Expr.adoc: typos

Also made a litle change to scanner function moveOn(): now it moves on
the last char passed and only if there are more than one chars.

README.adoc

@@ -144,4 +144,4 @@ Variables and functions can be added to a context both programmatically and ad a
 
 == Expressions syntax
 
-See #TODO link to doc/Expr.html#
+See https://cdn.paas.portale-stac.it/howto/go-pkg/expr/doc/Expr.html[Expr documentation] for a complete reference of the expression syntax and available functions.

ast.go

@@ -1,138 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// ast.go
-package expr
-
-import (
-	"strings"
-)
-
-type Expr interface {
-	Eval(ctx ExprContext) (result any, err error)
-	eval(ctx ExprContext, preset bool) (result any, err error)
-	String() string
-}
-
-//-------- ast
-
-type ast struct {
-	forest []*term
-	root   *term
-}
-
-func NewAst() *ast {
-	return &ast{}
-}
-
-func (self *ast) ToForest() {
-	if self.root != nil {
-		if self.forest == nil {
-			self.forest = make([]*term, 0)
-		}
-		self.forest = append(self.forest, self.root)
-		self.root = nil
-	}
-}
-
-func (self *ast) String() string {
-	var sb strings.Builder
-	if self.root == nil {
-		sb.WriteString("(nil)")
-	} else {
-		self.root.toString(&sb)
-	}
-	return sb.String()
-}
-
-func (self *ast) addTokens(tokens ...*Token) (err error) {
-	for _, tk := range tokens {
-		if err = self.addToken(tk); err != nil {
-			break
-		}
-	}
-	return
-}
-
-func (self *ast) addToken(tk *Token) (err error) {
-	_, err = self.addToken2(tk)
-	return
-}
-
-func (self *ast) addToken2(tk *Token) (t *term, err error) {
-	if t = newTerm(tk); t != nil {
-		err = self.addTerm(t)
-	} else {
-		err = tk.Errorf("unexpected token %q", tk.String())
-	}
-	return
-}
-
-func (self *ast) addTerm(node *term) (err error) {
-	if self.root == nil {
-		self.root = node
-	} else {
-		self.root, err = self.insert(self.root, node)
-	}
-	return
-}
-
-func (self *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 = self.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 (self *ast) Finish() {
-	if self.root == nil && self.forest != nil && len(self.forest) >= 1 {
-		self.root = self.forest[len(self.forest)-1]
-		self.forest = self.forest[0 : len(self.forest)-1]
-	}
-}
-
-func (self *ast) Eval(ctx ExprContext) (result any, err error) {
-	return self.eval(ctx, true)
-}
-
-func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
-	self.Finish()
-
-	if self.root != nil {
-		if preset {
-			initDefaultVars(ctx)
-		}
-		if self.forest != nil {
-			for _, root := range self.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 = self.root.compute(ctx); err == nil {
-				ctx.UnsafeSetVar(ControlLastResult, result)
-			}
-		}
-		// } else {
-		// 	err = errors.New("empty expression")
-	}
-	return
-}

bind-expr-functions.go

@@ -0,0 +1,63 @@
+// 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 {
+	kern.BaseFunctor
+	params []kern.ExprFuncParam
+	expr   kern.Expr
+	defCtx kern.ExprContext
+}
+
+func (functor *exprFunctor) GetParams() (params []kern.ExprFuncParam) {
+	return functor.params
+}
+
+func newExprFunctor(e kern.Expr, params []kern.ExprFuncParam, ctx kern.ExprContext) *exprFunctor {
+	var defCtx kern.ExprContext
+	if ctx != nil {
+		defCtx = ctx
+	}
+	return &exprFunctor{expr: e, params: params, defCtx: defCtx}
+}
+
+func (functor *exprFunctor) TypeName() string {
+	return "ExprFunctor"
+}
+
+func (functor *exprFunctor) GetDefinitionContext() kern.ExprContext {
+	return functor.defCtx
+}
+
+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.(kern.Functor); ok {
+				paramSpecs := funcArg.GetParams()
+				ctx.RegisterFunc(p.Name(), funcArg, kern.TypeAny, paramSpecs)
+			} else {
+				ctx.UnsafeSetVar(p.Name(), arg)
+			}
+		} else {
+			if missing == nil {
+				missing = make([]string, 0, 1)
+			}
+			missing = append(missing, p.Name())
+			// ctx.UnsafeSetVar(p.Name(), nil)
+		}
+	}
+	if missing != nil {
+		err = kern.ErrMissingParams(name, missing)
+	} else {
+		result, err = functor.expr.Eval(ctx)
+	}
+	return
+}

builtin-base.go

@@ -0,0 +1,339 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-base.go
+package expr
+
+import (
+	"fmt"
+	"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 kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = args[kern.ParamValue] == nil
+	return
+}
+
+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 kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsFloat(args[kern.ParamValue])
+	return
+}
+
+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 kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsString(args[kern.ParamValue])
+	return
+}
+
+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 kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsRational(args[kern.ParamValue])
+	return
+}
+
+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 kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = kern.IsDict(args[kern.ParamValue])
+	return
+}
+
+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 *kern.FractionType:
+		result = v.N() != 0
+	case float64:
+		result = v != 0.0
+	case bool:
+		result = v
+	case string:
+		result = len(v) > 0
+	case *kern.ListType:
+		result = len(*v) > 0
+	case *kern.DictType:
+		result = len(*v) > 0
+	default:
+		err = kern.ErrCantConvert(name, v, "bool")
+	}
+	return
+}
+
+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:
+		result = int64(math.Trunc(v))
+	case bool:
+		if v {
+			result = int64(1)
+		} else {
+			result = int64(0)
+		}
+	case string:
+		var i int
+		if i, err = strconv.Atoi(v); err == nil {
+			result = int64(i)
+		}
+	case *kern.FractionType:
+		result = int64(v.N() / v.D())
+	default:
+		err = kern.ErrCantConvert(name, v, "int")
+	}
+	return
+}
+
+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:
+		result = v
+	case bool:
+		if v {
+			result = float64(1)
+		} else {
+			result = float64(0)
+		}
+	case string:
+		var f float64
+		if f, err = strconv.ParseFloat(v, 64); err == nil {
+			result = f
+		}
+	case *kern.FractionType:
+		result = v.ToFloat()
+	default:
+		err = kern.ErrCantConvert(name, v, "float")
+	}
+	return
+}
+
+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:
+		result = strconv.FormatFloat(v, 'g', -1, 64)
+	case bool:
+		if v {
+			result = "true"
+		} else {
+			result = "false"
+		}
+	case string:
+		result = v
+	case *kern.FractionType:
+		result = v.ToString(0)
+	case kern.Formatter:
+		result = v.ToString(0)
+	case fmt.Stringer:
+		result = v.String()
+	default:
+		err = kern.ErrCantConvert(name, v, "string")
+	}
+	return
+}
+
+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 = kern.ErrExpectedGot(name, "integer", args[ParamDenominator])
+		} else if den == 0 {
+			err = kern.ErrFuncDivisionByZero(name)
+		}
+
+		if err == nil {
+			result = kern.NewFraction(v, den)
+		}
+	case float64:
+		result, err = kern.Float64ToFraction(v)
+	case bool:
+		if v {
+			result = kern.NewFraction(1, 1)
+		} else {
+			result = kern.NewFraction(0, 1)
+		}
+	case string:
+		result, err = kern.MakeGeneratingFraction(v)
+	case *kern.FractionType:
+		result = v
+	default:
+		err = kern.ErrCantConvert(name, v, "float")
+	}
+	return
+}
+
+// func iteratorFunc(ctx expr.ExprContext, name string, args []any) (result any, err error) {
+// 	return
+// }
+
+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 = NewSimpleStoreWithoutGlobalContext()
+		}
+
+		r := strings.NewReader(source)
+		scanner := scan.NewScanner(r, scan.DefaultTranslations())
+
+		if ast, err = parser.Parse(scanner); err == nil {
+			CtrlEnable(ctx, kern.ControlExportAll)
+			result, err = ast.Eval(ctx)
+		}
+	} else {
+		err = kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+	return
+}
+
+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[kern.ParamName].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
+	}
+
+	if result, ok = args[kern.ParamValue]; ok && result != nil {
+		ctx.GetParent().UnsafeSetVar(varName, result)
+		// } else {
+		// 	err = expr.ErrWrongParamType(name, expr.ParamSource, expr.TypeString, args[expr.ParamSource])
+		// }
+	} else if result, ok = ctx.GetVar(varName); !ok {
+		err = kern.ErrUnknownVar(name, varName)
+	}
+	return
+}
+
+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[kern.ParamName].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
+	}
+
+	if result, ok = args[kern.ParamValue]; ok {
+		ctx.GetParent().UnsafeSetVar(varName, result)
+	} else {
+		err = kern.ErrWrongParamType(name, kern.ParamValue, kern.TypeAny, args[kern.ParamValue])
+	}
+	return
+}
+
+func charFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var ord int
+
+	if n, ok := args[kern.ParamValue].(byte); ok {
+		ord = int(n)
+	} else if n, ok := args[kern.ParamValue].(int64); ok {
+		ord = int(n)
+	} else if n, ok := args[kern.ParamValue].(int); ok {
+		ord = n
+	} else {
+		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
+	}
+	if ord < 0 || ord > 255 {
+		err = kern.ErrFuncInvalidArg(name, fmt.Sprintf("character code must be in range 0-255, got %d", ord))
+	} else {
+		result = string(rune(ord))
+	}
+	return
+}
+
+func seqFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	list := kern.NewLinkedList()
+	items := args[kern.ParamValue].([]any)
+	for _, arg := range items {
+		list.PushBack(arg)
+	}
+	result = list
+	return
+}
+
+//// import
+
+func ImportBuiltinsFuncs(ctx kern.ExprContext) {
+	anyParams := []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamValue),
+	}
+
+	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", 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", kern.NewGolangFunctor(evalFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+	})
+
+	ctx.RegisterFunc("var", kern.NewGolangFunctor(varFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamName),
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault, nil),
+	})
+
+	ctx.RegisterFunc("set", kern.NewGolangFunctor(setFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamName),
+		kern.NewFuncParam(kern.ParamValue),
+	})
+
+	ctx.RegisterFunc("char", kern.NewGolangFunctor(charFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamValue),
+	})
+
+	ctx.RegisterFunc("seq", kern.NewGolangFunctor(seqFunc), kern.TypeLinkedList, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamValue, kern.PfRepeat),
+	})
+}
+
+func init() {
+	RegisterBuiltinModule("base", ImportBuiltinsFuncs, "Base expression tools like isNil(), int(), etc.")
+}

builtin-fmt.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-fmt.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+func getStdout(ctx kern.ExprContext) io.Writer {
+	var w io.Writer
+	if wany, exists := ctx.GetVar(kern.ControlStdout); exists && wany != nil {
+		w, _ = wany.(io.Writer)
+	}
+	if w == nil {
+		w = os.Stdout
+	}
+	return w
+}
+
+func printFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var n int = 0
+	if v, exists := args[kern.ParamItem]; exists && v != nil {
+		argv := v.([]any)
+		n, err = fmt.Fprint(getStdout(ctx), argv...)
+	}
+	result = int64(n)
+	return
+}
+
+func printLnFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var n int = 0
+	if v, exists := args[kern.ParamItem]; exists && v != nil {
+		argv := v.([]any)
+		n, err = fmt.Fprintln(getStdout(ctx), argv...)
+	} else {
+		n, err = fmt.Fprintln(getStdout(ctx))
+	}
+	result = int64(n)
+	return
+}
+
+func ImportFmtFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("print", kern.NewGolangFunctor(printFunc), kern.TypeInt, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
+	})
+	ctx.RegisterFunc("println", kern.NewGolangFunctor(printLnFunc), kern.TypeInt, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
+	})
+}
+
+func init() {
+	RegisterBuiltinModule("fmt", ImportFmtFuncs, "String and console formatting functions")
+}

builtin-import.go

@@ -0,0 +1,81 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-import.go
+package expr
+
+import (
+	"io"
+	"os"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+func importFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	return importGeneral(ctx, name, args)
+}
+
+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 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 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, int(it.Index())); err != nil {
+			break
+		}
+		if sourceFilepath, err = makeFilepath(v.(string), dirList); err != nil {
+			break
+		}
+		var file *os.File
+		if file, err = os.Open(sourceFilepath); err == nil {
+			defer file.Close()
+			var expr *scan.Ast
+			scanner := scan.NewScanner(file, scan.DefaultTranslations())
+			parser := NewParser()
+			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymEos); err == nil {
+				result, err = expr.Eval(ctx)
+			}
+			if err != nil {
+				break
+			}
+		} else {
+			break
+		}
+	}
+	if err != nil {
+		if err == io.EOF {
+			err = nil
+		} else {
+			result = nil
+		}
+	}
+	return
+}
+
+func ImportImportFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("import", kern.NewGolangFunctor(importFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamFilepath, kern.PfRepeat),
+	})
+	ctx.RegisterFunc("importAll", kern.NewGolangFunctor(importAllFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamFilepath, kern.PfRepeat),
+	})
+}
+
+func init() {
+	RegisterBuiltinModule("import", ImportImportFuncs, "Functions import() and include()")
+}

builtin-iterator.go

@@ -0,0 +1,105 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-iterator.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const (
+	iterParamOperator = "operator"
+	iterParamVars     = "vars"
+	iterVarStatus     = "status"
+)
+
+func parseRunArgs(localCtx kern.ExprContext, args map[string]any) (it kern.Iterator, op kern.Functor, err error) {
+	var ok bool
+
+	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].(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 *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
+	}
+
+	if vars != nil {
+		for key, value := range *vars {
+			var varName string
+			if varName, ok = key.(string); ok {
+				localCtx.UnsafeSetVar(varName, value)
+			}
+		}
+	}
+
+	return
+}
+
+func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var it kern.Iterator
+	var ok bool
+	var op kern.Functor
+	var v any
+	// var usingDefaultOp = false
+	var params map[string]any
+	var item any
+
+	localCtx := ctx.Clone()
+	localCtx.UnsafeSetVar(iterVarStatus, nil)
+
+	if it, op, err = parseRunArgs(localCtx, args); err != nil {
+		return
+	}
+
+	for item, err = it.Next(); err == nil; item, err = it.Next() {
+		if op != nil {
+			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 = kern.ToBool(v); !success || !ok {
+					break
+				}
+			}
+		}
+	}
+
+	if err == io.EOF {
+		err = nil
+	}
+	if err == nil {
+		if op == nil {
+			ctx.UnsafeSetVar(iterVarStatus, it.Count())
+		}
+		result, _ = localCtx.GetVar(iterVarStatus)
+	}
+	return
+}
+
+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),
+	})
+}
+
+func init() {
+	RegisterBuiltinModule("iterator", ImportIterFuncs, "Iterator helper functions")
+}

builtin-math-arith.go

@@ -0,0 +1,185 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-math-arith.go
+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 !(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 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 *kern.FractionType
+	var v any
+
+	level++
+
+	for v, err = it.Next(); err == nil; v, err = it.Next() {
+		if list, ok := v.(*kern.ListType); ok {
+			v = NewListIterator(list, nil)
+		}
+		if subIter, ok := v.(kern.Iterator); ok {
+			if v, err = doAdd(ctx, name, subIter, count, level); err != nil {
+				break
+			}
+			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, int(it.Index())); err != nil {
+			break
+		}
+		count++
+
+		if !sumAsFloat {
+			if kern.IsFloat(v) {
+				sumAsFloat = true
+				if sumAsFract {
+					floatSum = fractSum.ToFloat()
+				} else {
+					floatSum = float64(intSum)
+				}
+			} else if !sumAsFract && kern.IsFraction(v) {
+				fractSum = kern.NewFraction(intSum, 1)
+				sumAsFract = true
+			}
+		}
+
+		if sumAsFloat {
+			floatSum += kern.NumAsFloat(v)
+		} else if sumAsFract {
+			var item *kern.FractionType
+			var ok bool
+			if item, ok = v.(*kern.FractionType); !ok {
+				iv, _ := v.(int64)
+				item = kern.NewFraction(iv, 1)
+			}
+			fractSum = kern.SumFract(fractSum, item)
+		} else {
+			iv, _ := v.(int64)
+			intSum += iv
+		}
+	}
+	if err == nil || err == io.EOF {
+		err = nil
+		if sumAsFloat {
+			result = floatSum
+		} else if sumAsFract {
+			result = fractSum
+		} else {
+			result = intSum
+		}
+	}
+	return
+}
+
+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 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 *kern.FractionType
+	var v any
+
+	level++
+	for v, err = it.Next(); err == nil; v, err = it.Next() {
+		if list, ok := v.(*kern.ListType); ok {
+			v = NewListIterator(list, nil)
+		}
+		if subIter, ok := v.(kern.Iterator); ok {
+			if v, err = doMul(ctx, name, subIter, count, level); err != nil {
+				break
+			}
+			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, int(it.Index())); err != nil {
+				break
+			}
+		}
+		count++
+
+		if !mulAsFloat {
+			if kern.IsFloat(v) {
+				mulAsFloat = true
+				if mulAsFract {
+					floatProd = fractProd.ToFloat()
+				} else {
+					floatProd = float64(intProd)
+				}
+			} else if !mulAsFract && kern.IsFraction(v) {
+				fractProd = kern.NewFraction(intProd, 1)
+				mulAsFract = true
+			}
+		}
+
+		if mulAsFloat {
+			floatProd *= kern.NumAsFloat(v)
+		} else if mulAsFract {
+			var item *kern.FractionType
+			var ok bool
+			if item, ok = v.(*kern.FractionType); !ok {
+				iv, _ := v.(int64)
+				item = kern.NewFraction(iv, 1)
+			}
+			fractProd = kern.MulFract(fractProd, item)
+		} else {
+			iv, _ := v.(int64)
+			intProd *= iv
+		}
+	}
+	if err == nil || err == io.EOF {
+		err = nil
+		if mulAsFloat {
+			result = floatProd
+		} else if mulAsFract {
+			result = fractProd
+		} else {
+			result = intProd
+		}
+	}
+	return
+}
+
+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 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", kern.NewGolangFunctor(mulFunc), kern.TypeNumber, []kern.ExprFuncParam{
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, int64(1)),
+	})
+}
+
+func init() {
+	RegisterBuiltinModule("math.arith", ImportMathFuncs, "Functions add() and mul()")
+}

builtin-os-file-iter-byte.go

@@ -0,0 +1,102 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/file"
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const fileByteIteratorType = "fileByteIterator"
+
+type fileFileByteIterator struct {
+	fileIterBase
+	b byte
+}
+
+func newFileByteIterator(r *file.Reader, autoClose bool) *fileFileByteIterator {
+	return &fileFileByteIterator{
+		fileIterBase: fileIterBase{reader: r, index: -1, count: 0, autoClose: autoClose},
+		b:            0}
+}
+
+func (it *fileFileByteIterator) TypeName() string {
+	return fileByteIteratorType
+}
+
+func (it *fileFileByteIterator) String() string {
+	return it.repr(fileByteIteratorType)
+}
+
+func (it *fileFileByteIterator) Next() (item any, err error) { // must return io.EOF after the last item
+	if it.b, err = it.reader.ReadByte(); err == nil {
+		it.increment()
+		item = it.b
+	} else if it.autoClose {
+		it.Clean()
+	}
+	return
+}
+
+func (it *fileFileByteIterator) Current() (item any, err error) {
+	item = it.b
+	return
+}
+
+func (it *fileFileByteIterator) Reset() (err error) {
+	if err = it.reader.Reset(); err == nil {
+		it.reset()
+		it.b = 0
+	}
+	return
+}
+
+func (it *fileFileByteIterator) Clean() (err error) {
+	if it.reader.Valid() {
+		if err = it.reader.GetFile().Close(); err == nil {
+			it.reader = nil
+		}
+	}
+	it.reset()
+	it.b = 0
+	return
+}
+
+func (it *fileFileByteIterator) 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 fileByteIteratorFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle *file.Reader
+	var invalidFileHandle any
+	var autoClose bool
+
+	if handle, invalidFileHandle, autoClose, err = initFileHandle(ctx, name, args); err == nil {
+		if handle != nil {
+			result = newFileByteIterator(handle, autoClose)
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}

