFunc("fract", kern.NewGolangFunctor(fractFunc), kern.TypeFraction, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamValue),
+		kern.NewFuncParamFlagDef(ParamDenominator, kern.PfDefault, int64(1)),
 	})
 
-	ctx.RegisterFunc("eval", NewGolangFunctor(evalFunc), TypeAny, []ExprFuncParam{
-		NewFuncParam(ParamSource),
+	ctx.RegisterFunc("eval", kern.NewGolangFunctor(evalFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
 	})
 
-	ctx.RegisterFunc("var", NewGolangFunctor(varFunc), TypeAny, []ExprFuncParam{
-		NewFuncParam(ParamName),
-		NewFuncParamFlagDef(ParamValue, PfDefault, nil),
+	ctx.RegisterFunc("var", kern.NewGolangFunctor(varFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamName),
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault, nil),
 	})
 
-	ctx.RegisterFunc("set", NewGolangFunctor(setFunc), TypeAny, []ExprFuncParam{
-		NewFuncParam(ParamName),
-		NewFuncParam(ParamValue),
+	ctx.RegisterFunc("set", kern.NewGolangFunctor(setFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamName),
+		kern.NewFuncParam(kern.ParamValue),
 	})
 
-	ctx.RegisterFunc("unset", NewGolangFunctor(unsetFunc), TypeAny, []ExprFuncParam{
-		NewFuncParam(ParamName),
-		NewFuncParam(ParamValue),
-	})
+	// ctx.RegisterFunc("unset", kern.NewGolangFunctor(unsetFunc), kern.TypeAny, []kern.ExprFuncParam{
+	// 	kern.NewFuncParam(kern.ParamName),
+	// 	kern.NewFuncParam(kern.ParamValue),
+	// })
 }
 
 func init() {

builtin-fmt.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-fmt.go
@@ -8,11 +8,13 @@ import (
 	"fmt"
 	"io"
 	"os"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
-func getStdout(ctx ExprContext) io.Writer {
+func getStdout(ctx kern.ExprContext) io.Writer {
 	var w io.Writer
-	if wany, exists := ctx.GetVar(ControlStdout); exists && wany != nil {
+	if wany, exists := ctx.GetVar(kern.ControlStdout); exists && wany != nil {
 		w, _ = wany.(io.Writer)
 	}
 	if w == nil {
@@ -21,9 +23,9 @@ func getStdout(ctx ExprContext) io.Writer {
 	return w
 }
 
-func printFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func printFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var n int = 0
-	if v, exists := args[ParamItem]; exists && v != nil {
+	if v, exists := args[kern.ParamItem]; exists && v != nil {
 		argv := v.([]any)
 		n, err = fmt.Fprint(getStdout(ctx), argv...)
 	}
@@ -31,9 +33,9 @@ func printFunc(ctx ExprContext, name string, args map[string]any) (result any, e
 	return
 }
 
-func printLnFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func printLnFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var n int = 0
-	if v, exists := args[ParamItem]; exists && v != nil {
+	if v, exists := args[kern.ParamItem]; exists && v != nil {
 		argv := v.([]any)
 		n, err = fmt.Fprintln(getStdout(ctx), argv...)
 	} else {
@@ -43,12 +45,12 @@ func printLnFunc(ctx ExprContext, name string, args map[string]any) (result any,
 	return
 }
 
-func ImportFmtFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("print", NewGolangFunctor(printFunc), TypeInt, []ExprFuncParam{
-		NewFuncParamFlag(ParamItem, PfRepeat),
+func ImportFmtFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("print", kern.NewGolangFunctor(printFunc), kern.TypeInt, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
 	})
-	ctx.RegisterFunc("println", NewGolangFunctor(printLnFunc), TypeInt, []ExprFuncParam{
-		NewFuncParamFlag(ParamItem, PfRepeat),
+	ctx.RegisterFunc("println", kern.NewGolangFunctor(printLnFunc), kern.TypeInt, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
 	})
 }
 

builtin-import.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-import.go
@@ -7,32 +7,35 @@ package expr
 import (
 	"io"
 	"os"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
-func importFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func importFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	return importGeneral(ctx, name, args)
 }
 
-func importAllFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	CtrlEnable(ctx, control_export_all)
+func importAllFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	CtrlEnable(ctx, kern.ControlExportAll)
 	return importGeneral(ctx, name, args)
 }
 
-func importGeneral(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	dirList := buildSearchDirList("sources", ENV_EXPR_SOURCE_PATH)
-	if v, exists := args[ParamFilepath]; exists && v != nil {
+func importGeneral(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	dirList := buildSearchDirList(ctx, "sources", ENV_EXPR_SOURCE_PATH)
+	if v, exists := args[kern.ParamFilepath]; exists && v != nil {
 		argv := v.([]any)
 		result, err = doImport(ctx, name, dirList, NewArrayIterator(argv))
 	}
 	return
 }
 
-func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (result any, err error) {
+func doImport(ctx kern.ExprContext, name string, dirList []string, it kern.Iterator) (result any, err error) {
 	var v any
 	var sourceFilepath string
 
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if err = checkStringParamExpected(name, v, it.Index()); err != nil {
+		if err = checkStringParamExpected(name, v, int(it.Index())); err != nil {
 			break
 		}
 		if sourceFilepath, err = makeFilepath(v.(string), dirList); err != nil {
@@ -41,10 +44,10 @@ func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (resu
 		var file *os.File
 		if file, err = os.Open(sourceFilepath); err == nil {
 			defer file.Close()
-			var expr *ast
-			scanner := NewScanner(file, DefaultTranslations())
+			var expr *scan.Ast
+			scanner := scan.NewScanner(file, scan.DefaultTranslations())
 			parser := NewParser()
-			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, SymEos); err == nil {
+			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymEos); err == nil {
 				result, err = expr.Eval(ctx)
 			}
 			if err != nil {
@@ -64,12 +67,12 @@ func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (resu
 	return
 }
 
-func ImportImportFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("import", NewGolangFunctor(importFunc), TypeAny, []ExprFuncParam{
-		NewFuncParamFlag(ParamFilepath, PfRepeat),
+func ImportImportFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("import", kern.NewGolangFunctor(importFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamFilepath, kern.PfRepeat),
 	})
-	ctx.RegisterFunc("importAll", NewGolangFunctor(importAllFunc), TypeAny, []ExprFuncParam{
-		NewFuncParamFlag(ParamFilepath, PfRepeat),
+	ctx.RegisterFunc("importAll", kern.NewGolangFunctor(importAllFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamFilepath, kern.PfRepeat),
 	})
 }
 

builtin-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-iterator.go
@@ -7,6 +7,8 @@ package expr
 import (
 	"fmt"
 	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 const (
@@ -15,24 +17,24 @@ const (
 	iterVarStatus     = "status"
 )
 
-func parseRunArgs(localCtx ExprContext, args map[string]any) (it Iterator, op Functor, err error) {
+func parseRunArgs(localCtx kern.ExprContext, args map[string]any) (it kern.Iterator, op kern.Functor, err error) {
 	var ok bool
 
-	if it, ok = args[ParamIterator].(Iterator); !ok {
-		err = fmt.Errorf("paramter %q must be an iterator, passed %v [%s]", ParamIterator, args[ParamIterator], TypeName(args[ParamIterator]))
+	if it, ok = args[kern.ParamIterator].(kern.Iterator); !ok {
+		err = fmt.Errorf("paramter %q must be an iterator, passed %v [%s]", kern.ParamIterator, args[kern.ParamIterator], kern.TypeName(args[kern.ParamIterator]))
 		return
 	}
 
 	if args[iterParamOperator] != nil {
-		if op, ok = args[iterParamOperator].(Functor); !ok || op == nil {
-			err = fmt.Errorf("paramter %q must be a function, passed %v [%s]", iterParamOperator, args[iterParamOperator], TypeName(args[iterParamOperator]))
+		if op, ok = args[iterParamOperator].(kern.Functor); !ok || op == nil {
+			err = fmt.Errorf("paramter %q must be a function, passed %v [%s]", iterParamOperator, args[iterParamOperator], kern.TypeName(args[iterParamOperator]))
 			return
 		}
 	}
 
-	var vars *DictType
-	if vars, ok = args[iterParamVars].(*DictType); !ok && args[iterParamVars] != nil {
-		err = fmt.Errorf("paramter %q must be a dictionary, passed %v [%s]", iterParamVars, args[iterParamVars], TypeName(args[iterParamVars]))
+	var vars *kern.DictType
+	if vars, ok = args[iterParamVars].(*kern.DictType); !ok && args[iterParamVars] != nil {
+		err = fmt.Errorf("paramter %q must be a dictionary, passed %v [%s]", iterParamVars, args[iterParamVars], kern.TypeName(args[iterParamVars]))
 		return
 	}
 
@@ -48,10 +50,10 @@ func parseRunArgs(localCtx ExprContext, args map[string]any) (it Iterator, op Fu
 	return
 }
 
-func runFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	var it Iterator
+func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var it kern.Iterator
 	var ok bool
-	var op Functor
+	var op kern.Functor
 	var v any
 	// var usingDefaultOp = false
 	var params map[string]any
@@ -62,25 +64,16 @@ func runFunc(ctx ExprContext, name string, args map[string]any) (result any, err
 
 	if it, op, err = parseRunArgs(localCtx, args); err != nil {
 		return
-		// } else if op == nil {
-		// 	op = NewGolangFunctor(printLnFunc)
-		// 	usingDefaultOp = true
 	}
 
 	for item, err = it.Next(); err == nil; item, err = it.Next() {
-		// if usingDefaultOp {
-		// 	params = map[string]any{ParamItem: []any{item}}
-		// } else {
-		// params = map[string]any{ParamIndex: it.Index(), ParamItem: item}
-		// }
-
 		if op != nil {
-			params = map[string]any{ParamIndex: it.Index(), ParamItem: item}
+			params = map[string]any{kern.ParamIndex: it.Index(), kern.ParamItem: item}
 			if v, err = op.InvokeNamed(localCtx, iterParamOperator, params); err != nil {
 				break
 			} else {
 				var success bool
-				if success, ok = ToBool(v); !success || !ok {
+				if success, ok = kern.ToBool(v); !success || !ok {
 					break
 				}
 			}
@@ -99,11 +92,11 @@ func runFunc(ctx ExprContext, name string, args map[string]any) (result any, err
 	return
 }
 
-func ImportIterFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("run", NewGolangFunctor(runFunc), TypeAny, []ExprFuncParam{
-		NewFuncParam(ParamIterator),
-		NewFuncParamFlag(iterParamOperator, PfOptional),
-		NewFuncParamFlag(iterParamVars, PfOptional),
+func ImportIterFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("run", kern.NewGolangFunctor(runFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamIterator),
+		kern.NewFuncParamFlag(iterParamOperator, kern.PfOptional),
+		kern.NewFuncParamFlag(iterParamVars, kern.PfOptional),
 	})
 }
 

builtin-math-arith.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-math-arith.go
@@ -7,67 +7,69 @@ package expr
 import (
 	"fmt"
 	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 func checkNumberParamExpected(funcName string, paramValue any, paramPos, level, subPos int) (err error) {
-	if !(IsNumber(paramValue) || isFraction(paramValue)) /*|| isList(paramValue)*/ {
+	if !(kern.IsNumber(paramValue) || kern.IsFraction(paramValue)) /*|| isList(paramValue)*/ {
 		err = fmt.Errorf("%s(): param nr %d (%d in %d) has wrong type %T, number expected",
 			funcName, paramPos+1, subPos+1, level, paramValue)
 	}
 	return
 }
 
-func doAdd(ctx ExprContext, name string, it Iterator, count, level int) (result any, err error) {
+func doAdd(ctx kern.ExprContext, name string, it kern.Iterator, count, level int) (result any, err error) {
 	var sumAsFloat, sumAsFract bool
 	var floatSum float64 = 0.0
 	var intSum int64 = 0
-	var fractSum *FractionType
+	var fractSum *kern.FractionType
 	var v any
 
 	level++
 
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*ListType); ok {
+		if list, ok := v.(*kern.ListType); ok {
 			v = NewListIterator(list, nil)
 		}
-		if subIter, ok := v.(Iterator); ok {
+		if subIter, ok := v.(kern.Iterator); ok {
 			if v, err = doAdd(ctx, name, subIter, count, level); err != nil {
 				break
 			}
-			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(CleanName) {
-				if _, err = extIter.CallOperation(CleanName, nil); err != nil {
+			if extIter, ok := v.(kern.ExtIterator); ok && extIter.HasOperation(kern.CleanName) {
+				if _, err = extIter.CallOperation(kern.CleanName, nil); err != nil {
 					return
 				}
 			}
-		} else if err = checkNumberParamExpected(name, v, count, level, it.Index()); err != nil {
+		} else if err = checkNumberParamExpected(name, v, count, level, int(it.Index())); err != nil {
 			break
 		}
 		count++
 
 		if !sumAsFloat {
-			if IsFloat(v) {
+			if kern.IsFloat(v) {
 				sumAsFloat = true
 				if sumAsFract {
-					floatSum = fractSum.toFloat()
+					floatSum = fractSum.ToFloat()
 				} else {
 					floatSum = float64(intSum)
 				}
-			} else if !sumAsFract && isFraction(v) {
-				fractSum = newFraction(intSum, 1)
+			} else if !sumAsFract && kern.IsFraction(v) {
+				fractSum = kern.NewFraction(intSum, 1)
 				sumAsFract = true
 			}
 		}
 
 		if sumAsFloat {
-			floatSum += numAsFloat(v)
+			floatSum += kern.NumAsFloat(v)
 		} else if sumAsFract {
-			var item *FractionType
+			var item *kern.FractionType
 			var ok bool
-			if item, ok = v.(*FractionType); !ok {
+			if item, ok = v.(*kern.FractionType); !ok {
 				iv, _ := v.(int64)
-				item = newFraction(iv, 1)
+				item = kern.NewFraction(iv, 1)
 			}
-			fractSum = sumFract(fractSum, item)
+			fractSum = kern.SumFract(fractSum, item)
 		} else {
 			iv, _ := v.(int64)
 			intSum += iv
@@ -86,64 +88,64 @@ func doAdd(ctx ExprContext, name string, it Iterator, count, level int) (result
 	return
 }
 
-func addFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	argv := args[ParamValue].([]any)
+func addFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	argv := args[kern.ParamValue].([]any)
 	result, err = doAdd(ctx, name, NewArrayIterator(argv), 0, -1)
 	return
 }
 
-func doMul(ctx ExprContext, name string, it Iterator, count, level int) (result any, err error) {
+func doMul(ctx kern.ExprContext, name string, it kern.Iterator, count, level int) (result any, err error) {
 	var mulAsFloat, mulAsFract bool
 	var floatProd float64 = 1.0
 	var intProd int64 = 1
-	var fractProd *FractionType
+	var fractProd *kern.FractionType
 	var v any
 
 	level++
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*ListType); ok {
+		if list, ok := v.(*kern.ListType); ok {
 			v = NewListIterator(list, nil)
 		}
-		if subIter, ok := v.(Iterator); ok {
+		if subIter, ok := v.(kern.Iterator); ok {
 			if v, err = doMul(ctx, name, subIter, count, level); err != nil {
 				break
 			}
-			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(CleanName) {
-				if _, err = extIter.CallOperation(CleanName, nil); err != nil {
+			if extIter, ok := v.(kern.ExtIterator); ok && extIter.HasOperation(kern.CleanName) {
+				if _, err = extIter.CallOperation(kern.CleanName, nil); err != nil {
 					return
 				}
 			}
 		} else {
-			if err = checkNumberParamExpected(name, v, count, level, it.Index()); err != nil {
+			if err = checkNumberParamExpected(name, v, count, level, int(it.Index())); err != nil {
 				break
 			}
 		}
 		count++
 
 		if !mulAsFloat {
-			if IsFloat(v) {
+			if kern.IsFloat(v) {
 				mulAsFloat = true
 				if mulAsFract {
-					floatProd = fractProd.toFloat()
+					floatProd = fractProd.ToFloat()
 				} else {
 					floatProd = float64(intProd)
 				}
-			} else if !mulAsFract && isFraction(v) {
-				fractProd = newFraction(intProd, 1)
+			} else if !mulAsFract && kern.IsFraction(v) {
+				fractProd = kern.NewFraction(intProd, 1)
 				mulAsFract = true
 			}
 		}
 
 		if mulAsFloat {
-			floatProd *= numAsFloat(v)
+			floatProd *= kern.NumAsFloat(v)
 		} else if mulAsFract {
-			var item *FractionType
+			var item *kern.FractionType
 			var ok bool
-			if item, ok = v.(*FractionType); !ok {
+			if item, ok = v.(*kern.FractionType); !ok {
 				iv, _ := v.(int64)
-				item = newFraction(iv, 1)
+				item = kern.NewFraction(iv, 1)
 			}
-			fractProd = mulFract(fractProd, item)
+			fractProd = kern.MulFract(fractProd, item)
 		} else {
 			iv, _ := v.(int64)
 			intProd *= iv
@@ -162,19 +164,19 @@ func doMul(ctx ExprContext, name string, it Iterator, count, level int) (result
 	return
 }
 
-func mulFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	argv := args[ParamValue].([]any)
+func mulFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	argv := args[kern.ParamValue].([]any)
 	result, err = doMul(ctx, name, NewArrayIterator(argv), 0, -1)
 	return
 }
 
-func ImportMathFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("add", NewGolangFunctor(addFunc), TypeNumber, []ExprFuncParam{
-		NewFuncParamFlagDef(ParamValue, PfDefault|PfRepeat, int64(0)),
+func ImportMathFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("add", kern.NewGolangFunctor(addFunc), kern.TypeNumber, []kern.ExprFuncParam{
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, int64(0)),
 	})
 
-	ctx.RegisterFunc("mul", NewGolangFunctor(mulFunc), TypeNumber, []ExprFuncParam{
-		NewFuncParamFlagDef(ParamValue, PfDefault|PfRepeat, int64(1)),
+	ctx.RegisterFunc("mul", kern.NewGolangFunctor(mulFunc), kern.TypeNumber, []kern.ExprFuncParam{
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, int64(1)),
 	})
 }
 

builtin-os-file-iter.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-os-file.go
@@ -8,6 +8,8 @@ import (
 	"fmt"
 	"io"
 	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 const paramHandleOrPath = "handle-or-path"
@@ -15,8 +17,8 @@ const fileReadTextIteratorType = "fileReadTextIterator"
 
 type fileReadTextIterator struct {
 	osReader  *osReader
-	index     int
-	count     int
+	index     int64
+	count     int64
 	line      string
 	autoClose bool
 }
@@ -36,7 +38,7 @@ func (it *fileReadTextIterator) String() string {
 	return fmt.Sprintf("$(%s@<nil>)", fileReadTextIteratorType)
 }
 
-func (it *fileReadTextIterator) Count() int {
+func (it *fileReadTextIterator) Count() int64 {
 	return it.count
 }
 
@@ -60,7 +62,7 @@ func (it *fileReadTextIterator) Current() (item any, err error) {
 	return
 }
 
-func (it *fileReadTextIterator) Index() int {
+func (it *fileReadTextIterator) Index() int64 {
 	return it.index
 }
 
@@ -74,7 +76,7 @@ func (it *fileReadTextIterator) Reset() (err error) {
 }
 
 func (it *fileReadTextIterator) HasOperation(name string) bool {
-	return slices.Contains([]string{NextName, ResetName, IndexName, CountName, CurrentName, CleanName}, name)
+	return slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName}, name)
 }
 
 func (it *fileReadTextIterator) Clean() (err error) {
@@ -88,25 +90,25 @@ func (it *fileReadTextIterator) Clean() (err error) {
 
 func (it *fileReadTextIterator) CallOperation(name string, args map[string]any) (v any, err error) {
 	switch name {
-	case NextName:
+	case kern.NextName:
 		v, err = it.Next()
-	case ResetName:
+	case kern.ResetName:
 		err = it.Reset()
-	case CleanName:
+	case kern.CleanName:
 		err = it.Clean()
-	case IndexName:
+	case kern.IndexName:
 		v = int64(it.Index())
-	case CurrentName:
+	case kern.CurrentName:
 		v, err = it.Current()
-	case CountName:
+	case kern.CountName:
 		v = it.count
 	default:
-		err = errNoOperation(name)
+		err = kern.ErrNoOperation(name)
 	}
 	return
 }
 
-func fileReadIteratorFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func fileReadIteratorFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var handle *osReader
 	var invalidFileHandle any
 	var ok, autoClose bool
@@ -115,7 +117,7 @@ func fileReadIteratorFunc(ctx ExprContext, name string, args map[string]any) (re
 	if handle, ok = args[paramHandleOrPath].(*osReader); !ok {
 		if fileName, ok := args[paramHandleOrPath].(string); ok && len(fileName) > 0 {
 			var handleAny any
-			if handleAny, err = openFileFunc(ctx, name, map[string]any{ParamFilepath: fileName}); err != nil {
+			if handleAny, err = openFileFunc(ctx, name, map[string]any{kern.ParamFilepath: fileName}); err != nil {
 				return
 			}
 			if handleAny != nil {

builtin-os-file.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-os-file.go
@@ -9,6 +9,8 @@ import (
 	"fmt"
 	"io"
 	"os"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 const (
@@ -65,8 +67,8 @@ func errInvalidFileHandle(funcName string, v any) error {
 	}
 }
 
-func createFileFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	if filePath, ok := args[ParamFilepath].(string); ok && len(filePath) > 0 {
+func createFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if filePath, ok := args[kern.ParamFilepath].(string); ok && len(filePath) > 0 {
 		var fh *os.File
 		if fh, err = os.Create(filePath); err == nil {
 			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
@@ -77,8 +79,8 @@ func createFileFunc(ctx ExprContext, name string, args map[string]any) (result a
 	return
 }
 
-func openFileFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	if filePath, ok := args[ParamFilepath].(string); ok && len(filePath) > 0 {
+func openFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if filePath, ok := args[kern.ParamFilepath].(string); ok && len(filePath) > 0 {
 		var fh *os.File
 		if fh, err = os.Open(filePath); err == nil {
 			result = &osReader{fh: fh, reader: bufio.NewReader(fh)}
@@ -89,8 +91,8 @@ func openFileFunc(ctx ExprContext, name string, args map[string]any) (result any
 	return
 }
 
-func appendFileFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	if filePath, ok := args[ParamFilepath].(string); ok && len(filePath) > 0 {
+func appendFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if filePath, ok := args[kern.ParamFilepath].(string); ok && len(filePath) > 0 {
 		var fh *os.File
 		if fh, err = os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0660); err == nil {
 			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
@@ -101,13 +103,13 @@ func appendFileFunc(ctx ExprContext, name string, args map[string]any) (result a
 	return
 }
 
-func closeFileFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func closeFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var handle osHandle
 	var invalidFileHandle any
 	var ok bool
 
-	if handle, ok = args[ParamHandle].(osHandle); !ok {
-		invalidFileHandle = args[ParamHandle]
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok {
+		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
@@ -128,18 +130,18 @@ func closeFileFunc(ctx ExprContext, name string, args map[string]any) (result an
 	return
 }
 
-func fileWriteTextFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func fileWriteTextFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var handle osHandle
 	var invalidFileHandle any
 	var ok bool
 
-	if handle, ok = args[ParamHandle].(osHandle); !ok {
-		invalidFileHandle = args[ParamHandle]
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok {
+		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
 		if w, ok := handle.(*osWriter); ok {
-			if v, exists := args[ParamItem]; exists {
+			if v, exists := args[kern.ParamItem]; exists {
 				argv := v.([]any)
 				result, err = fmt.Fprint(w.writer, argv...)
 			}
@@ -154,14 +156,14 @@ func fileWriteTextFunc(ctx ExprContext, name string, args map[string]any) (resul
 	return
 }
 
-func fileReadTextFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func fileReadTextFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var handle osHandle
 	var invalidFileHandle any
 	var ok bool
 
 	result = nil
-	if handle, ok = args[ParamHandle].(osHandle); !ok || args[ParamHandle] == nil {
-		invalidFileHandle = args[ParamHandle]
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok || args[kern.ParamHandle] == nil {
+		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
@@ -194,14 +196,14 @@ func fileReadTextFunc(ctx ExprContext, name string, args map[string]any) (result
 	return
 }
 
-func fileReadTextAllFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func fileReadTextAllFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var handle osHandle
 	var invalidFileHandle any
 	var ok bool
 
 	result = nil
-	if handle, ok = args[ParamHandle].(osHandle); !ok || args[ParamHandle] == nil {
-		invalidFileHandle = args[ParamHandle]
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok || args[kern.ParamHandle] == nil {
+		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
@@ -220,39 +222,39 @@ func fileReadTextAllFunc(ctx ExprContext, name string, args map[string]any) (res
 	return
 }
 
-func ImportOsFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("fileOpen", NewGolangFunctor(openFileFunc), TypeFileHandle, []ExprFuncParam{
-		NewFuncParam(ParamFilepath),
+func ImportOsFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("fileOpen", kern.NewGolangFunctor(openFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamFilepath),
 	})
 
-	ctx.RegisterFunc("fileAppend", NewGolangFunctor(appendFileFunc), TypeFileHandle, []ExprFuncParam{
-		NewFuncParam(ParamFilepath),
+	ctx.RegisterFunc("fileAppend", kern.NewGolangFunctor(appendFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamFilepath),
 	})
 
-	ctx.RegisterFunc("fileCreate", NewGolangFunctor(createFileFunc), TypeFileHandle, []ExprFuncParam{
-		NewFuncParam(ParamFilepath),
+	ctx.RegisterFunc("fileCreate", kern.NewGolangFunctor(createFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamFilepath),
 	})
 
-	ctx.RegisterFunc("fileClose", NewGolangFunctor(closeFileFunc), TypeBoolean, []ExprFuncParam{
-		NewFuncParam(ParamHandle),
+	ctx.RegisterFunc("fileClose", kern.NewGolangFunctor(closeFileFunc), kern.TypeBoolean, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamHandle),
 	})
 
-	ctx.RegisterFunc("fileWriteText", NewGolangFunctor(fileWriteTextFunc), TypeInt, []ExprFuncParam{
-		NewFuncParam(ParamHandle),
-		NewFuncParamFlagDef(ParamItem, PfDefault|PfRepeat, ""),
+	ctx.RegisterFunc("fileWriteText", kern.NewGolangFunctor(fileWriteTextFunc), kern.TypeInt, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParamFlagDef(kern.ParamItem, kern.PfDefault|kern.PfRepeat, ""),
 	})
 
-	ctx.RegisterFunc("fileReadText", NewGolangFunctor(fileReadTextFunc), TypeString, []ExprFuncParam{
-		NewFuncParam(ParamHandle),
-		NewFuncParamFlagDef(osLimitCh, PfDefault, "\n"),
+	ctx.RegisterFunc("fileReadText", kern.NewGolangFunctor(fileReadTextFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParamFlagDef(osLimitCh, kern.PfDefault, "\n"),
 	})
 
-	ctx.RegisterFunc("fileReadTextAll", NewGolangFunctor(fileReadTextAllFunc), TypeString, []ExprFuncParam{
-		NewFuncParam(ParamHandle),
+	ctx.RegisterFunc("fileReadTextAll", kern.NewGolangFunctor(fileReadTextAllFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamHandle),
 	})
 
-	ctx.RegisterFunc("fileReadIterator", NewGolangFunctor(fileReadIteratorFunc), TypeIterator, []ExprFuncParam{
-		NewFuncParam(paramHandleOrPath),
+	ctx.RegisterFunc("fileReadIterator", kern.NewGolangFunctor(fileReadIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
+		kern.NewFuncParam(paramHandleOrPath),
 	})
 }
 

builtin-string.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-string.go
@@ -8,6 +8,8 @@ import (
 	"fmt"
 	"io"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 const (
@@ -15,7 +17,7 @@ const (
 )
 
 // --- Start of function definitions
-func doJoinStr(funcName string, sep string, it Iterator) (result any, err error) {
+func doJoinStr(funcName string, sep string, it kern.Iterator) (result any, err error) {
 	var sb strings.Builder
 	var v any
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
@@ -25,7 +27,7 @@ func doJoinStr(funcName string, sep string, it Iterator) (result any, err error)
 		if s, ok := v.(string); ok {
 			sb.WriteString(s)
 		} else {
-			err = ErrExpectedGot(funcName, TypeString, v)
+			err = kern.ErrExpectedGot(funcName, kern.TypeString, v)
 			return
 		}
 	}
@@ -36,45 +38,45 @@ func doJoinStr(funcName string, sep string, it Iterator) (result any, err error)
 	return
 }
 
-func joinStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	if sep, ok := args[ParamSeparator].(string); ok {
-		if v, exists := args[ParamItem]; exists {
+func joinStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if sep, ok := args[kern.ParamSeparator].(string); ok {
+		if v, exists := args[kern.ParamItem]; exists {
 			argv := v.([]any)
 			if len(argv) == 1 {
-				if ls, ok := argv[0].(*ListType); ok {
+				if ls, ok := argv[0].(*kern.ListType); ok {
 					result, err = doJoinStr(name, sep, NewListIterator(ls, nil))
-				} else if it, ok := argv[0].(Iterator); ok {
+				} else if it, ok := argv[0].(kern.Iterator); ok {
 					result, err = doJoinStr(name, sep, it)
 				} else if s, ok := argv[0].(string); ok {
 					result = s
 				} else {
-					err = ErrInvalidParameterValue(name, ParamItem, v)
+					err = kern.ErrInvalidParameterValue(name, kern.ParamItem, v)
 				}
 			} else {
 				result, err = doJoinStr(name, sep, NewArrayIterator(argv))
 			}
 		}
 	} else {
-		err = ErrWrongParamType(name, ParamSeparator, TypeString, args[ParamSeparator])
+		err = kern.ErrWrongParamType(name, kern.ParamSeparator, kern.TypeString, args[kern.ParamSeparator])
 	}
 	return
 }
 
-func subStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func subStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var start = 0
 	var count = -1
 	var source string
 	var ok bool
 
-	if source, ok = args[ParamSource].(string); !ok {
-		return nil, ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+	if source, ok = args[kern.ParamSource].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 
-	if start, err = ToGoInt(args[ParamStart], name+"()"); err != nil {
+	if start, err = kern.ToGoInt(args[kern.ParamStart], name+"()"); err != nil {
 		return
 	}
 
-	if count, err = ToGoInt(args[ParamCount], name+"()"); err != nil {
+	if count, err = kern.ToGoInt(args[kern.ParamCount], name+"()"); err != nil {
 		return
 	}
 
@@ -90,29 +92,29 @@ func subStrFunc(ctx ExprContext, name string, args map[string]any) (result any,
 	return
 }
 
-func trimStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func trimStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var source string
 	var ok bool
 
-	if source, ok = args[ParamSource].(string); !ok {
-		return nil, ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+	if source, ok = args[kern.ParamSource].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 	result = strings.TrimSpace(source)
 	return
 }
 
-func startsWithStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func startsWithStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var source, prefix string
 	var ok bool
 
 	result = false
 
-	if source, ok = args[ParamSource].(string); !ok {
-		return result, ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+	if source, ok = args[kern.ParamSource].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 
-	if prefix, ok = args[ParamPrefix].(string); !ok {
-		return result, ErrWrongParamType(name, ParamPrefix, TypeString, args[ParamPrefix])
+	if prefix, ok = args[kern.ParamPrefix].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamPrefix, kern.TypeString, args[kern.ParamPrefix])
 	}
 	if strings.HasPrefix(source, prefix) {
 		result = true
@@ -125,7 +127,7 @@ func startsWithStrFunc(ctx ExprContext, name string, args map[string]any) (resul
 					break
 				}
 			} else {
-				err = fmt.Errorf("target item nr %d is %s, string expected", i+1, TypeName(targetSpec))
+				err = fmt.Errorf("target item nr %d is %s, string expected", i+1, kern.TypeName(targetSpec))
 				break
 			}
 		}
@@ -133,18 +135,18 @@ func startsWithStrFunc(ctx ExprContext, name string, args map[string]any) (resul
 	return
 }
 
-func endsWithStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func endsWithStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var source, suffix string
 	var ok bool
 
 	result = false
 
-	if source, ok = args[ParamSource].(string); !ok {
-		return result, ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+	if source, ok = args[kern.ParamSource].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 
-	if suffix, ok = args[ParamSuffix].(string); !ok {
-		return result, ErrWrongParamType(name, ParamSuffix, TypeString, args[ParamSuffix])
+	if suffix, ok = args[kern.ParamSuffix].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamSuffix, kern.TypeString, args[kern.ParamSuffix])
 	}
 	if strings.HasPrefix(source, suffix) {
 		result = true
@@ -157,7 +159,7 @@ func endsWithStrFunc(ctx ExprContext, name string, args map[string]any) (result
 					break
 				}
 			} else {
-				err = fmt.Errorf("target item nr %d is %s, string expected", i+1, TypeName(targetSpec))
+				err = fmt.Errorf("target item nr %d is %s, string expected", i+1, kern.TypeName(targetSpec))
 				break
 			}
 		}
@@ -165,24 +167,24 @@ func endsWithStrFunc(ctx ExprContext, name string, args map[string]any) (result
 	return
 }
 
-func splitStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+func splitStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var source, sep string
 	var count int = -1
 	var parts []string
 	var ok bool
 
-	if source, ok = args[ParamSource].(string); !ok {
-		return result, ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+	if source, ok = args[kern.ParamSource].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 
-	if sep, ok = args[ParamSeparator].(string); !ok {
-		return nil, fmt.Errorf("separator param must be string, got %s (%v)", TypeName(args[ParamSeparator]), args[ParamSeparator])
+	if sep, ok = args[kern.ParamSeparator].(string); !ok {
+		return nil, fmt.Errorf("separator param must be string, got %s (%v)", kern.TypeName(args[kern.ParamSeparator]), args[kern.ParamSeparator])
 	}
 
-	if count64, ok := args[ParamCount].(int64); ok { // TODO replace type assertion with toInt()
+	if count64, ok := args[kern.ParamCount].(int64); ok { // TODO replace type assertion with toInt()
 		count = int(count64)
 	} else {
-		return nil, fmt.Errorf("part count must be integer, got %s (%v)", TypeName(args[ParamCount]), args[ParamCount])
+		return nil, fmt.Errorf("part count must be integer, got %s (%v)", kern.TypeName(args[kern.ParamCount]), args[kern.ParamCount])
 	}
 
 	if count > 0 {
@@ -192,7 +194,7 @@ func splitStrFunc(ctx ExprContext, name string, args map[string]any) (result any
 	} else {
 		parts = []string{}
 	}
-	list := make(ListType, len(parts))
+	list := make(kern.ListType, len(parts))
 	for i, part := range parts {
 		list[i] = part
 	}
@@ -200,20 +202,20 @@ func splitStrFunc(ctx ExprContext, name string, args map[string]any) (result any
 	return
 }
 
-func upperStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	if source, ok := args[ParamSource].(string); ok {
+func upperStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if source, ok := args[kern.ParamSource].(string); ok {
 		result = strings.ToUpper(source)
 	} else {
-		err = ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+		err = kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 	return
 }
 
-func lowerStrFunc(ctx ExprContext, name string, args map[string]any) (result any, err error) {
-	if source, ok := args[ParamSource].(string); ok {
+func lowerStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if source, ok := args[kern.ParamSource].(string); ok {
 		result = strings.ToLower(source)
 	} else {
-		err = ErrWrongParamType(name, ParamSource, TypeString, args[ParamSource])
+		err = kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 	return
 }
@@ -221,46 +223,46 @@ func lowerStrFunc(ctx ExprContext, name string, args map[string]any) (result any
 // --- End of function definitions
 
 // Import above functions in the context
-func ImportStringFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("strJoin", NewGolangFunctor(joinStrFunc), TypeString, []ExprFuncParam{
-		NewFuncParam(ParamSeparator),
-		NewFuncParamFlag(ParamItem, PfRepeat),
+func ImportStringFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("strJoin", kern.NewGolangFunctor(joinStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSeparator),
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
 	})
 
-	ctx.RegisterFunc("strSub", NewGolangFunctor(subStrFunc), TypeString, []ExprFuncParam{
-		NewFuncParam(ParamSource),
-		NewFuncParamFlagDef(ParamStart, PfDefault, int64(0)),
-		NewFuncParamFlagDef(ParamCount, PfDefault, int64(-1)),
+	ctx.RegisterFunc("strSub", kern.NewGolangFunctor(subStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParamFlagDef(kern.ParamStart, kern.PfDefault, int64(0)),
+		kern.NewFuncParamFlagDef(kern.ParamCount, kern.PfDefault, int64(-1)),
 	})
 
-	ctx.RegisterFunc("strSplit", NewGolangFunctor(splitStrFunc), "list of "+TypeString, []ExprFuncParam{
-		NewFuncParam(ParamSource),
-		NewFuncParamFlagDef(ParamSeparator, PfDefault, ""),
-		NewFuncParamFlagDef(ParamCount, PfDefault, int64(-1)),
+	ctx.RegisterFunc("strSplit", kern.NewGolangFunctor(splitStrFunc), "list of "+kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParamFlagDef(kern.ParamSeparator, kern.PfDefault, ""),
+		kern.NewFuncParamFlagDef(kern.ParamCount, kern.PfDefault, int64(-1)),
 	})
 
-	ctx.RegisterFunc("strTrim", NewGolangFunctor(trimStrFunc), TypeString, []ExprFuncParam{
-		NewFuncParam(ParamSource),
+	ctx.RegisterFunc("strTrim", kern.NewGolangFunctor(trimStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
 	})
 
-	ctx.RegisterFunc("strStartsWith", NewGolangFunctor(startsWithStrFunc), TypeBoolean, []ExprFuncParam{
-		NewFuncParam(ParamSource),
-		NewFuncParam(ParamPrefix),
-		NewFuncParamFlag(strParamOther, PfRepeat),
+	ctx.RegisterFunc("strStartsWith", kern.NewGolangFunctor(startsWithStrFunc), kern.TypeBoolean, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamPrefix),
+		kern.NewFuncParamFlag(strParamOther, kern.PfRepeat),
 	})
 
-	ctx.RegisterFunc("strEndsWith", NewGolangFunctor(endsWithStrFunc), TypeBoolean, []ExprFuncParam{
-		NewFuncParam(ParamSource),
-		NewFuncParam(ParamSuffix),
-		NewFuncParamFlag(strParamOther, PfRepeat),
+	ctx.RegisterFunc("strEndsWith", kern.NewGolangFunctor(endsWithStrFunc), kern.TypeBoolean, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSuffix),
+		kern.NewFuncParamFlag(strParamOther, kern.PfRepeat),
 	})
 
-	ctx.RegisterFunc("strUpper", NewGolangFunctor(upperStrFunc), TypeString, []ExprFuncParam{
-		NewFuncParam(ParamSource),
+	ctx.RegisterFunc("strUpper", kern.NewGolangFunctor(upperStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
 	})
 
-	ctx.RegisterFunc("strLower", NewGolangFunctor(lowerStrFunc), TypeString, []ExprFuncParam{
-		NewFuncParam(ParamSource),
+	ctx.RegisterFunc("strLower", kern.NewGolangFunctor(lowerStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
 	})
 }
 

builtins-register.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtins-register.go
@@ -6,21 +6,23 @@ package expr
 
 import (
 	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 type builtinModule struct {
-	importFunc  func(ExprContext)
+	importFunc  func(kern.ExprContext)
 	description string
 	imported    bool
 }
 
-func newBuiltinModule(importFunc func(ExprContext), description string) *builtinModule {
+func newBuiltinModule(importFunc func(kern.ExprContext), description string) *builtinModule {
 	return &builtinModule{importFunc, description, false}
 }
 
 var builtinModuleRegister map[string]*builtinModule
 
-func RegisterBuiltinModule(name string, importFunc func(ExprContext), description string) {
+func RegisterBuiltinModule(name string, importFunc func(kern.ExprContext), description string) {
 	if builtinModuleRegister == nil {
 		builtinModuleRegister = make(map[string]*builtinModule)
 	}

data-cursor.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // data-cursors.go
@@ -7,24 +7,26 @@ package expr
 import (
 	"io"
 	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 type dataCursor struct {
-	ds        map[string]Functor
-	ctx       ExprContext
+	ds        map[string]kern.Functor
+	ctx       kern.ExprContext
 	initState bool // true if no item has produced yet (this replace di initial Next() call in the contructor)
 	// cursorValid bool // true if resource is nil or if clean has not yet been called
-	index     int
-	count     int
+	index     int64
+	count     int64
 	current   any
 	lastErr   error
 	resource  any
-	nextFunc  Functor
-	cleanFunc Functor
-	resetFunc Functor
+	nextFunc  kern.Functor
+	cleanFunc kern.Functor
+	resetFunc kern.Functor
 }
 
-func NewDataCursor(ctx ExprContext, ds map[string]Functor, resource any) (dc *dataCursor) {
+func NewDataCursor(ctx kern.ExprContext, ds map[string]kern.Functor, resource any) (dc *dataCursor) {
 	dc = &dataCursor{
 		ds:        ds,
 		initState: true,
@@ -35,14 +37,14 @@ func NewDataCursor(ctx ExprContext, ds map[string]Functor, resource any) (dc *da
 		lastErr:   nil,
 		resource:  resource,
 		ctx:       ctx.Clone(),
-		nextFunc:  ds[NextName],
-		cleanFunc: ds[CleanName],
-		resetFunc: ds[ResetName],
+		nextFunc:  ds[kern.NextName],
+		cleanFunc: ds[kern.CleanName],
+		resetFunc: ds[kern.ResetName],
 	}
 	return
 }
 
-func (dc *dataCursor) Context() ExprContext {
+func (dc *dataCursor) Context() kern.ExprContext {
 	return dc.ctx
 }
 
@@ -79,27 +81,27 @@ func (dc *dataCursor) String() string {
 }
 
 func (dc *dataCursor) HasOperation(name string) (exists bool) {
-	exists = slices.Contains([]string{CleanName, ResetName, CurrentName, IndexName}, name)
+	exists = slices.Contains([]string{kern.CleanName, kern.ResetName, kern.CurrentName, kern.IndexName}, name)
 	if !exists {
 		f, ok := dc.ds[name]
-		exists = ok && isFunctor(f)
+		exists = ok && kern.IsFunctor(f)
 	}
 	return
 }
 
 func (dc *dataCursor) CallOperation(name string, args map[string]any) (value any, err error) {
-	if name == IndexName {
+	if name == kern.IndexName {
 		value = int64(dc.Index())
-	} else if name == CleanName {
+	} else if name == kern.CleanName {
 		err = dc.Clean()
-	} else if name == ResetName {
+	} else if name == kern.ResetName {
 		err = dc.Reset()
-	} else if functor, ok := dc.ds[name]; ok && isFunctor(functor) {
-		ctx := cloneContext(dc.ctx)
+	} else if functor, ok := dc.ds[name]; ok && kern.IsFunctor(functor) {
+		ctx := kern.CloneContext(dc.ctx)
 		value, err = functor.InvokeNamed(ctx, name, args)
-		exportObjects(dc.ctx, ctx)
+		kern.ExportObjects(dc.ctx, ctx)
 	} else {
-		err = errNoOperation(name)
+		err = kern.ErrNoOperation(name)
 	}
 	return
 }
@@ -127,10 +129,10 @@ func (dc *dataCursor) CallOperation(name string, args map[string]any) (value any
 
 func (dc *dataCursor) Reset() (err error) {
 	if dc.resetFunc != nil {
-		ctx := cloneContext(dc.ctx)
-		actualParams := bindActualParams(dc.resetFunc, []any{dc.resource})
-		_, err = dc.resetFunc.InvokeNamed(ctx, ResetName, actualParams)
-		exportObjects(dc.ctx, ctx)
+		ctx := kern.CloneContext(dc.ctx)
+		actualParams := kern.BindActualParams(dc.resetFunc, []any{dc.resource})
+		_, err = dc.resetFunc.InvokeNamed(ctx, kern.ResetName, actualParams)
+		kern.ExportObjects(dc.ctx, ctx)
 	}
 	dc.index = -1
 	dc.count = 0
@@ -142,10 +144,10 @@ func (dc *dataCursor) Reset() (err error) {
 
 func (dc *dataCursor) Clean() (err error) {
 	if dc.cleanFunc != nil {
-		ctx := cloneContext(dc.ctx)
-		actualParams := bindActualParams(dc.cleanFunc, []any{dc.resource})
-		_, err = dc.cleanFunc.InvokeNamed(ctx, CleanName, actualParams)
-		exportObjects(dc.ctx, ctx)
+		ctx := kern.CloneContext(dc.ctx)
+		actualParams := kern.BindActualParams(dc.cleanFunc, []any{dc.resource})
+		_, err = dc.cleanFunc.InvokeNamed(ctx, kern.CleanName, actualParams)
+		kern.ExportObjects(dc.ctx, ctx)
 	}
 	dc.lastErr = io.EOF
 	return
@@ -178,13 +180,13 @@ func (dc *dataCursor) Current() (item any, err error) { // must return io.EOF at
 	return
 }
 
-func (dc *dataCursor) checkFilter(filter Functor, item any) (accepted bool, err error) {
+func (dc *dataCursor) checkFilter(filter kern.Functor, item any) (accepted bool, err error) {
 	var v any
 	var ok bool
-	ctx := cloneContext(dc.ctx)
+	ctx := kern.CloneContext(dc.ctx)
 
-	actualParams := bindActualParams(filter, []any{item, dc.index})
-	if v, err = filter.InvokeNamed(ctx, FilterName, actualParams); err == nil && v != nil {
+	actualParams := kern.BindActualParams(filter, []any{item, dc.index})
+	if v, err = filter.InvokeNamed(ctx, kern.FilterName, actualParams); err == nil && v != nil {
 		if accepted, ok = v.(bool); !ok {
 			accepted = true // NOTE: A non-boolean value that is not nil means the item has been accepted
 		}
@@ -192,10 +194,10 @@ func (dc *dataCursor) checkFilter(filter Functor, item any) (accepted bool, err
 	return
 }
 
-func (dc *dataCursor) mapItem(mapper Functor, item any) (mappedItem any, err error) {
-	ctx := cloneContext(dc.ctx)
-	actualParams := bindActualParams(mapper, []any{item, dc.index})
-	mappedItem, err = mapper.InvokeNamed(ctx, MapName, actualParams)
+func (dc *dataCursor) mapItem(mapper kern.Functor, item any) (mappedItem any, err error) {
+	ctx := kern.CloneContext(dc.ctx)
+	actualParams := kern.BindActualParams(mapper, []any{item, dc.index})
+	mappedItem, err = mapper.InvokeNamed(ctx, kern.MapName, actualParams)
 	return
 }
 
@@ -213,15 +215,15 @@ func (dc *dataCursor) Next() (current any, err error) { // must return io.EOF af
 		return
 	}
 	current = dc.current
-	filter := dc.ds[FilterName]
-	mapper := dc.ds[MapName]
+	filter := dc.ds[kern.FilterName]
+	mapper := dc.ds[kern.MapName]
 	var item any
 	for item == nil && dc.lastErr == nil {
-		ctx := cloneContext(dc.ctx)
+		ctx := kern.CloneContext(dc.ctx)
 		dc.index++
 
-		actualParams := bindActualParams(dc.nextFunc, []any{dc.resource, dc.index})
-		if item, dc.lastErr = dc.nextFunc.InvokeNamed(ctx, NextName, actualParams); dc.lastErr == nil {
+		actualParams := kern.BindActualParams(dc.nextFunc, []any{dc.resource, dc.index})
+		if item, dc.lastErr = dc.nextFunc.InvokeNamed(ctx, kern.NextName, actualParams); dc.lastErr == nil {
 			if item == nil {
 				dc.lastErr = io.EOF
 			} else {
@@ -239,7 +241,7 @@ func (dc *dataCursor) Next() (current any, err error) { // must return io.EOF af
 				}
 			}
 		}
-		exportObjects(dc.ctx, ctx)
+		kern.ExportObjects(dc.ctx, ctx)
 	}
 	dc.current = item
 	if dc.lastErr != nil {
@@ -296,10 +298,10 @@ func (dc *dataCursor) Next() (current any, err error) { // must return io.EOF af
 // 	return
 // }
 
-func (dc *dataCursor) Index() int {
+func (dc *dataCursor) Index() int64 {
 	return dc.index - 1
 }
 
-func (dc *dataCursor) Count() int {
+func (dc *dataCursor) Count() int64 {
 	return dc.count
 }

dict-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // dict-iterator.go
@@ -9,6 +9,8 @@ import (
 	"io"
 	"slices"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 type dictIterMode int
@@ -20,9 +22,9 @@ const (
 )
 
 type DictIterator struct {
-	a        *DictType
-	count    int
-	index    int
+	a        *kern.DictType
+	count    int64
+	index    int64
 	keys     []any
 	iterMode dictIterMode
 }
@@ -65,7 +67,7 @@ func (it *DictIterator) makeKeys(m map[any]any, sort sortType) {
 	}
 }
 
-func NewDictIterator(dict *DictType, args []any) (it *DictIterator, err error) {
+func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err error) {
 	var sortType = sortTypeNone
 	var s string
 	var argAny any
@@ -76,7 +78,7 @@ func NewDictIterator(dict *DictType, args []any) (it *DictIterator, err error) {
 	} else {
 		argAny = "default"
 	}
-	if s, err = ToGoString(argAny, "sort type"); err == nil {
+	if s, err = kern.ToGoString(argAny, "sort type"); err == nil {
 		switch strings.ToLower(s) {
 		case "a", "asc":
 			sortType = sortTypeAsc
@@ -97,7 +99,7 @@ func NewDictIterator(dict *DictType, args []any) (it *DictIterator, err error) {
 				argAny = "default"
 			}
 
-			if s, err = ToGoString(argAny, "iteration mode"); err == nil {
+			if s, err = kern.ToGoString(argAny, "iteration mode"); err == nil {
 				switch strings.ToLower(s) {
 				case "k", "key", "keys":
 					dictIt.iterMode = dictIterModeKeys
@@ -114,20 +116,23 @@ func NewDictIterator(dict *DictType, args []any) (it *DictIterator, err error) {
 		}
 	}
 
-	dictIt.makeKeys(*dict, sortType)
-	return dictIt, err
+	if err == nil {
+		dictIt.makeKeys(*dict, sortType)
+		it = dictIt
+	}
+	return
 }
 
 func NewMapIterator(m map[any]any) (it *DictIterator) {
-	it = &DictIterator{a: (*DictType)(&m), count: 0, index: -1, keys: nil}
+	it = &DictIterator{a: (*kern.DictType)(&m), count: 0, index: -1, keys: nil}
 	it.makeKeys(m, sortTypeNone)
 	return
 }
 
 func (it *DictIterator) String() string {
-	var l = 0
+	var l = int64(0)
 	if it.a != nil {
-		l = len(*it.a)
+		l = int64(len(*it.a))
 	}
 	return fmt.Sprintf("$({#%d})", l)
 }
@@ -137,46 +142,45 @@ func (it *DictIterator) TypeName() string {
 }
 
 func (it *DictIterator) HasOperation(name string) bool {
-	// yes := name == NextName || name == ResetName || name == IndexName || name == CountName || name == CurrentName
-	yes := slices.Contains([]string{NextName, ResetName, IndexName, CountName, CurrentName, CleanName, KeyName, ValueName}, name)
+	yes := slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName, kern.KeyName, kern.ValueName}, name)
 	return yes
 }
 
 func (it *DictIterator) CallOperation(name string, args map[string]any) (v any, err error) {
 	switch name {
-	case NextName:
+	case kern.NextName:
 		v, err = it.Next()
-	case ResetName:
+	case kern.ResetName:
 		err = it.Reset()
-	case CleanName:
+	case kern.CleanName:
 		err = it.Clean()
-	case IndexName:
+	case kern.IndexName:
 		v = int64(it.Index())
-	case CurrentName:
+	case kern.CurrentName:
 		v, err = it.Current()
-	case CountName:
+	case kern.CountName:
 		v = it.count
-	case KeyName:
-		if it.index >= 0 && it.index < len(it.keys) {
+	case kern.KeyName:
+		if it.index >= 0 && it.index < int64(len(it.keys)) {
 			v = it.keys[it.index]
 		} else {
 			err = io.EOF
 		}
-	case ValueName:
-		if it.index >= 0 && it.index < len(it.keys) {
+	case kern.ValueName:
+		if it.index >= 0 && it.index < int64(len(it.keys)) {
 			a := *(it.a)
 			v = a[it.keys[it.index]]
 		} else {
 			err = io.EOF
 		}
 	default:
-		err = errNoOperation(name)
+		err = kern.ErrNoOperation(name)
 	}
 	return
 }
 
 func (it *DictIterator) Current() (item any, err error) {
-	if it.index >= 0 && it.index < len(it.keys) {
+	if it.index >= 0 && it.index < int64(len(it.keys)) {
 		switch it.iterMode {
 		case dictIterModeKeys:
 			item = it.keys[it.index]
@@ -186,7 +190,7 @@ func (it *DictIterator) Current() (item any, err error) {
 		case dictIterModeItems:
 			a := *(it.a)
 			pair := []any{it.keys[it.index], a[it.keys[it.index]]}
-			item = newList(pair)
+			item = kern.NewList(pair)
 		}
 	} else {
 		err = io.EOF
@@ -202,11 +206,11 @@ func (it *DictIterator) Next() (item any, err error) {
 	return
 }
 
-func (it *DictIterator) Index() int {
+func (it *DictIterator) Index() int64 {
 	return it.index
 }
 
-func (it *DictIterator) Count() int {
+func (it *DictIterator) Count() int64 {
 	return it.count
 }
 

doc/Expr.adoc

@@ -1421,12 +1421,38 @@ Same as <<_add,add()>> but returns the product of the values of the parameters.
 [green]`24`
 
 ==== Module "os.file"
+The "os.file" module provides functions for working with files.
+
+Activation: +
+`{4sp}builtin "os.file"`
+
+Currently available functions:
+
+* <<_fileOpen,fileOpen()>>
+* <<_fileAppend,fileAppend()>>
+* <<_fileCreate,fileCreate()>>
+* <<_fileClose,fileClose()>>
+* <<_fileWriteText,fileWriteText()>>
+* <<_fileReadText,fileReadText()>>
+* <<_fileReadTextAll,fileReadTextAll()>>
+
+More functions will be added in the future.
+
+---
 
 ===== fileOpen()
+Syntax: +
+`{4sp}fileOpen(<file-path>) -> file-handle`
+
+Returns a file handle for the specified file path. The file is opened in read-write mode. If the file does not exist, it is created.
 
 ===== fileAppend()
 
 ===== fileCreate()
+Syntax: +
+`{4sp}fileCreate(<file-path>) -> file-handle`
+
+Creates or truncates the named _<file-path>_. If the file already exists, it is truncated. If the file does not exist, it is created with mode 0o666 (before umask). The associated file descriptor has mode [O_RDWR]. The directory containing the file must already exist.
 
 ===== fileClose()
 
@@ -1438,6 +1464,24 @@ Same as <<_add,add()>> but returns the product of the values of the parameters.
 
 
 ==== Module "string"
+This module provides functions for working with strings.
+
+Activation: +
+`{4sp}builtin "string"`
+
+
+Currently available functions:
+
+* <<_strJoin,strJoin()>>
+* <<_strSub,strSub()>>
+* <<_strSplit,strSplit()>>
+* <<_strTrim,strTrim()>>
+* <<_strStartsWith,strStartsWith()>>
+* <<_strEndsWith,strEndsWith()>>
+* <<_strUpper,strUpper()>>
+* <<_strLower,strLower()>>
+
+---
 
 ===== strJoin()
 Syntax: +

function.go

@@ -1,386 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// function.go
-package expr
-
-import (
-	"fmt"
-	"strconv"
-	"strings"
-)
-
-// ---- Function template
-type FuncTemplate func(ctx ExprContext, name string, args map[string]any) (result any, err error)
-
-// ---- Common functor definition
-type baseFunctor struct {
-	info ExprFunc
-}
-
-func (functor *baseFunctor) ToString(opt FmtOpt) (s string) {
-	if functor.info != nil {
-		s = functor.info.ToString(opt)
-	} else {
-		s = "func(){}"
-	}
-	return s
-}
-
-func (functor *baseFunctor) GetParams() (params []ExprFuncParam) {
-	if functor.info != nil {
-		return functor.info.Params()
-	} else {
-		return []ExprFuncParam{}
-	}
-}
-
-func (functor *baseFunctor) SetFunc(info ExprFunc) {
-	functor.info = info
-}
-
-func (functor *baseFunctor) GetFunc() ExprFunc {
-	return functor.info
-}
-
-func (functor *baseFunctor) GetDefinitionContext() ExprContext {
-	return nil
-}
-
-// ---- Function Parameters
-type paramFlags uint16
-
-const (
-	PfDefault paramFlags = 1 << iota
-	PfOptional
-	PfRepeat
-)
-
-type funcParamInfo struct {
-	name         string
-	flags        paramFlags
-	defaultValue any
-}
-
-func NewFuncParam(name string) ExprFuncParam {
-	return &funcParamInfo{name: name}
-}
-
-func NewFuncParamFlag(name string, flags paramFlags) ExprFuncParam {
-	return &funcParamInfo{name: name, flags: flags}
-}
-
-func NewFuncParamFlagDef(name string, flags paramFlags, defValue any) *funcParamInfo {
-	return &funcParamInfo{name: name, flags: flags, defaultValue: defValue}
-}
-
-func (param *funcParamInfo) Name() string {
-	return param.name
-}
-
-func (param *funcParamInfo) Type() string {
-	return TypeAny
-}
-
-func (param *funcParamInfo) IsDefault() bool {
-	return (param.flags & PfDefault) != 0
-}
-
-func (param *funcParamInfo) IsOptional() bool {
-	return (param.flags & PfOptional) != 0
-}
-
-func (param *funcParamInfo) IsRepeat() bool {
-	return (param.flags & PfRepeat) != 0
-}
-
-func (param *funcParamInfo) DefaultValue() any {
-	return param.defaultValue
-}
-
-// --- Functions
-
-// funcInfo implements ExprFunc
-type funcInfo struct {
-	name         string
-	minArgs      int
-	maxArgs      int
-	functor      Functor
-	formalParams []ExprFuncParam
-	returnType   string
-}
-
-func newFuncInfo(name string, functor Functor, returnType string, params []ExprFuncParam) (info *funcInfo, err error) {
-	var minArgs = 0
-	var maxArgs = 0
-	for _, p := range params {
-		if maxArgs == -1 {
-			return nil, fmt.Errorf("no more params can be specified after the ellipsis symbol: %q", p.Name())
-		}
-		if p.IsDefault() || p.IsOptional() {
-			maxArgs++
-		} else if maxArgs == minArgs {
-			minArgs++
-			maxArgs++
-		} else {
-			return nil, fmt.Errorf("can't specify non-optional param after optional ones: %q", p.Name())
-		}
-		if p.IsRepeat() {
-			minArgs--
-			maxArgs = -1
-		}
-	}
-
-	info = &funcInfo{
-		name: name, minArgs: minArgs, maxArgs: maxArgs, functor: functor, returnType: returnType, formalParams: params,
-	}
-	functor.SetFunc(info)
-	return info, nil
-}
-
-func (info *funcInfo) Params() []ExprFuncParam {
-	return info.formalParams
-}
-
-func (info *funcInfo) ReturnType() string {
-	return info.returnType
-}
-
-func (info *funcInfo) ToString(opt FmtOpt) string {
-	var sb strings.Builder
-	if len(info.Name()) == 0 {
-		sb.WriteString("func")
-	} else {
-		sb.WriteString(info.Name())
-	}
-	sb.WriteByte('(')
-	if info.formalParams != nil {
-		for i, p := range info.formalParams {
-			if i > 0 {
-				sb.WriteString(", ")
-			}
-			sb.WriteString(p.Name())
-
-			if p.IsDefault() {
-				sb.WriteByte('=')
-				if s, ok := p.DefaultValue().(string); ok {
-					sb.WriteByte('"')
-					sb.WriteString(s)
-					sb.WriteByte('"')
-				} else {
-					sb.WriteString(fmt.Sprintf("%v", p.DefaultValue()))
-				}
-			}
-		}
-	}
-	if info.maxArgs < 0 {
-		sb.WriteString(" ...")
-	}
-	sb.WriteString("):")
-	if len(info.returnType) > 0 {
-		sb.WriteString(info.returnType)
-	} else {
-		sb.WriteString(TypeAny)
-	}
-	sb.WriteString("{}")
-	return sb.String()
-}
-
-func (info *funcInfo) Name() string {
-	return info.name
-}
-
-func (info *funcInfo) MinArgs() int {
-	return info.minArgs
-}
-
-func (info *funcInfo) MaxArgs() int {
-	return info.maxArgs
-}
-
-func (info *funcInfo) Functor() Functor {
-	return info.functor
-}
-
-func (info *funcInfo) AllocContext(parentCtx ExprContext) (ctx ExprContext) {
-	if defCtx := info.functor.GetDefinitionContext(); defCtx != nil {
-		ctx = defCtx.Clone()
-		ctx.SetParent(defCtx)
-	} else {
-		ctx = parentCtx.Clone()
-		ctx.SetParent(parentCtx)
-	}
-	return
-}
-
-func (info *funcInfo) ParamSpec(paramName string) ExprFuncParam {
-	for _, spec := range info.formalParams {
-		if spec.Name() == paramName {
-			return spec
-		}
-	}
-	return nil
-}
-
-func initActualParams(ctx ExprContext, info ExprFunc, callTerm *term) (actualParams map[string]any, err error) {
-	var varArgs []any
-	var varName string
-
-	namedParamsStarted := false
-
-	formalParams := info.Params()
-	actualParams = make(map[string]any, len(formalParams))
-	if callTerm == nil {
-		return
-	}
-
-	for i, tree := range callTerm.children {
-		var paramValue any
-		paramCtx := ctx.Clone()
-		if paramValue, err = tree.compute(paramCtx); err != nil {
-			break
-		}
-		if paramName, namedParam := getAssignVarName(tree); namedParam {
-			if info.ParamSpec(paramName) == nil {
-				err = fmt.Errorf("%s(): unknown param %q", info.Name(), paramName)
-				break
-			}
-			actualParams[paramName] = paramValue
-			namedParamsStarted = true
-		} else if !namedParamsStarted {
-			if varArgs != nil {
-				varArgs = append(varArgs, paramValue)
-			} else if i < len(formalParams) {
-				spec := formalParams[i]
-				if spec.IsRepeat() {
-					varArgs = make([]any, 0, len(callTerm.children)-i)
-					varArgs = append(varArgs, paramValue)
-					varName = spec.Name()
-				} else {
-					actualParams[spec.Name()] = paramValue
-				}
-			} else {
-				err = ErrTooManyParams(info.Name(), len(formalParams), len(callTerm.children))
-				break
-			}
-		} else {
-			err = fmt.Errorf("%s(): positional param nr %d not allowed after named params", info.Name(), i+1)
-			break
-		}
-	}
-	if err == nil {
-		if varArgs != nil {
-			actualParams[varName] = varArgs
-		}
-	}
-	return
-}
-
-func (info *funcInfo) PrepareCall(name string, actualParams map[string]any) (err error) {
-	passedCount := len(actualParams)
-	if info.MinArgs() > passedCount {
-		err = ErrTooFewParams(name, info.MinArgs(), info.MaxArgs(), passedCount)
-		return
-	}
-
-	if passedCount < len(info.formalParams) {
-		for _, p := range info.formalParams {
-			if _, exists := actualParams[p.Name()]; !exists {
-				if !p.IsDefault() {
-					break
-				}
-				if p.IsRepeat() {
-					varArgs := make([]any, 1)
-					varArgs[0] = p.DefaultValue()
-					actualParams[p.Name()] = varArgs
-				} else {
-					actualParams[p.Name()] = p.DefaultValue()
-				}
-			}
-		}
-	}
-
-	if info.MaxArgs() >= 0 && info.MaxArgs() < len(actualParams) {
-		err = ErrTooManyParams(name, info.MaxArgs(), len(actualParams))
-	}
-	return
-}
-
-// ----- Call a function ---
-
-func getAssignVarName(t *term) (name string, ok bool) {
-	if ok = t.symbol() == SymEqual; ok {
-		name = t.children[0].source()
-	}
-	return
-}
-
-func CallFunctionByTerm(parentCtx ExprContext, name string, callTerm *term) (result any, err error) {
-	var actualParams map[string]any
-	if info, exists := GetFuncInfo(parentCtx, name); exists {
-		if actualParams, err = initActualParams(parentCtx, info, callTerm); err == nil {
-			ctx := info.AllocContext(parentCtx)
-			if err = info.PrepareCall(name, actualParams); err == nil {
-				functor := info.Functor()
-				result, err = functor.InvokeNamed(ctx, name, actualParams)
-				exportObjectsToParent(ctx)
-			}
-		}
-	} else {
-		err = fmt.Errorf("unknown function %s()", name)
-	}
-	return
-}
-
-func CallFunctionByArgs(parentCtx ExprContext, name string, args []any) (result any, err error) {
-	var actualParams map[string]any
-	if info, exists := GetFuncInfo(parentCtx, name); exists {
-		functor := info.Functor()
-		actualParams = bindActualParams(functor, args)
-		ctx := info.AllocContext(parentCtx)
-		if err = info.PrepareCall(name, actualParams); err == nil {
-			result, err = functor.InvokeNamed(ctx, name, actualParams)
-			exportObjectsToParent(ctx)
-		}
-	} else {
-		err = fmt.Errorf("unknown function %s()", name)
-	}
-	return
-}
-
-func CallFunctionByParams(parentCtx ExprContext, name string, actualParams map[string]any) (result any, err error) {
-	//var actualParams map[string]any
-	if info, exists := GetFuncInfo(parentCtx, name); exists {
-		functor := info.Functor()
-		ctx := info.AllocContext(parentCtx)
-		if err = info.PrepareCall(name, actualParams); err == nil {
-			result, err = functor.InvokeNamed(ctx, name, actualParams)
-			exportObjectsToParent(ctx)
-		}
-	} else {
-		err = fmt.Errorf("unknown function %s()", name)
-	}
-	return
-}
-
-func GetParam(args map[string]any, paramName string, paramNum int) (value any, exists bool) {
-	if value, exists = args[paramName]; !exists {
-		if paramNum > 0 && paramNum <= len(args) {
-			value, exists = args["arg"+strconv.Itoa(paramNum)]
-		}
-	}
-	return
-}
-
-func bindActualParams(functor Functor, args []any) (actualParams map[string]any) {
-	formalParams := functor.GetParams()
-	actualParams = make(map[string]any, len(args))
-	for i, arg := range args {
-		if i < len(formalParams) {
-			actualParams[formalParams[i].Name()] = arg
-		} else {
-			actualParams["arg"+strconv.Itoa(i+1)] = arg
-		}
-	}
-	return
-}

global-context.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // global-context.go
@@ -7,101 +7,68 @@ package expr
 import (
 	"path/filepath"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
-var globalCtx *SimpleStore
+//var globalCtx *SimpleStore
 
-func ImportInContext(name string) (exists bool) {
-	var mod *builtinModule
-	if mod, exists = builtinModuleRegister[name]; exists {
-		mod.importFunc(globalCtx)
-		mod.imported = true
+func ImportInContext(ctx kern.ExprContext, name string) (exists bool) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		var mod *builtinModule
+		if mod, exists = builtinModuleRegister[name]; exists {
+			mod.importFunc(globalCtx)
+			mod.imported = true
+		}
 	}
 	return
 }
 
-func ImportInContextByGlobPattern(pattern string) (count int, err error) {
-	var matched bool
-	for name, mod := range builtinModuleRegister {
-		if matched, err = filepath.Match(pattern, name); err == nil {
-			if matched {
-				count++
-				mod.importFunc(globalCtx)
-				mod.imported = true
+func ImportInContextByGlobPattern(ctx kern.ExprContext, pattern string) (count int, err error) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		var matched bool
+		for name, mod := range builtinModuleRegister {
+			if matched, err = filepath.Match(pattern, name); err == nil {
+				if matched {
+					count++
+					mod.importFunc(globalCtx)
+					mod.imported = true
+				}
+			} else {
+				break
 			}
-		} else {
-			break
 		}
 	}
 	return
 }
 
-func GetVar(ctx ExprContext, name string) (value any, exists bool) {
-	if value, exists = ctx.GetVar(name); !exists {
-		value, exists = globalCtx.GetVar(name)
-	}
-	return
-}
-
-func GetLocalFuncInfo(ctx ExprContext, name string) (item ExprFunc, exists bool) {
-	var v any
-	if len(name) > 0 {
-		if v, exists = ctx.GetVar(name); exists && isFunctor(v) {
-			f, _ := v.(Functor)
-			item = f.GetFunc()
-		} else {
-			item, exists = ctx.GetFuncInfo(name)
+func GlobalCtrlSet(ctx kern.ExprContext, name string, newValue any) (currentValue any) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		if !strings.HasPrefix(name, "_") {
+			name = "_" + name
 		}
+
+		currentValue, _ = globalCtx.GetVar(name)
+		globalCtx.SetVar(name, newValue)
 	}
-	return
-}
-
-func GetFuncInfo(ctx ExprContext, name string) (item ExprFunc, exists bool) {
-	// if len(name) > 0 {
-	// 	if item, exists = GetLocalFuncInfo(ctx, name); exists {
-	// 		ownerCtx = ctx
-	// 	} else if item, exists = globalCtx.GetFuncInfo(name); exists {
-	// 		ownerCtx = globalCtx
-	// 	}
-	// }
-	item, exists, _ = GetFuncInfoAndOwner(ctx, name)
-	return
-}
-
-func GetFuncInfoAndOwner(ctx ExprContext, name string) (item ExprFunc, exists bool, ownerCtx ExprContext) {
-	if len(name) > 0 {
-		if item, exists = GetLocalFuncInfo(ctx, name); exists {
-			ownerCtx = ctx
-		} else if item, exists = globalCtx.GetFuncInfo(name); exists {
-			ownerCtx = globalCtx
-		}
-	}
-	return
-}
-
-func GlobalCtrlSet(name string, newValue any) (currentValue any) {
-	if !strings.HasPrefix(name, "_") {
-		name = "_" + name
-	}
-	currentValue, _ = globalCtx.GetVar(name)
-
-	globalCtx.SetVar(name, newValue)
 	return currentValue
 }
 
-func GlobalCtrlGet(name string) (currentValue any) {
-	if !strings.HasPrefix(name, "_") {
-		name = "_" + name
+func GlobalCtrlGet(ctx kern.ExprContext, name string) (currentValue any) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		if !strings.HasPrefix(name, "_") {
+			name = "_" + name
+		}
+		currentValue, _ = globalCtx.GetVar(name)
 	}
-	currentValue, _ = globalCtx.GetVar(name)
 	return currentValue
 }
 
-func CtrlEnable(ctx ExprContext, name string) (currentStatus bool) {
+func CtrlEnable(ctx kern.ExprContext, name string) (currentStatus bool) {
 	if !strings.HasPrefix(name, "_") {
 		name = "_" + name
 	}
-	if v, exists := ctx.GetVar(name); exists && IsBool(v) {
+	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
 		currentStatus, _ = v.(bool)
 	}
 
@@ -109,11 +76,11 @@ func CtrlEnable(ctx ExprContext, name string) (currentStatus bool) {
 	return currentStatus
 }
 
-func CtrlDisable(ctx ExprContext, name string) (currentStatus bool) {
+func CtrlDisable(ctx kern.ExprContext, name string) (currentStatus bool) {
 	if !strings.HasPrefix(name, "_") {
 		name = "_" + name
 	}
-	if v, exists := ctx.GetVar(name); exists && IsBool(v) {
+	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
 		currentStatus, _ = v.(bool)
 	}
 
@@ -121,36 +88,39 @@ func CtrlDisable(ctx ExprContext, name string) (currentStatus bool) {
 	return currentStatus
 }
 
-func CtrlIsEnabled(ctx ExprContext, name string) (status bool) {
-	var v any
-	var exists bool
+// func CtrlIsEnabled(ctx ExprContext, name string) (status bool) {
+// 	var v any
+// 	var exists bool
 
-	if !strings.HasPrefix(name, "_") {
-		name = "_" + name
-	}
+// 	if !strings.HasPrefix(name, "_") {
+// 		name = "_" + name
+// 	}
 
-	if v, exists = ctx.GetVar(name); !exists {
-		v, exists = globalCtx.GetVar(name)
-	}
+// 	if v, exists = ctx.GetVar(name); !exists {
+// 		v, exists = globalCtx.GetVar(name)
+// 	}
 
-	if exists {
-		if b, ok := v.(bool); ok {
-			status = b
+// 	if exists {
+// 		if b, ok := v.(bool); ok {
+// 			status = b
+// 		}
+// 	}
+// 	return
+// }
+
+func getControlString(ctx kern.ExprContext, name string) (s string, exists bool) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		var v any
+		if v, exists = globalCtx.GetVar(name); exists {
+			s, exists = v.(string)
 		}
 	}
 	return
 }
 
-func getControlString(name string) (s string, exists bool) {
-	var v any
-	if v, exists = globalCtx.GetVar(name); exists {
-		s, exists = v.(string)
-	}
+func InitGlobal() (ctx kern.ExprContext) {
+	ctx = NewSimpleStoreWithoutGlobalContext()
+	kern.InitDefaultVars(ctx)
+	ImportBuiltinsFuncs(ctx)
 	return
 }
-
-func init() {
-	globalCtx = NewSimpleStore()
-	initDefaultVars(globalCtx)
-	ImportBuiltinsFuncs(globalCtx)
-}

graph.go

@@ -1,6 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
+//go:build graph
+
 // graph.go
 package expr
 
@@ -53,7 +55,7 @@ func (r *Reticle) computeCharWidth() {
 			if v := ref.node.value(); v != nil {
 				ref.label = fmt.Sprintf("%v", v)
 			} else {
-				ref.label = ref.node.source()
+				ref.label = ref.node.Source()
 			}
 			r.colsWidth[c] = max(r.colsWidth[c], len(ref.label)+2) // +2 to make room for brakets
 		}

helpers.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // helpers.go
@@ -9,13 +9,17 @@ import (
 	"io"
 	"os"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/util"
 )
 
-func EvalString(ctx ExprContext, source string) (result any, err error) {
-	var tree *ast
+func EvalString(ctx kern.ExprContext, source string) (result any, err error) {
+	var tree *scan.Ast
 
 	r := strings.NewReader(source)
-	scanner := NewScanner(r, DefaultTranslations())
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
 	parser := NewParser()
 
 	if tree, err = parser.Parse(scanner); err == nil {
@@ -34,21 +38,21 @@ func EvalStringA(source string, args ...Arg) (result any, err error) {
 }
 
 func EvalStringV(source string, args []Arg) (result any, err error) {
-	ctx := NewSimpleStore()
+	ctx := NewSimpleStoreWithoutGlobalContext()
 	for _, arg := range args {
-		if isFunc(arg.Value) {
-			if f, ok := arg.Value.(FuncTemplate); ok {
-				functor := NewGolangFunctor(f)
+		if util.IsFunc(arg.Value) {
+			if f, ok := arg.Value.(kern.FuncTemplate); ok {
+				functor := kern.NewGolangFunctor(f)
 				// ctx.RegisterFunc(arg.Name, functor, 0, -1)
-				ctx.RegisterFunc(arg.Name, functor, TypeAny, []ExprFuncParam{
-					NewFuncParamFlagDef(ParamValue, PfDefault|PfRepeat, 0),
+				ctx.RegisterFunc(arg.Name, functor, kern.TypeAny, []kern.ExprFuncParam{
+					kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, 0),
 				})
 			} else {
 				err = fmt.Errorf("invalid function specification: %q", arg.Name)
 			}
-		} else if integer, ok := anyInteger(arg.Value); ok {
+		} else if integer, ok := kern.AnyInteger(arg.Value); ok {
 			ctx.SetVar(arg.Name, integer)
-		} else if float, ok := anyFloat(arg.Value); ok {
+		} else if float, ok := kern.AnyFloat(arg.Value); ok {
 			ctx.SetVar(arg.Name, float)
 		} else if _, ok := arg.Value.(string); ok {
 			ctx.SetVar(arg.Name, arg.Value)
@@ -65,9 +69,9 @@ func EvalStringV(source string, args []Arg) (result any, err error) {
 	return
 }
 
-func EvalStream(ctx ExprContext, r io.Reader) (result any, err error) {
-	var tree *ast
-	scanner := NewScanner(r, DefaultTranslations())
+func EvalStream(ctx kern.ExprContext, r io.Reader) (result any, err error) {
+	var tree *scan.Ast
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
 	parser := NewParser()
 
 	if tree, err = parser.Parse(scanner); err == nil {
@@ -76,7 +80,7 @@ func EvalStream(ctx ExprContext, r io.Reader) (result any, err error) {
 	return
 }
 