builtin-os-file-iter-line.go

@@ -0,0 +1,105 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/file"
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const fileLineIteratorType = "fileLineIterator"
+
+type fileFileLineIterator struct {
+	fileIterBase
+	line string
+}
+
+func newFileLineIterator(r *file.Reader, autoClose bool) *fileFileLineIterator {
+	return &fileFileLineIterator{
+		fileIterBase: fileIterBase{reader: r, index: -1, count: 0, autoClose: autoClose},
+		line:         "",
+	}
+}
+
+func (it *fileFileLineIterator) TypeName() string {
+	return fileLineIteratorType
+}
+
+func (it *fileFileLineIterator) String() string {
+	return it.repr(fileLineIteratorType)
+}
+
+func (it *fileFileLineIterator) Next() (item any, err error) { // must return io.EOF after the last item
+	if it.line, err = it.reader.ReadString('\n'); err == nil {
+		it.increment()
+		item = it.line[0 : len(it.line)-1]
+	} else if it.autoClose {
+		it.Clean()
+	}
+	return
+}
+
+func (it *fileFileLineIterator) Current() (item any, err error) {
+	if len(it.line) > 0 {
+		item = it.line[0 : len(it.line)-1]
+	}
+	return
+}
+
+func (it *fileFileLineIterator) Reset() (err error) {
+	if err = it.reader.Reset(); err == nil {
+		it.reset()
+		it.line = ""
+	}
+	return
+}
+
+func (it *fileFileLineIterator) Clean() (err error) {
+	if it.reader != nil {
+		if err = it.reader.Close(); err == nil {
+			it.reader = nil
+		}
+	}
+	it.reset()
+	it.line = ""
+	return
+}
+
+func (it *fileFileLineIterator) 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 fileLineIteratorFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle *file.Reader
+	var invalidFileHandle any
+	var autoClose bool
+
+	if handle, invalidFileHandle, autoClose, err = initFileHandle(ctx, name, args); err == nil {
+		if handle != nil {
+			result = newFileLineIterator(handle, autoClose)
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}

builtin-os-file-iter.go

@@ -0,0 +1,71 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"fmt"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/file"
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const paramHandleOrPath = "handle-or-path"
+
+type fileIterBase struct {
+	reader    *file.Reader
+	index     int64
+	count     int64
+	autoClose bool
+}
+
+func (it *fileIterBase) Count() int64 {
+	return it.count
+}
+
+func (it *fileIterBase) Index() int64 {
+	return it.index
+}
+
+func (it *fileIterBase) HasOperation(name string) bool {
+	return slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName}, name)
+}
+
+func (it *fileIterBase) reset() {
+	it.index = -1
+	it.count = 0
+}
+
+func (it *fileIterBase) increment() {
+	it.index++
+	it.count++
+}
+
+func (it *fileIterBase) repr(typeName string) string {
+	if it.reader.Valid() {
+		return fmt.Sprintf("$(%s@%q)", typeName, it.reader.GetName())
+	}
+	return fmt.Sprintf("$(%s@<nil>)", typeName)
+}
+
+func initFileHandle(ctx kern.ExprContext, name string, args map[string]any) (handle *file.Reader, invalidFileHandle any, autoClose bool, err error) {
+	var ok bool
+
+	if handle, ok = args[paramHandleOrPath].(*file.Reader); !ok {
+		if fileName, ok := args[paramHandleOrPath].(string); ok && len(fileName) > 0 {
+			var handleAny any
+			if handleAny, err = openFileFunc(ctx, name, map[string]any{kern.ParamFilepath: fileName}); err != nil {
+				return
+			}
+			if handleAny != nil {
+				handle = handleAny.(*file.Reader)
+				autoClose = true
+			}
+		} else {
+			invalidFileHandle = args[paramHandleOrPath]
+		}
+	}
+	return
+}

builtin-os-file.go

@@ -0,0 +1,233 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/file"
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const (
+	osLimitCh = "limitCh"
+)
+
+func errMissingFilePath(funcName string) error {
+	return fmt.Errorf("%s(): missing or invalid file path", funcName)
+}
+
+func errInvalidFileHandle(funcName string, v any) error {
+	if v != nil {
+		return fmt.Errorf("%s(): invalid file handle %v [%T]", funcName, v, v)
+	} else {
+		return fmt.Errorf("%s(): invalid file handle", funcName)
+	}
+}
+
+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 = file.NewReader(fh)
+		// }
+		result, err = file.OpenReader(filePath)
+	} else {
+		err = errMissingFilePath(name)
+	}
+	return
+}
+
+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 = file.NewWriter(fh)
+		// }
+		result, err = file.CreateWriter(filePath)
+	} else {
+		err = errMissingFilePath(name)
+	}
+	return
+}
+
+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 = file.NewWriter(fh)
+		// }
+		result, err = file.AppendWriter(filePath)
+	} else {
+		err = errMissingFilePath(name)
+	}
+	return
+}
+
+func closeFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle file.Handle
+	var invalidFileHandle any
+	var ok bool
+
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	if handle != nil {
+		if fh := handle.GetFile(); fh != nil {
+			if w, ok := handle.(*file.Writer); ok {
+				err = w.Flush()
+			}
+
+			if err == nil {
+				err = fh.Close()
+			}
+		}
+	}
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, handle)
+	}
+	result = err == nil
+	return
+}
+
+func fileWriteTextFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle file.Handle
+	var invalidFileHandle any
+	var ok bool
+
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	if handle != nil {
+		if w, ok := handle.(*file.Writer); ok {
+			if v, exists := args[kern.ParamItem]; exists {
+				argv := v.([]any)
+				// result, err = fmt.Fprint(w.writer, argv...)
+				result, err = w.Write(argv...)
+			}
+		} else {
+			invalidFileHandle = handle
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}
+
+func fileReadTextFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle file.Handle
+	var invalidFileHandle any
+	var ok bool
+
+	result = nil
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok || args[kern.ParamHandle] == nil {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	if handle != nil {
+		if r, ok := handle.(*file.Reader); ok {
+			var limit byte = '\n'
+			var v string
+			if s, ok := args[osLimitCh].(string); ok && len(s) > 0 {
+				limit = s[0]
+			}
+
+			v, err = r.ReadString(limit)
+			if err == io.EOF {
+				err = nil
+			}
+			if len(v) > 0 {
+				if v[len(v)-1] == limit {
+					result = v[0 : len(v)-1]
+				} else {
+					result = v
+				}
+			}
+		} else {
+			invalidFileHandle = handle
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}
+
+func fileReadTextAllFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle file.Handle
+	var invalidFileHandle any
+	var ok bool
+
+	result = nil
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok || args[kern.ParamHandle] == nil {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	if handle != nil {
+		if r, ok := handle.(*file.Reader); ok {
+			var b []byte
+			b, err = r.ReadAll()
+			result = string(b)
+		} else {
+			invalidFileHandle = handle
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}
+
+func ImportOsFuncs(ctx kern.ExprContext) {
+	ctx.RegisterFunc("fileOpen", kern.NewGolangFunctor(openFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamFilepath),
+	})
+
+	ctx.RegisterFunc("fileAppend", kern.NewGolangFunctor(appendFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamFilepath),
+	})
+
+	ctx.RegisterFunc("fileCreate", kern.NewGolangFunctor(createFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamFilepath),
+	})
+
+	ctx.RegisterFunc("fileClose", kern.NewGolangFunctor(closeFileFunc), kern.TypeBoolean, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamHandle),
+	})
+
+	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", kern.NewGolangFunctor(fileReadTextFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParamFlagDef(osLimitCh, kern.PfDefault, "\n"),
+	})
+
+	ctx.RegisterFunc("fileReadTextAll", kern.NewGolangFunctor(fileReadTextAllFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamHandle),
+	})
+
+	ctx.RegisterFunc("fileLineIterator", kern.NewGolangFunctor(fileLineIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
+		kern.NewFuncParam(paramHandleOrPath),
+	})
+
+	ctx.RegisterFunc("fileByteIterator", kern.NewGolangFunctor(fileByteIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
+		kern.NewFuncParam(paramHandleOrPath),
+	})
+
+}
+
+func init() {
+	RegisterBuiltinModule("os.file", ImportOsFuncs, "Operating system file functions")
+}

builtin-string.go

@@ -0,0 +1,273 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-string.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const (
+	strParamOther = "other"
+)
+
+// --- Start of function definitions
+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() {
+		if it.Index() > 0 {
+			sb.WriteString(sep)
+		}
+		if s, ok := v.(string); ok {
+			sb.WriteString(s)
+		} else {
+			err = kern.ErrExpectedGot(funcName, kern.TypeString, v)
+			return
+		}
+	}
+	if err == io.EOF {
+		err = nil
+		result = sb.String()
+	}
+	return
+}
+
+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].(*kern.ListType); ok {
+					result, err = doJoinStr(name, sep, NewListIterator(ls, nil))
+				} 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 = kern.ErrInvalidParameterValue(name, kern.ParamItem, v)
+				}
+			} else {
+				result, err = doJoinStr(name, sep, NewArrayIterator(argv))
+			}
+		}
+	} else {
+		err = kern.ErrWrongParamType(name, kern.ParamSeparator, kern.TypeString, args[kern.ParamSeparator])
+	}
+	return
+}
+
+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[kern.ParamSource].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+
+	if start, err = kern.ToGoInt(args[kern.ParamStart], name+"()"); err != nil {
+		return
+	}
+
+	if count, err = kern.ToGoInt(args[kern.ParamCount], name+"()"); err != nil {
+		return
+	}
+
+	if start < 0 {
+		start = len(source) + start
+	}
+
+	if count < 0 {
+		count = len(source) - start
+	}
+	end := min(start+count, len(source))
+	result = source[start:end]
+	return
+}
+
+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[kern.ParamSource].(string); !ok {
+		return nil, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+	result = strings.TrimSpace(source)
+	return
+}
+
+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[kern.ParamSource].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+
+	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
+	} else if v, exists := args[strParamOther]; exists {
+		argv := v.([]any)
+		for i, targetSpec := range argv {
+			if target, ok := targetSpec.(string); ok {
+				if strings.HasPrefix(source, target) {
+					result = true
+					break
+				}
+			} else {
+				err = fmt.Errorf("target item nr %d is %s, string expected", i+1, kern.TypeName(targetSpec))
+				break
+			}
+		}
+	}
+	return
+}
+
+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[kern.ParamSource].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+
+	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
+	} else if v, exists := args[strParamOther]; exists {
+		argv := v.([]any)
+		for i, targetSpec := range argv {
+			if target, ok := targetSpec.(string); ok {
+				if strings.HasSuffix(source, target) {
+					result = true
+					break
+				}
+			} else {
+				err = fmt.Errorf("target item nr %d is %s, string expected", i+1, kern.TypeName(targetSpec))
+				break
+			}
+		}
+	}
+	return
+}
+
+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[kern.ParamSource].(string); !ok {
+		return result, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+
+	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[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)", kern.TypeName(args[kern.ParamCount]), args[kern.ParamCount])
+	}
+
+	if count > 0 {
+		parts = strings.SplitN(source, sep, count)
+	} else if count < 0 {
+		parts = strings.Split(source, sep)
+	} else {
+		parts = []string{}
+	}
+	list := make(kern.ListType, len(parts))
+	for i, part := range parts {
+		list[i] = part
+	}
+	result = &list
+	return
+}
+
+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 = kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+	return
+}
+
+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 = kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
+	}
+	return
+}
+
+// --- End of function definitions
+
+// Import above functions in the context
+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", 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", 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", kern.NewGolangFunctor(trimStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+	})
+
+	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", kern.NewGolangFunctor(endsWithStrFunc), kern.TypeBoolean, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSuffix),
+		kern.NewFuncParamFlag(strParamOther, kern.PfRepeat),
+	})
+
+	ctx.RegisterFunc("strUpper", kern.NewGolangFunctor(upperStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+	})
+
+	ctx.RegisterFunc("strLower", kern.NewGolangFunctor(lowerStrFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamSource),
+	})
+}
+
+// Register the import function in the import-register.
+// That will allow to import all function of this module by the "builtin" operator."
+func init() {
+	RegisterBuiltinModule("string", ImportStringFuncs, "string utilities")
+}

builtins-register.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtins-register.go
+package expr
+
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type builtinModule struct {
+	importFunc  func(kern.ExprContext)
+	description string
+	imported    bool
+}
+
+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(kern.ExprContext), description string) {
+	if builtinModuleRegister == nil {
+		builtinModuleRegister = make(map[string]*builtinModule)
+	}
+	if _, exists := builtinModuleRegister[name]; exists {
+		panic(fmt.Errorf("module %q already registered", name))
+	}
+	builtinModuleRegister[name] = newBuiltinModule(importFunc, description)
+}
+
+func IterateBuiltinModules(op func(name, description string, imported bool) bool) {
+	if op != nil {
+		for name, mod := range builtinModuleRegister {
+			if !op(name, mod.description, mod.imported) {
+				break
+			}
+		}
+	}
+}
+
+// ----
+func init() {
+	if builtinModuleRegister == nil {
+		builtinModuleRegister = make(map[string]*builtinModule)
+	}
+}

byte-slider.go

@@ -1,34 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// byte-slider.go
-package expr
-
-import "bytes"
-
-type ByteSlider struct {
-	buf    []byte
-	length int
-}
-
-func NewByteSlider(size int) *ByteSlider {
-	return &ByteSlider{
-		buf:    make([]byte, max(1, size)),
-		length: 0,
-	}
-}
-
-func (self *ByteSlider) PushEnd(b byte) {
-	if self.length == cap(self.buf) {
-		self.length--
-		for i := 0; i < self.length; i++ {
-			self.buf[i] = self.buf[i+1]
-		}
-	}
-	self.buf[self.length] = b
-	self.length++
-}
-
-func (self *ByteSlider) Equal(target []byte) bool {
-	return target != nil && bytes.Equal(self.buf, target)
-}

common-errors.go

@@ -1,55 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// common-errors.go
-package expr
-
-import (
-	"fmt"
-)
-
-func errTooFewParams(funcName string, minArgs, maxArgs, argCount int) (err error) {
-	if maxArgs < 0 {
-		err = fmt.Errorf("%s(): too few params -- expected %d or more, got %d", funcName, minArgs, argCount)
-	} else {
-		err = fmt.Errorf("%s(): too few params -- expected %d, got %d", funcName, minArgs, argCount)
-	}
-	return
-}
-
-func errTooMuchParams(funcName string, maxArgs, argCount int) (err error) {
-	err = fmt.Errorf("%s(): too much params -- expected %d, got %d", funcName, maxArgs, argCount)
-	return
-}
-
-// --- General errors
-
-func errCantConvert(funcName string, value any, kind string) error {
-	return fmt.Errorf("%s(): can't convert %s to %s", funcName, typeName(value), kind)
-}
-
-func errExpectedGot(funcName string, kind string, value any) error {
-	return fmt.Errorf("%s() expected %s, got %s (%v)", funcName, kind, typeName(value), value)
-}
-
-func errFuncDivisionByZero(funcName string) error {
-	return fmt.Errorf("%s(): division by zero", funcName)
-}
-
-func errDivisionByZero() error {
-	return fmt.Errorf("division by zero")
-}
-
-// --- Parameter errors
-
-func errMissingRequiredParameter(funcName, paramName string) error {
-	return fmt.Errorf("%s() missing required parameter %q", funcName, paramName)
-}
-
-func errInvalidParameterValue(funcName, paramName string, paramValue any) error {
-	return fmt.Errorf("%s() invalid value %s (%v) for parameter %q", funcName, typeName(paramValue), paramValue, paramName)
-}
-
-func errWrongParamType(funcName, paramName, paramType string, paramValue any) error {
-	return fmt.Errorf("%s() the %q parameter must be a %s, got a %s (%v)", funcName, paramName, paramType, typeName(paramValue), paramValue)
-}

common-params.go

@@ -1,21 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// common-params.go
-package expr
-
-const (
-	paramCount     = "count"
-	paramItem      = "item"
-	paramParts     = "parts"
-	paramSeparator = "separator"
-	paramSource    = "source"
-	paramSuffix    = "suffix"
-	paramPrefix    = "prefix"
-	paramStart     = "start"
-	paramEnd       = "end"
-	paramValue     = "value"
-	paramEllipsis  = "..."
-	paramFilepath  = "filepath"
-	paramDirpath   = "dirpath"
-)

common-type-names.go

@@ -1,18 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// common-type-names.go
-package expr
-
-const (
-	typeAny      = "any"
-	typeBoolean  = "boolean"
-	typeFloat    = "float"
-	typeFraction = "fraction"
-	typeHandle   = "handle"
-	typeInt      = "integer"
-	typeItem     = "item"
-	typeNumber   = "number"
-	typePair     = "pair"
-	typeString   = "string"
-)

context.go

@@ -1,49 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// context.go
-package expr
-
-// ---- Functor interface
-type Functor interface {
-	Invoke(ctx ExprContext, name string, args []any) (result any, err error)
-	SetFunc(info ExprFunc)
-	GetFunc() ExprFunc
-	GetParams() []ExprFuncParam
-}
-
-// ---- Function Param Info
-type ExprFuncParam interface {
-	Name() string
-	Type() string
-	IsOptional() bool
-	IsRepeat() bool
-	DefaultValue() any
-}
-
-// ---- Function Info
-type ExprFunc interface {
-	Formatter
-	Name() string
-	MinArgs() int
-	MaxArgs() int
-	Functor() Functor
-	Params() []ExprFuncParam
-	ReturnType() string
-}
-
-// ----Expression Context
-type ExprContext interface {
-	Clone() ExprContext
-	Merge(ctx ExprContext)
-	GetVar(varName string) (value any, exists bool)
-	SetVar(varName string, value any)
-	UnsafeSetVar(varName string, value any)
-	EnumVars(func(name string) (accept bool)) (varNames []string)
-	EnumFuncs(func(name string) (accept bool)) (funcNames []string)
-	GetFuncInfo(name string) (item ExprFunc, exists bool)
-	Call(name string, args []any) (result any, err error)
-	// RegisterFunc(name string, f Functor, minArgs, maxArgs int)
-	RegisterFuncInfo(info ExprFunc)
-	RegisterFunc(name string, f Functor, returnType string, param []ExprFuncParam) error
-}

control.go

@@ -1,62 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// control.go
-package expr
-
-import "strings"
-
-// Preset control variables
-const (
-	ControlLastResult   = "last"
-	ControlBoolShortcut = "_bool_shortcut"
-	ControlImportPath   = "_import_path"
-)
-
-// Other control variables
-const (
-	control_export_all = "_export_all"
-)
-
-// Initial values
-const (
-	init_import_path = "~/.local/lib/go-pkg/expr:/usr/local/lib/go-pkg/expr:/usr/lib/go-pkg/expr"
-)
-
-func initDefaultVars(ctx ExprContext) {
-	ctx.SetVar(ControlBoolShortcut, true)
-	ctx.SetVar(ControlImportPath, init_import_path)
-}
-
-func enable(ctx ExprContext, name string) {
-	if strings.HasPrefix(name, "_") {
-		ctx.SetVar(name, true)
-	} else {
-		ctx.SetVar("_"+name, true)
-	}
-}
-
-func disable(ctx ExprContext, name string) {
-	if strings.HasPrefix(name, "_") {
-		ctx.SetVar(name, false)
-	} else {
-		ctx.SetVar("_"+name, false)
-	}
-}
-
-func isEnabled(ctx ExprContext, name string) (status bool) {
-	if v, exists := ctx.GetVar(name); exists {
-		if b, ok := v.(bool); ok {
-			status = b
-		}
-	}
-	return
-}
-
-func getControlString(ctx ExprContext, name string) (s string, exists bool) {
-	var v any
-	if v, exists = ctx.GetVar(name); exists {
-		s, exists = v.(string)
-	}
-	return
-}

data-cursor.go

@@ -1,34 +1,57 @@
-// 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
 package expr
 
 import (
-	"errors"
 	"io"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 type dataCursor struct {
-	ds          map[string]Functor
+	ds        map[string]kern.Functor
-	ctx         ExprContext
+	ctx       kern.ExprContext
-	index       int
+	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     int64
+	count     int64
+	current   any
+	lastErr   error
 	resource  any
-	nextFunc    Functor
+	nextFunc  kern.Functor
-	cleanFunc   Functor
+	cleanFunc kern.Functor
-	resetFunc   Functor
+	resetFunc kern.Functor
-	currentFunc Functor
 }
 
-func newDataCursor(ctx ExprContext, ds map[string]Functor) (dc *dataCursor) {
+func NewDataCursor(ctx kern.ExprContext, ds map[string]kern.Functor, resource any) (dc *dataCursor) {
 	dc = &dataCursor{
 		ds:        ds,
+		initState: true,
+		// cursorValid: true,
 		index:     -1,
+		count:     0,
+		current:   nil,
+		lastErr:   nil,
+		resource:  resource,
 		ctx:       ctx.Clone(),
+		nextFunc:  ds[kern.NextName],
+		cleanFunc: ds[kern.CleanName],
+		resetFunc: ds[kern.ResetName],
 	}
 	return
 }
 
+func (dc *dataCursor) Context() kern.ExprContext {
+	return dc.ctx
+}
+
+func (dc *dataCursor) TypeName() string {
+	return "DataCursor"
+}
+
 // func mapToString(m map[string]Functor) string {
 // 	var sb strings.Builder
 // 	sb.WriteByte('{')
@@ -58,97 +81,227 @@ func (dc *dataCursor) String() string {
 }
 
 func (dc *dataCursor) HasOperation(name string) (exists bool) {
-	exists = name == indexName
+	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 []any) (value any, err error) {
+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 functor, ok := dc.ds[name]; ok && isFunctor(functor) {
+	} else if name == kern.CleanName {
-		if functor == dc.cleanFunc {
+		err = dc.Clean()
-			value, err = dc.Clean()
+	} else if name == kern.ResetName {
-		} else if functor == dc.resetFunc {
+		err = dc.Reset()
-			value, err = dc.Reset()
+	} else if functor, ok := dc.ds[name]; ok && kern.IsFunctor(functor) {
+		ctx := kern.CloneContext(dc.ctx)
+		value, err = functor.InvokeNamed(ctx, name, args)
+		kern.ExportObjects(dc.ctx, ctx)
 	} else {
-			ctx := cloneContext(dc.ctx)
+		err = kern.ErrNoOperation(name)
-			value, err = functor.Invoke(ctx, name, []any{})
-			exportObjects(dc.ctx, ctx)
-		}
-	} else {
-		err = errNoOperation(name)
 	}
 	return
 }
 
-func (dc *dataCursor) Reset() (success bool, err error) {
+// func (dc *dataCursor) Reset() (err error) {
+// 	if dc.resetFunc != nil {
+// 		if dc.resource != nil {
+// 			ctx := cloneContext(dc.ctx)
+// 			actualParams := bindActualParams(dc.resetFunc, []any{dc.resource})
+// 			_, err = dc.resetFunc.InvokeNamed(ctx, ResetName, actualParams)
+// 			exportObjects(dc.ctx, ctx)
+// 			dc.index = -1
+// 			dc.count = 0
+// 			dc.initState = true
+// 			dc.current = nil
+// 			dc.lastErr = nil
+// 		} else {
+// 			err = errInvalidDataSource()
+// 		}
+// 	} else {
+// 		err = errNoOperation(ResetName)
+// 	}
+// 	return
+// }
+
+func (dc *dataCursor) Reset() (err error) {
 	if dc.resetFunc != nil {
-		if dc.resource != nil {
+		ctx := kern.CloneContext(dc.ctx)
-			ctx := cloneContext(dc.ctx)
+		actualParams := kern.BindActualParams(dc.resetFunc, []any{dc.resource})
-			if _, err = dc.resetFunc.Invoke(ctx, resetName, []any{dc.resource}); err == nil {
+		_, err = dc.resetFunc.InvokeNamed(ctx, kern.ResetName, actualParams)
+		kern.ExportObjects(dc.ctx, ctx)
+	}
 	dc.index = -1
-			}
+	dc.count = 0
-			exportObjects(dc.ctx, ctx)
+	dc.initState = true
-		} else {
+	dc.current = nil
-			err = errInvalidDataSource()
+	dc.lastErr = nil
-		}
-	} else {
-		err = errNoOperation(resetName)
-	}
-	success = err == nil
 	return
 }
 
-func (dc *dataCursor) Clean() (success bool, err error) {
+func (dc *dataCursor) Clean() (err error) {
 	if dc.cleanFunc != nil {
-		if dc.resource != nil {
+		ctx := kern.CloneContext(dc.ctx)
-			ctx := cloneContext(dc.ctx)
+		actualParams := kern.BindActualParams(dc.cleanFunc, []any{dc.resource})
-			_, err = dc.cleanFunc.Invoke(ctx, cleanName, []any{dc.resource})
+		_, err = dc.cleanFunc.InvokeNamed(ctx, kern.CleanName, actualParams)
-			dc.resource = nil
+		kern.ExportObjects(dc.ctx, ctx)
-			exportObjects(dc.ctx, ctx)
-		} else {
-			err = errInvalidDataSource()
 	}
-	} else {
+	dc.lastErr = io.EOF
-		err = errors.New("no 'clean' function defined in the data-source")
-	}
-	success = err == nil
 	return
 }
 
+// func (dc *dataCursor) Clean() (err error) {
+// 	if dc.cleanFunc != nil {
+// 		if dc.resource != nil {
+// 			ctx := cloneContext(dc.ctx)
+// 			actualParams := bindActualParams(dc.cleanFunc, []any{dc.resource})
+// 			_, err = dc.cleanFunc.InvokeNamed(ctx, CleanName, actualParams)
+// 			exportObjects(dc.ctx, ctx)
+// 		} else {
+// 			err = errInvalidDataSource()
+// 		}
+// 	} else {
+// 		err = errNoOperation(CleanName)
+// 	}
+// 	return
+// }
+
 func (dc *dataCursor) Current() (item any, err error) { // must return io.EOF at the last item
-	ctx := cloneContext(dc.ctx)
+	dc.init()
-	if item, err = dc.currentFunc.Invoke(ctx, currentName, []any{}); err == nil && item == nil {
+
+	if dc.current != nil {
+		item = dc.current
+	} else {
 		err = io.EOF
 	}
-	exportObjects(dc.ctx, ctx)
 	return
 }
 
-func (dc *dataCursor) Next() (item any, err error) { // must return io.EOF after the last item
+func (dc *dataCursor) checkFilter(filter kern.Functor, item any) (accepted bool, err error) {
-	if dc.resource != nil {
+	var v any
-		ctx := cloneContext(dc.ctx)
+	var ok bool
-		// fmt.Printf("Entering Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
+	ctx := kern.CloneContext(dc.ctx)
-		if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{dc.resource}); err == nil {
+
-			if item == nil {
+	actualParams := kern.BindActualParams(filter, []any{item, dc.index})
-				err = io.EOF
+	if v, err = filter.InvokeNamed(ctx, kern.FilterName, actualParams); err == nil && v != nil {
-			} else {
+		if accepted, ok = v.(bool); !ok {
+			accepted = true // NOTE: A non-boolean value that is not nil means the item has been accepted
+		}
+	}
+	return
+}
+
+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
+}
+
+func (dc *dataCursor) init() {
+	if dc.initState {
+		dc.initState = false
+		dc.Next()
+	}
+}
+
+func (dc *dataCursor) Next() (current any, err error) { // must return io.EOF after the last item
+	if dc.initState {
+		dc.init()
+	} else if err = dc.lastErr; err != nil {
+		return
+	}
+	current = dc.current
+	filter := dc.ds[kern.FilterName]
+	mapper := dc.ds[kern.MapName]
+	var item any
+	for item == nil && dc.lastErr == nil {
+		ctx := kern.CloneContext(dc.ctx)
 		dc.index++
-			}
+
-		}
+		actualParams := kern.BindActualParams(dc.nextFunc, []any{dc.resource, dc.index})
-		// fmt.Printf("Exiting Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
+		if item, dc.lastErr = dc.nextFunc.InvokeNamed(ctx, kern.NextName, actualParams); dc.lastErr == nil {
-		exportObjects(dc.ctx, ctx)
+			if item == nil {
-		// fmt.Printf("Outer-Ctx [%p]: %s\n", dc.ctx, CtxToString(dc.ctx, 0))
+				dc.lastErr = io.EOF
 			} else {
-		err = errInvalidDataSource()
+				accepted := true
+				if filter != nil {
+					if accepted, dc.lastErr = dc.checkFilter(filter, item); dc.lastErr != nil || !accepted {
+						item = nil
+					}
+				}
+				if accepted {
+					dc.count++
+				}
+				if item != nil && mapper != nil {
+					item, dc.lastErr = dc.mapItem(mapper, item)
+				}
+			}
+		}
+		kern.ExportObjects(dc.ctx, ctx)
+	}
+	dc.current = item
+	if dc.lastErr != nil {
+		dc.index--
+		dc.Clean()
 	}
 	return
 }
 
-func (dc *dataCursor) Index() int {
+// func (dc *dataCursor) Next() (current any, err error) { // must return io.EOF after the last item
-	return dc.index
+// 	if dc.initState {
+// 		dc.init()
+// 	} else if err = dc.lastErr; err != nil {
+// 		return
+// 	}
+// 	current = dc.current
+// 	if dc.resource != nil {
+// 		filter := dc.ds[FilterName]
+// 		mapper := dc.ds[MapName]
+// 		var item any
+// 		for item == nil && dc.lastErr == nil {
+// 			ctx := 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 {
+// 				if item == nil {
+// 					dc.lastErr = io.EOF
+// 				} else {
+// 					accepted := true
+// 					if filter != nil {
+// 						if accepted, dc.lastErr = dc.checkFilter(filter, item); dc.lastErr != nil || !accepted {
+// 							item = nil
+// 						}
+// 					}
+// 					if accepted {
+// 						dc.count++
+// 					}
+// 					if item != nil && mapper != nil {
+// 						item, dc.lastErr = dc.mapItem(mapper, item)
+// 					}
+// 				}
+// 			}
+// 			exportObjects(dc.ctx, ctx)
+// 		}
+// 		dc.current = item
+// 		if dc.lastErr != nil {
+// 			dc.index--
+// 			dc.Clean()
+// 		}
+// 	} else {
+// 		dc.lastErr = errInvalidDataSource()
+// 	}
+// 	return
+// }
+
+func (dc *dataCursor) Index() int64 {
+	return dc.index - 1
+}
+
+func (dc *dataCursor) Count() int64 {
+	return dc.count
 }

dict-iterator.go

@@ -0,0 +1,225 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// dict-iterator.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"slices"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type dictIterMode int
+
+const (
+	dictIterModeKeys dictIterMode = iota
+	dictIterModeValues
+	dictIterModeItems
+)
+
+type DictIterator struct {
+	a        *kern.DictType
+	count    int64
+	index    int64
+	keys     []any
+	iterMode dictIterMode
+}
+
+type sortType int
+
+const (
+	sortTypeNone sortType = iota
+	sortTypeAsc
+	sortTypeDesc
+	sortTypeDefault = sortTypeAsc
+)
+
+func (it *DictIterator) makeKeys(m map[any]any, sort sortType) {
+	it.keys = make([]any, 0, len(m))
+
+	if sort == sortTypeNone {
+		for keyAny := range m {
+			it.keys = append(it.keys, keyAny)
+		}
+	} else {
+		scalarMap := make(map[string]any, len(m))
+		scalerKeys := make([]string, 0, len(m))
+		for keyAny := range m {
+			keyStr := fmt.Sprint(keyAny)
+			scalarMap[keyStr] = keyAny
+			scalerKeys = append(scalerKeys, keyStr)
+		}
+
+		switch sort {
+		case sortTypeAsc:
+			slices.Sort(scalerKeys)
+		case sortTypeDesc:
+			slices.Sort(scalerKeys)
+			slices.Reverse(scalerKeys)
+		}
+		for _, keyStr := range scalerKeys {
+			it.keys = append(it.keys, scalarMap[keyStr])
+		}
+	}
+}
+
+func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err error) {
+	var sortType = sortTypeNone
+	var s string
+	var argAny any
+
+	dictIt := &DictIterator{a: dict, count: 0, index: -1, keys: nil, iterMode: dictIterModeKeys}
+	if len(args) > 0 {
+		argAny = args[0]
+	} else {
+		argAny = "default"
+	}
+	if s, err = kern.ToGoString(argAny, "sort type"); err == nil {
+		switch strings.ToLower(s) {
+		case "a", "asc":
+			sortType = sortTypeAsc
+		case "d", "desc":
+			sortType = sortTypeDesc
+		case "n", "none", "nosort", "no-sort":
+			sortType = sortTypeNone
+		case "", "default":
+			sortType = sortTypeDefault
+		default:
+			err = fmt.Errorf("invalid sort type %q", s)
+		}
+
+		if err == nil {
+			if len(args) > 1 {
+				argAny = args[1]
+			} else {
+				argAny = "default"
+			}
+
+			if s, err = kern.ToGoString(argAny, "iteration mode"); err == nil {
+				switch strings.ToLower(s) {
+				case "k", "key", "keys":
+					dictIt.iterMode = dictIterModeKeys
+				case "v", "value", "values":
+					dictIt.iterMode = dictIterModeValues
+				case "i", "item", "items":
+					dictIt.iterMode = dictIterModeItems
+				case "", "default":
+					dictIt.iterMode = dictIterModeKeys
+				default:
+					err = fmt.Errorf("invalid iteration mode %q", s)
+				}
+			}
+		}
+	}
+
+	if err == nil {
+		dictIt.makeKeys(*dict, sortType)
+		it = dictIt
+	}
+	return
+}
+
+func NewMapIterator(m map[any]any) (it *DictIterator) {
+	it = &DictIterator{a: (*kern.DictType)(&m), count: 0, index: -1, keys: nil}
+	it.makeKeys(m, sortTypeNone)
+	return
+}
+
+func (it *DictIterator) String() string {
+	var l = int64(0)
+	if it.a != nil {
+		l = int64(len(*it.a))
+	}
+	return fmt.Sprintf("$({#%d})", l)
+}
+
+func (it *DictIterator) TypeName() string {
+	return "DictIterator"
+}
+
+func (it *DictIterator) HasOperation(name string) bool {
+	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 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
+	case kern.KeyName:
+		if it.index >= 0 && it.index < int64(len(it.keys)) {
+			v = it.keys[it.index]
+		} else {
+			err = io.EOF
+		}
+	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 = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func (it *DictIterator) Current() (item any, err error) {
+	if it.index >= 0 && it.index < int64(len(it.keys)) {
+		switch it.iterMode {
+		case dictIterModeKeys:
+			item = it.keys[it.index]
+		case dictIterModeValues:
+			a := *(it.a)
+			item = a[it.keys[it.index]]
+		case dictIterModeItems:
+			a := *(it.a)
+			pair := []any{it.keys[it.index], a[it.keys[it.index]]}
+			item = kern.NewList(pair)
+		}
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (it *DictIterator) Next() (item any, err error) {
+	it.index++
+	if item, err = it.Current(); err != io.EOF {
+		it.count++
+	}
+	return
+}
+
+func (it *DictIterator) Index() int64 {
+	return it.index
+}
+
+func (it *DictIterator) Count() int64 {
+	return it.count
+}
+
+func (it *DictIterator) Reset() error {
+	it.index = -1
+	it.count = 0
+	return nil
+}
+
+func (it *DictIterator) Clean() error {
+	return nil
+}

dict-type.go

@@ -1,130 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// dict-type.go
-package expr
-
-import (
-	"fmt"
-	"reflect"
-	"strings"
-)
-
-type DictType map[any]any
-
-func newDict(dictAny map[any]*term) (dict *DictType) {
-	var d DictType
-	if dictAny != nil {
-		d = make(DictType, len(dictAny))
-		for i, item := range dictAny {
-			d[i] = item
-		}
-	} else {
-		d = make(DictType)
-	}
-	dict = &d
-	return
-}
-
-func (dict *DictType) toMultiLine(sb *strings.Builder, indent int) {
-	sb.WriteString(strings.Repeat("\t", indent))
-	sb.WriteString("{\n")
-
-	first := true
-	for name, value := range *dict {
-		if first {
-			first = false
-		} else {
-			sb.WriteByte(',')
-			sb.WriteByte('\n')
-		}
-
-		sb.WriteString(strings.Repeat("\t", indent+1))
-		if key, ok := name.(string); ok {
-			sb.WriteString(string('"') + key + string('"'))
-		} else {
-			sb.WriteString(fmt.Sprintf("%v", name))
-		}
-		sb.WriteString(": ")
-		if f, ok := value.(Formatter); ok {
-			sb.WriteString(f.ToString(MultiLine))
-		} else if _, ok = value.(Functor); ok {
-			sb.WriteString("func(){}")
-		} else {
-			sb.WriteString(fmt.Sprintf("%v", value))
-		}
-	}
-	sb.WriteString(strings.Repeat("\t", indent))
-	sb.WriteString("\n}")
-}
-
-func (dict *DictType) ToString(opt FmtOpt) string {
-	var sb strings.Builder
-	if opt&MultiLine != 0 {
-		dict.toMultiLine(&sb, 0)
-	} else {
-		sb.WriteByte('{')
-		first := true
-		for key, value := range *dict {
-			if first {
-				first = false
-			} else {
-				sb.WriteString(", ")
-			}
-			if s, ok := key.(string); ok {
-				sb.WriteString(string('"') + s + string('"'))
-			} else {
-				sb.WriteString(fmt.Sprintf("%v", key))
-			}
-			sb.WriteString(": ")
-			if formatter, ok := value.(Formatter); ok {
-				sb.WriteString(formatter.ToString(opt))
-			} else if t, ok := value.(*term); ok {
-				sb.WriteString(t.String())
-			} else {
-				sb.WriteString(fmt.Sprintf("%#v", value))
-			}
-		}
-		sb.WriteByte('}')
-	}
-	return sb.String()
-}
-
-func (dict *DictType) String() string {
-	return dict.ToString(0)
-}
-
-func (dict *DictType) TypeName() string {
-	return "dict"
-}
-
-func (dict *DictType) hasKey(target any) (ok bool) {
-	for key := range *dict {
-		if ok = reflect.DeepEqual(key, target); ok {
-			break
-		}
-	}
-	return
-}
-
-func (dict *DictType) clone() (c *DictType) {
-	c = newDict(nil)
-	for k, v := range *dict {
-		(*c)[k] = v
-	}
-	return
-}
-
-func (dict *DictType) merge(second *DictType) {
-	if second != nil {
-		for k, v := range *second {
-			(*dict)[k] = v
-		}
-	}
-}
-
-func (dict *DictType) setItem(key any, value any) (err error) {
-	(*dict)[key]=value
-	return
-}
-

file-reader.expr

@@ -1,33 +0,0 @@
-builtin ["os.file", "base"];
-
-readInt=func(fh){
-	line=readFile(fh);
-	line ? [nil] {nil} :: {int(line)}
-};
-
-ds={
-	"init":func(filename){
-		fh=openFile(filename);
-		fh ? [nil] {nil} :: { @current=readInt(fh); @prev=@current };
-		fh
-	},
-	"current":func(){
-		prev
-	},
-	"next":func(fh){
-		current ? 
-			[nil] {current}
-			:: {@prev=current; @current=readInt(fh) but current}
-	},
-	"clean":func(fh){
-		closeFile(fh)
-	}
-}
-
-//;f=$(ds, "int.list")
-/*
-;f++
-;f++
-;f++
-*/
-//;add(f)