-func EvalFile(ctx ExprContext, filePath string) (result any, err error) {
+func EvalFile(ctx kern.ExprContext, filePath string) (result any, err error) {
 	var fh *os.File
 	if fh, err = os.Open(filePath); err != nil {
 		return nil, err

import-utils.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // import-utils.go
@@ -11,6 +11,9 @@ import (
 	"path"
 	"path/filepath"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/util"
 )
 
 const (
@@ -19,8 +22,8 @@ const (
 )
 
 func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(IsString(paramValue) /*|| isList(paramValue)*/) {
-		err = fmt.Errorf("%s(): param nr %d has wrong type %s, string expected", funcName, paramPos+1, TypeName(paramValue))
+	if !(kern.IsString(paramValue) /*|| isList(paramValue)*/) {
+		err = fmt.Errorf("%s(): param nr %d has wrong type %s, string expected", funcName, paramPos+1, kern.TypeName(paramValue))
 	}
 	return
 }
@@ -45,8 +48,8 @@ func addEnvImportDirs(envVarName string, dirList []string) []string {
 	return dirList
 }
 
-func addSearchDirs(endingPath string, dirList []string) []string {
-	if dirSpec, exists := getControlString(ControlSearchPath); exists {
+func addSearchDirs(ctx kern.ExprContext, endingPath string, dirList []string) []string {
+	if dirSpec, exists := getControlString(ctx, kern.ControlSearchPath); exists {
 		dirs := strings.Split(dirSpec, ":")
 		if dirList == nil {
 			dirList = dirs
@@ -63,9 +66,9 @@ func addSearchDirs(endingPath string, dirList []string) []string {
 	return dirList
 }
 
-func buildSearchDirList(endingPath, envVarName string) (dirList []string) {
+func buildSearchDirList(ctx kern.ExprContext, endingPath, envVarName string) (dirList []string) {
 	dirList = addEnvImportDirs(envVarName, dirList)
-	dirList = addSearchDirs(endingPath, dirList)
+	dirList = addSearchDirs(ctx, endingPath, dirList)
 	return
 }
 
@@ -83,7 +86,7 @@ func searchAmongPath(filename string, dirList []string) (filePath string) {
 	}
 
 	for _, dir := range dirList {
-		if dir, err = ExpandPath(dir); err != nil {
+		if dir, err = util.ExpandPath(dir); err != nil {
 			continue
 		}
 		if fullPath := path.Join(dir, filename); isFile(fullPath) {
@@ -106,7 +109,7 @@ func isPathRelative(filePath string) bool {
 }
 
 func makeFilepath(filename string, dirList []string) (filePath string, err error) {
-	if filename, err = ExpandPath(filename); err != nil {
+	if filename, err = util.ExpandPath(filename); err != nil {
 		return
 	}
 

int-iterator.go

@@ -0,0 +1,137 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// int-iterator.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type IntIterator struct {
+	count int64
+	index int64
+	start int64
+	stop  int64
+	step  int64
+}
+
+func NewIntIterator(args []any) (it *IntIterator, err error) {
+	var argc int = 0
+	if args != nil {
+		argc = len(args)
+	}
+	it = &IntIterator{count: 0, index: -1, start: 0, stop: 0, step: 1}
+	if argc >= 1 {
+		if it.stop, err = kern.ToGoInt64(args[0], "start index"); err != nil {
+			return
+		}
+		if argc >= 2 {
+			it.start = it.stop
+			if it.stop, err = kern.ToGoInt64(args[1], "stop index"); err != nil {
+				return
+			}
+			if argc >= 3 {
+				if it.step, err = kern.ToGoInt64(args[2], "step"); err != nil {
+					return
+				}
+			} else if it.start > it.stop {
+				it.step = -1
+			}
+		}
+	}
+	if it.step == 0 {
+		err = fmt.Errorf("step cannot be zero")
+		return
+	}
+	if it.start < it.stop && it.step < 0 {
+		err = fmt.Errorf("step cannot be negative when start < stop")
+		return
+	}
+	if it.start > it.stop && it.step > 0 {
+		err = fmt.Errorf("step cannot be positive when start > stop")
+		return
+	}
+	it.Reset()
+	return
+}
+
+func (it *IntIterator) String() string {
+	return fmt.Sprintf("$(%d..%d..%d)", it.start, it.stop, it.step)
+}
+
+func (it *IntIterator) TypeName() string {
+	return "IntIterator"
+}
+
+func (it *IntIterator) HasOperation(name string) bool {
+	yes := slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName}, name)
+	return yes
+}
+
+func (it *IntIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	case kern.ResetName:
+		err = it.Reset()
+	case kern.CleanName:
+		err = it.Clean()
+	case kern.IndexName:
+		v = int64(it.Index())
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.count
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func (it *IntIterator) Current() (item any, err error) {
+	if it.start <= it.stop {
+		if it.index >= it.start && it.index < it.stop {
+			item = it.index
+		} else {
+			err = io.EOF
+		}
+	} else {
+		if it.index > it.stop && it.index <= it.start {
+			item = it.index
+		} else {
+			err = io.EOF
+		}
+	}
+	return
+}
+
+func (it *IntIterator) Next() (item any, err error) {
+	it.index += it.step
+	if item, err = it.Current(); err != io.EOF {
+		it.count++
+	}
+	return
+}
+
+func (it *IntIterator) Index() int64 {
+	return it.index
+}
+
+func (it *IntIterator) Count() int64 {
+	return it.count
+}
+
+func (it *IntIterator) Reset() error {
+	it.index = it.start - it.step
+	it.count = 0
+	return nil
+}
+
+func (it *IntIterator) Clean() error {
+	return nil
+}

iter-factory.go

@@ -1,25 +1,44 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // iter-factory.go
 package expr
 
-func NewIterator(value any) (it Iterator, err error) {
+import (
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+func NewIterator(ctx kern.ExprContext, value any, ops []*scan.Term) (it kern.Iterator, err error) {
 	if value == nil {
 		return NewArrayIterator([]any{}), nil
 	}
 
 	switch v := value.(type) {
-	case *ListType:
+	case *kern.ListType:
 		it = NewListIterator(v, nil)
-	case *DictType:
+	case *kern.DictType:
 		it, err = NewDictIterator(v, nil)
 	case []any:
 		it = NewArrayIterator(v)
-	case Iterator:
-		it = v
+	case kern.Iterator:
+		// var exprs []*scan.Term
+		it, err = NewIterIter(v, ctx, ops)
 	default:
 		it = NewArrayIterator([]any{value})
 	}
 	return
 }
+
+func HasIterStandardOperations(name string) bool {
+	return slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName}, name)
+}
+
+func HasIterOperations(name string, ops ...string) bool {
+	return slices.Contains([]string{
+		kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName,
+	}, name) ||
+		slices.Contains(ops, name)
+}

iter-iter.go

@@ -0,0 +1,127 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iter-iter.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+type IterIter struct {
+	it       kern.Iterator
+	count    int64
+	index    int64
+	ctx      kern.ExprContext
+	exprList []*scan.Term
+	current  any
+}
+
+func NewIterIter(it kern.Iterator, ctx kern.ExprContext, exprs []*scan.Term) (iter kern.Iterator, err error) {
+	iter = &IterIter{it: it, count: 0, index: -1, ctx: ctx, exprList: exprs, current: nil}
+	return
+}
+
+func (it *IterIter) String() string {
+	return fmt.Sprintf("$(%s)", it.it)
+}
+
+func (it *IterIter) TypeName() string {
+	return "IterIter"
+}
+
+func (it *IterIter) HasOperation(name string) bool {
+	return HasIterStandardOperations(name)
+}
+
+func (it *IterIter) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	case kern.ResetName:
+		err = it.Reset()
+	case kern.CleanName:
+		err = it.Clean()
+	case kern.IndexName:
+		v = int64(it.Index())
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.count
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func (it *IterIter) Current() (item any, err error) {
+	if it.current != nil {
+		item = it.current
+	} else if len(it.exprList) > 0 {
+		// Evaluate the expression list and use the result as the current item
+		var exprValue any
+		for _, expr := range it.exprList {
+			if exprValue, err = expr.Compute(it.ctx); err != nil {
+				break
+			}
+			it.ctx.UnsafeSetVar(kern.ControlLastResult, exprValue)
+		}
+		if err == nil {
+			item = exprValue
+		}
+	} else {
+		var exists bool
+		if it.current, exists = it.ctx.GetVar("_"); !exists {
+			err = fmt.Errorf("current item not available")
+		} else {
+			item = it.current
+		}
+	}
+	return
+}
+
+func (it *IterIter) Next() (item any, err error) {
+	var src any
+
+	it.current = nil
+	ctx := it.ctx
+	for src, err = it.it.Next(); src == nil && err == nil; src, err = it.it.Next() {
+	}
+
+	if err == nil {
+		if src == nil {
+			err = io.EOF
+		} else {
+			ctx.UnsafeSetVar("_", src)
+			ctx.UnsafeSetVar("__", it.it.Index())
+			ctx.UnsafeSetVar("_#", it.it.Count())
+			item, err = it.Current()
+			ctx.DeleteVar("_#")
+			ctx.DeleteVar("__")
+			ctx.DeleteVar("_")
+		}
+	}
+	return
+}
+
+func (it *IterIter) Index() int64 {
+	return it.index
+}
+
+func (it *IterIter) Count() int64 {
+	return it.count
+}
+
+func (it *IterIter) Reset() error {
+	it.index = -1
+	it.count = 0
+	return nil
+}
+
+func (it *IterIter) Clean() error {
+	return nil
+}

kern/bind-go-functions.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// bind-go-function.go
+package kern
+
+// ---- Linking with Go functions
+type GolangFunctor struct {
+	BaseFunctor
+	f FuncTemplate
+}
+
+func NewGolangFunctor(f FuncTemplate) *GolangFunctor {
+	return &GolangFunctor{f: f}
+}
+
+func (functor *GolangFunctor) TypeName() string {
+	return "GoFunctor"
+}
+
+func (functor *GolangFunctor) InvokeNamed(ctx ExprContext, name string, args map[string]any) (result any, err error) {
+	return functor.f(ctx, name, args)
+}

kern/bool.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// string.go
+package kern
+
+func IsBool(v any) (ok bool) {
+	_, ok = v.(bool)
+	return ok
+}
+
+func ToBool(v any) (b bool, ok bool) {
+	ok = true
+	switch x := v.(type) {
+	case string:
+		b = len(x) > 0
+	case float64:
+		b = x != 0.0
+	case int64:
+		b = x != 0
+	case bool:
+		b = x
+	default:
+		ok = false
+	}
+	return
+}

kern/common-errors.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // common-errors.go
-package expr
+package kern
 
 import (
 	"fmt"
@@ -34,7 +34,7 @@ func ErrCantConvert(funcName string, value any, kind string) error {
 }
 
 func ErrExpectedGot(funcName string, kind string, value any) error {
-	return fmt.Errorf("%s(): expected %s, got %s (%v)", funcName, kind, TypeName(value), value)
+	return fmt.Errorf("%s(): expected %s, got %s (%#v)", funcName, kind, TypeName(value), value)
 }
 
 func ErrFuncDivisionByZero(funcName string) error {
@@ -52,7 +52,7 @@ func ErrFuncDivisionByZero(funcName string) error {
 // }
 
 func ErrInvalidParameterValue(funcName, paramName string, paramValue any) error {
-	return fmt.Errorf("%s(): invalid value %s (%v) for parameter %q", funcName, TypeName(paramValue), paramValue, paramName)
+	return fmt.Errorf("%s(): invalid value %s (%#v) for parameter %q", funcName, TypeName(paramValue), paramValue, paramName)
 }
 
 func undefArticle(s string) (article string) {
@@ -86,6 +86,6 @@ func ErrUnknownVar(funcName, varName string) error {
 
 // --- Operator errors
 
-func ErrLeftOperandMustBeVariable(leftTerm, opTerm *term) error {
-	return leftTerm.Errorf("left operand of %q must be a variable", opTerm.source())
+func ErrLeftOperandMustBeVariable(leftTerm, opTerm Term) error {
+	return leftTerm.Errorf("left operand of %q must be a variable", opTerm.Source())
 }

kern/common-params.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // common-params.go
-package expr
+package kern
 
 const (
 	ParamArgs      = "args"

kern/common-type-names.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // common-type-names.go
-package expr
+package kern
 
 const (
 	TypeAny           = "any"

kern/compare.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+package kern
+
+import "reflect"
+
+func Equal(value1, value2 any) (equal bool) {
+	if value1 == nil && value2 == nil {
+		equal = true
+	} else if value1 == nil || value2 == nil {
+		equal = false
+	} else if IsBool(value1) && IsBool(value2) {
+		equal = value1.(bool) == value2.(bool)
+	} else if IsList(value1) && IsList(value2) {
+		ls1 := value1.(*ListType)
+		ls2 := value2.(*ListType)
+		equal = ls1.Equals(*ls2)
+	} else if IsDict(value1) && IsDict(value2) {
+		d1 := value1.(*DictType)
+		d2 := value2.(*DictType)
+		equal = d1.Equals(*d2)
+	} else if IsInteger(value1) && IsInteger(value2) {
+		equal = value1.(int64) == value2.(int64)
+	} else if IsString(value1) && IsString(value2) {
+		equal = value1.(string) == value2.(string)
+	} else if IsFloat(value1) && IsFloat(value2) {
+		equal = value1.(float64) == value2.(float64)
+	} else if IsNumOrFract(value1) && IsNumOrFract(value2) {
+		if eq, err := CmpAnyFract(value1, value2); err == nil {
+			equal = eq == 0
+		}
+	} else if !reflect.DeepEqual(value1, value2) {
+		equal = false
+	}
+	return
+}

kern/context-helpers.go

@@ -1,10 +1,10 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // context-helpers.go
-package expr
+package kern
 
-func cloneContext(sourceCtx ExprContext) (clonedCtx ExprContext) {
+func CloneContext(sourceCtx ExprContext) (clonedCtx ExprContext) {
 	if sourceCtx != nil {
 		clonedCtx = sourceCtx.Clone()
 	}
@@ -25,8 +25,8 @@ func exportFunc(ctx ExprContext, name string, info ExprFunc) {
 	ctx.RegisterFunc(name, info.Functor(), info.ReturnType(), info.Params())
 }
 
-func exportObjects(destCtx, sourceCtx ExprContext) {
-	exportAll := CtrlIsEnabled(sourceCtx, control_export_all)
+func ExportObjects(destCtx, sourceCtx ExprContext) {
+	exportAll := CtrlIsEnabled(sourceCtx, ControlExportAll)
 	// fmt.Printf("Exporting from sourceCtx [%p] to destCtx [%p] -- exportAll=%t\n", sourceCtx, destCtx, exportAll)
 	// Export variables
 	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return (exportAll || name[0] == '@') && !(name[0] == '_') }) {
@@ -44,6 +44,6 @@ func exportObjects(destCtx, sourceCtx ExprContext) {
 
 func exportObjectsToParent(sourceCtx ExprContext) {
 	if parentCtx := sourceCtx.GetParent(); parentCtx != nil {
-		exportObjects(parentCtx, sourceCtx)
+		ExportObjects(parentCtx, sourceCtx)
 	}
 }

kern/control.go

@@ -1,8 +1,10 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // control.go
-package expr
+package kern
+
+import "strings"
 
 // Preset control variables
 const (
@@ -16,7 +18,7 @@ const (
 
 // Other control variables
 const (
-	control_export_all = "_export_all"
+	ControlExportAll = "_export_all"
 )
 
 // Initial values
@@ -24,13 +26,34 @@ const (
 	init_search_path = "~/.local/lib/go-pkg/expr:/usr/local/lib/go-pkg/expr:/usr/lib/go-pkg/expr"
 )
 
+func CtrlIsEnabled(ctx ExprContext, name string) (status bool) {
+	var v any
+	var exists bool
+
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+
+	if v, exists = ctx.GetVar(name); !exists {
+		if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+			v, exists = globalCtx.GetVar(name)
+		}
+	}
+
+	if exists {
+		if b, ok := v.(bool); ok {
+			status = b
+		}
+	}
+	return
+}
 func SetCtrl(ctx ExprContext, name string, value any) (current any) {
 	current, _ = ctx.GetVar(name)
 	ctx.UnsafeSetVar(name, value)
 	return
 }
 
-func initDefaultVars(ctx ExprContext) {
+func InitDefaultVars(ctx ExprContext) {
 	if _, exists := ctx.GetVar(ControlPreset); exists {
 		return
 	}

kern/dict-type.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // dict-type.go
-package expr
+package kern
 
 import (
 	"fmt"
@@ -12,6 +12,11 @@ import (
 
 type DictType map[any]any
 
+func IsDict(v any) (ok bool) {
+	_, ok = v.(*DictType)
+	return ok
+}
+
 func MakeDict() (dict *DictType) {
 	d := make(DictType)
 	dict = &d
@@ -32,7 +37,7 @@ func NewDict(dictAny map[any]any) (dict *DictType) {
 	return
 }
 
-func newDict(dictAny map[any]*term) (dict *DictType) {
+func newDict(dictAny map[any]Term) (dict *DictType) {
 	// TODO Change with a call to NewDict()
 	var d DictType
 	if dictAny != nil {
@@ -110,7 +115,7 @@ func (dict *DictType) ToString(opt FmtOpt) string {
 			sb.WriteString(": ")
 			if formatter, ok := value.(Formatter); ok {
 				sb.WriteString(formatter.ToString(opt))
-			} else if t, ok := value.(*term); ok {
+			} else if t, ok := value.(Term); ok {
 				sb.WriteString(t.String())
 			} else {
 				sb.WriteString(fmt.Sprintf("%#v", value))
@@ -129,7 +134,7 @@ func (dict *DictType) TypeName() string {
 	return "dict"
 }
 
-func (dict *DictType) hasKey(target any) (ok bool) {
+func (dict *DictType) HasKey(target any) (ok bool) {
 	for key := range *dict {
 		if ok = reflect.DeepEqual(key, target); ok {
 			break
@@ -138,7 +143,16 @@ func (dict *DictType) hasKey(target any) (ok bool) {
 	return
 }
 
-func (dict *DictType) clone() (c *DictType) {
+func (dict *DictType) SetItem(key any, value any) {
+	(*dict)[key] = value
+}
+
+func (dict *DictType) GetItem(key any) (value any, exists bool) {
+	value, exists = (*dict)[key]
+	return
+}
+
+func (dict *DictType) Clone() (c *DictType) {
 	c = newDict(nil)
 	for k, v := range *dict {
 		(*c)[k] = v
@@ -146,7 +160,7 @@ func (dict *DictType) clone() (c *DictType) {
 	return
 }
 
-func (dict *DictType) merge(second *DictType) {
+func (dict *DictType) Merge(second *DictType) {
 	if second != nil {
 		for k, v := range *second {
 			(*dict)[k] = v
@@ -154,8 +168,21 @@ func (dict *DictType) merge(second *DictType) {
 	}
 }
 
-func (dict *DictType) setItem(key any, value any) (err error) {
-	(*dict)[key] = value
+func (dict *DictType) Equals(dict2 DictType) (answer bool) {
+	if dict2 != nil && len(*dict) == len(dict2) {
+		answer = true
+		for key, value1 := range *dict {
+			if value2, exists := dict2.GetItem(key); exists {
+				if !Equal(value1, value2) {
+					answer = false
+					break
+				}
+			} else {
+				answer = false
+				break
+			}
+		}
+	}
 	return
 }
 

kern/expr-context.go

@@ -1,14 +1,15 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr-context.go
-package expr
+package kern
 
 // ----Expression Context
 type ExprContext interface {
 	Clone() ExprContext
 	SetParent(ctx ExprContext)
 	GetParent() (ctx ExprContext)
+	GetGlobal() (ctx ExprContext)
 	GetVar(varName string) (value any, exists bool)
 	GetLast() any
 	SetVar(varName string, value any)
@@ -22,6 +23,7 @@ type ExprContext interface {
 	FuncCount() int
 	DeleteFunc(funcName string)
 
+	GetLocalFuncInfo(name string) (info ExprFunc, exists bool)
 	GetFuncInfo(name string) (item ExprFunc, exists bool)
 	Call(name string, args map[string]any) (result any, err error)
 	RegisterFuncInfo(info ExprFunc)

kern/expr-function.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr-function.go
-package expr
+package kern
 
 // ---- Functor interface
 type Functor interface {
@@ -37,3 +37,8 @@ type ExprFunc interface {
 	PrepareCall(name string, actualParams map[string]any) (err error)
 	AllocContext(parentCtx ExprContext) (ctx ExprContext)
 }
+
+func IsFunctor(v any) (ok bool) {
+	_, ok = v.(Functor)
+	return
+}

kern/expr.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr.go
-package expr
+package kern
 
 // ----Expression interface
 type Expr interface {

kern/float.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// float.go
+package kern
+
+func IsFloat(v any) (ok bool) {
+	_, ok = v.(float64)
+	return ok
+}
+
+func AnyFloat(v any) (float float64, ok bool) {
+	ok = true
+	switch floatval := v.(type) {
+	case float32:
+		float = float64(floatval)
+	case float64:
+		float = floatval
+	default:
+		ok = false
+	}
+	return
+}

kern/formatter.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // formatter.go
-package expr
+package kern
 
 import "fmt"
 
@@ -46,7 +46,7 @@ type Formatter interface {
 	ToString(options FmtOpt) string
 }
 
-func getFormatted(v any, opt FmtOpt) (text string) {
+func GetFormatted(v any, opt FmtOpt) (text string) {
 	if v == nil {
 		text = "(nil)"
 	} else if s, ok := v.(string); ok {

kern/fraction-type.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // fraction-type.go
-package expr
+package kern
 
 //https://www.youmath.it/lezioni/algebra-elementare/lezioni-di-algebra-e-aritmetica-per-scuole-medie/553-dalle-frazioni-a-numeri-decimali.html
 
@@ -18,12 +18,12 @@ type FractionType struct {
 	num, den int64
 }
 
-func newFraction(num, den int64) *FractionType {
+func NewFraction(num, den int64) *FractionType {
 	num, den = simplifyIntegers(num, den)
 	return &FractionType{num, den}
 }
 
-func float64ToFraction(f float64) (fract *FractionType, err error) {
+func Float64ToFraction(f float64) (fract *FractionType, err error) {
 	var sign string
 	intPart, decPart := math.Modf(f)
 	if decPart < 0.0 {
@@ -33,11 +33,11 @@ func float64ToFraction(f float64) (fract *FractionType, err error) {
 	}
 	dec := fmt.Sprintf("%.12f", decPart)
 	s := fmt.Sprintf("%s%.f%s", sign, intPart, dec[1:])
-	return makeGeneratingFraction(s)
+	return MakeGeneratingFraction(s)
 }
 
 // Based on https://cs.opensource.google/go/go/+/refs/tags/go1.22.3:src/math/big/rat.go;l=39
-func makeGeneratingFraction(s string) (f *FractionType, err error) {
+func MakeGeneratingFraction(s string) (f *FractionType, err error) {
 	var num, den int64
 	var sign int64 = 1
 	var parts []string
@@ -59,7 +59,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 		return
 	}
 	if len(parts) == 1 {
-		f = newFraction(sign*num, 1)
+		f = NewFraction(sign*num, 1)
 	} else if len(parts) == 2 {
 		subParts := strings.SplitN(parts[1], "(", 2)
 		if len(subParts) == 1 {
@@ -76,7 +76,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 				num = num*10 + int64(c-'0')
 				den = den * 10
 			}
-			f = newFraction(sign*num, den)
+			f = NewFraction(sign*num, den)
 		} else if len(subParts) == 2 {
 			sub := num
 			mul := int64(1)
@@ -103,7 +103,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 				den *= mul
 			}
 			num -= sub
-			f = newFraction(sign*num, den)
+			f = NewFraction(sign*num, den)
 		}
 	}
 exit:
@@ -113,7 +113,15 @@ exit:
 	return
 }
 
-func (f *FractionType) toFloat() float64 {
+func (f *FractionType) N() int64 {
+	return f.num
+}
+
+func (f *FractionType) D() int64 {
+	return f.den
+}
+
+func (f *FractionType) ToFloat() float64 {
 	return float64(f.num) / float64(f.den)
 }
 
@@ -168,7 +176,7 @@ func (f *FractionType) TypeName() string {
 // -------- fraction utility functions
 
 // greatest common divider
-func gcd(a, b int64) (g int64) {
+func Gcd(a, b int64) (g int64) {
 	if a < 0 {
 		a = -a
 	}
@@ -189,21 +197,21 @@ func gcd(a, b int64) (g int64) {
 
 // lower common multiple
 func lcm(a, b int64) (l int64) {
-	g := gcd(a, b)
+	g := Gcd(a, b)
 	l = a * b / g
 	return
 }
 
 // Sum two fractions
-func sumFract(f1, f2 *FractionType) (sum *FractionType) {
+func SumFract(f1, f2 *FractionType) (sum *FractionType) {
 	m := lcm(f1.den, f2.den)
-	sum = newFraction(f1.num*(m/f1.den)+f2.num*(m/f2.den), m)
+	sum = NewFraction(f1.num*(m/f1.den)+f2.num*(m/f2.den), m)
 	return
 }
 
 // Multiply two fractions
-func mulFract(f1, f2 *FractionType) (prod *FractionType) {
-	prod = newFraction(f1.num*f2.num, f1.den*f2.den)
+func MulFract(f1, f2 *FractionType) (prod *FractionType) {
+	prod = NewFraction(f1.num*f2.num, f1.den*f2.den)
 	return
 }
 
@@ -212,11 +220,12 @@ func anyToFract(v any) (f *FractionType, err error) {
 	if f, ok = v.(*FractionType); !ok {
 		if n, ok := v.(int64); ok {
 			f = intToFraction(n)
+		} else if dec, ok := v.(float64); ok {
+			f, err = Float64ToFraction(dec)
+		} else {
+			err = ErrExpectedGot("fract", TypeFraction, v)
 		}
 	}
-	if f == nil {
-		err = ErrExpectedGot("fract", TypeFraction, v)
-	}
 	return
 }
 
@@ -230,12 +239,12 @@ func anyPairToFract(v1, v2 any) (f1, f2 *FractionType, err error) {
 	return
 }
 
-func sumAnyFract(af1, af2 any) (sum any, err error) {
+func SumAnyFract(af1, af2 any) (sum any, err error) {
 	var f1, f2 *FractionType
 	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
 		return
 	}
-	f := sumFract(f1, f2)
+	f := SumFract(f1, f2)
 	if f.num == 0 {
 		sum = 0
 	} else {
@@ -250,7 +259,7 @@ func sumAnyFract(af1, af2 any) (sum any, err error) {
 //		 =0 if af1 == af2
 //		 >0 if af1 > af2
 //	 err if af1 or af2 is not convertible to fraction
-func cmpAnyFract(af1, af2 any) (result int, err error) {
+func CmpAnyFract(af1, af2 any) (result int, err error) {
 	var f1, f2 *FractionType
 	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
 		return
@@ -265,25 +274,27 @@ func cmpAnyFract(af1, af2 any) (result int, err error) {
 //	=0 if af1 == af2
 //	>0 if af1 > af2
 func cmpFract(f1, f2 *FractionType) (result int) {
-	f2.num = -f2.num
-	f := sumFract(f1, f2)
-	if f.num < 0 {
-		result = -1
-	} else if f.num > 0 {
-		result = 1
-	} else {
-		result = 0
+	if f1 != nil && f2 != nil {
+		f2.num = -f2.num
+		f := SumFract(f1, f2)
+		if f.num < 0 {
+			result = -1
+		} else if f.num > 0 {
+			result = 1
+		} else {
+			result = 0
+		}
 	}
 	return
 }
 
-func subAnyFract(af1, af2 any) (sum any, err error) {
+func SubAnyFract(af1, af2 any) (sum any, err error) {
 	var f1, f2 *FractionType
 	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
 		return
 	}
 	f2.num = -f2.num
-	f := sumFract(f1, f2)
+	f := SumFract(f1, f2)
 	if f.num == 0 {
 		sum = 0
 	} else {
@@ -292,7 +303,7 @@ func subAnyFract(af1, af2 any) (sum any, err error) {
 	return
 }
 
-func mulAnyFract(af1, af2 any) (prod any, err error) {
+func MulAnyFract(af1, af2 any) (prod any, err error) {
 	var f1, f2 *FractionType
 	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
 		return
@@ -306,7 +317,7 @@ func mulAnyFract(af1, af2 any) (prod any, err error) {
 	return
 }
 
-func divAnyFract(af1, af2 any) (quot any, err error) {
+func DivAnyFract(af1, af2 any) (quot any, err error) {
 	var f1, f2 *FractionType
 	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
 		return
@@ -345,7 +356,7 @@ func simplifyIntegers(num, den int64) (a, b int64) {
 		den = -den
 		num = -num
 	}
-	g := gcd(num, den)
+	g := Gcd(num, den)
 	a = num / g
 	b = den / g
 	return
@@ -355,7 +366,19 @@ func intToFraction(n int64) *FractionType {
 	return &FractionType{n, 1}
 }
 
-func isFraction(v any) (ok bool) {
+func IsFraction(v any) (ok bool) {
 	_, ok = v.(*FractionType)
 	return ok
 }
+
+// func IsFract(v any) (ok bool) {
+// 	_, ok = v.(*FractionType)
+// 	return ok
+// }
+
+func IsRational(v any) (ok bool) {
+	if _, ok = v.(*FractionType); !ok {
+		_, ok = v.(int64)
+	}
+	return ok
+}

kern/func-info.go

@@ -0,0 +1,164 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-info.go
+package kern
+
+import (
+	"fmt"
+	"strings"
+)
+
+// --- Functions
+
+// FuncInfo implements expr.ExprFunc
+type FuncInfo struct {
+	name         string
+	minArgs      int
+	maxArgs      int
+	functor      Functor
+	formalParams []ExprFuncParam
+	returnType   string
+}
+
+func NewFuncInfo(name string, functor Functor, returnType string, params []ExprFuncParam) (info *FuncInfo, err error) {
+	var minArgs = 0
+	var maxArgs = 0
+	for _, p := range params {
+		if maxArgs == -1 {
+			return nil, fmt.Errorf("no more params can be specified after the ellipsis symbol: %q", p.Name())
+		}
+		if p.IsDefault() || p.IsOptional() {
+			maxArgs++
+		} else if maxArgs == minArgs {
+			minArgs++
+			maxArgs++
+		} else {
+			return nil, fmt.Errorf("can't specify non-optional param after optional ones: %q", p.Name())
+		}
+		if p.IsRepeat() {
+			minArgs--
+			maxArgs = -1
+		}
+	}
+
+	info = &FuncInfo{
+		name: name, minArgs: minArgs, maxArgs: maxArgs, functor: functor, returnType: returnType, formalParams: params,
+	}
+	functor.SetFunc(info)
+	return info, nil
+}
+
+func (info *FuncInfo) Params() []ExprFuncParam {
+	return info.formalParams
+}
+
+func (info *FuncInfo) ReturnType() string {
+	return info.returnType
+}
+
+func (info *FuncInfo) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	if len(info.Name()) == 0 {
+		sb.WriteString("func")
+	} else {
+		sb.WriteString(info.Name())
+	}
+	sb.WriteByte('(')
+	if info.formalParams != nil {
+		for i, p := range info.formalParams {
+			if i > 0 {
+				sb.WriteString(", ")
+			}
+			sb.WriteString(p.Name())
+
+			if p.IsDefault() {
+				sb.WriteByte('=')
+				if s, ok := p.DefaultValue().(string); ok {
+					sb.WriteByte('"')
+					sb.WriteString(s)
+					sb.WriteByte('"')
+				} else {
+					sb.WriteString(fmt.Sprintf("%v", p.DefaultValue()))
+				}
+			}
+		}
+	}
+	if info.maxArgs < 0 {
+		sb.WriteString(" ...")
+	}
+	sb.WriteString("):")
+	if len(info.returnType) > 0 {
+		sb.WriteString(info.returnType)
+	} else {
+		sb.WriteString(TypeAny)
+	}
+	sb.WriteString("{}")
+	return sb.String()
+}
+
+func (info *FuncInfo) Name() string {
+	return info.name
+}
+
+func (info *FuncInfo) MinArgs() int {
+	return info.minArgs
+}
+
+func (info *FuncInfo) MaxArgs() int {
+	return info.maxArgs
+}
+
+func (info *FuncInfo) Functor() Functor {
+	return info.functor
+}
+
+func (info *FuncInfo) AllocContext(parentCtx ExprContext) (ctx ExprContext) {
+	if defCtx := info.functor.GetDefinitionContext(); defCtx != nil {
+		ctx = defCtx.Clone()
+		ctx.SetParent(defCtx)
+	} else {
+		ctx = parentCtx.Clone()
+		ctx.SetParent(parentCtx)
+	}
+	return
+}
+
+func (info *FuncInfo) ParamSpec(paramName string) ExprFuncParam {
+	for _, spec := range info.formalParams {
+		if spec.Name() == paramName {
+			return spec
+		}
+	}
+	return nil
+}
+
+func (info *FuncInfo) PrepareCall(name string, actualParams map[string]any) (err error) {
+	passedCount := len(actualParams)
+	if info.MinArgs() > passedCount {
+		err = ErrTooFewParams(name, info.MinArgs(), info.MaxArgs(), passedCount)
+		return
+	}
+
+	if passedCount < len(info.formalParams) {
+		for _, p := range info.formalParams {
+			if _, exists := actualParams[p.Name()]; !exists {
+				if !p.IsDefault() {
+					break
+				}
+				if p.IsRepeat() {
+					varArgs := make([]any, 1)
+					varArgs[0] = p.DefaultValue()
+					actualParams[p.Name()] = varArgs
+				} else {
+					actualParams[p.Name()] = p.DefaultValue()
+				}
+			}
+		}
+	}
+
+	if info.MaxArgs() >= 0 && info.MaxArgs() < len(actualParams) {
+		err = ErrTooManyParams(name, info.MaxArgs(), len(actualParams))
+	}
+	return
+}

kern/function.go

@@ -0,0 +1,273 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// function.go
+package kern
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// ---- Function templates
+type FuncTemplate func(ctx ExprContext, name string, args map[string]any) (result any, err error)
+
+type DeepFuncTemplate func(a, b any) (eq bool, err error)
+
+// ---- Common functor definition
+type BaseFunctor struct {
+	info ExprFunc
+}
+
+func (functor *BaseFunctor) ToString(opt FmtOpt) (s string) {
+	if functor.info != nil {
+		s = functor.info.ToString(opt)
+	} else {
+		s = "func(){}"
+	}
+	return s
+}
+
+func (functor *BaseFunctor) GetParams() (params []ExprFuncParam) {
+	if functor.info != nil {
+		return functor.info.Params()
+	} else {
+		return []ExprFuncParam{}
+	}
+}
+
+func (functor *BaseFunctor) SetFunc(info ExprFunc) {
+	functor.info = info
+}
+
+func (functor *BaseFunctor) GetFunc() ExprFunc {
+	return functor.info
+}
+
+func (functor *BaseFunctor) GetDefinitionContext() ExprContext {
+	return nil
+}
+
+// ---- Function Parameters
+type FuncParamFlags uint16
+
+const (
+	PfDefault FuncParamFlags = 1 << iota
+	PfOptional
+	PfRepeat
+)
+
+type funcParamInfo struct {
+	name         string
+	flags        FuncParamFlags
+	defaultValue any
+}
+
+func NewFuncParam(name string) ExprFuncParam {
+	return &funcParamInfo{name: name}
+}
+
+func NewFuncParamFlag(name string, flags FuncParamFlags) ExprFuncParam {
+	return &funcParamInfo{name: name, flags: flags}
+}
+
+func NewFuncParamFlagDef(name string, flags FuncParamFlags, defValue any) *funcParamInfo {
+	return &funcParamInfo{name: name, flags: flags, defaultValue: defValue}
+}
+
+func (param *funcParamInfo) Name() string {
+	return param.name
+}
+
+func (param *funcParamInfo) Type() string {
+	return TypeAny
+}
+
+func (param *funcParamInfo) IsDefault() bool {
+	return (param.flags & PfDefault) != 0
+}
+
+func (param *funcParamInfo) IsOptional() bool {
+	return (param.flags & PfOptional) != 0
+}
+
+func (param *funcParamInfo) IsRepeat() bool {
+	return (param.flags & PfRepeat) != 0
+}
+
+func (param *funcParamInfo) DefaultValue() any {
+	return param.defaultValue
+}
+
+func initActualParams(ctx ExprContext, info ExprFunc, callTerm Term) (actualParams map[string]any, err error) {
+	var varArgs []any
+	var varName string
+
+	namedParamsStarted := false
+
+	formalParams := info.Params()
+	actualParams = make(map[string]any, len(formalParams))
+	if callTerm == nil {
+		return
+	}
+
+	childCount := callTerm.GetChildCount()
+	for i := range childCount {
+		tree := callTerm.GetChild(i)
+		// for i, tree := range callTerm.Children() {
+		var paramValue any
+		paramCtx := ctx.Clone()
+		if paramValue, err = tree.Compute(paramCtx); err != nil {
+			break
+		}
+		if paramName, namedParam := GetAssignVarName(tree); namedParam {
+			if info.ParamSpec(paramName) == nil {
+				err = fmt.Errorf("%s(): unknown param %q", info.Name(), paramName)
+				break
+			}
+			actualParams[paramName] = paramValue
+			namedParamsStarted = true
+		} else if !namedParamsStarted {
+			if varArgs != nil {
+				varArgs = append(varArgs, paramValue)
+			} else if i < len(formalParams) {
+				spec := formalParams[i]
+				if spec.IsRepeat() {
+					varArgs = make([]any, 0, childCount-i)
+					varArgs = append(varArgs, paramValue)
+					varName = spec.Name()
+				} else {
+					actualParams[spec.Name()] = paramValue
+				}
+			} else {
+				err = ErrTooManyParams(info.Name(), len(formalParams), childCount)
+				break
+			}
+		} else {
+			err = fmt.Errorf("%s(): positional param nr %d not allowed after named params", info.Name(), i+1)
+			break
+		}
+	}
+	if err == nil {
+		if varArgs != nil {
+			actualParams[varName] = varArgs
+		}
+	}
+	return
+}
+
+// func (info *funcInfo) PrepareCall(name string, actualParams map[string]any) (err error) {
+// 	passedCount := len(actualParams)
+// 	if info.MinArgs() > passedCount {
+// 		err = ErrTooFewParams(name, info.MinArgs(), info.MaxArgs(), passedCount)
+// 		return
+// 	}
+
+// 	if passedCount < len(info.formalParams) {
+// 		for _, p := range info.formalParams {
+// 			if _, exists := actualParams[p.Name()]; !exists {
+// 				if !p.IsDefault() {
+// 					break
+// 				}
+// 				if p.IsRepeat() {
+// 					varArgs := make([]any, 1)
+// 					varArgs[0] = p.DefaultValue()
+// 					actualParams[p.Name()] = varArgs
+// 				} else {
+// 					actualParams[p.Name()] = p.DefaultValue()
+// 				}
+// 			}
+// 		}
+// 	}
+
+// 	if info.MaxArgs() >= 0 && info.MaxArgs() < len(actualParams) {
+// 		err = ErrTooManyParams(name, info.MaxArgs(), len(actualParams))
+// 	}
+// 	return
+// }
+
+// ----- Call a function ---
+
+// func getAssignVarName(t *term) (name string, ok bool) {
+// 	if ok = t.symbol() == SymEqual; ok {
+// 		name = t.children[0].source()
+// 	}
+// 	return
+// }
+
+func GetAssignVarName(t Term) (name string, ok bool) {
+	if ok = t.IsAssign(); ok {
+		name = t.GetChildSource(0)
+	}
+	return
+}
+
+func CallFunctionByTerm(parentCtx ExprContext, name string, callTerm Term) (result any, err error) {
+	var actualParams map[string]any
+	if info, exists := parentCtx.GetFuncInfo(name); exists {
+		if actualParams, err = initActualParams(parentCtx, info, callTerm); err == nil {
+			ctx := info.AllocContext(parentCtx)
+			if err = info.PrepareCall(name, actualParams); err == nil {
+				functor := info.Functor()
+				result, err = functor.InvokeNamed(ctx, name, actualParams)
+				exportObjectsToParent(ctx)
+			}
+		}
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}
+
+func CallFunctionByArgs(parentCtx ExprContext, name string, args []any) (result any, err error) {
+	var actualParams map[string]any
+	if info, exists := parentCtx.GetFuncInfo(name); exists {
+		functor := info.Functor()
+		actualParams = BindActualParams(functor, args)
+		ctx := info.AllocContext(parentCtx)
+		if err = info.PrepareCall(name, actualParams); err == nil {
+			result, err = functor.InvokeNamed(ctx, name, actualParams)
+			exportObjectsToParent(ctx)
+		}
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}
+
+func CallFunctionByParams(parentCtx ExprContext, name string, actualParams map[string]any) (result any, err error) {
+	//var actualParams map[string]any
+	if info, exists := parentCtx.GetFuncInfo(name); exists {
+		functor := info.Functor()
+		ctx := info.AllocContext(parentCtx)
+		if err = info.PrepareCall(name, actualParams); err == nil {
+			result, err = functor.InvokeNamed(ctx, name, actualParams)
+			exportObjectsToParent(ctx)
+		}
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}
+
+func GetParam(args map[string]any, paramName string, paramNum int) (value any, exists bool) {
+	if value, exists = args[paramName]; !exists {
+		if paramNum > 0 && paramNum <= len(args) {
+			value, exists = args["arg"+strconv.Itoa(paramNum)]
+		}
+	}
+	return
+}
+
+func BindActualParams(functor Functor, args []any) (actualParams map[string]any) {
+	formalParams := functor.GetParams()
+	actualParams = make(map[string]any, len(args))
+	for i, arg := range args {
+		if i < len(formalParams) {
+			actualParams[formalParams[i].Name()] = arg
+		} else {
+			actualParams["arg"+strconv.Itoa(i+1)] = arg
+		}
+	}
+	return
+}

kern/iterator.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // iterator.go
-package expr
+package kern
 
 import (
 	// "errors"
@@ -30,8 +30,8 @@ type Iterator interface {
 	fmt.Stringer
 	Next() (item any, err error) // must return io.EOF after the last item
 	Current() (item any, err error)
-	Index() int
-	Count() int
+	Index() int64
+	Count() int64
 	HasOperation(name string) bool
 	CallOperation(name string, args map[string]any) (value any, err error)
 }
@@ -42,10 +42,11 @@ type ExtIterator interface {
 	Clean() error
 }
 