file/coverage.html

@@ -0,0 +1,322 @@
+
+<!DOCTYPE html>
+<html>
+	<head>
+		<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+		<title>file: Go Coverage Report</title>
+		<style>
+			body {
+				background: black;
+				color: rgb(80, 80, 80);
+			}
+			body, pre, #legend span {
+				font-family: Menlo, monospace;
+				font-weight: bold;
+			}
+			#topbar {
+				background: black;
+				position: fixed;
+				top: 0; left: 0; right: 0;
+				height: 42px;
+				border-bottom: 1px solid rgb(80, 80, 80);
+			}
+			#content {
+				margin-top: 50px;
+			}
+			#nav, #legend {
+				float: left;
+				margin-left: 10px;
+			}
+			#legend {
+				margin-top: 12px;
+			}
+			#nav {
+				margin-top: 10px;
+			}
+			#legend span {
+				margin: 0 5px;
+			}
+			.cov0 { color: rgb(192, 0, 0) }
+.cov1 { color: rgb(128, 128, 128) }
+.cov2 { color: rgb(116, 140, 131) }
+.cov3 { color: rgb(104, 152, 134) }
+.cov4 { color: rgb(92, 164, 137) }
+.cov5 { color: rgb(80, 176, 140) }
+.cov6 { color: rgb(68, 188, 143) }
+.cov7 { color: rgb(56, 200, 146) }
+.cov8 { color: rgb(44, 212, 149) }
+.cov9 { color: rgb(32, 224, 152) }
+.cov10 { color: rgb(20, 236, 155) }
+
+		</style>
+	</head>
+	<body>
+		<div id="topbar">
+			<div id="nav">
+				<select id="files">
+				
+				<option value="file0">git.portale-stac.it/go-pkg/expr/file/file.go (88.9%)</option>
+				
+				<option value="file1">git.portale-stac.it/go-pkg/expr/file/reader.go (77.8%)</option>
+				
+				<option value="file2">git.portale-stac.it/go-pkg/expr/file/writer.go (100.0%)</option>
+				
+				</select>
+			</div>
+			<div id="legend">
+				<span>not tracked</span>
+			
+				<span class="cov0">not covered</span>
+				<span class="cov8">covered</span>
+			
+			</div>
+		</div>
+		<div id="content">
+		
+		<pre class="file" id="file0" style="display: none">// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// file.go
+package file
+
+import (
+        "os"
+
+        "git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type Handle interface {
+        kern.Typer
+        GetFile() *os.File
+        GetName() string
+        Valid() bool
+        Close() error
+}
+
+type handleBase struct {
+        fh *os.File
+}
+
+func (h *handleBase) GetFile() *os.File <span class="cov0" title="0">{
+        return h.fh
+}</span>
+
+func (h *handleBase) GetName() (name string) <span class="cov8" title="1">{
+        if h.fh != nil </span><span class="cov8" title="1">{
+                name = h.fh.Name()
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (h *handleBase) Valid() bool <span class="cov8" title="1">{
+        return h.fh != nil
+}</span>
+
+func (h *handleBase) Close() (err error) <span class="cov8" title="1">{
+        if h.fh != nil </span><span class="cov8" title="1">{
+                err = h.fh.Close()
+                h.fh = nil
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+</pre>
+		
+		<pre class="file" id="file1" style="display: none">// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// reader.go
+package file
+
+import (
+        "bufio"
+        "io"
+        "os"
+)
+
+type Reader struct {
+        // fh     *os.File
+        handleBase
+        reader *bufio.Reader
+}
+
+func NewReader(fh *os.File) *Reader <span class="cov8" title="1">{
+        return &amp;Reader{handleBase: handleBase{fh: fh}, reader: bufio.NewReader(fh)}
+}</span>
+
+func OpenReader(filePath string) (r *Reader, err error) <span class="cov8" title="1">{
+        var fh *os.File
+        if fh, err = os.Open(filePath); err == nil </span><span class="cov8" title="1">{
+                r = NewReader(fh)
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (h *Reader) TypeName() string <span class="cov8" title="1">{
+        return "fileReader"
+}</span>
+
+func (h *Reader) String() string <span class="cov8" title="1">{
+        return "reader"
+}</span>
+
+func (h *Reader) Valid() bool <span class="cov8" title="1">{
+        return h.handleBase.Valid() &amp;&amp; h.reader != nil
+}</span>
+
+func (w *Reader) Close() (err error) <span class="cov8" title="1">{
+        w.reader = nil
+        err = w.handleBase.Close()
+        return
+}</span>
+
+func (h *Reader) ReadByte() (b byte, err error) <span class="cov8" title="1">{
+        if h.reader != nil </span><span class="cov8" title="1">{
+                b, err = h.reader.ReadByte()
+        }</span> else<span class="cov0" title="0"> {
+                err = io.ErrClosedPipe
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (h *Reader) ReadAll() (p []byte, err error) <span class="cov8" title="1">{
+        if h.reader != nil </span><span class="cov8" title="1">{
+                p, err = io.ReadAll(h.reader)
+        }</span> else<span class="cov0" title="0"> {
+                err = io.ErrClosedPipe
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (h *Reader) ReadString(delim byte) (s string, err error) <span class="cov0" title="0">{
+        if h.reader != nil </span><span class="cov0" title="0">{
+                s, err = h.reader.ReadString(delim)
+        }</span> else<span class="cov0" title="0"> {
+                err = io.ErrClosedPipe
+        }</span>
+        <span class="cov0" title="0">return</span>
+}
+
+func (h *Reader) Reset() (err error) <span class="cov8" title="1">{
+        if h.fh != nil </span><span class="cov8" title="1">{
+                if _, err = h.fh.Seek(0, 0); err == nil </span><span class="cov8" title="1">{
+                        h.reader.Reset(h.fh)
+                }</span>
+        }
+        <span class="cov8" title="1">return</span>
+}
+</pre>
+		
+		<pre class="file" id="file2" style="display: none">// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// writer.go
+package file
+
+import (
+        "bufio"
+        "fmt"
+        "os"
+)
+
+type Writer struct {
+        // fh     *os.File
+        handleBase
+        writer *bufio.Writer
+}
+
+func NewWriter(fh *os.File) *Writer <span class="cov8" title="1">{
+        return &amp;Writer{handleBase: handleBase{fh: fh}, writer: bufio.NewWriter(fh)}
+}</span>
+
+func CreateWriter(filePath string) (w *Writer, err error) <span class="cov8" title="1">{
+        var fh *os.File
+        if fh, err = os.Create(filePath); err == nil </span><span class="cov8" title="1">{
+                w = NewWriter(fh)
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func AppendWriter(filePath string) (w *Writer, err error) <span class="cov8" title="1">{
+        var fh *os.File
+        if fh, err = os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY, 0644); err == nil </span><span class="cov8" title="1">{
+                w = NewWriter(fh)
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (w *Writer) TypeName() string <span class="cov8" title="1">{
+        return "fileWriter"
+}</span>
+
+func (w *Writer) String() string <span class="cov8" title="1">{
+        return "writer"
+}</span>
+
+func (w *Writer) Valid() bool <span class="cov8" title="1">{
+        return w.handleBase.Valid() &amp;&amp; w.writer != nil
+}</span>
+
+func (w *Writer) Close() (err error) <span class="cov8" title="1">{
+        var err1 error
+        if w.writer != nil </span><span class="cov8" title="1">{
+                err1 = w.Flush()
+                w.writer = nil
+        }</span>
+        <span class="cov8" title="1">if err = w.handleBase.Close(); err == nil </span><span class="cov8" title="1">{
+                err = err1
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (w *Writer) Flush() (err error) <span class="cov8" title="1">{
+        if w.writer != nil </span><span class="cov8" title="1">{
+                err = w.writer.Flush()
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (w *Writer) Write(args ...any) (n int, err error) <span class="cov8" title="1">{
+        if w.writer != nil </span><span class="cov8" title="1">{
+                n, err = fmt.Fprint(w.writer, args...)
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+
+func (w *Writer) Writef(format string, args ...any) (n int, err error) <span class="cov8" title="1">{
+        if w.writer != nil </span><span class="cov8" title="1">{
+                n, err = fmt.Fprintf(w.writer, format, args...)
+        }</span>
+        <span class="cov8" title="1">return</span>
+}
+</pre>
+		
+		</div>
+	</body>
+	<script>
+	(function() {
+		var files = document.getElementById('files');
+		var visible;
+		files.addEventListener('change', onChange, false);
+		function select(part) {
+			if (visible)
+				visible.style.display = 'none';
+			visible = document.getElementById(part);
+			if (!visible)
+				return;
+			files.value = part;
+			visible.style.display = 'block';
+			location.hash = part;
+		}
+		function onChange() {
+			select(files.value);
+			window.scrollTo(0, 0);
+		}
+		if (location.hash != "") {
+			select(location.hash.substr(1));
+		}
+		if (!visible) {
+			select("file0");
+		}
+	})();
+	</script>
+</html>

file/file.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// file.go
+package file
+
+import (
+	"os"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type Handle interface {
+	kern.Typer
+	GetFile() *os.File
+	GetName() string
+	Valid() bool
+	Close() error
+}
+
+type handleBase struct {
+	fh *os.File
+}
+
+func (h *handleBase) GetFile() *os.File {
+	return h.fh
+}
+
+func (h *handleBase) GetName() (name string) {
+	if h.fh != nil {
+		name = h.fh.Name()
+	}
+	return
+}
+
+func (h *handleBase) Valid() bool {
+	return h.fh != nil
+}
+
+func (h *handleBase) Close() (err error) {
+	if h.fh != nil {
+		err = h.fh.Close()
+		h.fh = nil
+	}
+	return
+}

file/reader.go

@@ -0,0 +1,83 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// reader.go
+package file
+
+import (
+	"bufio"
+	"io"
+	"os"
+)
+
+type Reader struct {
+	// fh     *os.File
+	handleBase
+	reader *bufio.Reader
+}
+
+func NewReader(fh *os.File) *Reader {
+	return &Reader{handleBase: handleBase{fh: fh}, reader: bufio.NewReader(fh)}
+}
+
+func OpenReader(filePath string) (r *Reader, err error) {
+	var fh *os.File
+	if fh, err = os.Open(filePath); err == nil {
+		r = NewReader(fh)
+	}
+	return
+}
+
+func (h *Reader) TypeName() string {
+	return "fileReader"
+}
+
+func (h *Reader) String() string {
+	return "reader"
+}
+
+func (h *Reader) Valid() bool {
+	return h.handleBase.Valid() && h.reader != nil
+}
+
+func (w *Reader) Close() (err error) {
+	w.reader = nil
+	err = w.handleBase.Close()
+	return
+}
+
+func (h *Reader) ReadByte() (b byte, err error) {
+	if h.reader != nil {
+		b, err = h.reader.ReadByte()
+	} else {
+		err = io.ErrClosedPipe
+	}
+	return
+}
+
+func (h *Reader) ReadAll() (p []byte, err error) {
+	if h.reader != nil {
+		p, err = io.ReadAll(h.reader)
+	} else {
+		err = io.ErrClosedPipe
+	}
+	return
+}
+
+func (h *Reader) ReadString(delim byte) (s string, err error) {
+	if h.reader != nil {
+		s, err = h.reader.ReadString(delim)
+	} else {
+		err = io.ErrClosedPipe
+	}
+	return
+}
+
+func (h *Reader) Reset() (err error) {
+	if h.fh != nil {
+		if _, err = h.fh.Seek(0, 0); err == nil {
+			h.reader.Reset(h.fh)
+		}
+	}
+	return
+}

file/t_reader_test.go

@@ -0,0 +1,62 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// reader.go
+package file
+
+import "testing"
+
+func TestOpenReader(t *testing.T) {
+	r, err := OpenReader("t_reader_test.go")
+	if err != nil {
+		t.Fatalf("OpenReader failed: %v", err)
+	}
+	defer r.Close()
+
+	if !r.Valid() {
+		t.Fatal("Reader should be valid after opening")
+	}
+
+	if r.TypeName() != "fileReader" {
+		t.Fatalf("Expected TypeName 'fileReader', got '%s'", r.TypeName())
+	}
+
+	if r.String() != "reader" {
+		t.Fatalf("Expected String 'reader', got '%s'", r.String())
+	}
+
+	// GetName may return either "t_reader_test.go" or "./t_reader_test.go" depending on the environment
+	name := r.GetName()
+	if (name != "t_reader_test.go") && (name != "./t_reader_test.go") {
+		t.Fatalf("Expected GetName 't_reader_test.go' or './t_reader_test.go', got '%s'", name)
+	}
+
+	// Test reading a byte
+	b, err := r.ReadByte()
+	if err != nil {
+		t.Fatalf("ReadByte failed: %v", err)
+	}
+	if b == 0 {
+		t.Fatal("ReadByte should not return zero byte")
+	}
+
+	err = r.Reset()
+	if err != nil {
+		t.Fatalf("Reset failed: %v", err)
+	}
+
+	if s, err := r.ReadString('\n'); err != nil {
+		t.Fatalf("ReadString failed: %v", err)
+	} else {
+		t.Logf("ReadString: %s", s)
+	}
+
+	// Test reading all content
+	content, err := r.ReadAll()
+	if err != nil {
+		t.Fatalf("ReadAll failed: %v", err)
+	}
+	if len(content) == 0 {
+		t.Fatal("ReadAll should return non-empty content")
+	}
+}

file/t_writer_test.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// writer.go
+package file
+
+import "testing"
+
+func TestCreateWriter(t *testing.T) {
+	w, err := CreateWriter("/tmp/test_writer.txt")
+	if err != nil {
+		t.Fatalf("CreateWriter failed: %v", err)
+	}
+	defer w.Close()
+
+	if !w.Valid() {
+		t.Fatal("Writer should be valid after creation")
+	}
+
+	if w.TypeName() != "fileWriter" {
+		t.Fatalf("Expected TypeName 'fileWriter', got '%s'", w.TypeName())
+	}
+
+	if w.String() != "writer" {
+		t.Fatalf("Expected String 'writer', got '%s'", w.String())
+	}
+
+	name := w.GetName()
+	if name != "/tmp/test_writer.txt" {
+		t.Fatalf("Expected GetName '/tmp/test_writer.txt', got '%s'", name)
+	}
+
+	if n, err := w.Write("Hello, World!\n"); err != nil {
+		t.Fatalf("Write failed: %v", err)
+	} else if n != len("Hello, World!\n") {
+		t.Fatalf("Expected to write %d bytes, wrote %d", len("Hello, World!\n"), n)
+	}
+
+	if n, err := w.Writef("This is a %s.\n", "test"); err != nil {
+		t.Fatalf("Writef failed: %v", err)
+	} else if n != len("This is a test.\n") {
+		t.Fatalf("Expected to write %d bytes, wrote %d", len("This is a test.\n"), n)
+	}
+}
+
+func TestAppendWriter(t *testing.T) {
+	w, err := AppendWriter("/tmp/test_writer.txt")
+	if err != nil {
+		t.Fatalf("AppendWriter failed: %v", err)
+	}
+	defer w.Close()
+
+	if !w.Valid() {
+		t.Fatal("Writer should be valid after opening for append")
+	}
+
+	if w.TypeName() != "fileWriter" {
+		t.Fatalf("Expected TypeName 'fileWriter', got '%s'", w.TypeName())
+	}
+
+	if w.String() != "writer" {
+		t.Fatalf("Expected String 'writer', got '%s'", w.String())
+	}
+
+	name := w.GetName()
+	if name != "/tmp/test_writer.txt" {
+		t.Fatalf("Expected GetName '/tmp/test_writer.txt', got '%s'", name)
+	}
+}

file/writer.go

@@ -0,0 +1,82 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// writer.go
+package file
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+type Writer struct {
+	// fh     *os.File
+	handleBase
+	writer *bufio.Writer
+}
+
+func NewWriter(fh *os.File) *Writer {
+	return &Writer{handleBase: handleBase{fh: fh}, writer: bufio.NewWriter(fh)}
+}
+
+func CreateWriter(filePath string) (w *Writer, err error) {
+	var fh *os.File
+	if fh, err = os.Create(filePath); err == nil {
+		w = NewWriter(fh)
+	}
+	return
+}
+
+func AppendWriter(filePath string) (w *Writer, err error) {
+	var fh *os.File
+	if fh, err = os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY, 0644); err == nil {
+		w = NewWriter(fh)
+	}
+	return
+}
+
+func (w *Writer) TypeName() string {
+	return "fileWriter"
+}
+
+func (w *Writer) String() string {
+	return "writer"
+}
+
+func (w *Writer) Valid() bool {
+	return w.handleBase.Valid() && w.writer != nil
+}
+
+func (w *Writer) Close() (err error) {
+	var err1 error
+	if w.writer != nil {
+		err1 = w.Flush()
+		w.writer = nil
+	}
+	if err = w.handleBase.Close(); err == nil {
+		err = err1
+	}
+	return
+}
+
+func (w *Writer) Flush() (err error) {
+	if w.writer != nil {
+		err = w.writer.Flush()
+	}
+	return
+}
+
+func (w *Writer) Write(args ...any) (n int, err error) {
+	if w.writer != nil {
+		n, err = fmt.Fprint(w.writer, args...)
+	}
+	return
+}
+
+func (w *Writer) Writef(format string, args ...any) (n int, err error) {
+	if w.writer != nil {
+		n, err = fmt.Fprintf(w.writer, format, args...)
+	}
+	return
+}

func-base.go

@@ -1,186 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-builtins.go
-package expr
-
-import (
-	"math"
-	"strconv"
-)
-
-func isNilFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = args[0] == nil
-	return
-}
-
-func isIntFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsInteger(args[0])
-	return
-}
-
-func isFloatFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsFloat(args[0])
-	return
-}
-
-func isBoolFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsBool(args[0])
-	return
-}
-
-func isStringFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsString(args[0])
-	return
-}
-
-func isFractionFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsFract(args[0])
-	return
-}
-
-func isRationalFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsRational(args[0])
-	return
-}
-
-func isListFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsList(args[0])
-	return
-}
-
-func isDictionaryFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result = IsDict(args[0])
-	return
-}
-
-func boolFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	switch v := args[0].(type) {
-	case int64:
-		result = (v != 0)
-	case *FractionType:
-		result = v.num != 0
-	case float64:
-		result = v != 0.0
-	case bool:
-		result = v
-	case string:
-		result = len(v) > 0
-	default:
-		err = errCantConvert(name, v, "bool")
-	}
-	return
-}
-
-func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	switch v := args[0].(type) {
-	case int64:
-		result = v
-	case float64:
-		result = int64(math.Trunc(v))
-	case bool:
-		if v {
-			result = int64(1)
-		} else {
-			result = int64(0)
-		}
-	case string:
-		var i int
-		if i, err = strconv.Atoi(v); err == nil {
-			result = int64(i)
-		}
-	default:
-		err = errCantConvert(name, v, "int")
-	}
-	return
-}
-
-func decFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	switch v := args[0].(type) {
-	case int64:
-		result = float64(v)
-	case float64:
-		result = v
-	case bool:
-		if v {
-			result = float64(1)
-		} else {
-			result = float64(0)
-		}
-	case string:
-		var f float64
-		if f, err = strconv.ParseFloat(v, 64); err == nil {
-			result = f
-		}
-	case *FractionType:
-		result = v.toFloat()
-	default:
-		err = errCantConvert(name, v, "float")
-	}
-	return
-}
-
-func fractFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	switch v := args[0].(type) {
-	case int64:
-		var den int64 = 1
-		if len(args) > 1 {
-			var ok bool
-			if den, ok = args[1].(int64); !ok {
-				err = errExpectedGot(name, "integer", args[1])
-			} else if den == 0 {
-				err = errFuncDivisionByZero(name)
-			}
-		}
-		if err == nil {
-			result = newFraction(v, den)
-		}
-	case float64:
-		result, err = float64ToFraction(v)
-	case bool:
-		if v {
-			result = newFraction(1, 1)
-		} else {
-			result = newFraction(0, 1)
-		}
-	case string:
-		result, err = makeGeneratingFraction(v)
-	case *FractionType:
-		result = v
-	default:
-		err = errCantConvert(name, v, "float")
-	}
-	return
-}
-
-func iteratorFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	return
-}
-
-func ImportBuiltinsFuncs(ctx ExprContext) {
-	anyParams := []ExprFuncParam{
-		newFuncParam(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("bool", newGolangFunctor(boolFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("int", newGolangFunctor(intFunc), typeInt, anyParams)
-	ctx.RegisterFunc("dec", newGolangFunctor(decFunc), typeFloat, anyParams)
-	ctx.RegisterFunc("fract", newGolangFunctor(fractFunc), typeFraction, []ExprFuncParam{
-		newFuncParam(paramValue),
-		newFuncParamFlagDef("denominator", pfOptional, 1),
-	})
-}
-
-func init() {
-	registerImport("base", ImportBuiltinsFuncs, "Base expression tools like isNil(), int(), etc.")
-}

func-fmt.go

@@ -1,36 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-fmt.go
-package expr
-
-import "fmt"
-
-func printFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var n int
-	if n, err = fmt.Print(args...); err == nil {
-		result = int64(n)
-	}
-	return
-}
-
-func printLnFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var n int
-	if n, err = fmt.Println(args...); err == nil {
-		result = int64(n)
-	}
-	return
-}
-
-func ImportFmtFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("print", newGolangFunctor(printFunc), typeInt, []ExprFuncParam{
-		newFuncParamFlag(paramItem, pfRepeat),
-	})
-	ctx.RegisterFunc("println", newGolangFunctor(printLnFunc), typeInt, []ExprFuncParam{
-		newFuncParamFlag(paramItem, pfRepeat),
-	})
-}
-
-func init() {
-	registerImport("fmt", ImportFmtFuncs, "String and console formatting functions")
-}

func-import.go

@@ -1,150 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-import.go
-package expr
-
-import (
-	"errors"
-	"fmt"
-	"io"
-	"os"
-	"path"
-	"path/filepath"
-	"strings"
-)
-
-const ENV_EXPR_PATH = "EXPR_PATH"
-
-func importFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	return importGeneral(ctx, name, args)
-}
-
-func importAllFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	enable(ctx, control_export_all)
-	return importGeneral(ctx, name, args)
-}
-
-func importGeneral(ctx ExprContext, name string, args []any) (result any, err error) {
-	var dirList []string
-
-	dirList = addEnvImportDirs(dirList)
-	dirList = addPresetImportDirs(ctx, dirList)
-	result, err = doImport(ctx, name, dirList, NewArrayIterator(args))
-	return
-}
-
-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 %T, string expected", funcName, paramPos+1, paramValue)
-	}
-	return
-}
-
-func addEnvImportDirs(dirList []string) []string {
-	if dirSpec, exists := os.LookupEnv(ENV_EXPR_PATH); exists {
-		dirs := strings.Split(dirSpec, ":")
-		if dirList == nil {
-			dirList = dirs
-		} else {
-			dirList = append(dirList, dirs...)
-		}
-	}
-	return dirList
-}
-
-func addPresetImportDirs(ctx ExprContext, dirList []string) []string {
-	if dirSpec, exists := getControlString(ctx, ControlImportPath); exists {
-		dirs := strings.Split(dirSpec, ":")
-		if dirList == nil {
-			dirList = dirs
-		} else {
-			dirList = append(dirList, dirs...)
-		}
-	}
-	return dirList
-}
-
-func isFile(filePath string) bool {
-	info, err := os.Stat(filePath)
-	return (err == nil || errors.Is(err, os.ErrExist)) && info.Mode().IsRegular()
-}
-
-func searchAmongPath(filename string, dirList []string) (filePath string) {
-	for _, dir := range dirList {
-		if fullPath := path.Join(dir, filename); isFile(fullPath) {
-			filePath = fullPath
-			break
-		}
-	}
-	return
-}
-
-func isPathRelative(filePath string) bool {
-	unixPath := filepath.ToSlash(filePath)
-	return strings.HasPrefix(unixPath, "./") || strings.HasPrefix(unixPath, "../")
-}
-
-func makeFilepath(filename string, dirList []string) (filePath string, err error) {
-	if path.IsAbs(filename) || isPathRelative(filename) {
-		if isFile(filename) {
-			filePath = filename
-		}
-	} else {
-		filePath = searchAmongPath(filename, dirList)
-	}
-	if len(filePath) == 0 {
-		err = fmt.Errorf("source file %q not found", filename)
-	}
-	return
-}
-
-func doImport(ctx ExprContext, name string, dirList []string, it 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 {
-			break
-		}
-		if sourceFilepath, err = makeFilepath(v.(string), dirList); err != nil {
-			break
-		}
-		var file *os.File
-		if file, err = os.Open(sourceFilepath); err == nil {
-			defer file.Close()
-			var expr *ast
-			scanner := NewScanner(file, DefaultTranslations())
-			parser := NewParser(ctx)
-			if expr, err = parser.parseGeneral(scanner, true, true); err == nil {
-				result, err = expr.eval(ctx, false)
-			}
-			if err != nil {
-				break
-			}
-		} else {
-			break
-		}
-	}
-	if err != nil {
-		if err == io.EOF {
-			err = nil
-		} else {
-			result = nil
-		}
-	}
-	return
-}
-
-func ImportImportFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("import", newGolangFunctor(importFunc), typeAny, []ExprFuncParam{
-		newFuncParamFlag(paramFilepath, pfRepeat),
-	})
-	ctx.RegisterFunc("importAll", newGolangFunctor(importAllFunc), typeAny, []ExprFuncParam{
-		newFuncParamFlag(paramFilepath, pfRepeat),
-	})
-}
-
-func init() {
-	registerImport("import", ImportImportFuncs, "Functions import() and include()")
-}

func-math.go

@@ -1,181 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// funcs-math.go
-package expr
-
-import (
-	"fmt"
-	"io"
-)
-
-func checkNumberParamExpected(funcName string, paramValue any, paramPos, level, subPos int) (err error) {
-	if !(IsNumber(paramValue) || 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) {
-	var sumAsFloat, sumAsFract bool
-	var floatSum float64 = 0.0
-	var intSum int64 = 0
-	var fractSum *FractionType
-	var v any
-
-	level++
-
-	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*ListType); ok {
-			v = NewListIterator(list, nil)
-		}
-		if subIter, ok := v.(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 {
-					return
-				}
-			}
-		} else if err = checkNumberParamExpected(name, v, count, level, it.Index()); err != nil {
-			break
-		}
-		count++
-
-		if !sumAsFloat {
-			if IsFloat(v) {
-				sumAsFloat = true
-				if sumAsFract {
-					floatSum = fractSum.toFloat()
-				} else {
-					floatSum = float64(intSum)
-				}
-			} else if !sumAsFract && isFraction(v) {
-				fractSum = newFraction(intSum, 1)
-				sumAsFract = true
-			}
-		}
-
-		if sumAsFloat {
-			floatSum += numAsFloat(v)
-		} else if sumAsFract {
-			var item *FractionType
-			var ok bool
-			if item, ok = v.(*FractionType); !ok {
-				iv, _ := v.(int64)
-				item = newFraction(iv, 1)
-			}
-			fractSum = sumFract(fractSum, item)
-		} else {
-			iv, _ := v.(int64)
-			intSum += iv
-		}
-	}
-	if err == nil || err == io.EOF {
-		err = nil
-		if sumAsFloat {
-			result = floatSum
-		} else if sumAsFract {
-			result = fractSum
-		} else {
-			result = intSum
-		}
-	}
-	return
-}
-
-func addFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result, err = doAdd(ctx, name, NewArrayIterator(args), 0, -1)
-	return
-}
-
-func doMul(ctx ExprContext, name string, it 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 v any
-
-	level++
-	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*ListType); ok {
-			v = NewListIterator(list, nil)
-		}
-		if subIter, ok := v.(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 {
-					return
-				}
-			}
-		} else {
-			if err = checkNumberParamExpected(name, v, count, level, it.Index()); err != nil {
-				break
-			}
-		}
-		count++
-
-		if !mulAsFloat {
-			if IsFloat(v) {
-				mulAsFloat = true
-				if mulAsFract {
-					floatProd = fractProd.toFloat()
-				} else {
-					floatProd = float64(intProd)
-				}
-			} else if !mulAsFract && isFraction(v) {
-				fractProd = newFraction(intProd, 1)
-				mulAsFract = true
-			}
-		}
-
-		if mulAsFloat {
-			floatProd *= numAsFloat(v)
-		} else if mulAsFract {
-			var item *FractionType
-			var ok bool
-			if item, ok = v.(*FractionType); !ok {
-				iv, _ := v.(int64)
-				item = newFraction(iv, 1)
-			}
-			fractProd = mulFract(fractProd, item)
-		} else {
-			iv, _ := v.(int64)
-			intProd *= iv
-		}
-	}
-	if err == nil || err == io.EOF {
-		err = nil
-		if mulAsFloat {
-			result = floatProd
-		} else if mulAsFract {
-			result = fractProd
-		} else {
-			result = intProd
-		}
-	}
-	return
-}
-
-func mulFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result, err = doMul(ctx, name, NewArrayIterator(args), 0, -1)
-	return
-}
-
-func ImportMathFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("add", &golangFunctor{f: addFunc}, typeNumber, []ExprFuncParam{
-		newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, int64(0)),
-	})
-
-	ctx.RegisterFunc("mul", &golangFunctor{f: mulFunc}, typeNumber, []ExprFuncParam{
-		newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, int64(1)),
-	})
-}
-
-func init() {
-	registerImport("math.arith", ImportMathFuncs, "Functions add() and mul()")
-}

func-os.go

@@ -1,214 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-os.go
-package expr
-
-import (
-	"bufio"
-	"fmt"
-	"io"
-	"os"
-)
-
-type osHandle interface {
-	getFile() *os.File
-}
-
-type osWriter struct {
-	fh     *os.File
-	writer *bufio.Writer
-}
-
-func (h *osWriter) TypeName() string {
-	return "osWriter"
-}
-
-func (h *osWriter) String() string {
-	return "writer"
-}
-
-func (h *osWriter) getFile() *os.File {
-	return h.fh
-}
-
-type osReader struct {
-	fh     *os.File
-	reader *bufio.Reader
-}
-
-func (h *osReader) TypeName() string {
-	return "osReader"
-}
-
-func (h *osReader) String() string {
-	return "reader"
-}
-
-func (h *osReader) getFile() *os.File {
-	return h.fh
-}
-
-func errMissingFilePath(funcName string) error {
-	return fmt.Errorf("%s(): missing or invalid file path", funcName)
-}
-
-func errInvalidFileHandle(funcName string, v any) error {
-	if v != nil {
-		return fmt.Errorf("%s(): invalid file handle %v [%T]", funcName, v, v)
-	} else {
-		return fmt.Errorf("%s(): invalid file handle", funcName)
-	}
-}
-
-func createFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	if filePath, ok := args[0].(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)}
-		}
-	} else {
-		err = errMissingFilePath("createFile")
-	}
-	return
-}
-
-func openFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	if filePath, ok := args[0].(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)}
-		}
-	} else {
-		err = errMissingFilePath("openFile")
-	}
-	return
-}
-
-func appendFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	if filePath, ok := args[0].(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)}
-		}
-	} else {
-		err = errMissingFilePath("openFile")
-	}
-	return
-}
-
-func closeFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var handle osHandle
-	var invalidFileHandle any
-	var ok bool
-
-	if handle, ok = args[0].(osHandle); !ok {
-		invalidFileHandle = args[0]
-	}
-
-	if handle != nil {
-		if fh := handle.getFile(); fh != nil {
-			if w, ok := handle.(*osWriter); ok {
-				err = w.writer.Flush()
-			}
-
-			if err == nil {
-				err = fh.Close()
-			}
-		}
-	}
-	if err == nil && (handle == nil || invalidFileHandle != nil) {
-		err = errInvalidFileHandle("closeFileFunc", handle)
-	}
-	result = err == nil
-	return
-}
-
-func writeFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var handle osHandle
-	var invalidFileHandle any
-	var ok bool
-
-	if handle, ok = args[0].(osHandle); !ok {
-		invalidFileHandle = args[0]
-	}
-
-	if handle != nil {
-		if w, ok := handle.(*osWriter); ok {
-			result, err = fmt.Fprint(w.writer, args[1:]...)
-		} else {
-			invalidFileHandle = handle
-		}
-	}
-
-	if err == nil && (handle == nil || invalidFileHandle != nil) {
-		err = errInvalidFileHandle("writeFileFunc", invalidFileHandle)
-	}
-	return
-}
-
-func readFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var handle osHandle
-	var invalidFileHandle any
-	var ok bool
-
-	result = nil
-	if handle, ok = args[0].(osHandle); !ok || args[0] == nil {
-		invalidFileHandle = args[0]
-	}
-
-	if handle != nil {
-		if r, ok := handle.(*osReader); ok {
-			var limit byte = '\n'
-			var v string
-			if s, ok := args[1].(string); ok && len(s) > 0 {
-				limit = s[0]
-			}
-
-			if v, err = r.reader.ReadString(limit); err == nil {
-				if len(v) > 0 && v[len(v)-1] == limit {
-					result = v[0 : len(v)-1]
-				} else {
-					result = v
-				}
-			}
-			if err == io.EOF {
-				err = nil
-			}
-		} else {
-			invalidFileHandle = handle
-		}
-	}
-
-	if err == nil && (handle == nil || invalidFileHandle != nil) {
-		err = errInvalidFileHandle("readFileFunc", invalidFileHandle)
-	}
-	return
-}
-
-func ImportOsFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("openFile", newGolangFunctor(openFileFunc), typeHandle, []ExprFuncParam{
-		newFuncParam(paramFilepath),
-	})
-	ctx.RegisterFunc("appendFile", newGolangFunctor(appendFileFunc), typeHandle, []ExprFuncParam{
-		newFuncParam(paramFilepath),
-	})
-	ctx.RegisterFunc("createFile", newGolangFunctor(createFileFunc), typeHandle, []ExprFuncParam{
-		newFuncParam(paramFilepath),
-	})
-	ctx.RegisterFunc("writeFile", newGolangFunctor(writeFileFunc), typeInt, []ExprFuncParam{
-		newFuncParam(typeHandle),
-		newFuncParamFlagDef(typeItem, pfOptional|pfRepeat, ""),
-	})
-	ctx.RegisterFunc("readFile", newGolangFunctor(readFileFunc), typeString, []ExprFuncParam{
-		newFuncParam(typeHandle),
-		newFuncParamFlagDef("limitCh", pfOptional, "\n"),
-	})
-	ctx.RegisterFunc("closeFile", newGolangFunctor(closeFileFunc), typeBoolean, []ExprFuncParam{
-		newFuncParam(typeHandle),
-	})
-}
-
-func init() {
-	registerImport("os.file", ImportOsFuncs, "Operating system file functions")
-}

func-string.go

@@ -1,223 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-string.go
-package expr
-
-import (
-	"fmt"
-	"io"
-	"strings"
-)
-
-// --- Start of function definitions
-func doJoinStr(funcName string, sep string, it Iterator) (result any, err error) {
-	var sb strings.Builder
-	var v any
-	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if it.Index() > 0 {
-			sb.WriteString(sep)
-		}
-		if s, ok := v.(string); ok {
-			sb.WriteString(s)
-		} else {
-			err = errExpectedGot(funcName, typeString, v)
-			return
-		}
-	}
-	if err == nil || err == io.EOF {
-		err = nil
-		result = sb.String()
-	}
-	return
-}
-
-func joinStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	//	if len(args) < 1 {
-	//		return nil, errMissingRequiredParameter(name, paramSeparator)
-	//	}
-	if sep, ok := args[0].(string); ok {
-		if len(args) == 1 {
-			result = ""
-		} else if len(args) == 2 {
-			if ls, ok := args[1].(*ListType); ok {
-				result, err = doJoinStr(name, sep, NewListIterator(ls, nil))
-			} else if it, ok := args[1].(Iterator); ok {
-				result, err = doJoinStr(name, sep, it)
-			} else {
-				err = errInvalidParameterValue(name, paramParts, args[1])
-			}
-		} else {
-			result, err = doJoinStr(name, sep, NewArrayIterator(args[1:]))
-		}
-	} else {
-		err = errWrongParamType(name, paramSeparator, typeString, args[0])
-	}
-	return
-}
-
-func subStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var start = 0
-	var count = -1
-	var source string
-	var ok bool
-
-	if source, ok = args[0].(string); !ok {
-		return nil, errWrongParamType(name, paramSource, typeString, args[0])
-	}
-
-	if start, err = toInt(args[1], name+"()"); err != nil {
-		return
-	}
-
-	if count, err = toInt(args[2], name+"()"); err != nil {
-		return
-	}
-
-	if start < 0 {
-		start = len(source) + start
-	}
-
-	if count < 0 {
-		count = len(source) - start
-	}
-	end := min(start+count, len(source))
-	result = source[start:end]
-	return
-}
-
-func trimStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var source string
-	var ok bool
-
-	if source, ok = args[0].(string); !ok {
-		return nil, errWrongParamType(name, paramSource, typeString, args[0])
-	}
-	result = strings.TrimSpace(source)
-	return
-}
-
-func startsWithStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var source string
-	var ok bool
-
-	result = false
-
-	if source, ok = args[0].(string); !ok {
-		return result, errWrongParamType(name, paramSource, typeString, args[0])
-	}
-	for i, targetSpec := range args[1:] {
-		if target, ok := targetSpec.(string); ok {
-			if strings.HasPrefix(source, target) {
-				result = true
-				break
-			}
-		} else {
-			err = fmt.Errorf("target item nr %d is %T, expected string", i+1, targetSpec)
-			break
-		}
-	}
-	return
-}
-
-func endsWithStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var source string
-	var ok bool
-
-	result = false
-
-	if source, ok = args[0].(string); !ok {
-		return result, errWrongParamType(name, paramSource, typeString, args[0])
-	}
-	for i, targetSpec := range args[1:] {
-		if target, ok := targetSpec.(string); ok {
-			if strings.HasSuffix(source, target) {
-				result = true
-				break
-			}
-		} else {
-			err = fmt.Errorf("target item nr %d is %T, expected string", i+1, targetSpec)
-			break
-		}
-	}
-	return
-}
-
-func splitStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	var source, sep string
-	var count int = -1
-	var parts []string
-	var ok bool
-
-	if source, ok = args[0].(string); !ok {
-		return result, errWrongParamType(name, paramSource, typeString, args[0])
-	}
-
-	if sep, ok = args[1].(string); !ok {
-		return nil, fmt.Errorf("separator param must be string, got %T (%v)", args[1], args[1])
-	}
-
-	if count64, ok := args[2].(int64); ok { // TODO replace type assertion with toInt()
-		count = int(count64)
-	} else {
-		return nil, fmt.Errorf("part count must be integer, got %T (%v)", args[2], args[2])
-	}
-
-	if count > 0 {
-		parts = strings.SplitN(source, sep, count)
-	} else if count < 0 {
-		parts = strings.Split(source, sep)
-	} else {
-		parts = []string{}
-	}
-	list := make(ListType, len(parts))
-	for i, part := range parts {
-		list[i] = part
-	}
-	result = &list
-	return
-}
-
-// --- End of function definitions
-
-// Import above functions in the context
-func ImportStringFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("joinStr", newGolangFunctor(joinStrFunc), typeString, []ExprFuncParam{
-		newFuncParam(paramSeparator),
-		newFuncParamFlag(paramItem, pfRepeat),
-	})
-
-	ctx.RegisterFunc("subStr", newGolangFunctor(subStrFunc), typeString, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParamFlagDef(paramStart, pfOptional, int64(0)),
-		newFuncParamFlagDef(paramCount, pfOptional, int64(-1)),
-	})
-
-	ctx.RegisterFunc("splitStr", newGolangFunctor(splitStrFunc), "list of "+typeString, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParamFlagDef(paramSeparator, pfOptional, ""),
-		newFuncParamFlagDef(paramCount, pfOptional, int64(-1)),
-	})
-
-	ctx.RegisterFunc("trimStr", newGolangFunctor(trimStrFunc), typeString, []ExprFuncParam{
-		newFuncParam(paramSource),
-	})
-
-	ctx.RegisterFunc("startsWithStr", newGolangFunctor(startsWithStrFunc), typeBoolean, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParam(paramPrefix),
-		newFuncParamFlag("other "+paramPrefix, pfRepeat),
-	})
-
-	ctx.RegisterFunc("endsWithStr", newGolangFunctor(endsWithStrFunc), typeBoolean, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParam(paramSuffix),
-		newFuncParamFlag("other "+paramSuffix, pfRepeat),
-	})
-}
-
-// Register the import function in the import-register.
-// That will allow to import all function of this module by the "builtin" operator."
-func init() {
-	registerImport("string", ImportStringFuncs, "string utilities")
-}

function.go

@@ -1,249 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// function.go
-package expr
-
-import (
-	"fmt"
-	"strings"
-)
-
-// ---- Function template
-type FuncTemplate func(ctx ExprContext, name string, args []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() {<body>}"
-	}
-	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
-}
-
-// ---- Linking with Go functions
-type golangFunctor struct {
-	baseFunctor
-	f FuncTemplate
-}
-
-func newGolangFunctor(f FuncTemplate) *golangFunctor {
-	return &golangFunctor{f: f}
-}
-
-func (functor *golangFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
-	return functor.f(ctx, name, args)
-}
-
-// ---- Linking with Expr functions
-type exprFunctor struct {
-	baseFunctor
-	params []ExprFuncParam
-	expr   Expr
-	defCtx ExprContext
-}
-
-// func newExprFunctor(e Expr, params []string, ctx ExprContext) *exprFunctor {
-// 	return &exprFunctor{expr: e, params: params, defCtx: ctx}
-// }
-
-func newExprFunctor(e Expr, params []ExprFuncParam, ctx ExprContext) *exprFunctor {
-	return &exprFunctor{expr: e, params: params, defCtx: ctx}
-}
-
-func (functor *exprFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
-	if functor.defCtx != nil {
-		ctx.Merge(functor.defCtx)
-	}
-
-	for i, p := range functor.params {
-		if i < len(args) {
-			arg := args[i]
-			if funcArg, ok := arg.(Functor); ok {
-				// ctx.RegisterFunc(p, functor, 0, -1)
-				paramSpecs := funcArg.GetParams()
-				ctx.RegisterFunc(p.Name(), funcArg, typeAny, paramSpecs)
-			} else {
-				ctx.UnsafeSetVar(p.Name(), arg)
-			}
-		} else {
-			ctx.UnsafeSetVar(p.Name(), nil)
-		}
-	}
-	result, err = functor.expr.eval(ctx, false)
-	return
-}
-
-// ---- Function Parameters
-type paramFlags uint16
-
-const (
-	pfOptional paramFlags = 1 << iota
-	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 "any"
-}
-
-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
-type funcInfo struct {
-	name       string
-	minArgs    int
-	maxArgs    int
-	functor    Functor
-	params     []ExprFuncParam
-	returnType string
-}
-
-func newFuncInfo(name string, functor Functor, returnType string, params []ExprFuncParam) (info *funcInfo, err error) {
-	var minArgs = 0
-	var maxArgs = 0
-	if params != nil {
-		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.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, params: params,
-	}
-	functor.SetFunc(info)
-	return info, nil
-}
-
-func newUnnamedFuncInfo(functor Functor, returnType string, params []ExprFuncParam) (info *funcInfo, err error) {
-	return newFuncInfo("unnamed", functor, returnType, params)
-}
-
-func (info *funcInfo) Params() []ExprFuncParam {
-	return info.params
-}
-
-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.params != nil {
-		for i, p := range info.params {
-			if i > 0 {
-				sb.WriteString(", ")
-			}
-			sb.WriteString(p.Name())
-
-			if p.IsOptional() {
-				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(" {<body>}")
-	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
-}

global-context.go

@@ -1,25 +1,33 @@
-// 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
 package expr
 
-import "path/filepath"
+import (
+	"path/filepath"
+	"strings"
 
-var globalCtx *SimpleStore
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
 