-func errNoOperation(name string) error {
+func ErrNoOperation(name string) error {
 	return fmt.Errorf("no %s() function defined in the data-source", name)
 }
 
-// func errInvalidDataSource() error {
-// 	return errors.New("invalid data-source")
-// }
+func IsIterator(v any) (ok bool) {
+	_, ok = v.(Iterator)
+	return
+}

kern/list-type.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // list-type.go
-package expr
+package kern
 
 import (
 	"fmt"
@@ -12,23 +12,21 @@ import (
 
 type ListType []any
 
-func newListA(listAny ...any) (list *ListType) {
+func IsList(v any) (ok bool) {
+	_, ok = v.(*ListType)
+	return ok
+}
+
+func NewListA(listAny ...any) (list *ListType) {
 	if listAny == nil {
 		listAny = []any{}
 	}
-	return newList(listAny)
-}
-
-func newList(listAny []any) (list *ListType) {
 	return NewList(listAny)
 }
 
 func NewList(listAny []any) (list *ListType) {
 	if listAny != nil {
 		ls := make(ListType, len(listAny))
-		//		for i, item := range listAny {
-		//			ls[i] = item
-		//		}
 		copy(ls, listAny)
 		list = &ls
 	}
@@ -52,13 +50,13 @@ func ListFromStrings(stringList []string) (list *ListType) {
 	return
 }
 
-func (ls *ListType) ToString(opt FmtOpt) (s string) {
+func (dict *ListType) ToString(opt FmtOpt) (s string) {
 	indent := GetFormatIndent(opt)
 	flags := GetFormatFlags(opt)
 
 	var sb strings.Builder
 	sb.WriteByte('[')
-	if len(*ls) > 0 {
+	if len(*dict) > 0 {
 		innerOpt := MakeFormatOptions(flags, indent+1)
 		nest := strings.Repeat("  ", indent+1)
 
@@ -66,7 +64,7 @@ func (ls *ListType) ToString(opt FmtOpt) (s string) {
 			sb.WriteByte('\n')
 			sb.WriteString(nest)
 		}
-		for i, item := range []any(*ls) {
+		for i, item := range []any(*dict) {
 			if i > 0 {
 				if flags&MultiLine != 0 {
 					sb.WriteString(",\n")
@@ -98,30 +96,19 @@ func (ls *ListType) ToString(opt FmtOpt) (s string) {
 	return
 }
 
-func (ls *ListType) String() string {
-	return ls.ToString(0)
+func (dict *ListType) String() string {
+	return dict.ToString(0)
 }
 
-func (ls *ListType) TypeName() string {
+func (dict *ListType) TypeName() string {
 	return "list"
 }
 
-// func (list *ListType) indexDeepCmp(target any) (index int) {
-// 	index = -1
-// 	for i, item := range *list {
-// 		if reflect.DeepEqual(item, target) {
-// 			index = i
-// 			break
-// 		}
-// 	}
-// 	return
-// }
-
-func (ls *ListType) contains(t *ListType) (answer bool) {
-	if len(*ls) >= len(*t) {
+func (dict *ListType) Contains(t *ListType) (answer bool) {
+	if len(*dict) >= len(*t) {
 		answer = true
 		for _, item := range *t {
-			if answer = ls.indexDeepSameCmp(item) >= 0; !answer {
+			if answer = dict.IndexDeepSameCmp(item) >= 0; !answer {
 				break
 			}
 		}
@@ -133,8 +120,11 @@ func (ls1 *ListType) Equals(ls2 ListType) (answer bool) {
 	if ls2 != nil && len(*ls1) == len(ls2) {
 		answer = true
 		for index, i1 := range *ls1 {
-			// if i1 != (ls2)[index] {
-			if reflect.DeepEqual(i1, ls2[index]) {
+			// if !reflect.DeepEqual(i1, ls2[index]) {
+			// 	answer = false
+			// 	break
+			// }
+			if !Equal(i1, ls2[index]) {
 				answer = false
 				break
 			}
@@ -143,12 +133,12 @@ func (ls1 *ListType) Equals(ls2 ListType) (answer bool) {
 	return
 }
 
-func (list *ListType) indexDeepSameCmp(target any) (index int) {
+func (dict *ListType) IndexDeepSameCmp(target any) (index int) {
 	var eq bool
 	var err error
 	index = -1
-	for i, item := range *list {
-		if eq, err = deepSame(item, target, sameContent); err != nil {
+	for i, item := range *dict {
+		if eq, err = deepSame(item, target, SameContent); err != nil {
 			break
 		} else if eq {
 			index = i
@@ -158,13 +148,13 @@ func (list *ListType) indexDeepSameCmp(target any) (index int) {
 	return
 }
 
-func sameContent(a, b any) (same bool, err error) {
+func SameContent(a, b any) (same bool, err error) {
 	la, _ := a.(*ListType)
 	lb, _ := b.(*ListType)
 	if len(*la) == len(*lb) {
 		same = true
 		for _, item := range *la {
-			if pos := lb.indexDeepSameCmp(item); pos < 0 {
+			if pos := lb.IndexDeepSameCmp(item); pos < 0 {
 				same = false
 				break
 			}
@@ -173,19 +163,19 @@ func sameContent(a, b any) (same bool, err error) {
 	return
 }
 
-func deepSame(a, b any, deepCmp deepFuncTemplate) (eq bool, err error) {
-	if isNumOrFract(a) && isNumOrFract(b) {
+func deepSame(a, b any, deepCmp DeepFuncTemplate) (eq bool, err error) {
+	if IsNumOrFract(a) && IsNumOrFract(b) {
 		if IsNumber(a) && IsNumber(b) {
 			if IsInteger(a) && IsInteger(b) {
 				li, _ := a.(int64)
 				ri, _ := b.(int64)
 				eq = li == ri
 			} else {
-				eq = numAsFloat(a) == numAsFloat(b)
+				eq = NumAsFloat(a) == NumAsFloat(b)
 			}
 		} else {
 			var cmp int
-			if cmp, err = cmpAnyFract(a, b); err == nil {
+			if cmp, err = CmpAnyFract(a, b); err == nil {
 				eq = cmp == 0
 			}
 		}
@@ -198,15 +188,15 @@ func deepSame(a, b any, deepCmp deepFuncTemplate) (eq bool, err error) {
 	return
 }
 
-func (list *ListType) setItem(index int64, value any) (err error) {
-	if index >= 0 && index < int64(len(*list)) {
-		(*list)[index] = value
+func (dict *ListType) SetItem(index int64, value any) (err error) {
+	if index >= 0 && index < int64(len(*dict)) {
+		(*dict)[index] = value
 	} else {
-		err = fmt.Errorf("index %d out of bounds (0, %d)", index, len(*list)-1)
+		err = fmt.Errorf("index %d out of bounds (0, %d)", index, len(*dict)-1)
 	}
 	return
 }
 
-func (list *ListType) appendItem(value any) {
-	*list = append(*list, value)
+func (dict *ListType) AppendItem(value any) {
+	*dict = append(*dict, value)
 }

kern/number.go

@@ -0,0 +1,88 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// number.go
+package kern
+
+import (
+	"fmt"
+)
+
+func IsInteger(v any) (ok bool) {
+	_, ok = v.(int64)
+	return ok
+}
+
+func IsNumber(v any) (ok bool) {
+	return IsFloat(v) || IsInteger(v)
+}
+
+func IsNumOrFract(v any) (ok bool) {
+	return IsFloat(v) || IsInteger(v) || IsFraction(v)
+}
+
+func IsNumberString(v any) (ok bool) {
+	return IsString(v) || IsNumber(v)
+}
+
+func NumAsFloat(v any) (f float64) {
+	var ok bool
+	if f, ok = v.(float64); !ok {
+		if fract, ok := v.(*FractionType); ok {
+			f = fract.ToFloat()
+		} else {
+			i, _ := v.(int64)
+			f = float64(i)
+		}
+	}
+	return
+}
+
+func AnyInteger(v any) (i int64, ok bool) {
+	ok = true
+	switch intval := v.(type) {
+	case int:
+		i = int64(intval)
+	case uint8:
+		i = int64(intval)
+	case uint16:
+		i = int64(intval)
+	case uint64:
+		i = int64(intval)
+	case uint32:
+		i = int64(intval)
+	case int8:
+		i = int64(intval)
+	case int16:
+		i = int64(intval)
+	case int32:
+		i = int64(intval)
+	case int64:
+		i = intval
+	default:
+		ok = false
+	}
+	return
+}
+
+func ToGoInt(value any, description string) (i int, err error) {
+	if valueInt64, ok := value.(int64); ok {
+		i = int(valueInt64)
+	} else if valueInt, ok := value.(int); ok {
+		i = valueInt
+	} else {
+		err = fmt.Errorf("%s expected integer, got %s (%v)", description, TypeName(value), value)
+	}
+	return
+}
+
+func ToGoInt64(value any, description string) (i int64, err error) {
+	if valueInt64, ok := value.(int64); ok {
+		i = valueInt64
+	} else if valueInt, ok := value.(int); ok {
+		i = int64(valueInt)
+	} else {
+		err = fmt.Errorf("%s expected integer, got %s (%v)", description, TypeName(value), value)
+	}
+	return
+}

kern/string.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// string.go
+package kern
+
+import (
+	"fmt"
+)
+
+func IsString(v any) (ok bool) {
+	_, ok = v.(string)
+	return ok
+}
+
+func ToGoString(value any, description string) (s string, err error) {
+	if s, ok := value.(string); ok {
+		return s, nil
+	} else {
+		err = fmt.Errorf("%s expected string, got %s (%v)", description, TypeName(value), value)
+	}
+	return
+}

kern/term.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// term.go
+package kern
+
+import (
+	"fmt"
+)
+
+type Term interface {
+	fmt.Stringer
+	// Children() []Term
+	Source() string
+	GetChildCount() (count int)
+	GetChild(index int) Term
+	GetChildSource(index int) string
+	Compute(ctx ExprContext) (result any, err error)
+	IsAssign() bool
+	Errorf(template string, args ...any) (err error)
+}

lib-ext-darwin.go

@@ -1,6 +1,6 @@
 //go:build darwin
 
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // lib-ext-darwin.go

lib-ext-linux.go

@@ -1,6 +1,6 @@
 //go:build linux
 
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // lib-ext-linux.go

lib-ext-windows.go

@@ -1,6 +1,6 @@
 //go:build windows
 
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // lib-ext-windows.go

list-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // list-iterator.go
@@ -7,40 +7,43 @@ package expr
 import (
 	"fmt"
 	"io"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 type ListIterator struct {
-	a     *ListType
-	count int
-	index int
-	start int
-	stop  int
-	step  int
+	a     *kern.ListType
+	count int64
+	index int64
+	start int64
+	stop  int64
+	step  int64
 }
 
-func NewListIterator(list *ListType, args []any) (it *ListIterator) {
+func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
 	var argc int = 0
-	listLen := len(([]any)(*list))
+	listLen := int64(len(([]any)(*list)))
 	if args != nil {
 		argc = len(args)
 	}
 	it = &ListIterator{a: list, count: 0, index: -1, start: 0, stop: listLen - 1, step: 1}
 	if argc >= 1 {
-		if i, err := ToGoInt(args[0], "start index"); err == nil {
+		if i, err := kern.ToGoInt64(args[0], "start index"); err == nil {
 			if i < 0 {
 				i = listLen + i
 			}
 			it.start = i
 		}
 		if argc >= 2 {
-			if i, err := ToGoInt(args[1], "stop index"); err == nil {
+			if i, err := kern.ToGoInt64(args[1], "stop index"); err == nil {
 				if i < 0 {
 					i = listLen + i
 				}
 				it.stop = i
 			}
 			if argc >= 3 {
-				if i, err := ToGoInt(args[2], "step"); err == nil {
+				if i, err := kern.ToGoInt64(args[2], "step"); err == nil {
 					if i < 0 {
 						i = -i
 					}
@@ -58,14 +61,14 @@ func NewListIterator(list *ListType, args []any) (it *ListIterator) {
 }
 
 func NewArrayIterator(array []any) (it *ListIterator) {
-	it = &ListIterator{a: (*ListType)(&array), count: 0, index: -1, start: 0, stop: len(array) - 1, step: 1}
+	it = &ListIterator{a: (*kern.ListType)(&array), count: 0, index: -1, start: 0, stop: int64(len(array)) - 1, step: 1}
 	return
 }
 
 func (it *ListIterator) String() string {
-	var l = 0
+	var l = int64(0)
 	if it.a != nil {
-		l = len(*it.a)
+		l = int64(len(*it.a))
 	}
 	return fmt.Sprintf("$([#%d])", l)
 }
@@ -75,26 +78,27 @@ func (it *ListIterator) TypeName() string {
 }
 
 func (it *ListIterator) HasOperation(name string) bool {
-	yes := name == NextName || name == ResetName || name == IndexName || name == CountName || name == CurrentName
+	//yes := name == expr.NextName || name == expr.ResetName || name == expr.IndexName || name == expr.CountName || name == expr.CurrentName
+	yes := slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName}, name)
 	return yes
 }
 
 func (it *ListIterator) CallOperation(name string, args map[string]any) (v any, err error) {
 	switch name {
-	case NextName:
+	case kern.NextName:
 		v, err = it.Next()
-	case ResetName:
+	case kern.ResetName:
 		err = it.Reset()
-	case CleanName:
+	case kern.CleanName:
 		err = it.Clean()
-	case IndexName:
+	case kern.IndexName:
 		v = int64(it.Index())
-	case CurrentName:
+	case kern.CurrentName:
 		v, err = it.Current()
-	case CountName:
+	case kern.CountName:
 		v = it.count
 	default:
-		err = errNoOperation(name)
+		err = kern.ErrNoOperation(name)
 	}
 	return
 }
@@ -102,13 +106,13 @@ func (it *ListIterator) CallOperation(name string, args map[string]any) (v any,
 func (it *ListIterator) Current() (item any, err error) {
 	a := *(it.a)
 	if it.start <= it.stop {
-		if it.stop < len(a) && it.index >= it.start && it.index <= it.stop {
+		if it.stop < int64(len(a)) && it.index >= it.start && it.index <= it.stop {
 			item = a[it.index]
 		} else {
 			err = io.EOF
 		}
 	} else {
-		if it.start < len(a) && it.index >= it.stop && it.index <= it.start {
+		if it.start < int64(len(a)) && it.index >= it.stop && it.index <= it.start {
 			item = a[it.index]
 		} else {
 			err = io.EOF
@@ -126,11 +130,11 @@ func (it *ListIterator) Next() (item any, err error) {
 	return
 }
 
-func (it *ListIterator) Index() int {
+func (it *ListIterator) Index() int64 {
 	return it.index
 }
 
-func (it *ListIterator) Count() int {
+func (it *ListIterator) Count() int64 {
 	return it.count
 }
 

operand-dict.go

@@ -1,29 +1,33 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-dict.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 // -------- dict term
-func newDictTerm(args map[any]*term) *term {
-	return &term{
-		tk:       *NewValueToken(0, 0, SymDict, "{}", args),
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalDict,
+func newDictTerm(args map[any]*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(0, 0, scan.SymDict, "{}", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalDict,
 	}
 }
 
 // -------- dict func
-func evalDict(ctx ExprContext, opTerm *term) (v any, err error) {
-	dict, _ := opTerm.value().(map[any]*term)
-	items := make(DictType, len(dict))
+func evalDict(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	dict, _ := opTerm.Value().(map[any]*scan.Term)
+	items := make(kern.DictType, len(dict))
 	for key, tree := range dict {
 		var param any
-		if param, err = tree.compute(ctx); err != nil {
+		if param, err = tree.Compute(ctx); err != nil {
 			break
 		}
 		items[key] = param

operand-expr.go

@@ -1,30 +1,35 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-expr.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 // -------- expr term
-func newExprTerm(root *term) *term {
-	tk := NewValueToken(root.tk.row, root.tk.col, SymExpression, root.source(), root)
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalExpr,
+func newExprTerm(root *scan.Term) *scan.Term {
+	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymExpression, root.Source(), root)
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalExpr,
 	}
 }
 
 // -------- eval expr
-func evalExpr(ctx ExprContext, opTerm *term) (v any, err error) {
-	if expr, ok := opTerm.value().(*term); ok {
-		v, err = expr.compute(ctx)
+func evalExpr(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	if ast, ok := opTerm.Value().(*scan.Term); ok {
+		v, err = ast.Compute(ctx)
 	} else {
-		err = fmt.Errorf("expression expected, got %T", opTerm.value())
+		err = fmt.Errorf("expression expected, got %T", opTerm.Value())
 	}
 	return
 }

operand-func.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-func.go
@@ -6,27 +6,34 @@ package expr
 
 import (
 	"errors"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- function call term
-func newFuncCallTerm(tk *Token, args []*term) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: args,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalFuncCall,
+func newFuncCallTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	var pos scan.TermPosition = scan.PosLeaf
+	if len(args) > 0 {
+		pos = scan.PosMultifix
+	}
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: args,
+		Position: pos,
+		Priority: scan.PriValue,
+		EvalFunc: evalFuncCall,
 	}
 }
 
 // -------- eval func call
 // func _evalFuncCall(ctx ExprContext, opTerm *term) (v any, err error) {
-// 	name, _ := opTerm.tk.Value.(string)
-// 	params := make([]any, len(opTerm.children), len(opTerm.children)+5)
-// 	for i, tree := range opTerm.children {
+// 	name, _ := opTerm.Tk.Value.(string)
+// 	params := make([]any, len(opTerm.Children), len(opTerm.Children)+5)
+// 	for i, tree := range opTerm.Children {
 // 		var param any
-// 		if param, err = tree.compute(ctx); err != nil {
+// 		if param, err = tree.Compute(ctx); err != nil {
 // 			break
 // 		}
 // 		params[i] = param
@@ -38,42 +45,42 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 // 	return
 // }
 
-func evalFuncCall(ctx ExprContext, opTerm *term) (v any, err error) {
-	name, _ := opTerm.tk.Value.(string)
-	v, err = CallFunctionByTerm(ctx, name, opTerm)
+func evalFuncCall(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	name, _ := opTerm.Tk.Value.(string)
+	v, err = kern.CallFunctionByTerm(ctx, name, opTerm)
 	return
 }
 
 // -------- function definition term
-func newFuncDefTerm(tk *Token, args []*term) *term {
-	return &term{
-		tk:       *tk, // value is the expression body
-		parent:   nil,
-		children: args, // function params
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalFuncDef,
+func newFuncDefTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk, // value is the expression body
+		Parent:   nil,
+		Children: args, // function params
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalFuncDef,
 	}
 }
 
 // -------- eval func def
-func evalFuncDef(ctx ExprContext, opTerm *term) (v any, err error) {
-	bodySpec := opTerm.value()
-	if expr, ok := bodySpec.(*ast); ok {
-		paramList := make([]ExprFuncParam, 0, len(opTerm.children))
-		for _, param := range opTerm.children {
+func evalFuncDef(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	bodySpec := opTerm.Value()
+	if ast, ok := bodySpec.(*scan.Ast); ok {
+		paramList := make([]kern.ExprFuncParam, 0, len(opTerm.Children))
+		for _, param := range opTerm.Children {
 			var defValue any
-			flags := paramFlags(0)
-			if len(param.children) > 0 {
-				flags |= PfDefault
-				if defValue, err = param.children[0].compute(ctx); err != nil {
+			flags := kern.FuncParamFlags(0)
+			if len(param.Children) > 0 {
+				flags |= kern.PfDefault
+				if defValue, err = param.Children[0].Compute(ctx); err != nil {
 					return
 				}
 			}
-			info := NewFuncParamFlagDef(param.source(), flags, defValue)
+			info := kern.NewFuncParamFlagDef(param.Source(), flags, defValue)
 			paramList = append(paramList, info)
 		}
-		v = newExprFunctor(expr, paramList, ctx)
+		v = newExprFunctor(ast, paramList, ctx)
 	} else {
 		err = errors.New("invalid function definition: the body specification must be an expression")
 	}

operand-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-iterator.go
@@ -7,29 +7,32 @@ package expr
 import (
 	"slices"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- iterator term
 
-func newIteratorTerm(tk *Token, args []*term) *term {
-	tk.Sym = SymIterator
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: args,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalIterator,
+func newIteratorTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	tk.Sym = scan.SymIterator
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: args,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalIterator,
 	}
 }
 
 // -------- eval iterator
 
-func evalTermArray(ctx ExprContext, terms []*term) (values []any, err error) {
+func evalTermArray(ctx kern.ExprContext, terms []*scan.Term) (values []any, err error) {
 	values = make([]any, len(terms))
 	for i, t := range terms {
 		var value any
-		if value, err = t.compute(ctx); err == nil {
+		if value, err = t.Compute(ctx); err == nil {
 			values[i] = value
 		} else {
 			break
@@ -38,25 +41,25 @@ func evalTermArray(ctx ExprContext, terms []*term) (values []any, err error) {
 	return
 }
 
-func evalFirstChild(ctx ExprContext, iteratorTerm *term) (value any, err error) {
-	if len(iteratorTerm.children) < 1 || iteratorTerm.children[0] == nil {
+func evalFirstChild(ctx kern.ExprContext, iteratorTerm *scan.Term) (value any, err error) {
+	if len(iteratorTerm.Children) < 1 || iteratorTerm.Children[0] == nil {
 		err = iteratorTerm.Errorf("missing the data-source parameter")
 		return
 	}
 
-	value, err = iteratorTerm.children[0].compute(ctx)
+	value, err = iteratorTerm.Children[0].Compute(ctx)
 	return
 }
 
-func getDataSourceDict(iteratorTerm *term, firstChildValue any) (ds map[string]Functor, err error) {
-	if dictAny, ok := firstChildValue.(*DictType); ok {
-		requiredFields := []string{NextName}
+func getDataSourceDict(iteratorTerm *scan.Term, firstChildValue any) (ds map[string]kern.Functor, err error) {
+	if dictAny, ok := firstChildValue.(*kern.DictType); ok {
+		requiredFields := []string{kern.NextName}
 		fieldsMask := 0b1
 		foundFields := 0
-		ds = make(map[string]Functor)
+		ds = make(map[string]kern.Functor)
 		for keyAny, item := range *dictAny {
 			if key, ok := keyAny.(string); ok {
-				if functor, ok := item.(Functor); ok {
+				if functor, ok := item.(kern.Functor); ok {
 					ds[key] = functor
 					if index := slices.Index(requiredFields, key); index >= 0 {
 						foundFields |= 1 << index
@@ -72,15 +75,15 @@ func getDataSourceDict(iteratorTerm *term, firstChildValue any) (ds map[string]F
 					missingFields = append(missingFields, field)
 				}
 			}
-			err = iteratorTerm.children[0].Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
+			err = iteratorTerm.Children[0].Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
 		}
 	}
 	return
 }
 
-func evalIterator(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalIterator(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var firstChildValue any
-	var ds map[string]Functor
+	var ds map[string]kern.Functor
 
 	if firstChildValue, err = evalFirstChild(ctx, opTerm); err != nil {
 		return
@@ -95,24 +98,24 @@ func evalIterator(ctx ExprContext, opTerm *term) (v any, err error) {
 		if len(ds) > 0 {
 			var dc *dataCursor
 			dcCtx := ctx.Clone()
-			if initFunc, exists := ds[InitName]; exists && initFunc != nil {
+			if initFunc, exists := ds[kern.InitName]; exists && initFunc != nil {
 				var args []any
 				var resource any
-				if len(opTerm.children) > 1 {
-					if args, err = evalTermArray(ctx, opTerm.children[1:]); err != nil {
+				if len(opTerm.Children) > 1 {
+					if args, err = evalTermArray(ctx, opTerm.Children[1:]); err != nil {
 						return
 					}
 				} else {
 					args = []any{}
 				}
 
-				actualParams := bindActualParams(initFunc, args)
+				actualParams := kern.BindActualParams(initFunc, args)
 
 				initCtx := ctx.Clone()
-				if resource, err = initFunc.InvokeNamed(initCtx, InitName, actualParams); err != nil {
+				if resource, err = initFunc.InvokeNamed(initCtx, kern.InitName, actualParams); err != nil {
 					return
 				}
-				exportObjects(dcCtx, initCtx)
+				kern.ExportObjects(dcCtx, initCtx)
 				dc = NewDataCursor(dcCtx, ds, resource)
 			} else {
 				dc = NewDataCursor(dcCtx, ds, nil)
@@ -120,30 +123,66 @@ func evalIterator(ctx ExprContext, opTerm *term) (v any, err error) {
 
 			v = dc
 		} else {
-			if dictIt, ok := firstChildValue.(*DictType); ok {
+			if dictIt, ok := firstChildValue.(*kern.DictType); ok {
 				var args []any
-				if args, err = evalSibling(ctx, opTerm.children, nil); err == nil {
+				if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
 					v, err = NewDictIterator(dictIt, args)
 				}
 			} else {
-				err = opTerm.children[0].Errorf("the data-source must be a dictionary")
+				err = opTerm.Children[0].Errorf("the data-source must be a dictionary")
 			}
 		}
-	} else if list, ok := firstChildValue.(*ListType); ok {
+	} else if list, ok := firstChildValue.(*kern.ListType); ok {
 		var args []any
-		if args, err = evalSibling(ctx, opTerm.children, nil); err == nil {
+		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
 			v = NewListIterator(list, args)
 		}
+	} else if intVal, ok := firstChildValue.(int64); ok {
+		var args []any
+		if args, err = evalSiblings(ctx, opTerm.Children, intVal); err == nil {
+			v, err = NewIntIterator(args)
+		}
+	} else if it, ok := firstChildValue.(kern.Iterator); ok {
+		v, err = NewIterIter(it, ctx, opTerm.Children[1:])
 	} else {
-		var list []any
-		if list, err = evalSibling(ctx, opTerm.children, firstChildValue); err == nil {
-			v = NewArrayIterator(list)
+		var siblings []any
+		if siblings, err = evalSiblings(ctx, opTerm.Children, firstChildValue); err == nil {
+			v = NewArrayIterator(siblings)
 		}
 	}
 	return
 }
 
-func evalSibling(ctx ExprContext, terms []*term, firstChildValue any) (list []any, err error) {
+// func evalIterIter(ctx kern.ExprContext, firstChildValue any, siblings []any) (v any, err error) {
+// 	var op kern.Functor
+// 	var args map[string]any
+
+// 	if it, ok := firstChildValue.(kern.Iterator); ok {
+// 		if len(siblings) > 1 {
+// 			if op, ok = siblings[1].(kern.Functor); ok {
+// 				args = make(map[string]any, len(siblings)-2)
+// 				for i, arg := range siblings[2:] {
+// 					switch a := arg.(type) {
+// 					case *kern.DictType:
+// 						for keyAny, item := range *a {
+// 							if key, ok := keyAny.(string); ok {
+// 								args[key] = item
+// 							}
+// 						}
+// 					default:
+// 						args["arg"+strconv.Itoa(i+1)] = arg
+// 					}
+// 				}
+// 			} else if op == nil {
+// 				return nil, fmt.Errorf("the first sibling parameter must be a functor to be used as operation for the iterator")
+// 			}
+// 		}
+// 		v, err = NewIterIter(it, ctx, op, args)
+// 	}
+// 	return
+// }
+
+func evalSiblings(ctx kern.ExprContext, terms []*scan.Term, firstChildValue any) (list []any, err error) {
 	items := make([]any, 0, len(terms))
 	for i, tree := range terms {
 		var param any
@@ -152,7 +191,7 @@ func evalSibling(ctx ExprContext, terms []*term, firstChildValue any) (list []an
 				continue
 			}
 			param = firstChildValue
-		} else if param, err = tree.compute(ctx); err != nil {
+		} else if param, err = tree.Compute(ctx); err != nil {
 			break
 		}
 		items = append(items, param)

operand-list.go

@@ -1,32 +1,37 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-list.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 // -------- list term
-func newListTermA(args ...*term) *term {
+func newListTermA(args ...*scan.Term) *scan.Term {
 	return newListTerm(0, 0, args)
 }
 
-func newListTerm(row, col int, args []*term) *term {
-	return &term{
-		tk:       *NewValueToken(row, col, SymList, "[]", args),
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalList,
+func newListTerm(row, col int, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(row, col, scan.SymList, "[]", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalList,
 	}
 }
 
 // -------- list func
-func evalList(ctx ExprContext, opTerm *term) (v any, err error) {
-	list, _ := opTerm.value().([]*term)
-	items := make(ListType, len(list))
+func evalList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	list, _ := opTerm.Value().([]*scan.Term)
+	items := make(kern.ListType, len(list))
 	for i, tree := range list {
 		var param any
-		if param, err = tree.compute(ctx); err != nil {
+		if param, err = tree.Compute(ctx); err != nil {
 			break
 		}
 		items[i] = param

operand-literal.go

@@ -1,33 +1,38 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-literal.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 // -------- literal term
-func newLiteralTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalLiteral,
+func newLiteralTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalLiteral,
 	}
 }
 
 // -------- eval func
-func evalLiteral(ctx ExprContext, opTerm *term) (v any, err error) {
-	v = opTerm.tk.Value
+func evalLiteral(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	v = opTerm.Tk.Value
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymString, newLiteralTerm)
-	registerTermConstructor(SymInteger, newLiteralTerm)
-	registerTermConstructor(SymFloat, newLiteralTerm)
-	registerTermConstructor(SymFraction, newLiteralTerm)
-	registerTermConstructor(SymBool, newLiteralTerm)
-	registerTermConstructor(SymKwNil, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymString, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymInteger, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFloat, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFraction, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymBool, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymKwNil, newLiteralTerm)
 }

operand-selector-case.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-selector-case.go
@@ -7,19 +7,22 @@ package expr
 import (
 	"fmt"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- selector case term
 
 type selectorCase struct {
-	filterList *term
-	caseExpr   Expr
+	filterList *scan.Term
+	caseExpr   kern.Expr
 }
 
 func (sc *selectorCase) String() string {
 	var sb strings.Builder
 	if sc.filterList != nil {
-		sc.filterList.toString(&sb)
+		sc.filterList.ToString(&sb)
 		sb.WriteByte(' ')
 	}
 	sb.WriteByte('{')
@@ -28,23 +31,23 @@ func (sc *selectorCase) String() string {
 	return sb.String()
 }
 
-func newSelectorCaseTerm(row, col int, filterList *term, caseExpr Expr) *term {
-	tk := NewValueToken(row, col, SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalSelectorCase,
+func newSelectorCaseTerm(row, col int, filterList *scan.Term, caseExpr kern.Expr) *scan.Term {
+	tk := scan.NewValueToken(row, col, scan.SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalSelectorCase,
 	}
 }
 
 // -------- eval selector case
-func evalSelectorCase(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalSelectorCase(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var ok bool
-	if v, ok = opTerm.value().(*selectorCase); !ok {
-		err = fmt.Errorf("selector-case expected, got %T", opTerm.value())
+	if v, ok = opTerm.Value().(*selectorCase); !ok {
+		err = fmt.Errorf("selector-case expected, got %T", opTerm.Value())
 	}
 	return
 }

operand-var.go

@@ -1,31 +1,36 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-var.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 // -------- variable term
-func newVarTerm(tk *Token) *term {
-	t := &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalVar,
+func newVarTerm(tk *scan.Token) *scan.Term {
+	t := &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalVar,
 	}
-	t.tk.Sym = SymVariable
+	t.Tk.Sym = scan.SymVariable
 	return t
 }
 
 // -------- eval func
-func evalVar(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalVar(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var exists bool
-	name := opTerm.source()
-	if v, exists = GetVar(ctx, name); !exists {
-		if info, exists := GetFuncInfo(ctx, name); exists {
+	name := opTerm.Source()
+	if v, exists = ctx.GetVar(name); !exists {
+		if info, exists := ctx.GetFuncInfo(name); exists {
 			v = info.Functor()
 		} else {
 			err = fmt.Errorf("undefined variable or function %q", name)
@@ -36,5 +41,5 @@ func evalVar(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymIdentifier, newVarTerm)
+	scan.RegisterTermConstructor(scan.SymIdentifier, newVarTerm)
 }

operator-assign.go

@@ -1,34 +1,40 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserightChilded.
 
 // operator-assign.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/util"
+)
+
 //-------- assign term
 
-func newAssignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priAssign,
-		evalFunc: evalAssign,
+func newAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAssign,
+		EvalFunc: evalAssign,
 	}
 }
 
-func assignCollectionItem(ctx ExprContext, collectionTerm, keyListTerm *term, value any) (err error) {
+func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term, value any) (err error) {
 	var collectionValue, keyListValue, keyValue any
-	var keyList *ListType
+	var keyList *kern.ListType
 	var ok bool
 
-	if collectionValue, err = collectionTerm.compute(ctx); err != nil {
+	if collectionValue, err = collectionTerm.Compute(ctx); err != nil {
 		return
 	}
 
-	if keyListValue, err = keyListTerm.compute(ctx); err != nil {
+	if keyListValue, err = keyListTerm.Compute(ctx); err != nil {
 		return
-	} else if keyList, ok = keyListValue.(*ListType); !ok || len(*keyList) != 1 {
-		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, TypeName(keyListValue))
+	} else if keyList, ok = keyListValue.(*kern.ListType); !ok || len(*keyList) != 1 {
+		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, kern.TypeName(keyListValue))
 		return
 	}
 	if keyValue = (*keyList)[0]; keyValue == nil {
@@ -37,54 +43,54 @@ func assignCollectionItem(ctx ExprContext, collectionTerm, keyListTerm *term, va
 	}
 
 	switch collection := collectionValue.(type) {
-	case *ListType:
+	case *kern.ListType:
 		if index, ok := keyValue.(int64); ok {
-			err = collection.setItem(index, value)
+			err = collection.SetItem(index, value)
 		} else {
-			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, TypeName(keyValue))
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
 		}
-	case *DictType:
-		err = collection.setItem(keyValue, value)
+	case *kern.DictType:
+		collection.SetItem(keyValue, value)
 	default:
 		err = collectionTerm.Errorf("collection expected")
 	}
 	return
 }
 
-func assignValue(ctx ExprContext, leftTerm *term, v any) (err error) {
-	if leftTerm.symbol() == SymIndex {
-		err = assignCollectionItem(ctx, leftTerm.children[0], leftTerm.children[1], v)
+func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any) (err error) {
+	if leftTerm.Symbol() == scan.SymIndex {
+		err = assignCollectionItem(ctx, leftTerm.Children[0], leftTerm.Children[1], v)
 	} else {
-		ctx.UnsafeSetVar(leftTerm.source(), v)
+		ctx.UnsafeSetVar(leftTerm.Source(), v)
 	}
 	return
 }
 
-func evalAssign(ctx ExprContext, opTerm *term) (v any, err error) {
-	if err = opTerm.checkOperands(); err != nil {
+func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	leftSym := leftTerm.symbol()
-	if leftSym != SymVariable && leftSym != SymIndex {
-		err = leftTerm.tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.tk.source)
+	leftTerm := opTerm.Children[0]
+	leftSym := leftTerm.Symbol()
+	if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
 
-	rightChild := opTerm.children[1]
+	rightChild := opTerm.Children[1]
 
-	if v, err = rightChild.compute(ctx); err == nil {
-		if functor, ok := v.(Functor); ok {
-			if leftSym == SymVariable {
+	if v, err = rightChild.Compute(ctx); err == nil {
+		if functor, ok := v.(kern.Functor); ok {
+			if leftSym == scan.SymVariable {
 				if info := functor.GetFunc(); info != nil {
-					ctx.RegisterFunc(leftTerm.source(), info.Functor(), info.ReturnType(), info.Params())
+					ctx.RegisterFunc(leftTerm.Source(), info.Functor(), info.ReturnType(), info.Params())
 				} else if funcDef, ok := functor.(*exprFunctor); ok {
-					paramSpecs := ForAll(funcDef.params, func(p ExprFuncParam) ExprFuncParam { return p })
+					paramSpecs := util.ForAll(funcDef.params, func(p kern.ExprFuncParam) kern.ExprFuncParam { return p })
 
-					ctx.RegisterFunc(leftTerm.source(), functor, TypeAny, paramSpecs)
+					ctx.RegisterFunc(leftTerm.Source(), functor, kern.TypeAny, paramSpecs)
 				} else {
-					err = opTerm.Errorf("unknown function %s()", rightChild.source())
+					err = opTerm.Errorf("unknown function %s()", rightChild.Source())
 				}
 			} else {
 				err = assignValue(ctx, leftTerm, v)
@@ -101,29 +107,29 @@ func evalAssign(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- assign term
 
-func newOpAssignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priAssign,
-		evalFunc: evalOpAssign,
+func newOpAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAssign,
+		EvalFunc: evalOpAssign,
 	}
 }
 
-func getCollectionItemValue(ctx ExprContext, collectionTerm, keyListTerm *term) (value any, err error) {
+func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term) (value any, err error) {
 	var collectionValue, keyListValue, keyValue any
-	var keyList *ListType
+	var keyList *kern.ListType
 	var ok bool
 
-	if collectionValue, err = collectionTerm.compute(ctx); err != nil {
+	if collectionValue, err = collectionTerm.Compute(ctx); err != nil {
 		return
 	}
 
-	if keyListValue, err = keyListTerm.compute(ctx); err != nil {
+	if keyListValue, err = keyListTerm.Compute(ctx); err != nil {
 		return
-	} else if keyList, ok = keyListValue.(*ListType); !ok || len(*keyList) != 1 {
-		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, TypeName(keyListValue))
+	} else if keyList, ok = keyListValue.(*kern.ListType); !ok || len(*keyList) != 1 {
+		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, kern.TypeName(keyListValue))
 		return
 	}
 	if keyValue = (*keyList)[0]; keyValue == nil {
@@ -132,13 +138,13 @@ func getCollectionItemValue(ctx ExprContext, collectionTerm, keyListTerm *term)
 	}
 
 	switch collection := collectionValue.(type) {
-	case *ListType:
+	case *kern.ListType:
 		if index, ok := keyValue.(int64); ok {
 			value = (*collection)[index]
 		} else {
-			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, TypeName(keyValue))
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
 		}
-	case *DictType:
+	case *kern.DictType:
 		value = (*collection)[keyValue]
 	default:
 		err = collectionTerm.Errorf("collection expected")
@@ -146,55 +152,55 @@ func getCollectionItemValue(ctx ExprContext, collectionTerm, keyListTerm *term)
 	return
 }
 
-func getAssignValue(ctx ExprContext, leftTerm *term) (value any, err error) {
-	if leftTerm.symbol() == SymIndex {
-		value, err = getCollectionItemValue(ctx, leftTerm.children[0], leftTerm.children[1])
+func getAssignValue(ctx kern.ExprContext, leftTerm *scan.Term) (value any, err error) {
+	if leftTerm.Symbol() == scan.SymIndex {
+		value, err = getCollectionItemValue(ctx, leftTerm.Children[0], leftTerm.Children[1])
 	} else {
-		value, _ = ctx.GetVar(leftTerm.source())
+		value, _ = ctx.GetVar(leftTerm.Source())
 	}
 	return
 }
 
-func evalOpAssign(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue, leftValue any
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	leftSym := leftTerm.symbol()
-	if leftSym != SymVariable && leftSym != SymIndex {
-		err = leftTerm.tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.tk.source)
+	leftTerm := opTerm.Children[0]
+	leftSym := leftTerm.Symbol()
+	if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
 
-	rightChild := opTerm.children[1]
+	rightChild := opTerm.Children[1]
 
-	if rightValue, err = rightChild.compute(ctx); err == nil {
+	if rightValue, err = rightChild.Compute(ctx); err == nil {
 		if leftValue, err = getAssignValue(ctx, leftTerm); err == nil {
-			switch opTerm.symbol() {
-			case SymPlusEqual:
+			switch opTerm.Symbol() {
+			case scan.SymPlusEqual:
 				v, err = sumValues(opTerm, leftValue, rightValue)
-			case SymMinusEqual:
+			case scan.SymMinusEqual:
 				v, err = diffValues(opTerm, leftValue, rightValue)
-			case SymStarEqual:
+			case scan.SymStarEqual:
 				v, err = mulValues(opTerm, leftValue, rightValue)
-			case SymSlashEqual:
+			case scan.SymSlashEqual:
 				v, err = divValues(opTerm, leftValue, rightValue)
-			case SymPercEqual:
+			case scan.SymPercEqual:
 				v, err = remainderValues(opTerm, leftValue, rightValue)
-			case SymAmpersandEqual:
+			case scan.SymAmpersandEqual:
 				v, err = bitwiseAnd(opTerm, leftValue, rightValue)
-			case SymVertBarEqual:
+			case scan.SymVertBarEqual:
 				v, err = bitwiseOr(opTerm, leftValue, rightValue)
-			case SymCaretEqual:
+			case scan.SymCaretEqual:
 				v, err = bitwiseXor(opTerm, leftValue, rightValue)
-			case SymDoubleLessEqual:
+			case scan.SymDoubleLessEqual:
 				v, err = bitLeftShift(opTerm, leftValue, rightValue)
-			case SymDoubleGreaterEqual:
+			case scan.SymDoubleGreaterEqual:
 				v, err = bitRightShift(opTerm, leftValue, rightValue)
 			default:
-				err = opTerm.Errorf("unsupported assign operator %q", opTerm.source())
+				err = opTerm.Errorf("unsupported assign operator %q", opTerm.Source())
 			}
 			if err == nil {
 				err = assignValue(ctx, leftTerm, v)
@@ -206,15 +212,15 @@ func evalOpAssign(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymEqual, newAssignTerm)
-	registerTermConstructor(SymPlusEqual, newOpAssignTerm)
-	registerTermConstructor(SymMinusEqual, newOpAssignTerm)
-	registerTermConstructor(SymStarEqual, newOpAssignTerm)
-	registerTermConstructor(SymSlashEqual, newOpAssignTerm)
-	registerTermConstructor(SymPercEqual, newOpAssignTerm)
-	registerTermConstructor(SymDoubleLessEqual, newOpAssignTerm)
-	registerTermConstructor(SymDoubleGreaterEqual, newOpAssignTerm)
-	registerTermConstructor(SymAmpersandEqual, newOpAssignTerm)
-	registerTermConstructor(SymVertBarEqual, newOpAssignTerm)
-	registerTermConstructor(SymCaretEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymEqual, newAssignTerm)
+	scan.RegisterTermConstructor(scan.SymPlusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymMinusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymStarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymSlashEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymPercEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleLessEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleGreaterEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymAmpersandEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymVertBarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymCaretEqual, newOpAssignTerm)
 }

operator-bitwise.go

@@ -1,50 +1,55 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-bitwise.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- Bitwise NOT term
 
-func newBitwiseNotTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priBitwiseNot,
-		evalFunc: evalBitwiseNot,
+func newBitwiseNotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriBitwiseNot,
+		EvalFunc: evalBitwiseNot,
 	}
 }
 
-func evalBitwiseNot(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var value any
 
-	if value, err = opTerm.evalPrefix(ctx); err != nil {
+	if value, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if IsInteger(value) {
+	if kern.IsInteger(value) {
 		i, _ := value.(int64)
 		v = ^i
 	} else {
-		err = opTerm.errIncompatibleType(value)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(value)
 	}
 	return
 }
 
 //-------- Bitwise AND term
 
-func newBitwiseAndTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBitwiseAnd,
-		evalFunc: evalBitwiseAnd,
+func newBitwiseAndTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBitwiseAnd,
+		EvalFunc: evalBitwiseAnd,
 	}
 }
 
-func bitwiseAnd(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitwiseAnd(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	var leftInt, rightInt int64
 	var lok, rok bool
 
@@ -54,15 +59,15 @@ func bitwiseAnd(opTerm *term, leftValue, rightValue any) (v any, err error) {
 	if lok && rok {
 		v = leftInt & rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalBitwiseAnd(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseAnd(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 	v, err = bitwiseAnd(opTerm, leftValue, rightValue)
@@ -71,17 +76,17 @@ func evalBitwiseAnd(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- Bitwise OR term
 
-func newBitwiseOrTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBitwiseOr,
-		evalFunc: evalBitwiseOr,
+func newBitwiseOrTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBitwiseOr,
+		EvalFunc: evalBitwiseOr,
 	}
 }
 
-func bitwiseOr(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitwiseOr(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	var leftInt, rightInt int64
 	var lok, rok bool
 
@@ -91,15 +96,15 @@ func bitwiseOr(opTerm *term, leftValue, rightValue any) (v any, err error) {
 	if lok && rok {
 		v = leftInt | rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalBitwiseOr(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseOr(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -109,17 +114,17 @@ func evalBitwiseOr(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- Bitwise XOR term
 
-func newBitwiseXorTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBitwiseOr,
-		evalFunc: evalBitwiseXor,
+func newBitwiseXorTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBitwiseXor,
+		EvalFunc: evalBitwiseXor,
 	}
 }
 
-func bitwiseXor(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitwiseXor(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	var leftInt, rightInt int64
 	var lok, rok bool
 
@@ -129,15 +134,15 @@ func bitwiseXor(opTerm *term, leftValue, rightValue any) (v any, err error) {
 	if lok && rok {
 		v = leftInt ^ rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalBitwiseXor(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseXor(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -147,8 +152,8 @@ func evalBitwiseXor(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymTilde, newBitwiseNotTerm)
-	registerTermConstructor(SymAmpersand, newBitwiseAndTerm)
-	registerTermConstructor(SymVertBar, newBitwiseOrTerm)
-	registerTermConstructor(SymCaret, newBitwiseXorTerm)
+	scan.RegisterTermConstructor(scan.SymTilde, newBitwiseNotTerm)
+	scan.RegisterTermConstructor(scan.SymAmpersand, newBitwiseAndTerm)
+	scan.RegisterTermConstructor(scan.SymVertBar, newBitwiseOrTerm)
+	scan.RegisterTermConstructor(scan.SymCaret, newBitwiseXorTerm)
 }

operator-bool.go

@@ -1,52 +1,57 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-bool.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 //-------- NOT term
 
-func newNotTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priNot,
-		evalFunc: evalNot,
+func newNotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriNot,
+		EvalFunc: evalNot,
 	}
 }
 
-func evalNot(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if rightValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if rightValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if b, ok := ToBool(rightValue); ok {
+	if b, ok := kern.ToBool(rightValue); ok {
 		v = !b
 	} else {
-		err = opTerm.errIncompatibleType(rightValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
 	}
 	return
 }
 
 //-------- AND term
 
-func newAndTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priAnd,
-		evalFunc: evalAnd,
+func newAndTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAnd,
+		EvalFunc: evalAnd,
 	}
 }
 
-func evalAnd(ctx ExprContext, self *term) (v any, err error) {
-	if CtrlIsEnabled(ctx, ControlBoolShortcut) {
+func evalAnd(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
+	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
 		v, err = evalAndWithShortcut(ctx, self)
 	} else {
 		v, err = evalAndWithoutShortcut(ctx, self)
@@ -54,47 +59,48 @@ func evalAnd(ctx ExprContext, self *term) (v any, err error) {
 	return
 }
 
-func evalAndWithoutShortcut(ctx ExprContext, self *term) (v any, err error) {
+func evalAndWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var leftBool, rightBool bool
 	var lok, rok bool
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = self.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	leftBool, lok = ToBool(leftValue)
-	rightBool, rok = ToBool(rightValue)
+	leftBool, lok = kern.ToBool(leftValue)
+	rightBool, rok = kern.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool && rightBool
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = self.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalAndWithShortcut(ctx ExprContext, self *term) (v any, err error) {
+func evalAndWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if err = self.checkOperands(); err != nil {
+	if err = self.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = self.children[0].compute(ctx); err != nil {
+	if leftValue, err = self.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if leftBool, lok := ToBool(leftValue); !lok {
-		err = fmt.Errorf("got %s as left operand type of 'AND' operator, it must be bool", TypeName(leftValue))
-		return
+	if leftBool, lok := kern.ToBool(leftValue); !lok {
+		// err = fmt.Errorf("got %s as left operand type of 'AND' operator, it must be bool", expr.TypeName(leftValue))
+		// return
+		err = self.ErrIncompatibleType(leftValue, "left")
 	} else if !leftBool {
 		v = false
-	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if rightBool, rok := ToBool(rightValue); rok {
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
+		if rightBool, rok := kern.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
-			err = self.errIncompatibleTypes(leftValue, rightValue)
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	}
 	return
@@ -102,18 +108,18 @@ func evalAndWithShortcut(ctx ExprContext, self *term) (v any, err error) {
 
 //-------- OR term
 
-func newOrTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priOr,
-		evalFunc: evalOr,
+func newOrTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriOr,
+		EvalFunc: evalOr,
 	}
 }
 
-func evalOr(ctx ExprContext, self *term) (v any, err error) {
-	if CtrlIsEnabled(ctx, ControlBoolShortcut) {
+func evalOr(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
+	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
 		v, err = evalOrWithShortcut(ctx, self)
 	} else {
 		v, err = evalOrWithoutShortcut(ctx, self)
@@ -121,47 +127,47 @@ func evalOr(ctx ExprContext, self *term) (v any, err error) {
 	return
 }
 
-func evalOrWithoutShortcut(ctx ExprContext, self *term) (v any, err error) {
+func evalOrWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var leftBool, rightBool bool
 	var lok, rok bool
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = self.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	leftBool, lok = ToBool(leftValue)
-	rightBool, rok = ToBool(rightValue)
+	leftBool, lok = kern.ToBool(leftValue)
+	rightBool, rok = kern.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool || rightBool
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = self.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalOrWithShortcut(ctx ExprContext, self *term) (v any, err error) {
+func evalOrWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if err = self.checkOperands(); err != nil {
+	if err = self.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = self.children[0].compute(ctx); err != nil {
+	if leftValue, err = self.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if leftBool, lok := ToBool(leftValue); !lok {
-		err = fmt.Errorf("got %s as left operand type of 'OR' operator, it must be bool", TypeName(leftValue))
+	if leftBool, lok := kern.ToBool(leftValue); !lok {
+		err = fmt.Errorf("got %s as left operand type of 'OR' operator, it must be bool", kern.TypeName(leftValue))
 		return
 	} else if leftBool {
 		v = true
-	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if rightBool, rok := ToBool(rightValue); rok {
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
+		if rightBool, rok := kern.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
-			err = self.errIncompatibleTypes(leftValue, rightValue)
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	}
 	return
@@ -169,7 +175,7 @@ func evalOrWithShortcut(ctx ExprContext, self *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymNot, newNotTerm)
-	registerTermConstructor(SymAnd, newAndTerm)
-	registerTermConstructor(SymOr, newOrTerm)
+	scan.RegisterTermConstructor(scan.SymNot, newNotTerm)
+	scan.RegisterTermConstructor(scan.SymAnd, newAndTerm)
+	scan.RegisterTermConstructor(scan.SymOr, newOrTerm)
 }

operator-builtin.go

@@ -1,50 +1,55 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-builtin.go
 package expr
 
-import "io"
+import (
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 //-------- builtin term
 
-func newBuiltinTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalBuiltin,
+func newBuiltinTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalBuiltin,
 	}
 }
 
-func evalBuiltin(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	count := 0
-	if IsString(childValue) {
+	if kern.IsString(childValue) {
 		module, _ := childValue.(string)
-		count, err = ImportInContextByGlobPattern(module)
+		count, err = ImportInContextByGlobPattern(ctx, module)
 	} else {
 		var moduleSpec any
-		var it Iterator
-		if it, err = NewIterator(childValue); err != nil {
+		var it kern.Iterator
+		if it, err = NewIterator(ctx, childValue, nil); err != nil {
 			return
 		}
 		for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
 			if module, ok := moduleSpec.(string); ok {
-				if ImportInContext(module) {
+				if ImportInContext(ctx, module) {
 					count++
 				} else {
 					err = opTerm.Errorf("unknown builtin module %q", module)
 					break
 				}
 			} else {
-				err = opTerm.Errorf("expected string at item nr %d, got %s", it.Index()+1, TypeName(moduleSpec))
+				err = opTerm.Errorf("expected string at item nr %d, got %s", it.Index()+1, kern.TypeName(moduleSpec))
 				break
 			}
 		}
@@ -60,5 +65,5 @@ func evalBuiltin(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwBuiltin, newBuiltinTerm)
+	scan.RegisterTermConstructor(scan.SymKwBuiltin, newBuiltinTerm)
 }

operator-but.go

@@ -1,27 +1,32 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-but.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- but term
 
-func newButTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBut,
-		evalFunc: evalBut,
+func newButTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBut,
+		EvalFunc: evalBut,
 	}
 }
 
-func evalBut(ctx ExprContext, opTerm *term) (v any, err error) {
-	_, v, err = opTerm.evalInfix(ctx)
+func evalBut(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	_, v, err = opTerm.EvalInfix(ctx)
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymKwBut, newButTerm)
+	scan.RegisterTermConstructor(scan.SymKwBut, newButTerm)
 }

operator-context.go

@@ -1,39 +1,44 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-context-value.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- context term
 
-func newContextTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priIncDec,
-		evalFunc: evalContextValue,
+func newContextTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalContextValue,
 	}
 }
 
-func evalContextValue(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	var sourceCtx ExprContext
-	if len(opTerm.children) == 0 {
+	var sourceCtx kern.ExprContext
+	if len(opTerm.Children) == 0 {
 		sourceCtx = ctx
-	} else if opTerm.children[0].symbol() == SymVariable && opTerm.children[0].source() == "global" {
-		sourceCtx = globalCtx
-	} else if childValue, err = opTerm.evalPrefix(ctx); err == nil {
+	} else if opTerm.Children[0].Symbol() == scan.SymVariable && opTerm.Children[0].Source() == "global" {
+		sourceCtx = ctx.GetGlobal()
+	} else if childValue, err = opTerm.EvalPrefix(ctx); err == nil {
 		if dc, ok := childValue.(*dataCursor); ok {
 			sourceCtx = dc.ctx
 		}
 	}
 
 	if sourceCtx != nil {
-		if formatter, ok := sourceCtx.(DictFormat); ok {
+		if formatter, ok := sourceCtx.(kern.DictFormat); ok {
 			v = formatter.ToDict()
-		} else if formatter, ok := sourceCtx.(Formatter); ok {
+		} else if formatter, ok := sourceCtx.(kern.Formatter); ok {
 			v = formatter.ToString(0)
 		} else {
 			// keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
@@ -49,12 +54,12 @@ func evalContextValue(ctx ExprContext, opTerm *term) (v any, err error) {
 			v = d
 		}
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleDollar, newContextTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleDollar, newContextTerm)
 }

operator-ctrl.go

@@ -1,27 +1,32 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-ctrl.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- export all term
 
-func newExportAllTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalExportAll,
+func newExportAllTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalExportAll,
 	}
 }
 
-func evalExportAll(ctx ExprContext, opTerm *term) (v any, err error) {
-	CtrlEnable(ctx, control_export_all)
+func evalExportAll(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	CtrlEnable(ctx, kern.ControlExportAll)
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleAt, newExportAllTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleAt, newExportAllTerm)
 }

operator-default.go

@@ -1,38 +1,43 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-default.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- default term
 
-func newDefaultTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDefault,
-		evalFunc: evalDefault,
+func newDefaultTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalDefault,
 	}
 }
 
-func evalDefault(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	if leftTerm.tk.Sym != SymVariable {
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
-		err = ErrLeftOperandMustBeVariable(leftTerm, opTerm)
+		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
 	}
 
-	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
+	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists {
 		v = leftValue
-	} else if rightValue, err = opTerm.children[1].compute(ctx); err == nil {
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 		v = rightValue
 	}
 	return
@@ -40,32 +45,32 @@ func evalDefault(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- alternate term
 
-func newAlternateTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDefault,
-		evalFunc: evalAlternate,
+func newAlternateTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalAlternate,
 	}
 }
 
-func evalAlternate(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalAlternate(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	if leftTerm.tk.Sym != SymVariable {
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
-		err = ErrLeftOperandMustBeVariable(leftTerm, opTerm)
+		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
 	}
 
-	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists && leftValue != nil {
-		if rightValue, err = opTerm.children[1].compute(ctx); err == nil {
+	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists && leftValue != nil {
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 			v = rightValue
 		}
 	} else {
@@ -76,41 +81,41 @@ func evalAlternate(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- default assign term
 
-func newDefaultAssignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDefault,
-		evalFunc: evalAssignDefault,
+func newDefaultAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalAssignDefault,
 	}
 }
 
-func evalAssignDefault(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	if leftTerm.tk.Sym != SymVariable {
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
-		err = ErrLeftOperandMustBeVariable(leftTerm, opTerm)
+		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
 	}
 
-	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
+	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists {
 		v = leftValue
-	} else if rightValue, err = opTerm.children[1].compute(ctx); err == nil {
-		if functor, ok := rightValue.(Functor); ok {
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+		if functor, ok := rightValue.(kern.Functor); ok {
 			//ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
-			ctx.RegisterFunc(leftTerm.source(), functor, TypeAny, []ExprFuncParam{
-				NewFuncParamFlag(ParamValue, PfDefault|PfRepeat),
+			ctx.RegisterFunc(leftTerm.Source(), functor, kern.TypeAny, []kern.ExprFuncParam{
+				kern.NewFuncParamFlag(kern.ParamValue, kern.PfDefault|kern.PfRepeat),
 			})
 		} else {
 			v = rightValue
-			ctx.UnsafeSetVar(leftTerm.source(), rightValue)
+			ctx.UnsafeSetVar(leftTerm.Source(), rightValue)
 		}
 	}
 	return
@@ -118,7 +123,7 @@ func evalAssignDefault(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleQuestion, newDefaultTerm)
-	registerTermConstructor(SymQuestionEqual, newDefaultAssignTerm)
-	registerTermConstructor(SymQuestionExclam, newAlternateTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleQuestion, newDefaultTerm)
+	scan.RegisterTermConstructor(scan.SymQuestionEqual, newDefaultAssignTerm)
+	scan.RegisterTermConstructor(scan.SymQuestionExclam, newAlternateTerm)
 }

operator-digest.go

@@ -0,0 +1,73 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-digest.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- digest term
+
+func newDigestTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalDigest,
+	}
+}
+
+func evalDigest(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var it kern.Iterator
+	var item, lastValue any
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+		return nil, fmt.Errorf("left operand of DIGEST must be an iterable data-source; got %s", kern.TypeName(leftValue))
+	}
+
+	lastValue = nil
+	for item, err = it.Next(); err == nil; item, err = it.Next() {
+		ctx.SetVar("_", item)
+		ctx.SetVar("__", it.Index())
+		ctx.SetVar("_#", it.Count())
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			if rightValue == nil {
+				break
+			} else {
+				lastValue = rightValue
+			}
+		}
+		ctx.DeleteVar("_#")
+		ctx.DeleteVar("__")
+		ctx.DeleteVar("_")
+		if err != nil {
+			break
+		}
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	v = lastValue
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwDigest, newDigestTerm)
+}

operator-dot.go

@@ -1,36 +1,41 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-dot.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 // -------- dot term
-func newDotTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDot,
-		evalFunc: evalDot,
+func newDotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDot,
+		EvalFunc: evalDot,
 	}
 }
 
-func evalDot(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
-	if leftValue, err = opTerm.children[0].compute(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	indexTerm := opTerm.children[1]
+	indexTerm := opTerm.Children[1]
 
 	switch unboxedValue := leftValue.(type) {
-	case ExtIterator:
-		if indexTerm.symbol() == SymVariable /*|| indexTerm.symbol() == SymString */ {
-			opName := indexTerm.source()
+	case kern.ExtIterator:
+		if indexTerm.Tk.Sym == scan.SymVariable /*|| indexTerm.Tk.Sym == scan.SymString */ {
+			opName := indexTerm.Source()
 			if unboxedValue.HasOperation(opName) {
 				v, err = unboxedValue.CallOperation(opName, map[string]any{})
 			} else {
@@ -38,11 +43,27 @@ func evalDot(ctx ExprContext, opTerm *term) (v any, err error) {
 				v = false
 			}
 		} else {
-			err = indexTerm.tk.ErrorExpectedGot("identifier")
+			err = indexTerm.Tk.ErrorExpectedGot("identifier")
+		}
+	case *kern.DictType:
+		var ok bool
+		s := opTerm.Children[1].Tk.Sym
+		if s == scan.SymVariable || s == scan.SymString {
+			src := opTerm.Children[1].Source()
+			if len(src) > 1 && src[0] == '"' && src[len(src)-1] == '"' {
+				src = src[1 : len(src)-1]
+			}
+			if v, ok = unboxedValue.GetItem(src); !ok {
+				err = opTerm.Errorf("key %q not found", src)
+			}
+		} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			if v, ok = unboxedValue.GetItem(rightValue); !ok {
+				err = opTerm.Errorf("key %q not found", rightValue)
+			}
 		}
 	default:
-		if rightValue, err = opTerm.children[1].compute(ctx); err == nil {
-			err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			err = opTerm.Errorf("incompatible types: %s and %s", kern.TypeName(leftValue), kern.TypeName(rightValue))
 		}
 	}
 	return
@@ -50,5 +71,5 @@ func evalDot(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDot, newDotTerm)
+	scan.RegisterTermConstructor(scan.SymDot, newDotTerm)
 }

operator-fact.go

@@ -1,31 +1,36 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-fact.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 //-------- fact term
 
-func newFactTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPostfix,
-		priority: priFact,
-		evalFunc: evalFact,
+func newFactTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPostfix,
+		Priority: scan.PriFact,
+		EvalFunc: evalFact,
 	}
 }
 
-func evalFact(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalFact(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue any
 
-	if leftValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if IsInteger(leftValue) {
+	if kern.IsInteger(leftValue) {
 		if i, _ := leftValue.(int64); i >= 0 {
 			f := int64(1)
 			for k := int64(1); k <= i; k++ {
@@ -36,12 +41,12 @@ func evalFact(ctx ExprContext, opTerm *term) (v any, err error) {
 			err = fmt.Errorf("factorial of a negative integer (%d) is not allowed", i)
 		}
 	} else {
-		err = opTerm.errIncompatibleType(leftValue)
+		err = opTerm.Errorf("incompatible type for factorial: %s", kern.TypeName(leftValue))
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymExclamation, newFactTerm)
+	scan.RegisterTermConstructor(scan.SymExclamation, newFactTerm)
 }

operator-filter.go

@@ -0,0 +1,78 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-filter.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- map term
+
+func newFilterTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalFilter,
+	}
+}
+
+func evalFilter(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var it kern.Iterator
+	var item any
+	var ok bool
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if it, ok = leftValue.(kern.Iterator); !ok {
+		if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of FILTER must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
+	}
+
+	values := kern.NewListA()
+	for item, err = it.Next(); err == nil; item, err = it.Next() {
+		ctx.SetVar("_", item)
+		ctx.SetVar("__", it.Index())
+		ctx.SetVar("_#", it.Count())
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			if success, valid := kern.ToBool(rightValue); valid {
+				if success {
+					values.AppendItem(item)
+				}
+			} else {
+				err = fmt.Errorf("filter expression must return a boolean or a castable to boolean, got %v [%T]", rightValue, rightValue)
+			}
+		}
+		ctx.DeleteVar("_#")
+		ctx.DeleteVar("__")
+		ctx.DeleteVar("_")
+		if err != nil {
+			break
+		}
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	v = values
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwFilter, newFilterTerm)
+}

operator-fraction.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-fraction.go
@@ -8,27 +8,29 @@ package expr
 
 import (
 	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- fraction term
-func newFractionTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priFraction,
-		evalFunc: evalFraction,
+func newFractionTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriFraction,
+		EvalFunc: evalFraction,
 	}
 }
 
 // -------- eval func
-func evalFraction(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalFraction(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var numValue, denValue any
 	var num, den int64
 	var ok bool
 
-	if numValue, denValue, err = opTerm.evalInfix(ctx); err != nil {
+	if numValue, denValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 	if num, ok = numValue.(int64); !ok {
@@ -40,7 +42,7 @@ func evalFraction(ctx ExprContext, opTerm *term) (v any, err error) {
 		return
 	}
 	if den == 0 {
-		err = opTerm.errDivisionByZero()
+		err = opTerm.Errorf("division by zero")
 		return
 	}
 
@@ -49,16 +51,19 @@ func evalFraction(ctx ExprContext, opTerm *term) (v any, err error) {
 		num = -num
 	}
 	if num != 0 {
-		g := gcd(num, den)
-		num = num / g
-		den = den / g
+		if g := kern.Gcd(num, den); g != 1 {
+			num = num / g
+			den = den / g
+		}
 		if den == 1 {
 			v = num
 		} else {
-			v = &FractionType{num, den}
+			// v = &expr.FractionType{num, den}
+			v = kern.NewFraction(num, den)
 		}
 	} else {
-		v = &FractionType{0, den}
+		// v = &FractionType{0, den}
+		v = kern.NewFraction(0, den)
 	}
 	return
 }
@@ -66,5 +71,5 @@ func evalFraction(ctx ExprContext, opTerm *term) (v any, err error) {
 // init
 func init() {
 	// registerTermConstructor(SymVertBar, newFractionTerm)
-	registerTermConstructor(SymColon, newFractionTerm)
+	scan.RegisterTermConstructor(scan.SymColon, newFractionTerm)
 }

operator-groupby.go

@@ -0,0 +1,109 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-groupby.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- group by term
+
+func newGroupByTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalGroupBy,
+	}
+}
+
+func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var it kern.Iterator
+	var item any
+	var sKey string
+	var keyByIndex bool
+	var ok bool
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if it, ok = leftValue.(kern.Iterator); !ok {
+		if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
+	}
+
+	rightTk := opTerm.Children[1].Tk
+	if rightTk.IsSymbol(scan.SymVariable) && rightTk.Source() == "__" {
+		keyByIndex = true
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
+		return
+	} else if kern.IsString(rightValue) {
+		sKey = rightValue.(string)
+	} else {
+		return nil, fmt.Errorf("right operand of GROUPBY must be a string or identifier '__'; got %s", kern.TypeName(rightValue))
+	}
+
+	values := kern.MakeDict()
+	for item, err = it.Next(); err == nil; item, err = it.Next() {
+		ctx.SetVar("_", item)
+		ctx.SetVar("__", it.Index())
+		ctx.SetVar("_#", it.Count())
+
+		var sItemKey string
+
+		if d, ok := item.(*kern.DictType); ok {
+			if keyByIndex || len(sKey) == 0 {
+				sItemKey = strconv.Itoa(int(it.Index()))
+			} else if d.HasKey(sKey) {
+				if keyValue, exists := d.GetItem(sKey); exists {
+					sItemKey = fmt.Sprintf("%v", keyValue)
+				} else {
+					sItemKey = "_"
+				}
+			} else {
+				sItemKey = "_"
+			}
+		} else {
+			sItemKey = strconv.Itoa(int(it.Index()))
+		}
+
+		var ls *kern.ListType
+		if lsAny, exists := values.GetItem(sItemKey); exists && lsAny != nil {
+			ls = lsAny.(*kern.ListType)
+		}
+		if ls == nil {
+			ls = kern.NewListA()
+		}
+		ls.AppendItem(item)
+		values.SetItem(sItemKey, ls)
+
+		ctx.DeleteVar("_#")
+		ctx.DeleteVar("__")
+		ctx.DeleteVar("_")
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	v = values
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwGroupBy, newGroupByTerm)
+}

operator-in.go

@@ -1,18 +1,23 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-in.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- in term
 
-func newInTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalIn,
+func newInTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalIn,
 	}
 }
 
@@ -21,26 +26,26 @@ func newInTerm(tk *Token) (inst *term) {
 // 	return
 // }
 
-func evalIn(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalIn(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	if IsList(rightValue) {
-		list, _ := rightValue.(*ListType)
-		v = list.indexDeepSameCmp(leftValue) >= 0
-	} else if IsDict(rightValue) {
-		dict, _ := rightValue.(*DictType)
-		v = dict.hasKey(leftValue)
+	if kern.IsList(rightValue) {
+		list, _ := rightValue.(*kern.ListType)
+		v = list.IndexDeepSameCmp(leftValue) >= 0
+	} else if kern.IsDict(rightValue) {
+		dict, _ := rightValue.(*kern.DictType)
+		v = dict.HasKey(leftValue)
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymKwIn, newInTerm)
+	scan.RegisterTermConstructor(scan.SymKwIn, newInTerm)
 }

operator-include.go

@@ -1,31 +1,36 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-include.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- include term
 
-func newIncludeTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalInclude,
+func newIncludeTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalInclude,
 	}
 }
 
-func evalInclude(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalInclude(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	count := 0
-	if IsList(childValue) {
-		list, _ := childValue.(*ListType)
+	if kern.IsList(childValue) {
+		list, _ := childValue.(*kern.ListType)
 		for i, filePathSpec := range *list {
 			if filePath, ok := filePathSpec.(string); ok {
 				if v, err = EvalFile(ctx, filePath); err == nil {
@@ -39,13 +44,13 @@ func evalInclude(ctx ExprContext, opTerm *term) (v any, err error) {
 				break
 			}
 		}
-	} else if IsString(childValue) {
+	} else if kern.IsString(childValue) {
 		filePath, _ := childValue.(string)
 		if v, err = EvalFile(ctx, filePath); err == nil {
 			count++
 		}
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	if err != nil {
 		//v = count
@@ -56,5 +61,5 @@ func evalInclude(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwInclude, newIncludeTerm)
+	scan.RegisterTermConstructor(scan.SymKwInclude, newIncludeTerm)
 }

operator-index.go

@@ -1,29 +1,34 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-index.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 // -------- index term
-func newIndexTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDot,
-		evalFunc: evalIndex,
+func newIndexTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDot,
+		EvalFunc: evalIndex,
 	}
 }
 
-func verifyKey(indexList *ListType) (index any, err error) {
+func verifyKey(indexList *kern.ListType) (index any, err error) {
 	index = (*indexList)[0]
 	return
 }
 
-func verifyIndex(indexTerm *term, indexList *ListType, maxValue int) (index int, err error) {
+func verifyIndex(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (index int, err error) {
 	var v int
 
-	if v, err = ToGoInt((*indexList)[0], "index expression"); err == nil {
+	if v, err = kern.ToGoInt((*indexList)[0], "index expression"); err == nil {
 		if v < 0 && v >= -maxValue {
 			v = maxValue + v
 		}
@@ -36,11 +41,11 @@ func verifyIndex(indexTerm *term, indexList *ListType, maxValue int) (index int,
 	return
 }
 
-func verifyRange(indexTerm *term, indexList *ListType, maxValue int) (startIndex, endIndex int, err error) {
+func verifyRange(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (startIndex, endIndex int, err error) {
 	v, _ := ((*indexList)[0]).(*intPair)
 	startIndex = v.a
 	endIndex = v.b
-	if endIndex == ConstLastIndex {
+	if endIndex == kern.ConstLastIndex {
 		endIndex = maxValue
 	}
 	if startIndex < 0 && startIndex >= -maxValue {
@@ -59,17 +64,17 @@ func verifyRange(indexTerm *term, indexList *ListType, maxValue int) (startIndex
 	return
 }
 
-func evalIndex(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
-	var indexList *ListType
+	var indexList *kern.ListType
 	var ok bool
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	indexTerm := opTerm.children[1]
-	if indexList, ok = rightValue.(*ListType); !ok {
+	indexTerm := opTerm.Children[1]
+	if indexList, ok = rightValue.(*kern.ListType); !ok {
 		err = opTerm.Errorf("invalid index expression")
 		return
 	} else if len(*indexList) != 1 {
@@ -77,9 +82,9 @@ func evalIndex(ctx ExprContext, opTerm *term) (v any, err error) {
 		return
 	}
 