-func ImportInContext(name string) (exists bool) {
+//var globalCtx *SimpleStore
-	var mod *module
+
-	if mod, exists = moduleRegister[name]; exists {
+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) {
+func ImportInContextByGlobPattern(ctx kern.ExprContext, pattern string) (count int, err error) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
 		var matched bool
-	for name, mod := range moduleRegister {
+		for name, mod := range builtinModuleRegister {
 			if matched, err = filepath.Match(pattern, name); err == nil {
 				if matched {
 					count++
@@ -30,40 +38,87 @@ func ImportInContextByGlobPattern(pattern string) (count int, err error) {
 				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) {
+func fixCtrlVar(name string) string {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	return name
+}
+
+func GlobalCtrlSet(ctx kern.ExprContext, name string, newValue any) (currentValue any) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		name = fixCtrlVar(name)
+		currentValue, _ = globalCtx.GetVar(name)
+		globalCtx.SetVar(name, newValue)
+	}
+	return currentValue
+}
+
+func GlobalCtrlGet(ctx kern.ExprContext, name string) (currentValue any) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		name = fixCtrlVar(name)
+		currentValue, _ = globalCtx.GetVar(name)
+	}
+	return currentValue
+}
+
+func CtrlEnable(ctx kern.ExprContext, name string) (currentStatus bool) {
+	name = fixCtrlVar(name)
+	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
+		currentStatus, _ = v.(bool)
+	}
+
+	ctx.SetVar(name, true)
+	return currentStatus
+}
+
+func CtrlDisable(ctx kern.ExprContext, name string) (currentStatus bool) {
+	name = fixCtrlVar(name)
+	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
+		currentStatus, _ = v.(bool)
+	}
+
+	ctx.SetVar(name, false)
+	return currentStatus
+}
+
+// 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 {
+// 		v, exists = globalCtx.GetVar(name)
+// 	}
+
+// 	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 len(name) > 0 {
+		if v, exists = globalCtx.GetVar(name); exists {
-		if v, exists = ctx.GetVar(name); exists && isFunctor(v) {
+			s, exists = v.(string)
-			f, _ := v.(Functor)
-			item = f.GetFunc()
-		} else {
-			item, exists = ctx.GetFuncInfo(name)
-		}
-	}
-	return
-}
-func GetFuncInfo(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 init() {
+func InitGlobal() (ctx kern.ExprContext) {
-	globalCtx = NewSimpleStore()
+	ctx = NewSimpleStoreWithoutGlobalContext()
-	ImportBuiltinsFuncs(globalCtx)
+	kern.InitDefaultVars(ctx)
+	ImportBuiltinsFuncs(ctx)
+	return
 }

go.mod

@@ -1,3 +1,7 @@
 module git.portale-stac.it/go-pkg/expr
 
-go 1.21.6
+go 1.22.0
+
+toolchain go1.23.3
+
+require golang.org/x/exp v0.0.0-20241204233417-43b7b7cde48d

go.sum

@@ -0,0 +1,4 @@
+github.com/yqylovy/goimportdot v0.0.0-20170519021755-eb181a7eeabe h1:bWYrKmmfv37uNgXTdwkLSKYiYPJ1yfWmjBnvtMyAYzk=
+github.com/yqylovy/goimportdot v0.0.0-20170519021755-eb181a7eeabe/go.mod h1:alTKUpAJ/zbp17qvZwcFNwzufrb5DljMDY4mgJlIHao=
+golang.org/x/exp v0.0.0-20241204233417-43b7b7cde48d h1:0olWaB5pg3+oychR51GUVCEsGkeCU/2JxjBgIo4f3M0=
+golang.org/x/exp v0.0.0-20241204233417-43b7b7cde48d/go.mod h1:qj5a5QZpwLU2NLQudwIN5koi3beDhSAlJwa67PuM98c=

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
@@ -9,17 +9,21 @@ 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) {
+func EvalString(ctx kern.ExprContext, source string) (result any, err error) {
-	var tree *ast
+	var tree *scan.Ast
 
 	r := strings.NewReader(source)
-	scanner := NewScanner(r, DefaultTranslations())
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
-	parser := NewParser(ctx)
+	parser := NewParser()
 
 	if tree, err = parser.Parse(scanner); err == nil {
-		result, err = tree.eval(ctx, true)
+		result, err = tree.Eval(ctx)
 	}
 	return
 }
@@ -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 util.IsFunc(arg.Value) {
-			if f, ok := arg.Value.(FuncTemplate); ok {
+			if f, ok := arg.Value.(kern.FuncTemplate); ok {
-				functor := newGolangFunctor(f)
+				functor := kern.NewGolangFunctor(f)
 				// ctx.RegisterFunc(arg.Name, functor, 0, -1)
-				ctx.RegisterFunc(arg.Name, functor, typeAny, []ExprFuncParam{
+				ctx.RegisterFunc(arg.Name, functor, kern.TypeAny, []kern.ExprFuncParam{
-					newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, 0),
+					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)
@@ -65,10 +69,10 @@ func EvalStringV(source string, args []Arg) (result any, err error) {
 	return
 }
 
-func EvalStream(ctx ExprContext, r io.Reader) (result any, err error) {
+func EvalStream(ctx kern.ExprContext, r io.Reader) (result any, err error) {
-	var tree *ast
+	var tree *scan.Ast
-	scanner := NewScanner(r, DefaultTranslations())
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
-	parser := NewParser(ctx)
+	parser := NewParser()
 
 	if tree, err = parser.Parse(scanner); err == nil {
 		result, err = tree.Eval(ctx)
@@ -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

@@ -0,0 +1,127 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// import-utils.go
+package expr
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/util"
+)
+
+const (
+	ENV_EXPR_SOURCE_PATH = "EXPR_PATH"
+	ENV_EXPR_PLUGIN_PATH = "EXPR_PLUGIN_PATH"
+)
+
+func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
+	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
+}
+
+// func addSourceEnvImportDirs(varName string, dirList []string) []string {
+// 	return addEnvImportDirs(ENV_EXPR_SOURCE_PATH, dirList)
+// }
+
+// func addPluginEnvImportDirs(varName string, dirList []string) []string {
+// 	return addEnvImportDirs(ENV_EXPR_PLUGIN_PATH, dirList)
+// }
+
+func addEnvImportDirs(envVarName string, dirList []string) []string {
+	if dirSpec, exists := os.LookupEnv(envVarName); exists {
+		dirs := strings.Split(dirSpec, ":")
+		if dirList == nil {
+			dirList = dirs
+		} else {
+			dirList = append(dirList, dirs...)
+		}
+	}
+	return dirList
+}
+
+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
+		} else {
+			if len(endingPath) > 0 {
+				for _, d := range dirs {
+					dirList = append(dirList, path.Join(d, endingPath))
+				}
+			} else {
+				dirList = append(dirList, dirs...)
+			}
+		}
+	}
+	return dirList
+}
+
+func buildSearchDirList(ctx kern.ExprContext, endingPath, envVarName string) (dirList []string) {
+	dirList = addEnvImportDirs(envVarName, dirList)
+	dirList = addSearchDirs(ctx, endingPath, dirList)
+	return
+}
+
+func isFile(filePath string) bool {
+	info, err := os.Stat(filePath)
+	return (err == nil || errors.Is(err, os.ErrExist)) && info.Mode().IsRegular()
+}
+
+func searchAmongPath(filename string, dirList []string) (filePath string) {
+	var err error
+
+	suffix := SHAREDLIBRARY_EXTENSION
+	if strings.HasSuffix(filename, ".debug") {
+		suffix += ".debug"
+	}
+
+	for _, dir := range dirList {
+		if dir, err = util.ExpandPath(dir); err != nil {
+			continue
+		}
+		if fullPath := path.Join(dir, filename); isFile(fullPath) {
+			filePath = fullPath
+			break
+		}
+
+		subdir := strings.TrimSuffix(filename, suffix)
+		if fullPath := path.Join(dir, subdir, filename); isFile(fullPath) {
+			filePath = fullPath
+			break
+		}
+	}
+	return
+}
+
+func isPathRelative(filePath string) bool {
+	unixPath := filepath.ToSlash(filePath)
+	return strings.HasPrefix(unixPath, "./") || strings.HasPrefix(unixPath, "../")
+}
+
+func makeFilepath(filename string, dirList []string) (filePath string, err error) {
+	if filename, err = util.ExpandPath(filename); err != nil {
+		return
+	}
+
+	if path.IsAbs(filename) || isPathRelative(filename) {
+		if isFile(filename) {
+			filePath = filename
+		}
+	} else {
+		filePath = searchAmongPath(filename, dirList)
+	}
+	if len(filePath) == 0 {
+		err = fmt.Errorf("file %q not found", filename)
+	}
+	return
+}

int-iterator.go

@@ -0,0 +1,141 @@
+// 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 NewIntIteratorA(args ...any) (it *IntIterator, err error) {
+	return NewIntIterator(args)
+}
+
+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

@@ -0,0 +1,55 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iter-factory.go
+package expr
+
+import (
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+func NewFormalIterator(value any) (it kern.Iterator) {
+	if value == nil {
+		it = NewArrayIterator([]any{})
+	} else {
+		it = NewArrayIterator([]any{value})
+	}
+	return
+}
+
+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 *kern.ListType:
+		it = NewListIterator(v, nil)
+	case *kern.LinkedList:
+		it = NewLinkedListIterator(v, nil)
+	case *kern.DictType:
+		it, err = NewDictIterator(v, nil)
+	case []any:
+		it = NewArrayIterator(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 +1,135 @@
+// 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"
+)
+
+const iterIterType = "IterIter"
+
+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) {
+	if ctx == nil {
+		err = fmt.Errorf("context is required for %s", iterIterType)
+	} else if it == nil {
+		err = fmt.Errorf("source iterator is required for %s", iterIterType)
+	} else {
+		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 iterIterType
+}
+
+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
+}

iter-list.go

@@ -1,141 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// iter-list.go
-package expr
-
-import (
-	"fmt"
-	"io"
-)
-
-type ListIterator struct {
-	a     *ListType
-	count int
-	index int
-	start int
-	stop  int
-	step  int
-}
-
-func NewListIterator(list *ListType, args []any) (it *ListIterator) {
-	var argc int = 0
-	listLen := 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 := toInt(args[0], "start index"); err == nil {
-			if i < 0 {
-				i = listLen + i
-			}
-			it.start = i
-		}
-		if argc >= 2 {
-			if i, err := toInt(args[1], "stop index"); err == nil {
-				if i < 0 {
-					i = listLen + i
-				}
-				it.stop = i
-			}
-			if argc >= 3 {
-				if i, err := toInt(args[2], "step"); err == nil {
-					if i < 0 {
-						i = -i
-					}
-					if it.start > it.stop {
-						it.step = -i
-					} else {
-						it.step = i
-					}
-				}
-			}
-		}
-	}
-	it.index = it.start - it.step
-	return
-}
-
-func NewArrayIterator(array []any) (it *ListIterator) {
-	it = &ListIterator{a: (*ListType)(&array), count: 0, index: -1, start: 0, stop: len(array) - 1, step: 1}
-	return
-}
-
-func NewAnyIterator(value any) (it *ListIterator) {
-	if value == nil {
-		it = NewArrayIterator([]any{})
-	} else if list, ok := value.(*ListType); ok {
-		it = NewListIterator(list, nil)
-	} else if array, ok := value.([]any); ok {
-		it = NewArrayIterator(array)
-	} else if it1, ok := value.(*ListIterator); ok {
-		it = it1
-	} else {
-		it = NewArrayIterator([]any{value})
-	}
-	return
-}
-
-func (it *ListIterator) String() string {
-	var l = 0
-	if it.a != nil {
-		l = len(*it.a)
-	}
-	return fmt.Sprintf("$(#%d)", l)
-}
-
-func (it *ListIterator) HasOperation(name string) bool {
-	yes := name == resetName || name == indexName || name == countName
-	return yes
-}
-
-func (it *ListIterator) CallOperation(name string, args []any) (v any, err error) {
-	switch name {
-	case resetName:
-		v, err = it.Reset()
-	case indexName:
-		v = int64(it.Index())
-	case countName:
-		v = it.count
-	default:
-		err = errNoOperation(name)
-	}
-	return
-}
-
-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 {
-			item = a[it.index]
-		} else {
-			err = io.EOF
-		}
-	} else {
-		if it.start < len(a) && it.index >= it.stop && it.index <= it.start {
-			item = a[it.index]
-		} else {
-			err = io.EOF
-		}
-
-	}
-	return
-}
-
-func (it *ListIterator) Next() (item any, err error) {
-	it.index += it.step
-	if item, err = it.Current(); err != io.EOF {
-		it.count++
-	}
-	return
-}
-
-func (it *ListIterator) Index() int {
-	return it.index
-}
-
-func (it *ListIterator) Reset() (bool, error) {
-	it.index = it.start
-	return true, nil
-}

iterator.go

@@ -1,42 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// iterator.go
-package expr
-
-import (
-	"errors"
-	"fmt"
-)
-
-// Operator names
-
-const (
-	initName    = "init"
-	cleanName   = "clean"
-	resetName   = "reset"
-	nextName    = "next"
-	currentName = "current"
-	indexName   = "index"
-	countName   = "count"
-)
-
-type Iterator interface {
-	Next() (item any, err error) // must return io.EOF after the last item
-	Current() (item any, err error)
-	Index() int
-}
-
-type ExtIterator interface {
-	Iterator
-	HasOperation(name string) bool
-	CallOperation(name string, args []any) (value any, err 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")
-}

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/clone-value.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// clone-value.go
+package kern
+
+func Clone(v any) (c any) {
+	if v == nil {
+		return
+	}
+	switch unboxed := v.(type) {
+	case int64:
+		c = unboxed
+	case float64:
+		c = unboxed
+	case string:
+		c = unboxed
+	case bool:
+		c = unboxed
+	case *ListType:
+		c = unboxed.Clone()
+	case *DictType:
+		c = unboxed.Clone()
+	case *LinkedList:
+		c = unboxed.Clone()
+	default:
+		c = v
+	}
+	return
+}

kern/common-errors.go

@@ -0,0 +1,95 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-errors.go
+package kern
+
+import (
+	"fmt"
+	"strings"
+)
+
+func ErrMissingParams(funcName string, missing []string) (err error) {
+	return fmt.Errorf("%s(): missing params -- %s", funcName, strings.Join(missing, ", "))
+}
+
+func ErrTooFewParams(funcName string, minArgs, maxArgs, argCount int) (err error) {
+	if maxArgs < 0 {
+		err = fmt.Errorf("%s(): too few params -- expected %d or more, got %d", funcName, minArgs, argCount)
+	} else {
+		err = fmt.Errorf("%s(): too few params -- expected %d, got %d", funcName, minArgs, argCount)
+	}
+	return
+}
+
+func ErrTooManyParams(funcName string, maxArgs, argCount int) (err error) {
+	err = fmt.Errorf("%s(): too many params -- expected %d, got %d", funcName, maxArgs, argCount)
+	return
+}
+
+// --- General errors
+
+func ErrCantConvert(funcName string, value any, kind string) error {
+	return fmt.Errorf("%s(): can't convert %s to %s", funcName, TypeName(value), kind)
+}
+
+func ErrExpectedGot(funcName string, kind string, value any) error {
+	return fmt.Errorf("%s(): expected %s, got %s (%#v)", funcName, kind, TypeName(value), value)
+}
+
+func ErrFuncDivisionByZero(funcName string) error {
+	return fmt.Errorf("%s(): division by zero", funcName)
+}
+
+// func ErrDivisionByZero() error {
+// 	return fmt.Errorf("division by zero")
+// }
+
+// --- Parameter errors
+
+// func ErrMissingRequiredParameter(funcName, paramName string) error {
+// 	return fmt.Errorf("%s(): missing required parameter %q", funcName, paramName)
+// }
+
+func ErrInvalidParameterValue(funcName, paramName string, paramValue any) error {
+	return fmt.Errorf("%s(): invalid value %s (%#v) for parameter %q", funcName, TypeName(paramValue), paramValue, paramName)
+}
+
+func undefArticle(s string) (article string) {
+	if len(s) > 0 && strings.Contains("aeiou", s[0:1]) {
+		article = "an"
+	} else {
+		article = "a"
+	}
+	return
+}
+
+func prependUndefArticle(s string) (result string) {
+	return undefArticle(s) + " " + s
+}
+
+func ErrWrongParamType(funcName, paramName, paramType string, paramValue any) error {
+	var artWantType, artGotType string
+	gotType := TypeName(paramValue)
+	artGotType = prependUndefArticle(gotType)
+	artWantType = prependUndefArticle(paramType)
+	return fmt.Errorf("%s(): the %q parameter must be %s, got %s (%v)", funcName, paramName, artWantType, artGotType, paramValue)
+}
+
+func ErrUnknownParam(funcName, paramName string) error {
+	return fmt.Errorf("%s(): unknown parameter %q", funcName, paramName)
+}
+
+func ErrUnknownVar(funcName, varName string) error {
+	return fmt.Errorf("%s(): unknown variable %q", funcName, varName)
+}
+
+func ErrFuncInvalidArg(funcName, details string) error {
+	return fmt.Errorf("%s(): invalid argument -- %s", funcName, details)
+}
+
+// --- Operator errors
+
+func ErrLeftOperandMustBeVariable(leftTerm, opTerm Term) error {
+	return leftTerm.Errorf("left operand of %q must be a variable", opTerm.Source())
+}

kern/common-params.go

@@ -0,0 +1,32 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-params.go
+package kern
+
+const (
+	ParamArgs      = "args"
+	ParamCount     = "count"
+	ParamItem      = "item"
+	ParamIndex     = "index"
+	ParamParts     = "parts"
+	ParamSeparator = "separator"
+	ParamSource    = "source"
+	ParamSuffix    = "suffix"
+	ParamPrefix    = "prefix"
+	ParamStart     = "start"
+	ParamEnd       = "end"
+	ParamValue     = "value"
+	ParamName      = "name"
+	ParamEllipsis  = "..."
+	ParamFilepath  = "filepath"
+	ParamDirpath   = "dirpath"
+	ParamHandle    = "handle"
+	ParamResource  = "resource"
+	ParamIterator  = "iterator"
+)
+
+// to be moved in its own source file
+const (
+	ConstLastIndex = 0xFFFF_FFFF
+)

kern/common-type-names.go

@@ -0,0 +1,24 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-type-names.go
+package kern
+
+const (
+	TypeAny           = "any"
+	TypeNil           = "nil"
+	TypeBoolean       = "boolean"
+	TypeFloat         = "float"
+	TypeFraction      = "fraction"
+	TypeFileHandle    = "file-handle"
+	TypeInt           = "integer"
+	TypeItem          = "item"
+	TypeIterator      = "iterator"
+	TypeNumber        = "number"
+	TypePair          = "pair"
+	TypeString        = "string"
+	TypeDict          = "dict"
+	TypeListOf        = "list-of-"
+	TypeListOfStrings = "list-of-strings"
+	TypeLinkedList    = "linked-list"
+)

kern/compare.go

@@ -0,0 +1,41 @@
+// 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 IsLinkedList(value1) && IsLinkedList(value2) {
+		ll1 := value1.(*LinkedList)
+		ll2 := value2.(*LinkedList)
+		equal = ll1.Equals(ll2)
+	} 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()
 	}
@@ -22,16 +22,14 @@ func exportFunc(ctx ExprContext, name string, info ExprFunc) {
 	if name[0] == '@' {
 		name = name[1:]
 	}
-	// ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
-	// ctx.RegisterFuncInfo(name, info)
 	ctx.RegisterFunc(name, info.Functor(), info.ReturnType(), info.Params())
 }
 
-func exportObjects(destCtx, sourceCtx ExprContext) {
+func ExportObjects(destCtx, sourceCtx ExprContext) {
-	exportAll := isEnabled(sourceCtx, control_export_all)
+	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] == '@' }) {
+	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return (exportAll || name[0] == '@') && !(name[0] == '_') }) {
 		// fmt.Printf("\tExporting %q\n", refName)
 		refValue, _ := sourceCtx.GetVar(refName)
 		exportVar(destCtx, refName, refValue)
@@ -43,3 +41,9 @@ func exportObjects(destCtx, sourceCtx ExprContext) {
 		}
 	}
 }
+
+func exportObjectsToParent(sourceCtx ExprContext) {
+	if parentCtx := sourceCtx.GetParent(); parentCtx != nil {
+		ExportObjects(parentCtx, sourceCtx)
+	}
+}

kern/control.go

@@ -0,0 +1,63 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// control.go
+package kern
+
+import "strings"
+
+// Preset control variables
+const (
+	ControlPreset        = "_preset"
+	ControlLastResult    = "last"
+	ControlBoolShortcut  = "_bool_shortcut"
+	ControlSearchPath    = "_search_path"
+	ControlParentContext = "_parent_context"
+	ControlStdout        = "_stdout"
+)
+
+// Other control variables
+const (
+	ControlExportAll = "_export_all"
+)
+
+// Initial values
+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) {
+	if _, exists := ctx.GetVar(ControlPreset); exists {
+		return
+	}
+	ctx.UnsafeSetVar(ControlPreset, true)
+	ctx.UnsafeSetVar(ControlBoolShortcut, true)
+	ctx.UnsafeSetVar(ControlSearchPath, init_search_path)
+}

kern/dict-type.go

@@ -0,0 +1,199 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// dict-type.go
+package kern
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+const DictTypeName = "dict"
+
+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
+	return
+}
+
+func NewDict(dictAny map[any]any) (dict *DictType) {
+	var d DictType
+	if dictAny != nil {
+		d = make(DictType, len(dictAny))
+		for i, item := range dictAny {
+			d[i] = item
+		}
+	} else {
+		d = make(DictType)
+	}
+	dict = &d
+	return
+}
+
+func newDict(dictAny map[any]Term) (dict *DictType) {
+	// TODO Change with a call to NewDict()
+	var d DictType
+	if dictAny != nil {
+		d = make(DictType, len(dictAny))
+		for i, item := range dictAny {
+			d[i] = item
+		}
+	} else {
+		d = make(DictType)
+	}
+	dict = &d
+	return
+}
+
+func (dict *DictType) toMultiLine(sb *strings.Builder, opt FmtOpt) {
+	indent := GetFormatIndent(opt)
+	flags := GetFormatFlags(opt)
+	//sb.WriteString(strings.Repeat("  ", indent))
+	sb.WriteByte('{')
+
+	if len(*dict) > 0 {
+		innerOpt := MakeFormatOptions(flags, indent+1)
+		nest := strings.Repeat("  ", indent+1)
+		sb.WriteByte('\n')
+
+		first := true
+		for name, value := range *dict {
+			if first {
+				first = false
+			} else {
+				sb.WriteByte(',')
+				sb.WriteByte('\n')
+			}
+
+			sb.WriteString(nest)
+			if key, ok := name.(string); ok {
+				sb.WriteByte('"')
+				sb.WriteString(key)
+				sb.WriteByte('"')
+			} else {
+				fmt.Fprintf(sb, "%v", name)
+			}
+			sb.WriteString(": ")
+			if f, ok := value.(Formatter); ok {
+				sb.WriteString(f.ToString(innerOpt))
+			} else if _, ok = value.(Functor); ok {
+				sb.WriteString("func(){}")
+			} else {
+				fmt.Fprintf(sb, "%v", value)
+			}
+		}
+		sb.WriteByte('\n')
+		sb.WriteString(strings.Repeat("  ", indent))
+	}
+	sb.WriteString("}")
+}
+
+func (dict *DictType) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	flags := GetFormatFlags(opt)
+	if flags&MultiLine != 0 {
+		dict.toMultiLine(&sb, opt)
+	} else {
+		sb.WriteByte('{')
+		first := true
+		for key, value := range *dict {
+			if first {
+				first = false
+			} else {
+				sb.WriteString(", ")
+			}
+			if s, ok := key.(string); ok {
+				sb.WriteByte('"')
+				sb.WriteString(s)
+				sb.WriteByte('"')
+			} else {
+				fmt.Fprintf(&sb, "%v", key)
+			}
+			sb.WriteString(": ")
+			if formatter, ok := value.(Formatter); ok {
+				sb.WriteString(formatter.ToString(opt))
+			} else if t, ok := value.(Term); ok {
+				sb.WriteString(t.String())
+			} else {
+				fmt.Fprintf(&sb, "%#v", value)
+			}
+		}
+		sb.WriteByte('}')
+	}
+	return sb.String()
+}
+
+func (dict *DictType) String() string {
+	return dict.ToString(0)
+}
+
+func (dict *DictType) TypeName() string {
+	return DictTypeName
+}
+
+func (dict *DictType) HasKey(target any) (ok bool) {
+	for key := range *dict {
+		if ok = reflect.DeepEqual(key, target); ok {
+			break
+		}
+	}
+	return
+}
+
+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] = Clone(v)
+	}
+	return
+}
+
+func (dict *DictType) Merge(second *DictType) {
+	if second != nil {
+		for k, v := range *second {
+			(*dict)[k] = v
+		}
+	}
+}
+
+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
+}
+
+////////////////
+
+type DictFormat interface {
+	ToDict() *DictType
+}

kern/expr-context.go

@@ -0,0 +1,63 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// expr-context.go
+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)
+	UnsafeSetVar(varName string, value any)
+
+	EnumVars(func(name string) (accept bool)) (varNames []string)
+	VarCount() int
+	DeleteVar(varName string)
+
+	EnumFuncs(func(name string) (accept bool)) (funcNames []string)
+	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)
+	RegisterFunc(name string, f Functor, returnType string, param []ExprFuncParam) (funcInfo ExprFunc, err error)
+
+	ToDict() (dict *DictType)
+	ToString(opt FmtOpt) string
+}
+
+func ContextToDict(ctx ExprContext) (dict *DictType) {
+	var keys []string
+	// Variables
+	keys = ctx.EnumVars(nil)
+	vars := MakeDict()
+	for _, key := range keys {
+		value, _ := ctx.GetVar(key)
+		vars.SetItem(key, value)
+	}
+
+	// Functions
+	keys = ctx.EnumFuncs(func(name string) bool { return true })
+	funcs := MakeDict()
+	for _, key := range keys {
+		funcInfo, _ := ctx.GetFuncInfo(key)
+		funcs.SetItem(key, funcInfo)
+	}
+
+	dict = MakeDict()
+	dict.SetItem("vars", vars)
+	dict.SetItem("funcs", funcs)
+	return
+}
+
+func ContextToString(ctx ExprContext, opt FmtOpt) string {
+	dict := ctx.ToDict()
+	return dict.ToString(opt)
+}

kern/expr-function.go

@@ -0,0 +1,44 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// expr-function.go
+package kern
+
+// ---- Functor interface
+type Functor interface {
+	Typer
+	InvokeNamed(ctx ExprContext, name string, args map[string]any) (result any, err error)
+	SetFunc(info ExprFunc)
+	GetFunc() ExprFunc
+	GetParams() []ExprFuncParam
+	GetDefinitionContext() ExprContext
+}
+
+// ---- Function Param Info
+type ExprFuncParam interface {
+	Name() string
+	Type() string
+	IsDefault() bool
+	IsOptional() bool
+	IsRepeat() bool
+	DefaultValue() any
+}
+
+// ---- Function Info
+type ExprFunc interface {
+	Formatter
+	Name() string
+	MinArgs() int
+	MaxArgs() int
+	Functor() Functor
+	Params() []ExprFuncParam
+	ParamSpec(paramName string) ExprFuncParam
+	ReturnType() string
+	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

@@ -0,0 +1,12 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// expr.go
+package kern
+
+// ----Expression interface
+type Expr interface {
+	Typer
+	Eval(ctx ExprContext) (result any, err error)
+	String() string
+}

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

@@ -1,12 +1,15 @@
-// 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"
+import (
+	"fmt"
+	"strings"
+)
 
-type FmtOpt uint16
+type FmtOpt uint32 // lower 16 bits hold a bit-mask, higher 16 bits hold an indentation number
 
 const (
 	TTY FmtOpt = 1 << iota
@@ -30,11 +33,35 @@ func TruncateString(s string) (trunc string) {
 	return
 }
 
+func MakeFormatOptions(flags FmtOpt, indent int) FmtOpt {
+	return FmtOpt(indent<<16) | flags
+}
+
+func GetFormatFlags(opt FmtOpt) FmtOpt {
+	return opt & 0xFFFF
+}
+
+func GetFormatIndent(opt FmtOpt) int {
+	return int(opt >> 16)
+}
+
 type Formatter interface {
 	ToString(options FmtOpt) string
 }
 
-func getFormatted(v any, opt FmtOpt) (text string) {
+func Format(sb *strings.Builder, item any, opt FmtOpt) {
+	if s, ok := item.(string); ok {
+		sb.WriteByte('"')
+		sb.WriteString(s)
+		sb.WriteByte('"')
+	} else if formatter, ok := item.(Formatter); ok {
+		sb.WriteString(formatter.ToString(opt))
+	} else {
+		fmt.Fprintf(sb, "%v", item)
+	}
+}
+
+func GetFormatted(v any, opt FmtOpt) (text string) {
 	if v == nil {
 		text = "(nil)"
 	} else if s, ok := v.(string); ok {
@@ -51,7 +78,7 @@ type Typer interface {
 	TypeName() string
 }
 
-func typeName(v any) (name string) {
+func TypeName(v any) (name string) {
 	if v == nil {
 		name = "nil"
 	} else if typer, ok := v.(Typer); 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 {
@@ -33,32 +33,34 @@ 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
 	if len(s) == 0 {
 		goto exit
 	}
-	if s[0] == '-' {
+	switch s[0] {
+	case '-':
 		sign = int64(-1)
 		s = s[1:]
-	} else if s[0] == '+' {
+	case '+':
 		s = s[1:]
 	}
-	if strings.HasSuffix(s, "()") {
+	//	if strings.HasSuffix(s, "()") {
-		s = s[0 : len(s)-2]
+	//		s = s[0 : len(s)-2]
-	}
+	//	}
+	s = strings.TrimSuffix(s, "()")
 	parts = strings.SplitN(s, ".", 2)
 	if num, err = strconv.ParseInt(parts[0], 10, 64); err != nil {
 		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 {
@@ -70,18 +72,18 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 			}
 			for _, c := range dec[0:lsd] {
 				if c < '0' || c > '9' {
-					return nil, errExpectedGot("fract", "digit", c)
+					return nil, ErrExpectedGot("fract", "digit", c)
 				}
 				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)
 			for _, c := range subParts[0] {
 				if c < '0' || c > '9' {
-					return nil, errExpectedGot("fract", "digit", c)
+					return nil, ErrExpectedGot("fract", "digit", c)
 				}
 				num = num*10 + int64(c-'0')
 				sub = sub*10 + int64(c-'0')
@@ -94,7 +96,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 				p := subParts[1][0 : len(subParts[1])-1]
 				for _, c := range p {
 					if c < '0' || c > '9' {
-						return nil, errExpectedGot("fract", "digit", c)
+						return nil, ErrExpectedGot("fract", "digit", c)
 					}
 					num = num*10 + int64(c-'0')
 					den = den*10 + 9
@@ -102,7 +104,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 				den *= mul
 			}
 			num -= sub
-			f = newFraction(sign*num, den)
+			f = NewFraction(sign*num, den)
 		}
 	}
 exit:
@@ -112,7 +114,15 @@ 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)
 }
 
@@ -123,36 +133,38 @@ func (f *FractionType) String() string {
 func (f *FractionType) ToString(opt FmtOpt) string {
 	var sb strings.Builder
 	if opt&MultiLine == 0 {
-		sb.WriteString(fmt.Sprintf("%d|%d", f.num, f.den))
+		sb.WriteString(fmt.Sprintf("%d:%d", f.num, f.den))
 	} else {
-		var s, num string
+		var sign, num string
 		if f.num < 0 && opt&TTY == 0 {
 			num = strconv.FormatInt(-f.num, 10)
-			s = "-"
+			sign = "-"
 		} else {
 			num = strconv.FormatInt(f.num, 10)
 		}
 		den := strconv.FormatInt(f.den, 10)
 		size := max(len(num), len(den))
 		if opt&TTY != 0 {
-			sb.WriteString(fmt.Sprintf("\x1b[4m%[1]*s\x1b[0m\n", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, s+num)))
+			sNum := fmt.Sprintf("\x1b[4m%[1]*s\x1b[0m\n", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, sign+num))
+			sb.WriteString(sNum)
 		} else {
-			if len(s) > 0 {
+			if len(sign) > 0 {
 				sb.WriteString("  ")
 			}
 			sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, num)))
 			sb.WriteByte('\n')
-			if len(s) > 0 {
+			if len(sign) > 0 {
-				sb.WriteString(s)
+				sb.WriteString(sign)
 				sb.WriteByte(' ')
 			}
 			sb.WriteString(strings.Repeat("-", size))
 			sb.WriteByte('\n')
-			if len(s) > 0 {
+			if len(sign) > 0 {
 				sb.WriteString("  ")
 			}
 		}
-		sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den)))
+		sDen := fmt.Sprintf("%[1]*s", size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den))
+		sb.WriteString(sDen)
 	}
 
 	return sb.String()
@@ -165,7 +177,7 @@ 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
 	}
@@ -186,21 +198,21 @@ 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) {
+func MulFract(f1, f2 *FractionType) (prod *FractionType) {
-	prod = newFraction(f1.num*f2.num, f1.den*f2.den)
+	prod = NewFraction(f1.num*f2.num, f1.den*f2.den)
 	return
 }
 
@@ -209,11 +221,12 @@ 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
 }
 
@@ -227,12 +240,12 @@ 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 {
@@ -247,7 +260,7 @@ 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
@@ -262,8 +275,9 @@ func cmpAnyFract(af1, af2 any) (result int, err error) {
 //	=0 if af1 == af2
 //	>0 if af1 > af2
 func cmpFract(f1, f2 *FractionType) (result int) {
+	if f1 != nil && f2 != nil {
 		f2.num = -f2.num
-	f := sumFract(f1, f2)
+		f := SumFract(f1, f2)
 		if f.num < 0 {
 			result = -1
 		} else if f.num > 0 {
@@ -271,16 +285,17 @@ func cmpFract(f1, f2 *FractionType) (result int) {
 		} 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 {
@@ -289,7 +304,7 @@ 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
@@ -303,7 +318,7 @@ 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
@@ -311,7 +326,6 @@ func divAnyFract(af1, af2 any) (quot any, err error) {
 	if f2.num == 0 {
 		err = errors.New("division by zero")
 		return
-		return
 	}
 	if f1.num == 0 || f2.den == 0 {
 		quot = 0
@@ -343,7 +357,7 @@ 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
@@ -353,7 +367,19 @@ 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

@@ -0,0 +1,95 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iterator.go
+package kern
+
+import (
+	// "errors"
+	"fmt"
+	"slices"
+)
+
+// Operator names
+
+const (
+	InitName    = "init"
+	CleanName   = "clean"
+	ResetName   = "reset"
+	NextName    = "next"
+	CurrentName = "current"
+	IndexName   = "index"
+	CountName   = "count"
+	FilterName  = "filter"
+	MapName     = "map"
+	KeyName     = "key"
+	ValueName   = "value"
+)
+
+type Iterator interface {
+	Typer
+	fmt.Stringer
+	Next() (item any, err error) // must return io.EOF after the last item
+	Current() (item any, err error)
+	Index() int64
+	Count() int64
+	HasOperation(name string) bool
+	CallOperation(name string, args map[string]any) (value any, err error)
+}
+
+type ExtIterator interface {
+	Iterator
+	Reset() error
+	Clean() error
+}
+
+func ErrNoOperation(name string) error {
+	return fmt.Errorf("no %s() function defined in the data-source", name)
+}
+
+func IsIterator(v any) (ok bool) {
+	_, ok = v.(Iterator)
+	return
+}
+
+type IteratorBase struct {
+	ItemIndex int64
+	ItemCount int64
+	current   any
+}
+
+func (it *IteratorBase) Current() (item any, err error) {
+	return it.current, nil
+}
+
+func (it *IteratorBase) Index() int64 {
+	return it.ItemIndex
+}
+
+func (it *IteratorBase) Count() int64 {
+	return it.ItemCount
+}
+
+func (it *IteratorBase) HasOperation(name string) bool {
+	return slices.Contains([]string{NextName, IndexName, CountName, CurrentName}, name)
+}
+
+func (it *IteratorBase) Clean() (err error) {
+	return
+}
+
+func (it *IteratorBase) Reset() (err error) {
+	it.ItemIndex = -1
+	it.ItemCount = 0
+	it.current = nil
+	return
+}
+
+func (it *IteratorBase) Increment() {
+	it.ItemIndex++
+	it.ItemCount++
+}
+
+func (it *IteratorBase) SetCurrent(v any) {
+	it.current = v
+}

kern/linked-list-type.go

@@ -0,0 +1,130 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// linked-list-type.go
+package kern
+
+import (
+	"strings"
+)
+
+const LinkedListTypeName = "lisked-list"
+const MaxUint64Allowed = uint64(9_223_372_036_854_775_807)
+
+func IsLinkedList(v any) (ok bool) {
+	_, ok = v.(*LinkedList)
+	return ok
+}
+
+func NewLinkedListA(listAny ...any) (list *LinkedList) {
+	if listAny == nil {
+		listAny = []any{}
+	}
+	list = NewLinkedList()
+	for _, item := range listAny {
+		list.PushBack(FixAnyNumber(item))
+	}
+	return
+}
+
+func LinkedListFromStrings(stringList []string) (list *LinkedList) {
+	list = NewLinkedList()
+	for _, s := range stringList {
+		list.PushBack(s)
+	}
+	return
+}
+
+func (ls *LinkedList) ToString(opt FmtOpt) (s string) {
+	indent := GetFormatIndent(opt)
+	flags := GetFormatFlags(opt)
+
+	var sb strings.Builder
+	sb.WriteString("[<")
+	if ls.Len() > 0 {
+		innerOpt := MakeFormatOptions(flags, indent+1)
+		nest := strings.Repeat("  ", indent+1)
+
+		if flags&MultiLine != 0 {
+			sb.WriteByte('\n')
+			sb.WriteString(nest)
+		}
+
+		i := 0
+		for item := ls.FirstNode(); item != nil; item = item.Next() {
+			if i > 0 {
+				if flags&MultiLine != 0 {
+					sb.WriteString(",\n")
+					sb.WriteString(nest)
+				} else {
+					sb.WriteString(", ")
+				}
+			}
+			// data := item.Data()
+			// if s, ok := data.(string); ok {
+			// 	sb.WriteByte('"')
+			// 	sb.WriteString(s)
+			// 	sb.WriteByte('"')
+			// } else if formatter, ok := data.(Formatter); ok {
+			// 	sb.WriteString(formatter.ToString(innerOpt))
+			// } else {
+			// 	fmt.Fprintf(&sb, "%v", data)
+			// }
+			Format(&sb, item.Data(), innerOpt)
+			i++
+		}
+		if flags&MultiLine != 0 {
+			sb.WriteByte('\n')
+			sb.WriteString(strings.Repeat("  ", indent))
+		}
+	}
+	sb.WriteString(">]")
+	s = sb.String()
+	if flags&Truncate != 0 && len(s) > TruncateSize {
+		s = TruncateString(s)
+	}
+	return
+}
+
+func (ls *LinkedList) String() string {
+	return ls.ToString(0)
+}
+
+func (ls *LinkedList) TypeName() string {
+	return LinkedListTypeName
+}
+
+// func (ls *LinkedList) Contains(t *ListType) (answer bool) {
+// 	if len(*ls) >= len(*t) {
+// 		answer = true
+// 		for _, item := range *t {
+// 			if answer = ls.IndexDeepSameCmp(item) >= 0; !answer {
+// 				break
+// 			}
+// 		}
+// 	}
+// 	return
+// }
+
+func (ls1 *LinkedList) Equals(ls2 *LinkedList) (answer bool) {
+	if ls2 != nil && ls1.Len() == ls2.Len() {
+		answer = true
+		i2 := ls2.FirstNode()
+		for i1 := ls1.FirstNode(); i1 != nil; i1 = i1.Next() {
+			if !Equal(i1.Data(), i2.Data()) {
+				answer = false
+				break
+			}
+			i2 = i2.Next()
+		}
+	}
+	return
+}
+
+func (ls1 *LinkedList) Clone() (ls2 *LinkedList) {
+	ls2 = NewLinkedListA()
+	for i1 := ls1.FirstNode(); i1 != nil; i1 = i1.Next() {
+		ls2.PushBack(Clone(i1.Data()))
+	}
+	return
+}