-	if IsInteger((*indexList)[0]) {
+	if kern.IsInteger((*indexList)[0]) {
 		switch unboxedValue := leftValue.(type) {
-		case *ListType:
+		case *kern.ListType:
 			var index int
 			if index, err = verifyIndex(indexTerm, indexList, len(*unboxedValue)); err == nil {
 				v = (*unboxedValue)[index]
@@ -89,17 +94,17 @@ func evalIndex(ctx ExprContext, opTerm *term) (v any, err error) {
 			if index, err = verifyIndex(indexTerm, indexList, len(unboxedValue)); err == nil {
 				v = string(unboxedValue[index])
 			}
-		case *DictType:
+		case *kern.DictType:
 			v, err = getDictItem(unboxedValue, indexTerm, indexList, rightValue)
 		default:
-			err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+			err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	} else if isIntPair((*indexList)[0]) {
 		switch unboxedValue := leftValue.(type) {
-		case *ListType:
+		case *kern.ListType:
 			var start, end int
 			if start, end, err = verifyRange(indexTerm, indexList, len(*unboxedValue)); err == nil {
-				sublist := ListType((*unboxedValue)[start:end])
+				sublist := kern.ListType((*unboxedValue)[start:end])
 				v = &sublist
 			}
 		case string:
@@ -108,19 +113,19 @@ func evalIndex(ctx ExprContext, opTerm *term) (v any, err error) {
 				v = unboxedValue[start:end]
 			}
 		default:
-			err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+			err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 		}
-	} else if IsDict(leftValue) {
-		d := leftValue.(*DictType)
+	} else if kern.IsDict(leftValue) {
+		d := leftValue.(*kern.DictType)
 		v, err = getDictItem(d, indexTerm, indexList, rightValue)
 	} else {
-		rightChild := opTerm.children[1]
+		rightChild := opTerm.Children[1]
 		err = rightChild.Errorf("invalid index type: %v", (*indexList)[0])
 	}
 	return
 }
 
-func getDictItem(d *DictType, indexTerm *term, indexList *ListType, rightValue any) (v any, err error) {
+func getDictItem(d *kern.DictType, indexTerm *scan.Term, indexList *kern.ListType, rightValue any) (v any, err error) {
 	var ok bool
 	var indexValue any
 
@@ -134,5 +139,5 @@ func getDictItem(d *DictType, indexTerm *term, indexList *ListType, rightValue a
 
 // init
 func init() {
-	registerTermConstructor(SymIndex, newIndexTerm)
+	scan.RegisterTermConstructor(scan.SymIndex, newIndexTerm)
 }

operator-insert.go

@@ -1,67 +1,72 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-insert.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- prepend term
 
-func newPrependTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priInsert,
-		evalFunc: evalPrepend,
+func newPrependTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriInsert,
+		EvalFunc: evalPrepend,
 	}
 }
 
-func newAppendTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priInsert,
-		evalFunc: evalAppend,
+func newAppendTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriInsert,
+		EvalFunc: evalAppend,
 	}
 }
 
-func evalPrepend(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalPrepend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	if IsList(rightValue) {
-		list, _ := rightValue.(*ListType)
-		newList := append(ListType{leftValue}, *list...)
+	if kern.IsList(rightValue) {
+		list, _ := rightValue.(*kern.ListType)
+		newList := append(kern.ListType{leftValue}, *list...)
 		v = &newList
-		if opTerm.children[1].symbol() == SymVariable {
-			ctx.UnsafeSetVar(opTerm.children[1].source(), v)
+		if opTerm.Children[1].Symbol() == scan.SymVariable {
+			ctx.UnsafeSetVar(opTerm.Children[1].Source(), v)
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalAppend(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalAppend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	if IsList(leftValue) {
-		list, _ := leftValue.(*ListType)
+	if kern.IsList(leftValue) {
+		list, _ := leftValue.(*kern.ListType)
 		newList := append(*list, rightValue)
 		v = &newList
-		if opTerm.children[0].symbol() == SymVariable {
-			ctx.UnsafeSetVar(opTerm.children[0].source(), v)
+		if opTerm.Children[0].Symbol() == scan.SymVariable {
+			ctx.UnsafeSetVar(opTerm.Children[0].Source(), v)
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
@@ -86,6 +91,6 @@ func evalAppend(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymPlusGreater, newPrependTerm)
-	registerTermConstructor(SymLessPlus, newAppendTerm)
+	scan.RegisterTermConstructor(scan.SymPlusGreater, newPrependTerm)
+	scan.RegisterTermConstructor(scan.SymLessPlus, newAppendTerm)
 }

operator-iter-value.go

@@ -1,32 +1,37 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-iter-value.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- iter value term
 
-func newIterValueTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priDereference,
-		evalFunc: evalIterValue,
+func newIterValueTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriDereference,
+		EvalFunc: evalIterValue,
 	}
 }
 
-func evalIterValue(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalIterValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if it, ok := childValue.(Iterator); ok {
+	if it, ok := childValue.(kern.Iterator); ok {
 		v, err = it.Current()
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
@@ -34,5 +39,5 @@ func evalIterValue(ctx ExprContext, opTerm *term) (v any, err error) {
 // init
 func init() {
 	//	registerTermConstructor(SymOpenClosedRound, newIterValueTerm)
-	registerTermConstructor(SymDereference, newIterValueTerm)
+	scan.RegisterTermConstructor(scan.SymDereference, newIterValueTerm)
 }

operator-join.go

@@ -0,0 +1,73 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-join.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- join term
+
+func newJoinTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalJoin,
+	}
+}
+
+func evalJoin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var itLeft, itRight kern.Iterator
+	var item any
+	var ok bool
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
+		return
+	}
+
+	if itLeft, ok = leftValue.(kern.Iterator); !ok {
+		if itLeft, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of JOIN must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
+	}
+
+	if itRight, ok = rightValue.(kern.Iterator); !ok {
+		if itRight, err = NewIterator(ctx, rightValue, nil); err != nil {
+			return nil, fmt.Errorf("right operand of JOIN must be an iterable data-source; got %s", kern.TypeName(rightValue))
+		}
+	}
+
+	values := kern.NewListA()
+	for _, it := range []kern.Iterator{itLeft, itRight} {
+		for item, err = it.Next(); err == nil; item, err = it.Next() {
+			values.AppendItem(item)
+		}
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	v = values
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwJoin, newJoinTerm)
+}

operator-length.go

@@ -1,38 +1,43 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-length.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- length term
 
-func newLengthTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalLength,
+func newLengthTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalLength,
 	}
 }
 
-func evalLength(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalLength(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if IsList(childValue) {
-		ls, _ := childValue.(*ListType)
+	if kern.IsList(childValue) {
+		ls, _ := childValue.(*kern.ListType)
 		v = int64(len(*ls))
-	} else if IsString(childValue) {
+	} else if kern.IsString(childValue) {
 		s, _ := childValue.(string)
 		v = int64(len(s))
-	} else if IsDict(childValue) {
-		m, _ := childValue.(*DictType)
+	} else if kern.IsDict(childValue) {
+		m, _ := childValue.(*kern.DictType)
 		v = int64(len(*m))
-	} else if it, ok := childValue.(Iterator); ok {
+	} else if it, ok := childValue.(kern.Iterator); ok {
 		v = int64(it.Count())
 		// if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(CountName) {
 		// 	count, _ := extIt.CallOperation(CountName, nil)
@@ -41,12 +46,12 @@ func evalLength(ctx ExprContext, opTerm *term) (v any, err error) {
 		// 	v = int64(it.Index() + 1)
 		// }
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymHash, newLengthTerm)
+	scan.RegisterTermConstructor(scan.SymHash, newLengthTerm)
 }

operator-map.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-map.go
@@ -7,45 +7,53 @@ package expr
 import (
 	"fmt"
 	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- map term
 
-func newMapTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priIterOp,
-		evalFunc: evalMap,
+func newMapTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalMap,
 	}
 }
 
-func evalMap(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalMap(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
-	var it Iterator
+	var it kern.Iterator
 	var item any
+	var ok bool
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = opTerm.children[0].compute(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
-		return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", TypeName(leftValue))
+	if it, ok = leftValue.(kern.Iterator); !ok {
+		if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
 	}
 
-	values := newListA()
+	values := kern.NewListA()
 	for item, err = it.Next(); err == nil; item, err = it.Next() {
 		ctx.SetVar("_", item)
-		ctx.SetVar("_index", it.Index())
-		ctx.SetVar("_count", it.Count())
-		if rightValue, err = opTerm.children[1].compute(ctx); err == nil {
-			values.appendItem(rightValue)
+		ctx.SetVar("__", it.Index())
+		ctx.SetVar("_#", it.Count())
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			values.AppendItem(rightValue)
 		}
+		ctx.DeleteVar("_#")
+		ctx.DeleteVar("__")
 		ctx.DeleteVar("_")
 		if err != nil {
 			break
@@ -54,11 +62,13 @@ func evalMap(ctx ExprContext, opTerm *term) (v any, err error) {
 	if err == io.EOF {
 		err = nil
 	}
-	v = values
+	if err == nil {
+		v = values
+	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymKwMap, newMapTerm)
+	scan.RegisterTermConstructor(scan.SymKwMap, newMapTerm)
 }

operator-plugin.go

@@ -1,30 +1,35 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-plugin.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- plugin term
 
-func newPluginTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalPlugin,
+func newPluginTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalPlugin,
 	}
 }
 
-func evalPlugin(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalPlugin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 	var count int
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if count, err = importPluginFromSearchPath(childValue); err == nil {
+	if count, err = importPluginFromSearchPath(ctx, childValue); err == nil {
 		v = int64(count)
 	}
 	return
@@ -32,5 +37,5 @@ func evalPlugin(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwPlugin, newPluginTerm)
+	scan.RegisterTermConstructor(scan.SymKwPlugin, newPluginTerm)
 }

operator-post-inc-dec.go

@@ -1,93 +1,96 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-post-inc-dec.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 // -------- post increment term
 
-func newPostIncTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPostfix,
-		priority: priIncDec,
-		evalFunc: evalPostInc,
+func newPostIncTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPostfix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPostInc,
 	}
 }
 
-func evalPostInc(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalPostInc(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if it, ok := childValue.(Iterator); ok {
+	if it, ok := childValue.(kern.Iterator); ok {
 		var namePrefix string
 		v, err = it.Next()
 
-		if opTerm.children[0].symbol() == SymVariable {
-			namePrefix = opTerm.children[0].source()
+		if opTerm.Children[0].Symbol() == scan.SymVariable {
+			namePrefix = opTerm.Children[0].Source()
 		}
 		ctx.UnsafeSetVar(namePrefix+"_index", it.Index())
 		if c, err1 := it.Current(); err1 == nil {
 			ctx.UnsafeSetVar(namePrefix+"_current", c)
 		}
 
-		if it.HasOperation(KeyName) {
-			if k, err1 := it.CallOperation(KeyName, nil); err1 == nil {
+		if it.HasOperation(kern.KeyName) {
+			if k, err1 := it.CallOperation(kern.KeyName, nil); err1 == nil {
 				ctx.UnsafeSetVar(namePrefix+"_key", k)
 			}
 		}
-		if it.HasOperation(ValueName) {
-			if v1, err1 := it.CallOperation(ValueName, nil); err1 == nil {
+		if it.HasOperation(kern.ValueName) {
+			if v1, err1 := it.CallOperation(kern.ValueName, nil); err1 == nil {
 				ctx.UnsafeSetVar(namePrefix+"_value", v1)
 			}
 		}
-	} else if IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	} else if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		v = childValue
 		i, _ := childValue.(int64)
-		ctx.SetVar(opTerm.children[0].source(), i+1)
+		ctx.SetVar(opTerm.Children[0].Source(), i+1)
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // -------- post decrement term
 
-func newPostDecTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPostfix,
-		priority: priIncDec,
-		evalFunc: evalPostDec,
+func newPostDecTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPostfix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPostDec,
 	}
 }
 
-func evalPostDec(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalPostDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	/* if it, ok := childValue.(Iterator); ok {
 		v, err = it.Next()
-	} else  */if IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	} else  */if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		v = childValue
 		i, _ := childValue.(int64)
-		ctx.SetVar(opTerm.children[0].source(), i-1)
+		ctx.SetVar(opTerm.Children[0].Source(), i-1)
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoublePlus, newPostIncTerm)
-	registerTermConstructor(SymDoubleMinus, newPostDecTerm)
+	scan.RegisterTermConstructor(scan.SymDoublePlus, newPostIncTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleMinus, newPostDecTerm)
 }

operator-pre-inc-dec.go

@@ -1,69 +1,73 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-pre-inc-dec.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 // -------- pre increment term
 
-func newPreIncTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priIncDec,
-		evalFunc: evalPreInc,
+func newPreIncTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPreInc,
 	}
 }
 
-func evalPreInc(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalPreInc(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		i := childValue.(int64) + 1
-		ctx.SetVar(opTerm.children[0].source(), i)
+		ctx.SetVar(opTerm.Children[0].Source(), i)
 		v = i
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // -------- pre decrement term
 
-func newPreDecTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priIncDec,
-		evalFunc: evalPreDec,
+func newPreDecTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPreDec,
 	}
 }
 
-func evalPreDec(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalPreDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		i := childValue.(int64) - 1
-		ctx.SetVar(opTerm.children[0].source(), i)
+		ctx.SetVar(opTerm.Children[0].Source(), i)
 		v = i
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymPreInc, newPreIncTerm)
-	registerTermConstructor(SymPreDec, newPreDecTerm)
+	scan.RegisterTermConstructor(scan.SymPreInc, newPreIncTerm)
+	scan.RegisterTermConstructor(scan.SymPreDec, newPreDecTerm)
 }

operator-prod.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-prod.go
@@ -6,45 +6,48 @@ package expr
 
 import (
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- multiply term
 
-func newMultiplyTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalMultiply,
+func newMultiplyTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalMultiply,
 	}
 }
 
-func mulValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
-	if IsString(leftValue) && IsInteger(rightValue) {
+func mulValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsString(leftValue) && kern.IsInteger(rightValue) {
 		s, _ := leftValue.(string)
 		n, _ := rightValue.(int64)
 		v = strings.Repeat(s, int(n))
-	} else if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
-		if IsFloat(leftValue) || IsFloat(rightValue) {
-			v = numAsFloat(leftValue) * numAsFloat(rightValue)
-		} else if isFraction(leftValue) || isFraction(rightValue) {
-			v, err = mulAnyFract(leftValue, rightValue)
+	} else if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) * kern.NumAsFloat(rightValue)
+		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+			v, err = kern.MulAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt * rightInt
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalMultiply(ctx ExprContext, prodTerm *term) (v any, err error) {
+func evalMultiply(ctx kern.ExprContext, prodTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = prodTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = prodTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -53,44 +56,44 @@ func evalMultiply(ctx ExprContext, prodTerm *term) (v any, err error) {
 
 //-------- divide term
 
-func newDivideTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalDivide,
+func newDivideTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalDivide,
 	}
 }
 
-func divValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
-	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
-		if IsFloat(leftValue) || IsFloat(rightValue) {
-			d := numAsFloat(rightValue)
+func divValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			d := kern.NumAsFloat(rightValue)
 			if d == 0.0 {
-				err = opTerm.errDivisionByZero()
+				err = opTerm.ErrDivisionByZero()
 			} else {
-				v = numAsFloat(leftValue) / d
+				v = kern.NumAsFloat(leftValue) / d
 			}
-		} else if isFraction(leftValue) || isFraction(rightValue) {
-			v, err = divAnyFract(leftValue, rightValue)
+		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+			v, err = kern.DivAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			if rightInt, _ := rightValue.(int64); rightInt == 0 {
-				err = opTerm.errDivisionByZero()
+				err = opTerm.ErrDivisionByZero()
 			} else {
 				v = leftInt / rightInt
 			}
 		}
-	} else if IsString(leftValue) && IsString(rightValue) {
+	} else if kern.IsString(leftValue) && kern.IsString(rightValue) {
 		source := leftValue.(string)
 		sep := rightValue.(string)
-		v = ListFromStrings(strings.Split(source, sep))
-	} else if IsString(leftValue) && IsInteger(rightValue) {
+		v = kern.ListFromStrings(strings.Split(source, sep))
+	} else if kern.IsString(leftValue) && kern.IsInteger(rightValue) {
 		source := leftValue.(string)
 		partSize := int(rightValue.(int64))
 		if partSize == 0 {
-			err = opTerm.errDivisionByZero()
+			err = opTerm.ErrDivisionByZero()
 		} else {
 			partCount := len(source) / partSize
 			remainder := len(source) % partSize
@@ -105,18 +108,18 @@ func divValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
 			if remainder > 0 {
 				parts = append(parts, source[len(source)-remainder:])
 			}
-			v = newList(parts)
+			v = kern.NewList(parts)
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalDivide(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalDivide(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -125,66 +128,66 @@ func evalDivide(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- divide as float term
 
-func newDivideAsFloatTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalDivideAsFloat,
+func newDivideAsFloatTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalDivideAsFloat,
 	}
 }
 
-func evalDivideAsFloat(ctx ExprContext, floatDivTerm *term) (v any, err error) {
+func evalDivideAsFloat(ctx kern.ExprContext, floatDivTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = floatDivTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = floatDivTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
-		d := numAsFloat(rightValue)
+	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		d := kern.NumAsFloat(rightValue)
 		if d == 0.0 {
-			err = floatDivTerm.errDivisionByZero()
+			err = floatDivTerm.ErrDivisionByZero()
 		} else {
-			v = numAsFloat(leftValue) / d
+			v = kern.NumAsFloat(leftValue) / d
 		}
 	} else {
-		err = floatDivTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = floatDivTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
 //-------- reminder term
 
-func newRemainderTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalRemainder,
+func newRemainderTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalRemainder,
 	}
 }
-func remainderValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
-	if IsInteger(leftValue) && IsInteger(rightValue) {
+func remainderValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
 		rightInt, _ := rightValue.(int64)
 		if rightInt == 0 {
-			err = opTerm.errDivisionByZero()
+			err = opTerm.ErrDivisionByZero()
 		} else {
 			leftInt, _ := leftValue.(int64)
 			v = leftInt % rightInt
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalRemainder(ctx ExprContext, remainderTerm *term) (v any, err error) {
+func evalRemainder(ctx kern.ExprContext, remainderTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = remainderTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = remainderTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -193,8 +196,8 @@ func evalRemainder(ctx ExprContext, remainderTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymStar, newMultiplyTerm)
-	registerTermConstructor(SymSlash, newDivideTerm)
-	registerTermConstructor(SymDotSlash, newDivideAsFloatTerm)
-	registerTermConstructor(SymPercent, newRemainderTerm)
+	scan.RegisterTermConstructor(scan.SymStar, newMultiplyTerm)
+	scan.RegisterTermConstructor(scan.SymSlash, newDivideTerm)
+	scan.RegisterTermConstructor(scan.SymDotSlash, newDivideAsFloatTerm)
+	scan.RegisterTermConstructor(scan.SymPercent, newRemainderTerm)
 }

operator-range.go

@@ -1,10 +1,15 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-range.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 // -------- range term
 type intPair struct {
@@ -12,10 +17,10 @@ type intPair struct {
 }
 
 func (p *intPair) TypeName() string {
-	return TypePair
+	return kern.TypePair
 }
 
-func (p *intPair) ToString(opt FmtOpt) string {
+func (p *intPair) ToString(opt kern.FmtOpt) string {
 	return fmt.Sprintf("(%d, %d)", p.a, p.b)
 }
 
@@ -24,38 +29,38 @@ func isIntPair(v any) bool {
 	return ok
 }
 
-func newRangeTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRange,
-		evalFunc: evalRange,
+func newRangeTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRange,
+		EvalFunc: evalRange,
 	}
 }
 
-func changeColonToRange(t *term) {
-	if t.tk.IsSymbol(SymColon) {
-		t.tk.Sym = SymRange
-		t.evalFunc = evalRange
+func changeColonToRange(t *scan.Term) {
+	if t.Tk.IsSymbol(scan.SymColon) {
+		t.Tk.Sym = scan.SymRange
+		t.EvalFunc = evalRange
 	}
 }
 
-func evalRange(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalRange(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if len(opTerm.children) == 0 {
+	if len(opTerm.Children) == 0 {
 		leftValue = int64(0)
 		rightValue = int64(-1)
-	} else if len(opTerm.children) == 1 {
-		if leftValue, err = opTerm.children[0].compute(ctx); err != nil {
+	} else if len(opTerm.Children) == 1 {
+		if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 			return
 		}
-		rightValue = int64(ConstLastIndex)
-	} else if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+		rightValue = int64(kern.ConstLastIndex)
+	} else if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
-	if !(IsInteger(leftValue) && IsInteger(rightValue)) {
+	if !(kern.IsInteger(leftValue) && kern.IsInteger(rightValue)) {
 		// err = opTerm.errIncompatibleTypes(leftValue, rightValue)
 		err = errRangeInvalidSpecification(opTerm)
 		return
@@ -68,15 +73,15 @@ func evalRange(ctx ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
-func errRangeInvalidSpecification(t *term) error {
+func errRangeInvalidSpecification(t *scan.Term) error {
 	return t.Errorf("invalid range specification")
 }
 
-func errRangeUnexpectedExpression(t *term) error {
+func errRangeUnexpectedExpression(t *scan.Term) error {
 	return t.Errorf("unexpected range expression")
 }
 
 // init
 func init() {
-	registerTermConstructor(SymRange, newRangeTerm)
+	scan.RegisterTermConstructor(scan.SymRange, newRangeTerm)
 }

operator-rel.go

@@ -1,42 +1,47 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-rel.go
 package expr
 
-import "reflect"
+import (
+	"reflect"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 //-------- equal term
 
-func newEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalEqual,
+func newEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalEqual,
 	}
 }
 
-type deepFuncTemplate func(a, b any) (eq bool, err error)
+// type deepFuncTemplate func(a, b any) (eq bool, err error)
 
-func equals(a, b any, deepCmp deepFuncTemplate) (eq bool, err error) {
-	if isNumOrFract(a) && isNumOrFract(b) {
-		if IsNumber(a) && IsNumber(b) {
-			if IsInteger(a) && IsInteger(b) {
+func equals(a, b any, deepCmp kern.DeepFuncTemplate) (eq bool, err error) {
+	if kern.IsNumOrFract(a) && kern.IsNumOrFract(b) {
+		if kern.IsNumber(a) && kern.IsNumber(b) {
+			if kern.IsInteger(a) && kern.IsInteger(b) {
 				li, _ := a.(int64)
 				ri, _ := b.(int64)
 				eq = li == ri
 			} else {
-				eq = numAsFloat(a) == numAsFloat(b)
+				eq = kern.NumAsFloat(a) == kern.NumAsFloat(b)
 			}
 		} else {
 			var cmp int
-			if cmp, err = cmpAnyFract(a, b); err == nil {
+			if cmp, err = kern.CmpAnyFract(a, b); err == nil {
 				eq = cmp == 0
 			}
 		}
-	} else if deepCmp != nil && IsList(a) && IsList(b) {
+	} else if deepCmp != nil && kern.IsList(a) && kern.IsList(b) {
 		eq, err = deepCmp(a, b)
 	} else {
 		eq = reflect.DeepEqual(a, b)
@@ -45,10 +50,10 @@ func equals(a, b any, deepCmp deepFuncTemplate) (eq bool, err error) {
 	return
 }
 
-func evalEqual(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -58,19 +63,19 @@ func evalEqual(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- not equal term
 
-func newNotEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalNotEqual,
+func newNotEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalNotEqual,
 	}
 }
 
-func evalNotEqual(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalNotEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	if v, err = evalEqual(ctx, opTerm); err == nil {
-		b, _ := ToBool(v)
+		b, _ := kern.ToBool(v)
 		v = !b
 	}
 	return
@@ -78,51 +83,51 @@ func evalNotEqual(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- less term
 
-func newLessTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalLess,
+func newLessTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalLess,
 	}
 }
 
-func lessThan(self *term, a, b any) (isLess bool, err error) {
-	if isNumOrFract(a) && isNumOrFract(b) {
-		if IsNumber(a) && IsNumber(b) {
-			if IsInteger(a) && IsInteger(b) {
+func lessThan(self *scan.Term, a, b any) (isLess bool, err error) {
+	if kern.IsNumOrFract(a) && kern.IsNumOrFract(b) {
+		if kern.IsNumber(a) && kern.IsNumber(b) {
+			if kern.IsInteger(a) && kern.IsInteger(b) {
 				li, _ := a.(int64)
 				ri, _ := b.(int64)
 				isLess = li < ri
 			} else {
-				isLess = numAsFloat(a) < numAsFloat(b)
+				isLess = kern.NumAsFloat(a) < kern.NumAsFloat(b)
 			}
 		} else {
 			var cmp int
-			if cmp, err = cmpAnyFract(a, b); err == nil {
+			if cmp, err = kern.CmpAnyFract(a, b); err == nil {
 				isLess = cmp < 0
 			}
 		}
-	} else if IsString(a) && IsString(b) {
+	} else if kern.IsString(a) && kern.IsString(b) {
 		ls, _ := a.(string)
 		rs, _ := b.(string)
 		isLess = ls < rs
 		// Inclusion test
-	} else if IsList(a) && IsList(b) {
-		aList, _ := a.(*ListType)
-		bList, _ := b.(*ListType)
-		isLess = len(*aList) < len(*bList) && bList.contains(aList)
+	} else if kern.IsList(a) && kern.IsList(b) {
+		aList, _ := a.(*kern.ListType)
+		bList, _ := b.(*kern.ListType)
+		isLess = len(*aList) < len(*bList) && bList.Contains(aList)
 	} else {
-		err = self.errIncompatibleTypes(a, b)
+		err = self.ErrIncompatibleTypes(a, b)
 	}
 	return
 }
 
-func evalLess(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalLess(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 	v, err = lessThan(opTerm, leftValue, rightValue)
@@ -131,21 +136,21 @@ func evalLess(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- less or equal term
 
-func newLessEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalLessEqual,
+func newLessEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalLessEqual,
 	}
 }
 
-func lessThanOrEqual(self *term, a, b any) (isLessEq bool, err error) {
+func lessThanOrEqual(self *scan.Term, a, b any) (isLessEq bool, err error) {
 	if isLessEq, err = lessThan(self, a, b); err == nil {
 		if !isLessEq {
-			if IsList(a) && IsList(b) {
-				isLessEq, err = sameContent(a, b)
+			if kern.IsList(a) && kern.IsList(b) {
+				isLessEq, err = kern.SameContent(a, b)
 			} else {
 				isLessEq, err = equals(a, b, nil)
 			}
@@ -154,10 +159,10 @@ func lessThanOrEqual(self *term, a, b any) (isLessEq bool, err error) {
 	return
 }
 
-func evalLessEqual(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalLessEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -168,20 +173,20 @@ func evalLessEqual(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- greater term
 
-func newGreaterTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalGreater,
+func newGreaterTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalGreater,
 	}
 }
 
-func evalGreater(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalGreater(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -191,20 +196,20 @@ func evalGreater(ctx ExprContext, opTerm *term) (v any, err error) {
 
 //-------- greater or equal term
 
-func newGreaterEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalGreaterEqual,
+func newGreaterEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalGreaterEqual,
 	}
 }
 
-func evalGreaterEqual(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalGreaterEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -214,10 +219,10 @@ func evalGreaterEqual(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleEqual, newEqualTerm)
-	registerTermConstructor(SymNotEqual, newNotEqualTerm)
-	registerTermConstructor(SymLess, newLessTerm)
-	registerTermConstructor(SymLessOrEqual, newLessEqualTerm)
-	registerTermConstructor(SymGreater, newGreaterTerm)
-	registerTermConstructor(SymGreaterOrEqual, newGreaterEqualTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleEqual, newEqualTerm)
+	scan.RegisterTermConstructor(scan.SymNotEqual, newNotEqualTerm)
+	scan.RegisterTermConstructor(scan.SymLess, newLessTerm)
+	scan.RegisterTermConstructor(scan.SymLessOrEqual, newLessEqualTerm)
+	scan.RegisterTermConstructor(scan.SymGreater, newGreaterTerm)
+	scan.RegisterTermConstructor(scan.SymGreaterOrEqual, newGreaterEqualTerm)
 }

operator-selector.go

@@ -1,27 +1,32 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-selector.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- selector term
 
-func newSelectorTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 3),
-		position: posInfix,
-		priority: priSelector,
-		evalFunc: evalSelector,
+func newSelectorTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 3),
+		Position: scan.PosInfix,
+		Priority: scan.PriSelector,
+		EvalFunc: evalSelector,
 	}
 }
 
-func trySelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (match bool, selectedValue any, err error) {
+func trySelectorCase(ctx kern.ExprContext, exprValue, caseSel any, caseIndex int) (match bool, selectedValue any, err error) {
 	caseData, _ := caseSel.(*selectorCase)
 	if caseData.filterList == nil {
 		selectedValue, err = caseData.caseExpr.Eval(ctx)
 		match = true
-	} else if filterList, ok := caseData.filterList.value().([]*term); ok {
+	} else if filterList, ok := caseData.filterList.Value().([]*scan.Term); ok {
 		if len(filterList) == 0 {
 			var valueAsInt = int64(0)
 			if b, ok := exprValue.(bool); ok {
@@ -38,7 +43,7 @@ func trySelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (ma
 		} else {
 			var caseValue any
 			for _, caseTerm := range filterList {
-				if caseValue, err = caseTerm.compute(ctx); err != nil || caseValue == exprValue {
+				if caseValue, err = caseTerm.Compute(ctx); err != nil || caseValue == exprValue {
 					selectedValue, err = caseData.caseExpr.Eval(ctx)
 					match = true
 					break
@@ -49,33 +54,33 @@ func trySelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (ma
 	return
 }
 
-func evalSelector(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalSelector(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var exprValue any
 	var match bool
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
-	exprTerm := opTerm.children[0]
-	if exprValue, err = exprTerm.compute(ctx); err != nil {
+	exprTerm := opTerm.Children[0]
+	if exprValue, err = exprTerm.Compute(ctx); err != nil {
 		return
 	}
 
-	caseListTerm := opTerm.children[1]
-	caseList, _ := caseListTerm.value().([]*term)
+	caseListTerm := opTerm.Children[1]
+	caseList, _ := caseListTerm.Value().([]*scan.Term)
 	for i, caseTerm := range caseList {
-		caseSel := caseTerm.value()
+		caseSel := caseTerm.Value()
 		if match, v, err = trySelectorCase(ctx, exprValue, caseSel, i); err != nil || match {
 			break
 		}
 	}
 	if err == nil && !match {
-		err = exprTerm.tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
+		err = exprTerm.Tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymSelector, newSelectorTerm)
+	scan.RegisterTermConstructor(scan.SymSelector, newSelectorTerm)
 }

operator-shift.go

@@ -1,36 +1,41 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-shift.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- bit right shift term
 
-func newRightShiftTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBinShift,
-		evalFunc: evalRightShift,
+func newRightShiftTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBinShift,
+		EvalFunc: evalRightShift,
 	}
 }
 
-func bitRightShift(opTerm *term, leftValue, rightValue any) (v any, err error) {
-	if IsInteger(leftValue) && IsInteger(rightValue) {
+func bitRightShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
 		leftInt := leftValue.(int64)
 		rightInt := rightValue.(int64)
 		v = leftInt >> rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalRightShift(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalRightShift(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -38,31 +43,31 @@ func evalRightShift(ctx ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
-func newLeftShiftTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBinShift,
-		evalFunc: evalLeftShift,
+func newLeftShiftTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBinShift,
+		EvalFunc: evalLeftShift,
 	}
 }
 
-func bitLeftShift(opTerm *term, leftValue, rightValue any) (v any, err error) {
-	if IsInteger(leftValue) && IsInteger(rightValue) {
+func bitLeftShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
 		leftInt := leftValue.(int64)
 		rightInt := rightValue.(int64)
 		v = leftInt << rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalLeftShift(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalLeftShift(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -72,6 +77,6 @@ func evalLeftShift(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleGreater, newRightShiftTerm)
-	registerTermConstructor(SymDoubleLess, newLeftShiftTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleGreater, newRightShiftTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleLess, newLeftShiftTerm)
 }

operator-sign.go

@@ -1,62 +1,65 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-sign.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- plus sign term
 
-func newPlusSignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk: *tk,
-		// class:    classOperator,
-		// kind:     kindUnknown,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalSign,
+func newPlusSignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalSign,
 	}
 }
 
-func newMinusSignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalSign,
+func newMinusSignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalSign,
 	}
 }
 
-func evalSign(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalSign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if rightValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if rightValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if IsFloat(rightValue) {
-		if opTerm.tk.Sym == SymChangeSign {
+	if kern.IsFloat(rightValue) {
+		if opTerm.Tk.Sym == scan.SymChangeSign {
 			f, _ := rightValue.(float64)
 			v = -f
 		} else {
 			v = rightValue
 		}
-	} else if IsInteger(rightValue) {
-		if opTerm.tk.Sym == SymChangeSign {
+	} else if kern.IsInteger(rightValue) {
+		if opTerm.Tk.Sym == scan.SymChangeSign {
 			i, _ := rightValue.(int64)
 			v = -i
 		} else {
 			v = rightValue
 		}
 	} else {
-		err = opTerm.errIncompatibleType(rightValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymUnchangeSign, newPlusSignTerm)
-	registerTermConstructor(SymChangeSign, newMinusSignTerm)
+	scan.RegisterTermConstructor(scan.SymUnchangeSign, newPlusSignTerm)
+	scan.RegisterTermConstructor(scan.SymChangeSign, newMinusSignTerm)
 }

operator-sum.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-sum.go
@@ -7,64 +7,67 @@ package expr
 import (
 	"fmt"
 	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- plus term
 
-func newPlusTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priSum,
-		evalFunc: evalPlus,
+func newPlusTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriSum,
+		EvalFunc: evalPlus,
 	}
 }
 
-func sumValues(plusTerm *term, leftValue, rightValue any) (v any, err error) {
-	if (IsString(leftValue) && isNumberString(rightValue)) || (IsString(rightValue) && isNumberString(leftValue)) {
+func sumValues(plusTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if (kern.IsString(leftValue) && kern.IsNumberString(rightValue)) || (kern.IsString(rightValue) && kern.IsNumberString(leftValue)) {
 		v = fmt.Sprintf("%v%v", leftValue, rightValue)
-	} else if IsNumber(leftValue) && IsNumber(rightValue) {
-		if IsFloat(leftValue) || IsFloat(rightValue) {
-			v = numAsFloat(leftValue) + numAsFloat(rightValue)
+	} else if kern.IsNumber(leftValue) && kern.IsNumber(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) + kern.NumAsFloat(rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt + rightInt
 		}
-	} else if IsList(leftValue) && IsList(rightValue) {
-		var leftList, rightList *ListType
-		leftList, _ = leftValue.(*ListType)
-		rightList, _ = rightValue.(*ListType)
+	} else if kern.IsList(leftValue) && kern.IsList(rightValue) {
+		var leftList, rightList *kern.ListType
+		leftList, _ = leftValue.(*kern.ListType)
+		rightList, _ = rightValue.(*kern.ListType)
 
-		sumList := make(ListType, 0, len(*leftList)+len(*rightList))
+		sumList := make(kern.ListType, 0, len(*leftList)+len(*rightList))
 		sumList = append(sumList, *leftList...)
 		sumList = append(sumList, *rightList...)
 		v = &sumList
-	} else if (isFraction(leftValue) && IsNumber(rightValue)) || (isFraction(rightValue) && IsNumber(leftValue)) {
-		if IsFloat(leftValue) || IsFloat(rightValue) {
-			v = numAsFloat(leftValue) + numAsFloat(rightValue)
+	} else if (kern.IsFraction(leftValue) && kern.IsNumber(rightValue)) || (kern.IsFraction(rightValue) && kern.IsNumber(leftValue)) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) + kern.NumAsFloat(rightValue)
 		} else {
-			v, err = sumAnyFract(leftValue, rightValue)
+			v, err = kern.SumAnyFract(leftValue, rightValue)
 		}
-	} else if IsDict(leftValue) && IsDict(rightValue) {
-		leftDict, _ := leftValue.(*DictType)
-		rightDict, _ := rightValue.(*DictType)
-		c := leftDict.clone()
-		c.merge(rightDict)
+	} else if kern.IsDict(leftValue) && kern.IsDict(rightValue) {
+		leftDict, _ := leftValue.(*kern.DictType)
+		rightDict, _ := rightValue.(*kern.DictType)
+		c := leftDict.Clone()
+		c.Merge(rightDict)
 		v = c
-	} else if isFraction(leftValue) && isFraction(rightValue) {
-		v, err = sumAnyFract(leftValue, rightValue)
+	} else if kern.IsFraction(leftValue) && kern.IsFraction(rightValue) {
+		v, err = kern.SumAnyFract(leftValue, rightValue)
 	} else {
-		err = plusTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = plusTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return v, err
 }
 
-func evalPlus(ctx ExprContext, plusTerm *term) (v any, err error) {
+func evalPlus(ctx kern.ExprContext, plusTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = plusTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = plusTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -73,31 +76,31 @@ func evalPlus(ctx ExprContext, plusTerm *term) (v any, err error) {
 
 //-------- minus term
 
-func newMinusTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priSum,
-		evalFunc: evalMinus,
+func newMinusTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriSum,
+		EvalFunc: evalMinus,
 	}
 }
 
-func diffValues(minusTerm *term, leftValue, rightValue any) (v any, err error) {
-	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
-		if IsFloat(leftValue) || IsFloat(rightValue) {
-			v = numAsFloat(leftValue) - numAsFloat(rightValue)
-		} else if isFraction(leftValue) || isFraction(rightValue) {
-			v, err = subAnyFract(leftValue, rightValue)
+func diffValues(minusTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) - kern.NumAsFloat(rightValue)
+		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+			v, err = kern.SubAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt - rightInt
 		}
-	} else if IsList(leftValue) && IsList(rightValue) {
-		leftList, _ := leftValue.(*ListType)
-		rightList, _ := rightValue.(*ListType)
-		diffList := make(ListType, 0, len(*leftList)-len(*rightList))
+	} else if kern.IsList(leftValue) && kern.IsList(rightValue) {
+		leftList, _ := leftValue.(*kern.ListType)
+		rightList, _ := rightValue.(*kern.ListType)
+		diffList := make(kern.ListType, 0, len(*leftList)-len(*rightList))
 		for _, item := range *leftList {
 			if slices.Index(*rightList, item) < 0 {
 				diffList = append(diffList, item)
@@ -105,15 +108,15 @@ func diffValues(minusTerm *term, leftValue, rightValue any) (v any, err error) {
 		}
 		v = &diffList
 	} else {
-		err = minusTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = minusTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalMinus(ctx ExprContext, minusTerm *term) (v any, err error) {
+func evalMinus(ctx kern.ExprContext, minusTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = minusTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = minusTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -122,6 +125,6 @@ func evalMinus(ctx ExprContext, minusTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymPlus, newPlusTerm)
-	registerTermConstructor(SymMinus, newMinusTerm)
+	scan.RegisterTermConstructor(scan.SymPlus, newPlusTerm)
+	scan.RegisterTermConstructor(scan.SymMinus, newMinusTerm)
 }

operator-unset.go

@@ -1,24 +1,29 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-unset.go
 package expr
 
-import "strings"
+import (
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 //-------- unset term
 
-func newUnsetTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalUnset,
+func newUnsetTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalUnset,
 	}
 }
 
-func deleteContextItem(ctx ExprContext, opTerm *term, item any) (deleted bool, err error) {
+func deleteContextItem(ctx kern.ExprContext, opTerm *scan.Term, item any) (deleted bool, err error) {
 	if name, ok := item.(string); ok {
 		var size int
 		if strings.HasSuffix(name, "()") {
@@ -31,22 +36,22 @@ func deleteContextItem(ctx ExprContext, opTerm *term, item any) (deleted bool, e
 			deleted = ctx.VarCount() < size
 		}
 	} else {
-		err = opTerm.errIncompatibleType(item)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(item)
 	}
 	return
 }
 
-func evalUnset(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalUnset(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 	var deleted bool
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	count := 0
-	if IsList(childValue) {
-		list, _ := childValue.(*ListType)
+	if kern.IsList(childValue) {
+		list, _ := childValue.(*kern.ListType)
 		for _, item := range *list {
 			if deleted, err = deleteContextItem(ctx, opTerm, item); err != nil {
 				break
@@ -65,5 +70,5 @@ func evalUnset(ctx ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwUnset, newUnsetTerm)
+	scan.RegisterTermConstructor(scan.SymKwUnset, newUnsetTerm)
 }

parser.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // parser.go
@@ -7,6 +7,7 @@ package expr
 import (
 	"errors"
 
+	"git.portale-stac.it/go-pkg/expr/scan"
 	"golang.org/x/exp/constraints"
 )
 
@@ -54,34 +55,34 @@ func NewParser() (p *parser) {
 	return p
 }
 
-func (parser *parser) Next(scanner *scanner) (tk *Token) {
-	for tk = scanner.Next(); tk.IsSymbol(SymComment); tk = scanner.Next() {
+func (parser *parser) Next(scanner *scan.Scanner) (tk *scan.Token) {
+	for tk = scanner.Next(); tk.IsSymbol(scan.SymComment); tk = scanner.Next() {
 	}
 	return
 }
 
-func (parser *parser) parseFuncCall(scanner *scanner, ctx parserContext, tk *Token) (tree *term, err error) {
-	args := make([]*term, 0, 10)
+func (parser *parser) parseFuncCall(scanner *scan.Scanner, ctx parserContext, tk *scan.Token) (tree *scan.Term, err error) {
+	args := make([]*scan.Term, 0, 10)
 	itemExpected := false
-	lastSym := SymUnknown
-	for lastSym != SymClosedRound && lastSym != SymEos {
-		var subTree *ast
-		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedRound); err != nil {
+	lastSym := scan.SymUnknown
+	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
+		var subTree *scan.Ast
+		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedRound); err != nil {
 			break
 		}
 		prev := scanner.Previous()
-		if subTree.root != nil {
-			args = append(args, subTree.root)
+		if subTree.Root() != nil {
+			args = append(args, subTree.Root())
 		} else if itemExpected {
 			err = prev.ErrorExpectedGot("function-param-value")
 			break
 		}
 
-		itemExpected = prev.Sym == SymComma
+		itemExpected = prev.Sym == scan.SymComma
 		lastSym = scanner.Previous().Sym
 	}
 	if err == nil {
-		if lastSym != SymClosedRound {
+		if lastSym != scan.SymClosedRound {
 			err = errors.New("unterminated arguments list")
 		} else {
 			tree = newFuncCallTerm(tk, args)
@@ -90,33 +91,33 @@ func (parser *parser) parseFuncCall(scanner *scanner, ctx parserContext, tk *Tok
 	return
 }
 
-func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
+func (parser *parser) parseFuncDef(scanner *scan.Scanner) (tree *scan.Term, err error) {
 	// Example: "add = func(x,y) {x+y}
-	var body *ast
-	args := make([]*term, 0)
-	lastSym := SymUnknown
+	var body *scan.Ast
+	args := make([]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	defaultParamsStarted := false
 	itemExpected := false
 	tk := scanner.Previous()
-	for lastSym != SymClosedRound && lastSym != SymEos {
+	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
 		tk = parser.Next(scanner)
-		if tk.IsSymbol(SymIdentifier) {
-			param := newTerm(tk)
+		if tk.IsSymbol(scan.SymIdentifier) {
+			param := scan.NewTerm(tk)
 			if len(args) > 0 {
 				if pos := paramAlreadyDefined(args, param); pos > 0 {
-					err = tk.Errorf("parameter %q at position %d already defined at position %d", param.source(), len(args)+1, pos)
+					err = tk.Errorf("parameter %q at position %d already defined at position %d", param.Source(), len(args)+1, pos)
 					break
 				}
 			}
 			args = append(args, param)
 			tk = parser.Next(scanner)
-			if tk.Sym == SymEqual {
-				var paramExpr *ast
+			if tk.Sym == scan.SymEqual {
+				var paramExpr *scan.Ast
 				defaultParamsStarted = true
-				if paramExpr, err = parser.parseItem(scanner, parserNoFlags, SymComma, SymClosedRound); err != nil {
+				if paramExpr, err = parser.parseItem(scanner, parserNoFlags, scan.SymComma, scan.SymClosedRound); err != nil {
 					break
 				}
-				param.forceChild(paramExpr.root)
+				param.ForceChild(paramExpr.Root())
 			} else if defaultParamsStarted {
 				err = tk.Errorf("can't mix default and non-default parameters")
 				break
@@ -127,74 +128,74 @@ func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == SymComma
+		itemExpected = lastSym == scan.SymComma
 	}
 
-	if err == nil && lastSym != SymClosedRound {
+	if err == nil && lastSym != scan.SymClosedRound {
 		err = tk.ErrorExpectedGot(")")
 	}
 	if err == nil {
 		tk = parser.Next(scanner)
-		if tk.IsSymbol(SymOpenBrace) {
-			body, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, SymClosedBrace)
+		if tk.IsSymbol(scan.SymOpenBrace) {
+			body, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymClosedBrace)
 		} else {
 			err = tk.ErrorExpectedGot("{")
 		}
 	}
 	if err == nil {
-		if scanner.Previous().Sym != SymClosedBrace {
+		if scanner.Previous().Sym != scan.SymClosedBrace {
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
-			tk = scanner.makeValueToken(SymExpression, "", body)
+			tk = scanner.MakeValueToken(scan.SymExpression, "", body)
 			tree = newFuncDefTerm(tk, args)
 		}
 	}
 	return
 }
 
-func paramAlreadyDefined(args []*term, param *term) (position int) {
+func paramAlreadyDefined(args []*scan.Term, param *scan.Term) (position int) {
 	position = 0
 	for i, arg := range args {
-		if arg.source() == param.source() {
+		if arg.Source() == param.Source() {
 			position = i + 1
 		}
 	}
 	return
 }
 
-func (parser *parser) parseList(scanner *scanner, ctx parserContext) (listTerm *term, err error) {
-	r, c := scanner.lastPos()
-	args := make([]*term, 0)
-	lastSym := SymUnknown
+func (parser *parser) parseList(scanner *scan.Scanner, ctx parserContext) (listTerm *scan.Term, err error) {
+	r, c := scanner.LastPos()
+	args := make([]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	itemExpected := false
 	itemCtx := remFlags(ctx, allowIndex)
-	for lastSym != SymClosedSquare && lastSym != SymEos {
-		zeroRequired := scanner.current.Sym == SymColon
-		var itemTree *ast
-		if itemTree, err = parser.parseItem(scanner, itemCtx, SymComma, SymClosedSquare); err == nil {
-			root := itemTree.root
+	for lastSym != scan.SymClosedSquare && lastSym != scan.SymEos {
+		zeroRequired := scanner.Current().Sym == scan.SymColon
+		var itemTree *scan.Ast
+		if itemTree, err = parser.parseItem(scanner, itemCtx, scan.SymComma, scan.SymClosedSquare); err == nil {
+			root := itemTree.Root()
 			if root != nil {
-				if hasFlag(ctx, allowIndex) && root.symbol() == SymColon {
+				if hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymColon {
 					changeColonToRange(root)
 				}
-				if !hasFlag(ctx, allowIndex) && root.symbol() == SymRange {
+				if !hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymRange {
 					// err = root.Errorf("unexpected range expression")
 					err = errRangeUnexpectedExpression(root)
 					break
 				}
 				args = append(args, root)
-				if hasFlag(ctx, allowIndex) && root.symbol() == SymRange && zeroRequired { //len(root.children) == 0 {
-					if len(root.children) == 1 {
-						root.children = append(root.children, root.children[0])
-					} else if len(root.children) > 1 {
+				if hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymRange && zeroRequired { //len(root.children) == 0 {
+					if len(root.Children) == 1 {
+						root.Children = append(root.Children, root.Children[0])
+					} else if len(root.Children) > 1 {
 						// err = root.Errorf("invalid range specification")
 						err = errRangeInvalidSpecification(root)
 						break
 					}
-					zeroTk := NewValueToken(root.tk.row, root.tk.col, SymInteger, "0", int64(0))
-					zeroTerm := newTerm(zeroTk)
-					zeroTerm.setParent(root)
-					root.children[0] = zeroTerm
+					zeroTk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymInteger, "0", int64(0))
+					zeroTerm := scan.NewTerm(zeroTk)
+					zeroTerm.SetParent(root)
+					root.Children[0] = zeroTerm
 				}
 			} else if itemExpected {
 				prev := scanner.Previous()
@@ -205,12 +206,12 @@ func (parser *parser) parseList(scanner *scanner, ctx parserContext) (listTerm *
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		if itemExpected = lastSym == SymComma; itemExpected {
+		if itemExpected = lastSym == scan.SymComma; itemExpected {
 			remFlags(ctx, allowIndex)
 		}
 	}
 	if err == nil {
-		if lastSym != SymClosedSquare {
+		if lastSym != scan.SymClosedSquare {
 			err = scanner.Previous().ErrorExpectedGot("]")
 		} else {
 			listTerm = newListTerm(r, c, args)
@@ -219,16 +220,16 @@ func (parser *parser) parseList(scanner *scanner, ctx parserContext) (listTerm *
 	return
 }
 
-func (parser *parser) parseIterDef(scanner *scanner, ctx parserContext) (subtree *term, err error) {
+func (parser *parser) parseIterDef(scanner *scan.Scanner, ctx parserContext) (subtree *scan.Term, err error) {
 	tk := scanner.Previous()
-	args := make([]*term, 0)
-	lastSym := SymUnknown
+	args := make([]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	itemExpected := false
-	for lastSym != SymClosedRound && lastSym != SymEos {
-		var subTree *ast
-		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedRound); err == nil {
-			if subTree.root != nil {
-				args = append(args, subTree.root)
+	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
+		var subTree *scan.Ast
+		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedRound); err == nil {
+			if subTree.Root() != nil {
+				args = append(args, subTree.Root())
 			} else if itemExpected {
 				prev := scanner.Previous()
 				err = prev.ErrorExpectedGot("iterator-param")
@@ -238,10 +239,10 @@ func (parser *parser) parseIterDef(scanner *scanner, ctx parserContext) (subtree
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == SymComma
+		itemExpected = lastSym == scan.SymComma
 	}
 	if err == nil {
-		if lastSym != SymClosedRound {
+		if lastSym != scan.SymClosedRound {
 			err = scanner.Previous().ErrorExpectedGot(")")
 		} else {
 			subtree = newIteratorTerm(tk, args)
@@ -250,18 +251,18 @@ func (parser *parser) parseIterDef(scanner *scanner, ctx parserContext) (subtree
 	return
 }
 
-func (parser *parser) parseDictKey(scanner *scanner) (key any, err error) {
+func (parser *parser) parseDictKey(scanner *scan.Scanner) (key any, err error) {
 	tk := parser.Next(scanner)
-	if tk.Sym == SymError {
+	if tk.Sym == scan.SymError {
 		err = tk.Error()
 		return
 	}
-	if tk.Sym == SymClosedBrace || tk.Sym == SymEos {
+	if tk.Sym == scan.SymClosedBrace || tk.Sym == scan.SymEos {
 		return
 	}
-	if tk.Sym == SymInteger || tk.Sym == SymString {
+	if tk.Sym == scan.SymInteger || tk.Sym == scan.SymString {
 		tkSep := parser.Next(scanner)
-		if tkSep.Sym != SymColon {
+		if tkSep.Sym != scan.SymColon {
 			err = tkSep.ErrorExpectedGot(":")
 		} else {
 			key = tk.Value
@@ -272,12 +273,12 @@ func (parser *parser) parseDictKey(scanner *scanner) (key any, err error) {
 	return
 }
 
-func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subtree *term, err error) {
-	args := make(map[any]*term, 0)
-	lastSym := SymUnknown
+func (parser *parser) parseDictionary(scanner *scan.Scanner, ctx parserContext) (subtree *scan.Term, err error) {
+	args := make(map[any]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	itemExpected := false
-	for lastSym != SymClosedBrace && lastSym != SymEos {
-		var subTree *ast
+	for lastSym != scan.SymClosedBrace && lastSym != scan.SymEos {
+		var subTree *scan.Ast
 		var key any
 		if key, err = parser.parseDictKey(scanner); err != nil {
 			break
@@ -289,9 +290,9 @@ func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subt
 			}
 			break
 		}
-		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedBrace); err == nil {
-			if subTree.root != nil {
-				args[key] = subTree.root
+		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedBrace); err == nil {
+			if subTree.Root() != nil {
+				args[key] = subTree.Root()
 			} else /*if key != nil*/ {
 				prev := scanner.Previous()
 				err = prev.ErrorExpectedGot("dictionary-value")
@@ -301,10 +302,10 @@ func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subt
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == SymComma
+		itemExpected = lastSym == scan.SymComma
 	}
 	if err == nil {
-		if lastSym != SymClosedBrace {
+		if lastSym != scan.SymClosedBrace {
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
 			subtree = newDictTerm(args)
@@ -313,14 +314,14 @@ func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subt
 	return
 }
 
-func (parser *parser) parseSelectorCase(scanner *scanner, ctx parserContext, defaultCase bool) (caseTerm *term, err error) {
-	var filterList *term
-	var caseExpr *ast
+func (parser *parser) parseSelectorCase(scanner *scan.Scanner, ctx parserContext, defaultCase bool) (caseTerm *scan.Term, err error) {
+	var filterList *scan.Term
+	var caseExpr *scan.Ast
 	ctx = remFlags(ctx, allowIndex)
 	tk := parser.Next(scanner)
-	startRow := tk.row
-	startCol := tk.col
-	if tk.Sym == SymOpenSquare {
+	startRow := tk.Row()
+	startCol := tk.Col()
+	if tk.Sym == scan.SymOpenSquare {
 		if defaultCase {
 			err = tk.Errorf("case list in default clause")
 			return
@@ -329,14 +330,14 @@ func (parser *parser) parseSelectorCase(scanner *scanner, ctx parserContext, def
 			return
 		}
 		tk = parser.Next(scanner)
-		startRow = tk.row
-		startCol = tk.col
+		startRow = tk.Row()
+		startCol = tk.Col()
 	} else if !defaultCase {
-		filterList = newListTerm(startRow, startCol, make([]*term, 0))
+		filterList = newListTerm(startRow, startCol, make([]*scan.Term, 0))
 	}
 
-	if tk.Sym == SymOpenBrace {
-		if caseExpr, err = parser.parseGeneral(scanner, ctx|allowMultiExpr, SymClosedBrace); err != nil {
+	if tk.Sym == scan.SymOpenBrace {
+		if caseExpr, err = parser.parseGeneral(scanner, ctx|allowMultiExpr, scan.SymClosedBrace); err != nil {
 			return
 		}
 	} else {
@@ -349,25 +350,25 @@ func (parser *parser) parseSelectorCase(scanner *scanner, ctx parserContext, def
 	return
 }
 
-func addSelectorCase(selectorTerm, caseTerm *term) {
-	if len(selectorTerm.children) < 2 {
+func addSelectorCase(selectorTerm, caseTerm *scan.Term) {
+	if len(selectorTerm.Children) < 2 {
 		caseListTerm := newListTermA(caseTerm)
-		selectorTerm.children = append(selectorTerm.children, caseListTerm)
+		selectorTerm.Children = append(selectorTerm.Children, caseListTerm)
 	} else {
-		caseListTerm := selectorTerm.children[1]
-		caseList, _ := caseListTerm.value().([]*term)
+		caseListTerm := selectorTerm.Children[1]
+		caseList, _ := caseListTerm.Value().([]*scan.Term)
 		caseList = append(caseList, caseTerm)
-		caseListTerm.tk.Value = caseList
+		caseListTerm.Tk.Value = caseList
 	}
-	caseTerm.parent = selectorTerm
+	caseTerm.Parent = selectorTerm
 }
 
-func (parser *parser) parseSelector(scanner *scanner, tree *ast, ctx parserContext) (selectorTerm *term, err error) {
-	var caseTerm *term
+func (parser *parser) parseSelector(scanner *scan.Scanner, tree *scan.Ast, ctx parserContext) (selectorTerm *scan.Term, err error) {
+	var caseTerm *scan.Term
 
 	ctx = remFlags(ctx, allowIndex)
-	tk := scanner.makeToken(SymSelector, '?')
-	if selectorTerm, err = tree.addToken(tk); err != nil {
+	tk := scanner.MakeToken(scan.SymSelector, '?')
+	if selectorTerm, err = tree.AddToken(tk); err != nil {
 		return
 	}
 
@@ -377,61 +378,70 @@ func (parser *parser) parseSelector(scanner *scanner, tree *ast, ctx parserConte
 	return
 }
 
-func (parser *parser) parseItem(scanner *scanner, ctx parserContext, termSymbols ...Symbol) (tree *ast, err error) {
+func (parser *parser) parseItem(scanner *scan.Scanner, ctx parserContext, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
 	return parser.parseGeneral(scanner, ctx|allowVarRef, termSymbols...)
 }
 
-func (parser *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, err error) {
-	termSymbols = append(termSymbols, SymEos)
+func (parser *parser) Parse(scanner *scan.Scanner, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if errVal, ok := r.(error); ok {
+				err = errVal
+			} else {
+				err = errors.New("unexpected error while parsing the expression")
+			}
+		}
+	}()
+	termSymbols = append(termSymbols, scan.SymEos)
 	return parser.parseGeneral(scanner, allowMultiExpr, termSymbols...)
 }
 
-func couldBeACollection(t *term) bool {
-	var sym = SymUnknown
+func couldBeACollection(t *scan.Term) bool {
+	var sym = scan.SymUnknown
 	if t != nil {
-		sym = t.symbol()
+		sym = t.Symbol()
 	}
-	return sym == SymList || sym == SymString || sym == SymDict || sym == SymExpression || sym == SymVariable
+	return sym == scan.SymList || sym == scan.SymString || sym == scan.SymDict || sym == scan.SymExpression || sym == scan.SymVariable
 }
 
-func listSubTree(tree *ast, listTerm *term, allowIndeces bool) (root *term, err error) {
-	var tk *Token
+func listSubTree(tree *scan.Ast, listTerm *scan.Term, allowIndeces bool) (root *scan.Term, err error) {
+	var tk *scan.Token
 	if allowIndeces {
-		tk = NewToken(listTerm.tk.row, listTerm.tk.col, SymIndex, listTerm.source())
-		root = newTerm(tk)
-		if err = tree.addTerm(root); err == nil {
-			err = tree.addTerm(listTerm)
+		tk = scan.NewToken(listTerm.Tk.Row(), listTerm.Tk.Col(), scan.SymIndex, listTerm.Source())
+		root = scan.NewTerm(tk)
+		if err = tree.AddTerm(root); err == nil {
+			err = tree.AddTerm(listTerm)
 		}
 	} else {
 		root = listTerm
-		err = tree.addTerm(listTerm)
+		err = tree.AddTerm(listTerm)
 	}
 	return
 }
 
-func changePrefix(tk *Token) {
+func changePrefix(tk *scan.Token) {
 	switch tk.Sym {
-	case SymMinus:
-		tk.SetSymbol(SymChangeSign)
-	case SymPlus:
-		tk.SetSymbol(SymUnchangeSign)
-	case SymStar:
-		tk.SetSymbol(SymDereference)
-	case SymExclamation:
-		tk.SetSymbol(SymNot)
-	case SymDoublePlus:
-		tk.SetSymbol(SymPreInc)
-	case SymDoubleMinus:
-		tk.SetSymbol(SymPreDec)
+	case scan.SymMinus:
+		tk.SetSymbol(scan.SymChangeSign)
+	case scan.SymPlus:
+		tk.SetSymbol(scan.SymUnchangeSign)
+	case scan.SymStar:
+		tk.SetSymbol(scan.SymDereference)
+	case scan.SymExclamation:
+		tk.SetSymbol(scan.SymNot)
+	case scan.SymDoublePlus:
+		tk.SetSymbol(scan.SymPreInc)
+	case scan.SymDoubleMinus:
+		tk.SetSymbol(scan.SymPreDec)
 	}
 }
 
-func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymbols ...Symbol) (tree *ast, err error) {
-	var selectorTerm *term = nil
-	var currentTerm *term = nil
-	var tk *Token
+func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
+	var selectorTerm *scan.Term = nil
+	var currentTerm *scan.Term = nil
+	var tk *scan.Token
 
-	tree = NewAst()
+	tree = scan.NewAst()
 	firstToken := true
 	// lastSym := SymUnknown
 	for tk = parser.Next(scanner); err == nil && tk != nil && !tk.IsTerm(termSymbols); /*&& !areSymbolsOutOfCtx(tk, selectorTerm, SymColon, SymDoubleColon)*/ tk = parser.Next(scanner) {
@@ -439,7 +449,7 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 		// 	continue
 		// }
 
-		if tk.Sym == SymSemiColon {
+		if tk.Sym == scan.SymSemiColon {
 			if hasFlag(ctx, allowMultiExpr) {
 				tree.ToForest()
 				firstToken = true
@@ -447,7 +457,7 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 				selectorTerm = nil
 				continue
 			} else {
-				err = tk.Errorf(`unexpected token %q, expected ",", "]", or ")"`, tk.source)
+				err = tk.Errorf(`unexpected token %q, expected ",", "]", or ")"`, tk.Source())
 				break
 			}
 		}
@@ -455,99 +465,91 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 		//fmt.Println("Token:", tk)
 		if firstToken {
 			changePrefix(tk)
-			// if tk.Sym == SymMinus {
-			// 	tk.Sym = SymChangeSign
-			// } else if tk.Sym == SymPlus {
-			// 	tk.Sym = SymUnchangeSign
-			// } else if tk.IsSymbol(SymStar) {
-			// 	tk.SetSymbol(SymDereference)
-			// } else if tk.IsSymbol(SymExclamation) {
-			// 	tk.SetSymbol(SymNot)
-			// }
 			firstToken = false
 		}
 
 		switch tk.Sym {
-		case SymOpenRound:
-			var subTree *ast
-			if subTree, err = parser.parseGeneral(scanner, ctx, SymClosedRound); err == nil {
-				exprTerm := newExprTerm(subTree.root)
-				err = tree.addTerm(exprTerm)
-				currentTerm = exprTerm
-				// subTree.root.priority = priValue
-				// err = tree.addTerm(newExprTerm(subTree.root))
-				// currentTerm = subTree.root
+		case scan.SymOpenRound:
+			var subTree *scan.Ast
+			if subTree, err = parser.parseGeneral(scanner, ctx, scan.SymClosedRound); err == nil {
+				if subTree.Root() == nil {
+					err = tk.ErrorExpectedGotString("expression", "()")
+				} else {
+					exprTerm := newExprTerm(subTree.Root())
+					err = tree.AddTerm(exprTerm)
+					currentTerm = exprTerm
+				}
 			}
-		case SymFuncCall:
-			var funcCallTerm *term
+		case scan.SymFuncCall:
+			var funcCallTerm *scan.Term
 			if funcCallTerm, err = parser.parseFuncCall(scanner, ctx, tk); err == nil {
-				err = tree.addTerm(funcCallTerm)
+				err = tree.AddTerm(funcCallTerm)
 				currentTerm = funcCallTerm
 			}
-		case SymOpenSquare:
-			var listTerm *term
+		case scan.SymOpenSquare:
+			var listTerm *scan.Term
 			newCtx := addFlagsCond(addFlags(ctx, squareContext), allowIndex, couldBeACollection(currentTerm))
 			if listTerm, err = parser.parseList(scanner, newCtx); err == nil {
 				currentTerm, err = listSubTree(tree, listTerm, hasFlag(newCtx, allowIndex))
 			}
-		case SymOpenBrace:
-			if currentTerm != nil && currentTerm.symbol() == SymColon {
+		case scan.SymOpenBrace:
+			if currentTerm != nil && currentTerm.Symbol() == scan.SymColon {
 				err = currentTerm.Errorf(`selector-case outside of a selector context`)
 			} else {
-				var mapTerm *term
+				var mapTerm *scan.Term
 				if mapTerm, err = parser.parseDictionary(scanner, ctx); err == nil {
-					err = tree.addTerm(mapTerm)
+					err = tree.AddTerm(mapTerm)
 					currentTerm = mapTerm
 				}
 			}
-		case SymEqual, SymPlusEqual, SymMinusEqual, SymStarEqual, SymSlashEqual, SymPercEqual, SymAmpersandEqual, SymVertBarEqual, SymDoubleLessEqual, SymDoubleGreaterEqual, SymCaretEqual:
-			currentTerm, err = tree.addToken(tk)
+		case scan.SymEqual, scan.SymPlusEqual, scan.SymMinusEqual, scan.SymStarEqual, scan.SymSlashEqual, scan.SymPercEqual, scan.SymAmpersandEqual, scan.SymVertBarEqual, scan.SymDoubleLessEqual, scan.SymDoubleGreaterEqual, scan.SymCaretEqual:
+			currentTerm, err = tree.AddToken(tk)
 			firstToken = true
-		case SymFuncDef:
-			var funcDefTerm *term
+		case scan.SymFuncDef:
+			var funcDefTerm *scan.Term
 			if funcDefTerm, err = parser.parseFuncDef(scanner); err == nil {
-				err = tree.addTerm(funcDefTerm)
+				err = tree.AddTerm(funcDefTerm)
 				currentTerm = funcDefTerm
 			}
-		case SymDollarRound:
-			var iterDefTerm *term
+		case scan.SymDollarRound:
+			var iterDefTerm *scan.Term
 			if iterDefTerm, err = parser.parseIterDef(scanner, ctx); err == nil {
-				err = tree.addTerm(iterDefTerm)
+				err = tree.AddTerm(iterDefTerm)
 				currentTerm = iterDefTerm
 			}
-		case SymIdentifier:
-			if tk.source[0] == '@' && !hasFlag(ctx, allowVarRef) {
-				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.source)
+		case scan.SymIdentifier:
+			if tk.Source()[0] == '@' && !hasFlag(ctx, allowVarRef) {
+				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.Source())
 			} else {
-				currentTerm, err = tree.addToken(tk)
+				currentTerm, err = tree.AddToken(tk)
 			}
-		case SymQuestion:
+		case scan.SymQuestion:
 			if selectorTerm, err = parser.parseSelector(scanner, tree, ctx); err == nil {
 				currentTerm = selectorTerm
 				addFlags(ctx, selectorContext)
 			}
-		case SymColon, SymDoubleColon:
-			var caseTerm *term
+		case scan.SymColon, scan.SymDoubleColon:
+			var caseTerm *scan.Term
 			if selectorTerm != nil {
-				if caseTerm, err = parser.parseSelectorCase(scanner, ctx, tk.Sym == SymDoubleColon); err == nil {
+				if caseTerm, err = parser.parseSelectorCase(scanner, ctx, tk.Sym == scan.SymDoubleColon); err == nil {
 					addSelectorCase(selectorTerm, caseTerm)
 					currentTerm = caseTerm
-					if tk.Sym == SymDoubleColon {
+					if tk.Sym == scan.SymDoubleColon {
 						selectorTerm = nil
 					}
 				}
 			} else {
-				currentTerm, err = tree.addToken(tk)
-				if tk.IsOneOfA(SymColon, SymRange) {
+				currentTerm, err = tree.AddToken(tk)
+				if tk.IsOneOfA(scan.SymColon, scan.SymRange) {
 					// Colon outside a selector term acts like a separator
 					firstToken = true
 				}
 			}
 		default:
-			currentTerm, err = tree.addToken(tk)
+			currentTerm, err = tree.AddToken(tk)
 		}
 
-		if currentTerm != nil && currentTerm.tk.Sym != SymSelector && currentTerm.parent != nil && currentTerm.parent.tk.Sym != SymSelector {
+		if currentTerm != nil && currentTerm.Tk.Sym != scan.SymSelector && currentTerm.Parent != nil && currentTerm.Parent.Tk.Sym != scan.SymSelector {
 			selectorTerm = nil
 			remFlags(ctx, selectorContext)
 		}
@@ -557,12 +559,12 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 	if err == nil {
 		if !tk.IsOneOf(termSymbols) {
 			var symDesc string
-			if tk.IsSymbol(SymError) {
+			if tk.IsSymbol(scan.SymError) {
 				symDesc = tk.ErrorText()
 			} else {
-				symDesc = SymToString(tk.Sym)
+				symDesc = scan.SymToString(tk.Sym)
 			}
-			err = tk.ErrorExpectedGotStringWithPrefix("expected one of", SymListToString(termSymbols, true), symDesc)
+			err = tk.ErrorExpectedGotStringWithPrefix("expected one of", scan.SymListToString(termSymbols, true), symDesc)
 		} else {
 			err = tk.Error()
 		}

plugins.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // plugin.go
@@ -10,6 +10,8 @@ import (
 	"os"
 	"plugin"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 var pluginRegister map[string]*plugin.Plugin
@@ -39,12 +41,12 @@ func makePluginName(name string) (decorated string) {
 	return
 }
 
-func importPlugin( /*ctx ExprContext,*/ dirList []string, name string) (err error) {
+func importPlugin(ctx kern.ExprContext, dirList []string, name string) (err error) {
 	var filePath string
 	var p *plugin.Plugin
 	var sym plugin.Symbol
 	var moduleName string
-	var importFunc func(ExprContext)
+	var importFunc func(kern.ExprContext)
 	var ok bool
 
 	decoratedName := makePluginName(name)
@@ -71,7 +73,7 @@ func importPlugin( /*ctx ExprContext,*/ dirList []string, name string) (err erro
 	}
 	if deps := *sym.(*[]string); len(deps) > 0 {
 		// var count int
-		if err = loadModules(dirList, deps); err != nil {
+		if err = loadModules(ctx, dirList, deps); err != nil {
 			return
 		}
 	}
@@ -80,33 +82,35 @@ func importPlugin( /*ctx ExprContext,*/ dirList []string, name string) (err erro
 		return
 	}
 
-	if importFunc, ok = sym.(func(ExprContext)); !ok {
+	if importFunc, ok = sym.(func(kern.ExprContext)); !ok {
 		err = fmt.Errorf("plugin %q does not provide a valid import function", decoratedName)
 		return
 	}
 
 	registerPlugin(moduleName, p)
-	importFunc(globalCtx)
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		importFunc(globalCtx)
+	}
 
 	return
 }
 
-func importPluginFromSearchPath(name any) (count int, err error) {
+func importPluginFromSearchPath(ctx kern.ExprContext, name any) (count int, err error) {
 	var moduleSpec any
-	var it Iterator
-	dirList := buildSearchDirList("plugin", ENV_EXPR_PLUGIN_PATH)
+	var it kern.Iterator
+	dirList := buildSearchDirList(ctx, "plugin", ENV_EXPR_PLUGIN_PATH)
 	count = 0
-	if it, err = NewIterator(name); err != nil {
+	if it, err = NewIterator(ctx, name, nil); err != nil {
 		return
 	}
 	for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
 		if module, ok := moduleSpec.(string); ok {
-			if err = importPlugin(dirList, module); err != nil {
+			if err = importPlugin(ctx, dirList, module); err != nil {
 				break
 			}
 			count++
 		} else {
-			err = fmt.Errorf("expected string as item nr %d, got %s", it.Index()+1, TypeName(moduleSpec))
+			err = fmt.Errorf("expected string as item nr %d, got %s", it.Index()+1, kern.TypeName(moduleSpec))
 			break
 		}
 	}
@@ -116,10 +120,10 @@ func importPluginFromSearchPath(name any) (count int, err error) {
 	return
 }
 
-func loadModules(dirList []string, moduleNames []string) (err error) {
+func loadModules(ctx kern.ExprContext, dirList []string, moduleNames []string) (err error) {
 	for _, name := range moduleNames {
-		if err1 := importPlugin(dirList, name); err1 != nil {
-			if !ImportInContext(name) {
+		if err1 := importPlugin(ctx, dirList, name); err1 != nil {
+			if !ImportInContext(ctx, name) {
 				err = err1
 				break
 			}

scan/ast.go

@@ -0,0 +1,147 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// ast.go
+package scan
+
+import (
+	"errors"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+//-------- ast
+
+type Ast struct {
+	forest []*Term
+	root   *Term
+}
+
+func NewAst() *Ast {
+	return &Ast{}
+}
+
+func (ast *Ast) TypeName() string {
+	return "Expression"
+}
+
+func (ast *Ast) Root() *Term {
+	return ast.root
+}
+
+func (ast *Ast) ToForest() {
+	if ast.root != nil {
+		if ast.forest == nil {
+			ast.forest = make([]*Term, 0)
+		}
+		ast.forest = append(ast.forest, ast.root)
+		ast.root = nil
+	}
+}
+
+func (ast *Ast) String() string {
+	var sb strings.Builder
+	if ast.root == nil {
+		sb.WriteString("(nil)")
+	} else {
+		ast.root.ToString(&sb)
+	}
+	return sb.String()
+}
+
+func (ast *Ast) AddTokens(tokens ...*Token) (err error) {
+	for _, tk := range tokens {
+		if _, err = ast.AddToken(tk); err != nil {
+			break
+		}
+	}
+	return
+}
+
+// func (expr *ast) addToken(tk *Token) (err error) {
+// 	_, err = expr.addToken2(tk)
+// 	return
+// }
+
+func (ast *Ast) AddToken(tk *Token) (t *Term, err error) {
+	if t = NewTerm(tk); t != nil {
+		err = ast.AddTerm(t)
+	} else {
+		err = tk.Errorf("unexpected token %q", tk.String())
+	}
+	return
+}
+
+func (ast *Ast) AddTerm(node *Term) (err error) {
+	if ast.root == nil {
+		ast.root = node
+	} else {
+		ast.root, err = ast.insert(ast.root, node)
+	}
+	return
+}
+
+func (ast *Ast) insert(tree, node *Term) (root *Term, err error) {
+	if tree.getPriority() < node.getPriority() {
+		root = tree
+		if tree.isComplete() {
+			var subRoot *Term
+			last := tree.removeLastChild()
+			if subRoot, err = ast.insert(last, node); err == nil {
+				subRoot.SetParent(tree)
+			}
+		} else {
+			node.SetParent(tree)
+		}
+	} else if !node.isLeaf() {
+		root = node
+		tree.SetParent(node)
+	} else {
+		err = node.Errorf("two adjacent operators: %q and %q", tree, node)
+	}
+	return
+}
+
+func (ast *Ast) Finish() {
+	if ast.root == nil && ast.forest != nil && len(ast.forest) >= 1 {
+		ast.root = ast.forest[len(ast.forest)-1]
+		ast.forest = ast.forest[0 : len(ast.forest)-1]
+	}
+}
+
+func (ast *Ast) Eval(ctx kern.ExprContext) (result any, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if errVal, ok := r.(error); ok {
+				err = errVal
+			} else {
+				err = errors.New("unexpected error while evaluating the expression")
+			}
+		}
+	}()
+
+	ast.Finish()
+
+	if ast.root != nil {
+		// initDefaultVars(ctx)
+		if ast.forest != nil {
+			for _, tree := range ast.forest {
+				if result, err = tree.Compute(ctx); err == nil {
+					ctx.UnsafeSetVar(kern.ControlLastResult, result)
+				} else {
+					//err = fmt.Errorf("error in expression nr %d: %v", i+1, err)
+					break
+				}
+			}
+		}
+		if err == nil {
+			if result, err = ast.root.Compute(ctx); err == nil {
+				ctx.UnsafeSetVar(kern.ControlLastResult, result)
+			}
+		}
+		// } else {
+		// 	err = errors.New("empty expression")
+	}
+	return
+}

scan/scanner.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr project scanner.go
-package expr
+package scan
 
 import (
 	"bufio"
@@ -11,9 +11,12 @@ import (
 	"io"
 	"strconv"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/util"
 )
 
-type scanner struct {
+type Scanner struct {
 	current      *Token
 	prev         *Token
 	stage        *Token
@@ -23,8 +26,8 @@ type scanner struct {
 	translations map[Symbol]Symbol
 }
 
-func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *scanner) {
-	inst = &scanner{
+func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *Scanner) {
+	inst = &Scanner{
 		stream:       bufio.NewReader(s),
 		row:          1,
 		column:       1,
@@ -50,7 +53,11 @@ func DefaultTranslations() map[Symbol]Symbol {
 // 	return self.current
 // }
 
-func (scanner *scanner) readChar() (ch byte, err error) {
+func (scanner *Scanner) Current() *Token {
+	return scanner.current
+}
+
+func (scanner *Scanner) readChar() (ch byte, err error) {
 	if ch, err = scanner.stream.ReadByte(); err == nil {
 		if ch == '\n' {
 			scanner.row++
@@ -62,7 +69,7 @@ func (scanner *scanner) readChar() (ch byte, err error) {
 	return
 }
 
-func (scanner *scanner) unreadChar() (err error) {
+func (scanner *Scanner) unreadChar() (err error) {
 	if err = scanner.stream.UnreadByte(); err == nil {
 		if scanner.column--; scanner.column == 0 {
 			if scanner.row--; scanner.row == 0 {
@@ -75,7 +82,7 @@ func (scanner *scanner) unreadChar() (err error) {
 	return
 }
 
-func (scanner *scanner) UnreadToken() (err error) {
+func (scanner *Scanner) UnreadToken() (err error) {
 	if scanner.stage == nil {
 		scanner.stage = scanner.current
 		scanner.current = scanner.prev
@@ -85,7 +92,7 @@ func (scanner *scanner) UnreadToken() (err error) {
 	return
 }
 
-func (scanner *scanner) lastPos() (r, c int) {
+func (scanner *Scanner) LastPos() (r, c int) {
 	if scanner.prev != nil {
 		r = scanner.prev.row
 		c = scanner.prev.col
@@ -93,11 +100,11 @@ func (scanner *scanner) lastPos() (r, c int) {
 	return
 }
 
-func (scanner *scanner) Previous() *Token {
+func (scanner *Scanner) Previous() *Token {
 	return scanner.prev
 }
 
-func (scanner *scanner) Next() (tk *Token) {
+func (scanner *Scanner) Next() (tk *Token) {
 	scanner.prev = scanner.current
 	tk = scanner.current
 	if scanner.stage != nil {
@@ -109,7 +116,7 @@ func (scanner *scanner) Next() (tk *Token) {
 	return tk
 }
 
-func (scanner *scanner) fetchNextToken() (tk *Token) {
+func (scanner *Scanner) fetchNextToken() (tk *Token) {
 	var ch byte
 	if err := scanner.skipBlanks(); err != nil {
 		return scanner.makeErrorToken(err)
@@ -127,7 +134,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '>' {
 				tk = scanner.moveOn(SymPlusGreater, ch, next)
 			} else {
-				tk = scanner.makeToken(SymPlus, ch)
+				tk = scanner.MakeToken(SymPlus, ch)
 			}
 		case '-':
 			if next, _ := scanner.peek(); next == '-' {
@@ -135,7 +142,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '=' {
 				tk = scanner.moveOn(SymMinusEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymMinus, ch)
+				tk = scanner.MakeToken(SymMinus, ch)
 			}
 		case '*':
 			if next, _ := scanner.peek(); next == '*' {
@@ -145,7 +152,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next, _ = scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymStarEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymStar, ch)
+				tk = scanner.MakeToken(SymStar, ch)
 			}
 		case '/':
 			if next, _ := scanner.peek(); next == '*' {
@@ -157,11 +164,11 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 				scanner.readChar()
 				tk = scanner.fetchOnLineComment()
 			} else {
-				tk = scanner.makeToken(SymSlash, ch)
+				tk = scanner.MakeToken(SymSlash, ch)
 			}
 		case '\\':
 			if escape {
-				tk = scanner.makeToken(SymBackSlash, ch)
+				tk = scanner.MakeToken(SymBackSlash, ch)
 				escape = false
 			} else {
 				escape = true
@@ -172,24 +179,24 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next, _ = scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymVertBarEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymVertBar, ch)
+				tk = scanner.MakeToken(SymVertBar, ch)
 			}
 		case ',':
-			tk = scanner.makeToken(SymComma, ch)
+			tk = scanner.MakeToken(SymComma, ch)
 		case '^':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymCaretEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymCaret, ch)
+				tk = scanner.MakeToken(SymCaret, ch)
 			}
 		case ':':
 			if next, _ := scanner.peek(); next == ':' {
 				tk = scanner.moveOn(SymDoubleColon, ch, next)
 			} else {
-				tk = scanner.makeToken(SymColon, ch)
+				tk = scanner.MakeToken(SymColon, ch)
 			}
 		case ';':
-			tk = scanner.makeToken(SymSemiColon, ch)
+			tk = scanner.MakeToken(SymSemiColon, ch)
 		case '.':
 			//if next, _ := self.peek(); next >= '0' && next <= '9' {
 			//	tk = self.parseNumber(ch)
@@ -203,29 +210,29 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 					tk = scanner.moveOn(SymDoubleDot, ch, next)
 				}
 			} else {
-				tk = scanner.makeToken(SymDot, ch)
+				tk = scanner.MakeToken(SymDot, ch)
 			}
 		case '\'':
 			if escape {
-				tk = scanner.makeToken(SymQuote, ch)
+				tk = scanner.MakeToken(SymQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '"':
 			if escape {
-				tk = scanner.makeToken(SymDoubleQuote, ch)
+				tk = scanner.MakeToken(SymDoubleQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '`':
-			tk = scanner.makeToken(SymBackTick, ch)
+			tk = scanner.MakeToken(SymBackTick, ch)
 		case '!':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymNotEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymExclamation, ch)
+				tk = scanner.MakeToken(SymExclamation, ch)
 			}
 		case '?':
 			if next, _ := scanner.peek(); next == '?' {
@@ -235,7 +242,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '!' {
 				tk = scanner.moveOn(SymQuestionExclam, ch, next)
 			} else {
-				tk = scanner.makeToken(SymQuestion, ch)
+				tk = scanner.MakeToken(SymQuestion, ch)
 			}
 		case '&':
 			if next, _ := scanner.peek(); next == '&' {
@@ -243,16 +250,16 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next, _ = scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymAmpersandEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymAmpersand, ch)
+				tk = scanner.MakeToken(SymAmpersand, ch)
 			}
 		case '%':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymPercEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymPercent, ch)
+				tk = scanner.MakeToken(SymPercent, ch)
 			}
 		case '#':
-			tk = scanner.makeToken(SymHash, ch)
+			tk = scanner.MakeToken(SymHash, ch)
 		case '@':
 			if next, _ := scanner.peek(); (next >= 'a' && next <= 'z') || (next >= 'A' && next <= 'Z') {
 				scanner.readChar()
@@ -265,15 +272,15 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '@' {
 				tk = scanner.moveOn(SymDoubleAt, ch, next)
 			} else {
-				tk = scanner.makeToken(SymAt, ch)
+				tk = scanner.MakeToken(SymAt, ch)
 			}
 		case '_':
-			tk = scanner.makeToken(SymUndescore, ch)
+			tk = scanner.MakeToken(SymUndescore, ch)
 		case '=':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymDoubleEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymEqual, ch)
+				tk = scanner.MakeToken(SymEqual, ch)
 			}
 		case '<':
 			if next, _ := scanner.peek(); next == '=' {
@@ -292,7 +299,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '+' {
 				tk = scanner.moveOn(SymLessPlus, ch, next)
 			} else {
-				tk = scanner.makeToken(SymLess, ch)
+				tk = scanner.MakeToken(SymLess, ch)
 			}
 		case '>':
 			if next, _ := scanner.peek(); next == '=' {
@@ -307,7 +314,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 					tk = scanner.accept(SymDoubleGreater, ch, next)
 				}
 			} else {
-				tk = scanner.makeToken(SymGreater, ch)
+				tk = scanner.MakeToken(SymGreater, ch)
 			}
 		case '$':
 			if next, _ := scanner.peek(); next == '(' {
@@ -324,26 +331,26 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 				scanner.readChar()
 				tk = scanner.fetchIdentifier(next)
 			} else {
-				tk = scanner.makeToken(SymDollar, ch)
+				tk = scanner.MakeToken(SymDollar, ch)
 			}
 		case '(':
 			//			if next, _ := scanner.peek(); next == ')' {
 			//				tk = scanner.moveOn(SymOpenClosedRound, ch, next)
 			//			} else {
-			tk = scanner.makeToken(SymOpenRound, ch)
+			tk = scanner.MakeToken(SymOpenRound, ch)
 			//			}
 		case ')':
-			tk = scanner.makeToken(SymClosedRound, ch)
+			tk = scanner.MakeToken(SymClosedRound, ch)
 		case '[':
-			tk = scanner.makeToken(SymOpenSquare, ch)
+			tk = scanner.MakeToken(SymOpenSquare, ch)
 		case ']':
-			tk = scanner.makeToken(SymClosedSquare, ch)
+			tk = scanner.MakeToken(SymClosedSquare, ch)
 		case '{':
-			tk = scanner.makeToken(SymOpenBrace, ch)
+			tk = scanner.MakeToken(SymOpenBrace, ch)
 		case '}':
-			tk = scanner.makeToken(SymClosedBrace, ch)
+			tk = scanner.MakeToken(SymClosedBrace, ch)
 		case '~':
-			tk = scanner.makeToken(SymTilde, ch)
+			tk = scanner.MakeToken(SymTilde, ch)
 		case 0:
 			if escape {
 				tk = scanner.makeErrorToken(errors.New("incomplete escape sequence"))
@@ -370,7 +377,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 	return
 }
 
-func (scanner *scanner) sync(err error) error {
+func (scanner *Scanner) sync(err error) error {
 	if err == nil {
 		err = scanner.unreadChar()
 	}
@@ -393,7 +400,7 @@ func isHexDigit(ch byte) bool {
 	return (ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'f') || (ch >= 'A' && ch <= 'F')
 }
 
-func (scanner *scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int, digitFunc func(byte) bool, err error) {
+func (scanner *Scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int, digitFunc func(byte) bool, err error) {
 	var ch byte
 	var digitType string
 	firstCh = currentFirstCh
@@ -432,7 +439,7 @@ func (scanner *scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int
 	return
 }
 
-func (scanner *scanner) parseNumber(firstCh byte) (tk *Token) {
+func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sym Symbol = SymInteger
@@ -503,12 +510,12 @@ func (scanner *scanner) parseNumber(firstCh byte) (tk *Token) {
 		if sym == SymFloat {
 			value, err = strconv.ParseFloat(txt, 64)
 		} else if sym == SymFraction {
-			value, err = makeGeneratingFraction(txt)
+			value, err = kern.MakeGeneratingFraction(txt)
 		} else {
 			value, err = strconv.ParseInt(txt, numBase, 64)
 		}
 		if err == nil {
-			tk = scanner.makeValueToken(sym, txt, value)
+			tk = scanner.MakeValueToken(sym, txt, value)
 		} else {
 			tk = scanner.makeErrorToken(err)
 		}
@@ -516,7 +523,7 @@ func (scanner *scanner) parseNumber(firstCh byte) (tk *Token) {
 	return
 }
 
-func (scanner *scanner) fetchIdentifier(firstCh byte) (tk *Token) {
+func (scanner *Scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 	var err error
 	var sb strings.Builder
 	for ch := firstCh; err == nil && (ch == '_' || (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9')); ch, err = scanner.readChar() {
@@ -533,14 +540,14 @@ func (scanner *scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 		if sym, ok := keywords[uptxt]; ok {
 			tk = scanner.makeKeywordToken(sym, uptxt)
 		} else if uptxt == `TRUE` {
-			tk = scanner.makeValueToken(SymBool, txt, true)
+			tk = scanner.MakeValueToken(SymBool, txt, true)
 		} else if uptxt == `FALSE` {
-			tk = scanner.makeValueToken(SymBool, txt, false)
+			tk = scanner.MakeValueToken(SymBool, txt, false)
 		} else if ch, _ := scanner.peek(); ch == '(' {
 			scanner.readChar()
-			tk = scanner.makeValueToken(SymFuncCall, txt+"(", txt)
+			tk = scanner.MakeValueToken(SymFuncCall, txt+"(", txt)
 		} else {
-			tk = scanner.makeValueToken(SymIdentifier, txt, txt)
+			tk = scanner.MakeValueToken(SymIdentifier, txt, txt)
 		}
 	}
 
@@ -560,20 +567,20 @@ func (scanner *scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 	return
 }
 
-func (scanner *scanner) fetchBlockComment() *Token {
+func (scanner *Scanner) fetchBlockComment() *Token {
 	return scanner.fetchUntil(SymComment, false, '*', '/')
 }
 
-func (scanner *scanner) fetchOnLineComment() *Token {
+func (scanner *Scanner) fetchOnLineComment() *Token {
 	return scanner.fetchUntil(SymComment, true, '\n')
 }
 
-func (scanner *scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (tk *Token) {
+func (scanner *Scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sb strings.Builder
 	var value string
-	ring := NewByteSlider(len(endings))
+	ring := util.NewByteSlider(len(endings))
 	endReached := false
 	for ch, err = scanner.readChar(); err == nil && !endReached; {
 		sb.WriteByte(ch)
@@ -591,14 +598,14 @@ func (scanner *scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (
 	}
 
 	if endReached {
-		tk = scanner.makeValueToken(sym, "", value)
+		tk = scanner.MakeValueToken(sym, "", value)
 	} else {
 		tk = scanner.makeErrorToken(err)
 	}
 	return
 }
 
-func (scanner *scanner) fetchString(termCh byte, addQuote bool) (tk *Token) {
+func (scanner *Scanner) fetchString(termCh byte, addQuote bool) (tk *Token) {
 	var err error
 	var ch, prev byte
 	var sb strings.Builder
@@ -637,15 +644,15 @@ func (scanner *scanner) fetchString(termCh byte, addQuote bool) (tk *Token) {
 	} else {
 		txt := sb.String()
 		if addQuote {
-			tk = scanner.makeValueToken(SymString, `"`+txt+`"`, txt)
+			tk = scanner.MakeValueToken(SymString, `"`+txt+`"`, txt)
 		} else {
-			tk = scanner.makeValueToken(SymString, txt, txt)
+			tk = scanner.MakeValueToken(SymString, txt, txt)
 		}
 	}
 	return
 }
 
-func (scanner *scanner) peek() (next byte, err error) {
+func (scanner *Scanner) peek() (next byte, err error) {
 	var one []byte
 	if one, err = scanner.stream.Peek(1); err == nil {
 		next = one[0]
@@ -653,7 +660,7 @@ func (scanner *scanner) peek() (next byte, err error) {
 	return
 }
 
-func (scanner *scanner) skipBlanks() (err error) {
+func (scanner *Scanner) skipBlanks() (err error) {
 	var one []byte
 	for one, err = scanner.stream.Peek(1); err == nil && one[0] <= 32; one, err = scanner.stream.Peek(1) {
 		scanner.readChar()
@@ -661,7 +668,7 @@ func (scanner *scanner) skipBlanks() (err error) {
 	return
 }
 
-func (scanner *scanner) translate(sym Symbol) Symbol {
+func (scanner *Scanner) translate(sym Symbol) Symbol {
 	if scanner.translations != nil {
 		if translatedSym, ok := scanner.translations[sym]; ok {
 			return translatedSym
@@ -670,7 +677,7 @@ func (scanner *scanner) translate(sym Symbol) Symbol {
 	return sym
 }
 
-func (scanner *scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	// for i := 1; i < len(chars); i++ {
 	if len(chars) > 1 {
@@ -680,26 +687,26 @@ func (scanner *scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
 	return
 }
 
-func (scanner *scanner) accept(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) accept(sym Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	return
 }
 
-func (scanner *scanner) makeToken(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) MakeToken(sym Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	return
 }
 
-func (scanner *scanner) makeKeywordToken(sym Symbol, upperCaseKeyword string) (tk *Token) {
+func (scanner *Scanner) makeKeywordToken(sym Symbol, upperCaseKeyword string) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), upperCaseKeyword)
 	return
 }
 
-func (scanner *scanner) makeValueToken(sym Symbol, source string, value any) (tk *Token) {
+func (scanner *Scanner) MakeValueToken(sym Symbol, source string, value any) (tk *Token) {
 	tk = NewValueToken(scanner.row, scanner.column, scanner.translate(sym), source, value)
 	return
 }
 
-func (scanner *scanner) makeErrorToken(err error) *Token {
+func (scanner *Scanner) makeErrorToken(err error) *Token {
 	return NewErrorToken(scanner.row, scanner.column, err)
 }

scan/symbol-map.go

@@ -0,0 +1,231 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// Symbol.go
+package scan
+
+import (
+	"strings"
+)
+
+var symbolMap map[Symbol]symbolSpec
+
+type SymbolClass int16
+
+const (
+	SymClassOperator SymbolClass = iota
+	SymClassCommand
+	SymClassIdentifier
+	SymClassDelimiter
+	SymClassParenthesis
+	SymClassDeclaration
+	SymClassValue
+	SymClassOther
+)
+
+type symbolSpec struct {
+	repr   string
+	kind   SymbolClass
+	opType TermPosition
+}
+
+func init() {
+
+	symbolMap = map[Symbol]symbolSpec{
+		SymUnknown:            {"<unknown>", SymClassOther, PosLeaf},  //  -1: Unknown symbol
+		SymNone:               {"<null>", SymClassOther, PosLeaf},     //   0: Null value for variable of type symbol
+		SymError:              {"<error>", SymClassOther, PosLeaf},    //   1: Error reading from stream
+		SymEos:                {"<eos>", SymClassOther, PosLeaf},      //   2: End of stream
+		SymMinus:              {"-", SymClassOperator, PosInfix},      //   3: '-'
+		SymMinusEqual:         {"-=", SymClassOperator, PosInfix},     //   4: '-='
+		SymDoubleMinus:        {"--", SymClassOperator, PosPostfix},   //   5: '--'
+		SymPlus:               {"+", SymClassOperator, PosInfix},      //   6: '+'
+		SymPlusEqual:          {"+=", SymClassOperator, PosInfix},     //   7: '+='
+		SymDoublePlus:         {"++", SymClassOperator, PosPostfix},   //   8: '++'
+		SymStar:               {"*", SymClassOperator, PosInfix},      //   9: '*'
+		SymDoubleStar:         {"**", SymClassOperator, PosInfix},     //  10: '**'
+		SymSlash:              {"/", SymClassOperator, PosInfix},      //  11: '/'
+		SymBackSlash:          {"\\", SymClassOperator, PosLeaf},      //  12: '\'
+		SymVertBar:            {"|", SymClassOperator, PosInfix},      //  13: '|'
+		SymDoubleVertBar:      {"||", SymClassOperator, PosInfix},     //  14: '||'
+		SymComma:              {",", SymClassOperator, PosInfix},      //  15: ','
+		SymColon:              {":", SymClassOperator, PosInfix},      //  16: ':'
+		SymSemiColon:          {";", SymClassOperator, PosInfix},      //  17: ';'
+		SymDot:                {".", SymClassOperator, PosInfix},      //  18: '.'
+		SymDotSlash:           {"./", SymClassOperator, PosInfix},     //  19: './'
+		SymQuote:              {"'", SymClassDelimiter, PosLeaf},      //  20: '\''
+		SymDoubleQuote:        {"\"", SymClassDelimiter, PosLeaf},     //  21: '"'
+		SymBackTick:           {"`", SymClassDelimiter, PosLeaf},      //  22: '`'
+		SymExclamation:        {"!", SymClassOperator, PosPostfix},    //  23: '!'
+		SymQuestion:           {"?", SymClassOperator, PosInfix},      //  24: '?'
+		SymAmpersand:          {"&", SymClassOperator, PosInfix},      //  25: '&'
+		SymDoubleAmpersand:    {"&&", SymClassOperator, PosInfix},     //  26: '&&'
+		SymPercent:            {"%", SymClassOperator, PosInfix},      //  27: '%'
+		SymAt:                 {"@", SymClassOperator, PosPrefix},     //  28: '@'
+		SymUndescore:          {"_", SymClassIdentifier, PosLeaf},     //  29: '_'
+		SymEqual:              {"=", SymClassOperator, PosInfix},      //  30: '='
+		SymDoubleEqual:        {"==", SymClassOperator, PosInfix},     //  31: '=='
+		SymLess:               {"<", SymClassOperator, PosInfix},      //  32: '<'
+		SymLessOrEqual:        {"<=", SymClassOperator, PosInfix},     //  33: '<='
+		SymGreater:            {">", SymClassOperator, PosInfix},      //  34: '>'
+		SymGreaterOrEqual:     {">=", SymClassOperator, PosInfix},     //  35: '>='
+		SymLessGreater:        {"<>", SymClassOperator, PosInfix},     //  36: '<>'
+		SymNotEqual:           {"!=", SymClassOperator, PosInfix},     //  37: '!='
+		SymDollar:             {"$", SymClassOperator, PosPrefix},     //  38: '$'
+		SymHash:               {"#", SymClassOperator, PosPrefix},     //  39: '#'
+		SymOpenRound:          {"(", SymClassParenthesis, PosPrefix},  //  40: '('
+		SymClosedRound:        {")", SymClassParenthesis, PosPostfix}, //  41: ')'
+		SymOpenSquare:         {"[", SymClassParenthesis, PosPrefix},  //  42: '['
+		SymClosedSquare:       {"]", SymClassParenthesis, PosPostfix}, //  43: ']'
+		SymOpenBrace:          {"{", SymClassParenthesis, PosPrefix},  //  44: '{'
+		SymClosedBrace:        {"}", SymClassParenthesis, PosPostfix}, //  45: '}'
+		SymTilde:              {"~", SymClassOperator, PosPrefix},     //  46: '~'
+		SymDoubleQuestion:     {"??", SymClassOperator, PosInfix},     //  47: '??'
+		SymQuestionEqual:      {"?=", SymClassOperator, PosInfix},     //  48: '?='
+		SymQuestionExclam:     {"?!", SymClassOperator, PosInfix},     //  49: '?!'
+		SymDoubleAt:           {"@@", SymClassCommand, PosLeaf},       //  50: '@@'
+		SymDoubleColon:        {"::", SymClassOperator, PosInfix},     //  51: '::'
+		SymDoubleGreater:      {">>", SymClassOperator, PosInfix},     //  52: '>>'
+		SymDoubleLess:         {"<<", SymClassOperator, PosInfix},     //  53: '<<'
+		SymCaret:              {"^", SymClassOperator, PosInfix},      //  54: '^'
+		SymDollarRound:        {"$(", SymClassOperator, PosPrefix},    //  55: '$('
+		SymOpenClosedRound:    {"()", SymClassOperator, PosPostfix},   //  56: '()'
+		SymDoubleDollar:       {"$$", SymClassCommand, PosLeaf},       //  57: '$$'
+		SymDoubleDot:          {"..", SymClassOperator, PosInfix},     //  58: '..'
+		SymTripleDot:          {"...", SymClassOperator, PosPostfix},  //  59: '...'
+		SymStarEqual:          {"*=", SymClassOperator, PosInfix},     //  60: '*='
+		SymSlashEqual:         {"/=", SymClassOperator, PosInfix},     //  61: '/='
+		SymPercEqual:          {"%=", SymClassOperator, PosInfix},     //  62: '%='
+		SymDoubleLessEqual:    {"<<=", SymClassOperator, PosInfix},    //  63: '<<='
+		SymDoubleGreaterEqual: {">>=", SymClassOperator, PosInfix},    //  64: '>>='
+		SymAmpersandEqual:     {"&=", SymClassOperator, PosInfix},     //  65: '&='
+		SymVertBarEqual:       {"|=", SymClassOperator, PosInfix},     //  65: '|='
+		SymCaretEqual:         {"^=", SymClassOperator, PosInfix},     //  66: '^='
+		SymPlusGreater:        {"+>", SymClassOperator, PosInfix},     //  67: '+>'
+		SymLessPlus:           {"<+", SymClassOperator, PosInfix},     //  68: '<+'
+		SymPreInc:             {"++", SymClassOperator, PosPrefix},    //    : '++'
+		SymPreDec:             {"--", SymClassOperator, PosPrefix},    //    : '--'
+		// SymChangeSign
+		// SymUnchangeSign
+		// SymIdentifier
+		// SymBool
+		// SymInteger
+		// SymVariable
+		// SymFloat
+		// SymFraction
+		// SymString
+		// SymIterator
+		// SymOr:  "or",
+		// SymAnd: "and",
+		// SymNot: "not",
+		// SymComment
+		// SymFuncCall
+		// SymFuncDef
+		// SymList
+		// SymDict
+		// SymIndex
+		// SymExpression
+		// SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
+		// SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
+		// // SymOpenComment                       //   0: '/*'
+		// // SymClosedComment                     //   0: '*/'
+		// // SymOneLineComment                    //   0: '//'
+		// keywordBase
+		SymKwAnd:     {"and", SymClassOperator, PosInfix},
+		SymKwNot:     {"not", SymClassOperator, PosInfix},
+		SymKwOr:      {"or", SymClassOperator, PosInfix},
+		SymKwBut:     {"but", SymClassOperator, PosInfix},
+		SymKwMap:     {"map", SymClassOperator, PosInfix},
+		SymKwFilter:  {"filter", SymClassOperator, PosInfix},
+		SymKwDigest:  {"digest", SymClassOperator, PosInfix},
+		SymKwJoin:    {"join", SymClassOperator, PosInfix},
+		SymKwGroupBy: {"groupby", SymClassOperator, PosInfix},
+		SymKwFunc:    {"func(", SymClassDeclaration, PosPrefix},
+		SymKwBuiltin: {"builtin", SymClassOperator, PosPrefix},
+		SymKwPlugin:  {"plugin", SymClassOperator, PosPrefix},
+		SymKwIn:      {"in", SymClassOperator, PosInfix},
+		SymKwInclude: {"include", SymClassOperator, PosPrefix},
+		SymKwNil:     {"nil", SymClassValue, PosLeaf},
+		SymKwUnset:   {"unset", SymClassOperator, PosPrefix},
+	}
+}
+
+func SymToString(sym Symbol) string {
+	if s, ok := symbolMap[sym]; ok {
+		return s.repr
+	}
+	return ""
+}
+
+func SymListToString(symList []Symbol, quote bool) string {
+	var sb strings.Builder
+	if len(symList) == 0 {
+		sb.WriteString("<nothing>")
+	} else {
+		for _, sym := range symList {
+			if sb.Len() > 0 {
+				sb.WriteByte(',')
+				sb.WriteByte(' ')
+			}
+			if quote {
+				sb.WriteByte('`')
+			}
+			sb.WriteString(SymToString(sym))
+			if quote {
+				sb.WriteByte('`')
+			}
+		}
+	}
+	return sb.String()
+}
+
+func StringEndsWithOperator(s string) bool {
+	return endingOperator(s) != SymNone
+}
+
+// func endingOperator(s string) (sym Symbol) {
+// 	var matchLength = 0
+// 	sym = SymNone
+// 	lower := strings.TrimRight(strings.ToLower(s), " \t")
+// 	for symbol, spec := range symbolMap {
+// 		if strings.HasSuffix(lower, spec.repr) {
+// 			if len(spec.repr) > matchLength {
+// 				matchLength = len(spec.repr)
+// 				if spec.kind == symClassOperator && (spec.opType == PosInfix || spec.opType == PosPrefix) {
+// 					sym = symbol
+// 				} else {
+// 					sym = SymNone
+// 				}
+// 			}
+// 		}
+// 	}
+// 	return
+// }
+
+func endingOperator(s string) (sym Symbol) {
+	var matchLength = 0
+	var repr string
+	sym = SymNone
+	lower := strings.TrimRight(strings.ToLower(s), " \t")
+	for symbol, spec := range symbolMap {
+		if len(spec.repr) > matchLength || repr == spec.repr {
+			if strings.HasSuffix(lower, spec.repr) {
+				if isNotEndingSymbol(spec) && repr != spec.repr {
+					repr = spec.repr
+					matchLength = len(spec.repr)
+					sym = symbol
+				} else {
+					sym = SymNone
+					break
+					// matchLength = 0
+				}
+			}
+		}
+	}
+	return
+}
+
+func isNotEndingSymbol(spec symbolSpec) bool {
+	return (spec.kind == SymClassOperator && (spec.opType == PosInfix || spec.opType == PosPrefix)) ||
+		(spec.kind == SymClassParenthesis && spec.opType == PosPrefix)
+}

scan/symbol.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // Symbol.go
-package expr
+package scan
 
 type Symbol int16
 
@@ -120,6 +120,10 @@ const (
 	SymKwIn
 	SymKwInclude
 	SymKwMap
+	SymKwFilter
+	SymKwDigest
+	SymKwGroupBy
+	SymKwJoin
 	SymKwNil
 	SymKwUnset
 )
@@ -137,9 +141,13 @@ func init() {
 		"IN":      SymKwIn,
 		"INCLUDE": SymKwInclude,
 		"MAP":     SymKwMap,
+		"FILTER":  SymKwFilter,
 		"NOT":     SymKwNot,
 		"OR":      SymKwOr,
 		"NIL":     SymKwNil,
 		"UNSET":   SymKwUnset,
+		"DIGEST":  SymKwDigest,
+		"JOIN":    SymKwJoin,
+		"GROUPBY": SymKwGroupBy,
 	}
 }

scan/t_scanner_test.go

@@ -1,14 +1,16 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // t_scanner_test.go
-package expr
+package scan
 
 import (
 	"errors"
 	"reflect"
 	"strings"
 	"testing"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 func TestScanner(t *testing.T) {
@@ -60,7 +62,7 @@ func TestScanner(t *testing.T) {
 		/* 38 */ {`\`, SymError, errors.New("incomplete escape sequence"), nil},
 		/* 39 */ {`"string"`, SymString, "string", nil},
 		/* 40 */ {`identifier`, SymIdentifier, "identifier", nil},
-		/* 41 */ {`1.2(3)`, SymFraction, newFraction(37, 30), nil},
+		/* 41 */ {`1.2(3)`, SymFraction, kern.NewFraction(37, 30), nil},
 	}
 
 	for i, input := range inputs {

scan/term-constructor-registry.go

@@ -1,23 +1,23 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// op-registry.go
-package expr
+// term-constructor-registry.go
+package scan
 
 const initialRegistryCapacity = 10
 
-type termContructor func(tk *Token) *term
+type termContructor func(tk *Token) *Term
 
 var constructorRegistry map[Symbol]termContructor = nil
 
-func registerTermConstructor(sym Symbol, constructor termContructor) {
+func RegisterTermConstructor(sym Symbol, constructor termContructor) {
 	if constructorRegistry == nil {
 		constructorRegistry = make(map[Symbol]termContructor, initialRegistryCapacity)
 	}
 	constructorRegistry[sym] = constructor
 }
 
-func newTerm(tk *Token) (inst *term) {
+func NewTerm(tk *Token) (inst *Term) {
 	if constructorRegistry != nil {
 		if construct, exists := constructorRegistry[tk.Sym]; exists {
 			inst = construct(tk)

scan/term.go

@@ -0,0 +1,301 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// term.go
+package scan
+
+import (
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type TermPriority uint32
+
+const (
+	PriNone TermPriority = iota
+	PriRange
+	PriIterOp // map, filter, digest, etc
+	PriBut
+	PriAssign
+	PriInsert
+	PriOr
+	PriAnd
+	PriNot
+	PriRelational
+	PriBitwiseOr
+	PriBitwiseAnd
+	PriBitwiseNot
+	PriSum
+	PriProduct
+	PriFraction
+	PriSelector
+	PriBinShift
+	PriSign
+	PriFact
+	PriIterValue
+	PriDefault
+	PriIncDec
+	PriDot
+	PriDereference
+	PriValue
+	PriBitwiseXor = PriBitwiseOr
+)
+
+type TermPosition uint8
+
+const (
+	PosLeaf TermPosition = iota
+	PosInfix
+	PosPrefix
+	PosPostfix
+	PosMultifix
+)
+
+type EvalFuncType func(ctx kern.ExprContext, self *Term) (v any, err error)
+
+type Term struct {
+	Tk       Token
+	Parent   *Term
+	Children []*Term
+	Position TermPosition // operator position: leaf, infix, prefix, postfix, multifix
+	Priority TermPriority // operator priority: higher value means higher priority
+	EvalFunc EvalFuncType
+}
+
+func (t *Term) Clone() (d *Term) {
+	var children []*Term
+	if t.Children != nil {
+		children = make([]*Term, len(t.Children))
+		for i, c := range t.Children {
+			children[i] = c.Clone()
+		}
+	}
+	d = &Term{
+		Tk:       *t.Tk.Clone(),
+		Parent:   t.Parent,
+		Children: children,
+		Position: t.Position,
+		Priority: t.Priority,
+		EvalFunc: t.EvalFunc,
+	}
+	return
+}
+
+func (t *Term) String() string {
+	var sb strings.Builder
+	t.ToString(&sb)
+	return sb.String()
+}
+
+func (t *Term) ToString(sb *strings.Builder) {
+	if t.Position == PosLeaf {
+		sb.WriteString(t.Tk.String())
+	} else {
+		sb.WriteByte('[')
+		sb.WriteString(t.Tk.String())
+		if t.Children != nil {
+			sb.WriteByte('(')
+			for i, c := range t.Children {
+				if i > 0 {
+					sb.WriteByte(' ')
+				}
+				c.ToString(sb)
+			}
+			sb.WriteByte(')')
+		}
+		sb.WriteByte(']')
+	}
+}
+
+func (t *Term) GetChildCount() (count int) {
+	if t.Position == PosLeaf || t.Children == nil {
+		count = 0
+	} else {
+		count = len(t.Children)
+	}
+	return
+}
+
+func (t *Term) GetRoom() (room int) {
+	switch t.Position {
+	case PosLeaf:
+		room = 0
+	case PosInfix:
+		room = 2
+	case PosPostfix, PosPrefix:
+		room = 1
+	default:
+		panic("Invalid node position")
+	}
+	return
+}
+
+func (t *Term) isComplete() bool {
+	return t.GetChildCount() == t.GetRoom()
+}
+
+func (t *Term) removeLastChild() (child *Term) {
+	if t.Children != nil {
+		child = t.Children[len(t.Children)-1]
+		t.Children = t.Children[0 : len(t.Children)-1]
+	} else {
+		panic("Can't get last child")
+	}
+	return
+}
+
+func (t *Term) isLeaf() bool {
+	return t.Position == PosLeaf
+}
+
+func (t *Term) getPriority() TermPriority {
+	return t.Priority
+}
+
+func (t *Term) SetParent(parent *Term) {
+	t.Parent = parent
+	if parent != nil && len(parent.Children) < cap(parent.Children) {
+		parent.Children = append(parent.Children, t)
+	}
+}
+
+func (t *Term) Symbol() Symbol {
+	return t.Tk.Sym
+}
+
+func (t *Term) Source() string {
+	return t.Tk.source
+}
+
+func (t *Term) Value() any {
+	return t.Tk.Value
+}
+
+func (t *Term) GetChild(index int) (c kern.Term) {
+	if index >= 0 && index < len(t.Children) {
+		c = t.Children[index]
+	}
+	return
+}
+
+func (t *Term) GetChildSource(index int) (s string) {
+	if index >= 0 && index < len(t.Children) {
+		s = t.Children[index].Tk.source
+	}
+	return
+}
+
+func (t *Term) IsAssign() bool {
+	return t.Symbol() == SymEqual
+}
+
+func (t *Term) Compute(ctx kern.ExprContext) (v any, err error) {
+	if t.EvalFunc == nil {
+		err = t.Errorf("undefined eval-func for %q term", t.Source())
+	} else {
+		v, err = t.EvalFunc(ctx, t)
+	}
+	return
+}
+
+// func (term *term) toInt(computedValue any, valueDescription string) (i int, err error) {
+// 	if index64, ok := computedValue.(int64); ok {
+// 		i = int(index64)
+// 	} else {
+// 		err = term.Errorf("%s, got %s (%v)", valueDescription, TypeName(computedValue), computedValue)
+// 	}
+// 	return
+// }
+
+func (t *Term) ErrIncompatibleTypes(leftValue, rightValue any) error {
+	leftType := kern.TypeName(leftValue)
+	leftText := kern.GetFormatted(leftValue, kern.Truncate)
+	rightType := kern.TypeName(rightValue)
+	rightText := kern.GetFormatted(rightValue, kern.Truncate)
+	return t.Tk.Errorf(
+		"left operand '%s' [%s] and right operand '%s' [%s] are not compatible with operator %q",
+		leftText, leftType,
+		rightText, rightType,
+		t.Source())
+}
+
+func (t *Term) ErrIncompatibleType(value any, side string) error {
+	return t.Tk.Errorf(
+		"operator %q does not support operand '%v' [%s] on its %s side",
+		t.Source(), value, kern.TypeName(value), side)
+}
+
+func (t *Term) ErrIncompatiblePrefixPostfixType(value any) error {
+	return t.Tk.Errorf(
+		"prefix/postfix operator %q does not support operand '%v' [%s]",
+		t.Source(), value, kern.TypeName(value))
+}
+
+func (t *Term) ErrDivisionByZero() error {
+	return t.Tk.Errorf("division by zero")
+}
+
+func (t *Term) ErrKeyNotFound(key any) error {
+	return t.Tk.Errorf("key '%v' not found", key)
+}
+
+func (t *Term) Errorf(template string, args ...any) (err error) {
+	err = t.Tk.Errorf(template, args...)
+	return
+}
+
+func (t *Term) CheckOperands() (err error) {
+	switch t.Position {
+	case PosInfix:
+		if t.Children == nil || len(t.Children) != 2 || t.anyChildrenNil() {
+			err = t.Tk.Errorf("infix operator %q requires two non-nil operands, got %d", t.Source(), t.GetChildCount())
+		}
+	case PosPrefix:
+		if t.Children == nil || len(t.Children) != 1 || t.Children[0] == nil {
+			err = t.Tk.Errorf("prefix operator %q requires one non-nil operand", t.Tk.String())
+		}
+	case PosPostfix:
+		if t.Children == nil || len(t.Children) != 1 || t.anyChildrenNil() {
+			err = t.Tk.Errorf("postfix operator %q requires one non-nil operand", t.Tk.String())
+		}
+	case PosMultifix:
+		if len(t.Children) < 3 || t.anyChildrenNil() {
+			err = t.Tk.Errorf("infix operator %q requires at least three not operands, got %d", t.Source(), t.GetChildCount())
+		}
+	}
+	return
+}
+
+func (t *Term) anyChildrenNil() bool {
+	for _, child := range t.Children {
+		if child == nil {
+			return true
+		}
+	}
+	return false
+}
+func (t *Term) EvalInfix(ctx kern.ExprContext) (leftValue, rightValue any, err error) {
+	if err = t.CheckOperands(); err == nil {
+		if leftValue, err = t.Children[0].Compute(ctx); err == nil {
+			rightValue, err = t.Children[1].Compute(ctx)
+		}
+	}
+	return
+}
+
+func (t *Term) EvalPrefix(ctx kern.ExprContext) (childValue any, err error) {
+	if err = t.CheckOperands(); err == nil {
+		childValue, err = t.Children[0].Compute(ctx)
+	}
+	return
+}
+
+// NOTE Temporary solution to support function parameters with default value
+
+func (t *Term) ForceChild(c *Term) {
+	if t.Children == nil {
+		t.Children = make([]*Term, 0, 1)
+	}
+	t.Children = append(t.Children, c)
+}

scan/token.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // token.go
-package expr
+package scan
 
 import (
 	"fmt"
@@ -51,6 +51,18 @@ func NewErrorToken(row, col int, err error) *Token {
 	return NewValueToken(row, col, SymError, fmt.Sprintf("[%d:%d]", row, col), err)
 }
 
+func (tk *Token) Source() string {
+	return tk.source
+}
+
+func (tk *Token) Row() int {
+	return tk.row
+}
+
+func (tk *Token) Col() int {
+	return tk.col
+}
+
 func (tk *Token) Clone() (c *Token) {
 	return NewValueToken(tk.row, tk.col, tk.Sym, tk.source, tk.Value)
 }