kern/linked-list.go

@@ -0,0 +1,284 @@
+// simple-list project slist.go
+package kern
+
+import (
+	"fmt"
+)
+
+type ListNode struct {
+	data any
+	next *ListNode
+}
+
+func (node *ListNode) Next() *ListNode {
+	return node.next
+}
+
+func (self *ListNode) Data() any {
+	return self.data
+}
+
+type LinkedList struct {
+	count int
+	first *ListNode
+	last  *ListNode
+}
+
+func NewLinkedList() (list *LinkedList) {
+	list = &LinkedList{0, nil, nil}
+	return
+}
+
+func (ls *LinkedList) Len() int {
+	return ls.count
+}
+
+func (ls *LinkedList) Empty() bool {
+	return ls.count == 0
+}
+
+func (ls *LinkedList) PushFront(data any) *ListNode {
+	ls.first = &ListNode{data, ls.first}
+	if ls.last == nil {
+		ls.last = ls.first
+	}
+	ls.count++
+	return ls.first
+}
+
+func (ls *LinkedList) SeqPushFront(data any) (result *LinkedList) {
+	switch seq := data.(type) {
+	case Iterator:
+		result = ls.IterPushFront(seq)
+	default:
+		ls.PushFront(data)
+		result = ls
+	}
+	return
+}
+
+func (ls *LinkedList) IterPushFront(it Iterator) *LinkedList {
+	for item, err1 := it.Next(); err1 == nil; item, err1 = it.Next() {
+		ls.PushFront(item)
+	}
+	return ls
+}
+
+func (ls *LinkedList) PushBack(data any) (node *ListNode) {
+	node = &ListNode{data, nil}
+	if ls.last != nil {
+		ls.last.next = node
+	}
+	ls.last = node
+	if ls.first == nil {
+		ls.first = node
+	}
+	ls.count++
+	return
+}
+
+func (ls *LinkedList) SeqPushBack(data any) (result *LinkedList) {
+	switch seq := data.(type) {
+	case Iterator:
+		result = ls.IterPushBack(seq)
+	default:
+		ls.PushBack(data)
+		result = ls
+	}
+	return
+}
+
+func (ls *LinkedList) IterPushBack(it Iterator) *LinkedList {
+	for item, err1 := it.Next(); err1 == nil; item, err1 = it.Next() {
+		ls.PushBack(item)
+	}
+	return ls
+}
+
+func (ls *LinkedList) FirstNode() *ListNode {
+	return ls.first
+}
+
+func (ls *LinkedList) First() (data any, err error) {
+	if ls.first != nil {
+		data = ls.first.data
+	} else {
+		err = errorListEmpty()
+	}
+	return
+}
+
+func (ls *LinkedList) LastNode() *ListNode {
+	return ls.last
+}
+
+func (ls *LinkedList) Last() (data interface{}, err error) {
+	if ls.last != nil {
+		data = ls.last.data
+	} else {
+		err = errorListEmpty()
+	}
+	return
+}
+
+func (ls *LinkedList) NodeAt(index int) (node *ListNode, err error) {
+	if ls.count == 0 {
+		err = errorListEmpty()
+	} else if index > ls.count {
+		err = errorOutOfRange()
+	} else if index == ls.count-1 {
+		node = ls.last
+	} else {
+		current := ls.first
+		for range index {
+			current = current.next
+		}
+		node = current
+	}
+	return
+}
+
+func (ls *LinkedList) At(index int) (data interface{}, err error) {
+	node, err := ls.NodeAt(index)
+	if err == nil {
+		data = node.data
+	}
+	return
+}
+
+func (ls *LinkedList) Insert(index int, data any) *ListNode {
+	var prev *ListNode
+
+	prev = nil
+	current := ls.first
+	for pos := 0; current != nil && pos < index; pos++ {
+		prev = current
+		current = current.next
+	}
+
+	node := &ListNode{data, current}
+
+	if prev != nil {
+		prev.next = node
+	}
+
+	if ls.first == current {
+		ls.first = node
+	}
+	if node.next == nil {
+		ls.last = node
+	}
+	ls.count++
+	return node
+}
+
+func (ls *LinkedList) PushBackStringArray(items []string) {
+	for _, v := range items {
+		ls.PushBack(v)
+	}
+}
+
+func (ls *LinkedList) Sub(start, end int) (subList *LinkedList) {
+	subList = NewLinkedList()
+	if node, err := ls.NodeAt(start); err == nil {
+		for i := start; i < end && node != nil; i++ {
+			subList.PushBack(node.data)
+			node = node.next
+		}
+	}
+	return
+}
+
+// type TraverseOperator func(index int, elem interface{}, userData interface{}) (err error)
+
+// func (self *LinkedList) Traverse(op TraverseOperator, user_data interface{}) (err error) {
+// 	index := int(0)
+// 	for current := self.first; current != nil; current = current.next {
+// 		err = op(index, current.data, user_data)
+// 		if err != nil {
+// 			break
+// 		}
+// 		index++
+// 	}
+// 	return
+// }
+
+// func (self *LinkedList) Traverse2(observer Observer, abortOnError bool) (err error) {
+// 	index := int(0)
+// 	for current := self.first; current != nil; current = current.next {
+// 		err = observer.Observe(current, index)
+// 		if err != nil && abortOnError {
+// 			break
+// 		}
+// 		index++
+// 	}
+// 	return
+// }
+
+type EqualFunc func(current, target any) bool
+
+func (ls *LinkedList) FindFirst(eqFunc EqualFunc, targetData any) (targetNode *ListNode) {
+	for current := ls.first; current != nil && targetNode == nil; current = current.next {
+		if eqFunc(current.data, targetData) {
+			targetNode = current
+		}
+	}
+	return
+}
+
+func (ls *LinkedList) FindNext(eqFunc EqualFunc, startNode *ListNode) (targetNode *ListNode) {
+	if startNode != nil {
+		for current := startNode.next; current != nil && targetNode == nil; current = current.next {
+			if eqFunc(current.data, startNode.Data()) {
+				targetNode = current
+			}
+		}
+	}
+	return
+}
+
+// type DataFeeder func(user_data interface{}) interface{}
+// type NodeObserver func(node *ListNode, index int, userData interface{})
+
+// func (self *LinkedList) FeedTail(feeder DataFeeder, feederUserData interface{}, observer NodeObserver, observerUserData interface{}) (count int) {
+// 	count = 0
+// 	for item := feeder(feederUserData); item != nil; item = feeder(feederUserData) {
+// 		// fmt.Println("Item", count, item)
+// 		node := self.PushBack(item)
+// 		if observer != nil {
+// 			observer(node, count, observerUserData)
+// 		}
+// 		count++
+// 	}
+// 	return
+// }
+
+// func (self *LinkedList) FeedTail2(feeder Feeder, observer Observer, abortOnError bool) (count int, err error) {
+// 	count = 0
+// 	// item := feeder.Next()
+// 	for item, err1 := feeder.Next(); item != nil; item, err1 = feeder.Next() {
+// 		if err1 != nil {
+// 			if err == nil {
+// 				err = err1
+// 			}
+// 			if abortOnError {
+// 				break
+// 			}
+// 		}
+// 		// fmt.Println("Item", count, item)
+// 		node := self.PushBack(item)
+// 		if observer != nil {
+// 			observer.Observe(node, count)
+// 		}
+// 		count++
+// 	}
+// 	return
+// }
+
+func errorListEmpty() error {
+	return fmt.Errorf("List is empty")
+}
+
+func errorOutOfRange() error {
+	return fmt.Errorf("Out of range")
+}

kern/list-type.go

@@ -0,0 +1,203 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// list-type.go
+package kern
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+type ListType []any
+
+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) {
+	if listAny != nil {
+		ls := make(ListType, len(listAny))
+		copy(ls, listAny)
+		list = &ls
+	}
+	return
+}
+
+func MakeList(length, capacity int) (list *ListType) {
+	if capacity < length {
+		capacity = length
+	}
+	ls := make(ListType, length, capacity)
+	list = &ls
+	return
+}
+
+func ListFromStrings(stringList []string) (list *ListType) {
+	list = MakeList(len(stringList), 0)
+	for i, s := range stringList {
+		(*list)[i] = s
+	}
+	return
+}
+
+func (ls *ListType) ToString(opt FmtOpt) (s string) {
+	indent := GetFormatIndent(opt)
+	flags := GetFormatFlags(opt)
+
+	var sb strings.Builder
+	sb.WriteByte('[')
+	if len(*ls) > 0 {
+		innerOpt := MakeFormatOptions(flags, indent+1)
+		nest := strings.Repeat("  ", indent+1)
+
+		if flags&MultiLine != 0 {
+			sb.WriteByte('\n')
+			sb.WriteString(nest)
+		}
+		for i, item := range []any(*ls) {
+			if i > 0 {
+				if flags&MultiLine != 0 {
+					sb.WriteString(",\n")
+					sb.WriteString(nest)
+				} else {
+					sb.WriteString(", ")
+				}
+			}
+			Format(&sb, item, innerOpt)
+		}
+		if flags&MultiLine != 0 {
+			sb.WriteByte('\n')
+			sb.WriteString(strings.Repeat("  ", indent))
+		}
+	}
+	sb.WriteByte(']')
+	s = sb.String()
+	if flags&Truncate != 0 && len(s) > TruncateSize {
+		s = TruncateString(s)
+	}
+	return
+}
+
+func (ls *ListType) String() string {
+	return ls.ToString(0)
+}
+
+func (ls *ListType) TypeName() string {
+	return "list"
+}
+
+func (ls *ListType) Contains(t *ListType) (answer bool) {
+	if len(*ls) >= len(*t) {
+		answer = true
+		for _, item := range *t {
+			if answer = ls.IndexDeepSameCmp(item) >= 0; !answer {
+				break
+			}
+		}
+	}
+	return
+}
+
+func (ls *ListType) Equals(ls2 ListType) (answer bool) {
+	if ls2 != nil && len(*ls) == len(ls2) {
+		answer = true
+		for index, i1 := range *ls {
+			// if !reflect.DeepEqual(i1, ls2[index]) {
+			// 	answer = false
+			// 	break
+			// }
+			if !Equal(i1, ls2[index]) {
+				answer = false
+				break
+			}
+		}
+	}
+	return
+}
+
+func (ls1 *ListType) Clone() (ls2 *ListType) {
+	ls := make(ListType, len(*ls1))
+	for i, item := range *ls1 {
+		ls[i] = Clone(item)
+	}
+	ls2 = &ls
+	return
+}
+
+func (ls *ListType) IndexDeepSameCmp(target any) (index int) {
+	var eq bool
+	var err error
+	index = -1
+	for i, item := range *ls {
+		if eq, err = deepSame(item, target, SameContent); err != nil {
+			break
+		} else if eq {
+			index = i
+			break
+		}
+	}
+	return
+}
+
+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 {
+				same = false
+				break
+			}
+		}
+	}
+	return
+}
+
+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)
+			}
+		} else {
+			var cmp int
+			if cmp, err = CmpAnyFract(a, b); err == nil {
+				eq = cmp == 0
+			}
+		}
+	} else if deepCmp != nil && IsList(a) && IsList(b) {
+		eq, err = deepCmp(a, b)
+	} else {
+		eq = reflect.DeepEqual(a, b)
+	}
+
+	return
+}
+
+func (ls *ListType) SetItem(index int64, value any) (err error) {
+	if index >= 0 && index < int64(len(*ls)) {
+		(*ls)[index] = value
+	} else {
+		err = fmt.Errorf("index %d out of bounds (0, %d)", index, len(*ls)-1)
+	}
+	return
+}
+
+func (ls *ListType) AppendItem(value any) {
+	*ls = append(*ls, value)
+}

kern/number.go

@@ -0,0 +1,120 @@
+// 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 FixAnyNumber(v any) (fixed any) {
+	switch unboxed := v.(type) {
+	case int:
+		fixed = int64(unboxed)
+	case int8:
+		fixed = int64(unboxed)
+	case int16:
+		fixed = int64(unboxed)
+	case int32:
+		fixed = int64(unboxed)
+	case uint:
+		fixed = int64(unboxed)
+	case uint8:
+		fixed = int64(unboxed)
+	case uint16:
+		fixed = int64(unboxed)
+	case uint32:
+		fixed = int64(unboxed)
+	case uint64:
+		if unboxed <= MaxUint64Allowed {
+			fixed = int64(unboxed)
+		} else {
+			fixed = float64(unboxed)
+		}
+	case float32:
+		fixed = float64(unboxed)
+	default:
+		fixed = v
+	}
+	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

@@ -0,0 +1,9 @@
+//go:build darwin
+
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// lib-ext-darwin.go
+package expr
+
+const SHAREDLIBRARY_EXTENSION = ".dylib"

lib-ext-linux.go

@@ -0,0 +1,9 @@
+//go:build linux
+
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// lib-ext-linux.go
+package expr
+
+const SHAREDLIBRARY_EXTENSION = ".so"

lib-ext-windows.go

@@ -0,0 +1,9 @@
+//go:build windows
+
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// lib-ext-windows.go
+package expr
+
+const SHAREDLIBRARY_EXTENSION = ".dll"

linked-list-iterator.go

@@ -0,0 +1,102 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// list-iterator.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type LinkedListIterator struct {
+	a       *kern.LinkedList
+	count   int64
+	index   int64
+	current *kern.ListNode
+}
+
+func NewLinkedListIterator(list *kern.LinkedList, args []any) (it *LinkedListIterator) {
+	it = &LinkedListIterator{a: list, count: 0, index: -1, current: list.FirstNode()}
+	return
+}
+
+func (it *LinkedListIterator) String() string {
+	var l = int64(0)
+	if it.a != nil {
+		l = int64(it.a.Len())
+	}
+	return fmt.Sprintf("$([<#%d>])", l)
+}
+
+func (it *LinkedListIterator) TypeName() string {
+	return "LinkedListIterator"
+}
+
+func (it *LinkedListIterator) HasOperation(name string) bool {
+	yes := slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName}, name)
+	return yes
+}
+
+func (it *LinkedListIterator) 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 *LinkedListIterator) Current() (item any, err error) {
+	if it.current != nil {
+		item = it.current.Data()
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (it *LinkedListIterator) Next() (item any, err error) {
+	if it.current != nil {
+		item = it.current.Data()
+		it.current = it.current.Next()
+		it.index++
+		it.count++
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (it *LinkedListIterator) Index() int64 {
+	return it.index
+}
+
+func (it *LinkedListIterator) Count() int64 {
+	return it.count
+}
+
+func (it *LinkedListIterator) Reset() error {
+	it.current = it.a.FirstNode()
+	it.index = -1
+	it.count = 0
+	return nil
+}
+
+func (it *LinkedListIterator) Clean() error {
+	return nil
+}

list-iterator.go

@@ -0,0 +1,149 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// list-iterator.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type ListIterator struct {
+	a     *kern.ListType
+	count int64
+	index int64
+	start int64
+	stop  int64
+	step  int64
+}
+
+func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
+	var argc int = 0
+	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 := kern.ToGoInt64(args[0], "start index"); err == nil {
+			if i < 0 {
+				i = listLen + i
+			}
+			it.start = i
+		}
+		if argc >= 2 {
+			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 := kern.ToGoInt64(args[2], "step"); err == nil {
+					if i < 0 {
+						i = -i
+					}
+					if it.start > it.stop {
+						it.step = -i
+					} else {
+						it.step = i
+					}
+				}
+			}
+		}
+	}
+	it.index = it.start - it.step
+	return
+}
+
+func NewArrayIterator(array []any) (it *ListIterator) {
+	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 = int64(0)
+	if it.a != nil {
+		l = int64(len(*it.a))
+	}
+	return fmt.Sprintf("$([#%d])", l)
+}
+
+func (it *ListIterator) TypeName() string {
+	return "ListIterator"
+}
+
+func (it *ListIterator) HasOperation(name string) bool {
+	//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 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 *ListIterator) Current() (item any, err error) {
+	a := *(it.a)
+	if it.start <= 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 < int64(len(a)) && it.index >= it.stop && it.index <= it.start {
+			item = a[it.index]
+		} else {
+			err = io.EOF
+		}
+
+	}
+	return
+}
+
+func (it *ListIterator) Next() (item any, err error) {
+	it.index += it.step
+	if item, err = it.Current(); err != io.EOF {
+		it.count++
+	}
+	return
+}
+
+func (it *ListIterator) Index() int64 {
+	return it.index
+}
+
+func (it *ListIterator) Count() int64 {
+	return it.count
+}
+
+func (it *ListIterator) Reset() error {
+	it.index = it.start - it.step
+	it.count = 0
+	return nil
+}
+
+func (it *ListIterator) Clean() error {
+	return nil
+}

list-type.go

@@ -1,162 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// list-type.go
-package expr
-
-import (
-	"fmt"
-	"reflect"
-	"strings"
-)
-
-type ListType []any
-
-func newListA(listAny ...any) (list *ListType) {
-	if listAny == nil {
-		listAny = []any{}
-	}
-	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
-		}
-		list = &ls
-	}
-	return
-}
-
-func (ls *ListType) ToString(opt FmtOpt) (s string) {
-	var sb strings.Builder
-	sb.WriteByte('[')
-	if len(*ls) > 0 {
-		if opt&MultiLine != 0 {
-			sb.WriteString("\n  ")
-		}
-		for i, item := range []any(*ls) {
-			if i > 0 {
-				if opt&MultiLine != 0 {
-					sb.WriteString(",\n  ")
-				} else {
-					sb.WriteString(", ")
-				}
-			}
-			if s, ok := item.(string); ok {
-				sb.WriteByte('"')
-				sb.WriteString(s)
-				sb.WriteByte('"')
-			} else {
-				sb.WriteString(fmt.Sprintf("%v", item))
-			}
-		}
-		if opt&MultiLine != 0 {
-			sb.WriteByte('\n')
-		}
-	}
-	sb.WriteByte(']')
-	s = sb.String()
-	if opt&Truncate != 0 && len(s) > TruncateSize {
-		s = TruncateString(s)
-	}
-	return
-}
-
-func (ls *ListType) String() string {
-	return ls.ToString(0)
-}
-
-func (ls *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) {
-		answer = true
-		for _, item := range *t {
-			if answer = ls.indexDeepSameCmp(item) >= 0; !answer {
-				break
-			}
-		}
-	}
-	return
-}
-
-func (list *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 {
-			break
-		} else if eq {
-			index = i
-			break
-		}
-	}
-	return
-}
-
-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 {
-				same = false
-				break
-			}
-		}
-	}
-	return
-}
-
-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)
-			}
-		} else {
-			var cmp int
-			if cmp, err = cmpAnyFract(a, b); err == nil {
-				eq = cmp == 0
-			}
-		}
-	} else if deepCmp != nil && IsList(a) && IsList(b) {
-		eq, err = deepCmp(a, b)
-	} else {
-		eq = reflect.DeepEqual(a, b)
-	}
-
-	return
-}
-
-func (list *ListType) setItem(index int64, value any) (err error) {
-	if index >= 0 && index < int64(len(*list)) {
-		(*list)[index] = value
-	} else {
-		err = fmt.Errorf("index %d out of bounds (0, %d)", index, len(*list)-1)
-	}
-	return
-}
-

module-register.go

@@ -1,48 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// module-register.go
-package expr
-
-import (
-	"fmt"
-)
-
-type module struct {
-	importFunc  func(ExprContext)
-	description string
-	imported    bool
-}
-
-func newModule(importFunc func(ExprContext), description string) *module {
-	return &module{importFunc, description, false}
-}
-
-var moduleRegister map[string]*module
-
-func registerImport(name string, importFunc func(ExprContext), description string) {
-	if moduleRegister == nil {
-		moduleRegister = make(map[string]*module)
-	}
-	if _, exists := moduleRegister[name]; exists {
-		panic(fmt.Errorf("module %q already registered", name))
-	}
-	moduleRegister[name] = newModule(importFunc, description)
-}
-
-func IterateModules(op func(name, description string, imported bool) bool) {
-	if op != nil {
-		for name, mod := range moduleRegister {
-			if !op(name, mod.description, mod.imported) {
-				break
-			}
-		}
-	}
-}
-
-// ----
-func init() {
-	if moduleRegister == nil {
-		moduleRegister = make(map[string]*module)
-	}
-}

operand-dict.go

@@ -1,32 +1,43 @@
-// 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 {
+func newDictTerm(args map[any]*scan.Term) *scan.Term {
-	return &term{
+	return &scan.Term{
-		tk:       *NewValueToken(0, 0, SymDict, "{}", args),
+		Tk:       *scan.NewValueToken(0, 0, scan.SymDict, "{}", args),
-		parent:   nil,
+		Parent:   nil,
-		children: nil,
+		Children: nil,
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalDict,
+		EvalFunc: evalDict,
 	}
 }
 
 // -------- dict func
-func evalDict(ctx ExprContext, self *term) (v any, err error) {
+func evalDict(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	dict, _ := self.value().(map[any]*term)
+	dict, _ := opTerm.Value().(map[any]*scan.Term)
-	items := make(DictType, len(dict))
+	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
+		var keyValue any
+		if keyValue, err = (key.(*scan.Term)).Compute(ctx); err == nil {
+			if kern.IsInteger(keyValue) || kern.IsString(keyValue) {
+				items[keyValue] = param
+			} else {
+				err = key.(*scan.Term).Errorf("dict key can be integer or string, got %s", kern.TypeName(keyValue))
+			}
+		}
 	}
 	if err == nil {
 		v = &items

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 {
+func newExprTerm(root *scan.Term) *scan.Term {
-	tk := NewValueToken(root.tk.row, root.tk.col, SymExpression, root.source(), root)
+	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymExpression, root.Source(), root)
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		parent:   nil,
+		Parent:   nil,
-		children: nil,
+		Children: nil,
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalExpr,
+		EvalFunc: evalExpr,
 	}
 }
 
 // -------- eval expr
-func evalExpr(ctx ExprContext, self *term) (v any, err error) {
+func evalExpr(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	if expr, ok := self.value().(*term); ok {
+	if ast, ok := opTerm.Value().(*scan.Term); ok {
-		v, err = expr.compute(ctx)
+		v, err = ast.Compute(ctx)
 	} else {
-		err = fmt.Errorf("expression expected, got %T", self.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
@@ -6,100 +6,81 @@ package expr
 
 import (
 	"errors"
-	"fmt"
+
+	"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 {
+func newFuncCallTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
-	return &term{
+	var pos scan.TermPosition = scan.PosLeaf
-		tk:       *tk,
+	if len(args) > 0 {
-		parent:   nil,
+		pos = scan.PosMultifix
-		children: args,
+	}
-		position: posLeaf,
+	return &scan.Term{
-		priority: priValue,
+		Tk:       *tk,
-		evalFunc: evalFuncCall,
+		Parent:   nil,
+		Children: args,
+		Position: pos,
+		Priority: scan.PriValue,
+		EvalFunc: evalFuncCall,
 	}
 }
 
 // -------- eval func call
-func checkFunctionCall(ctx ExprContext, name string, varParams *[]any) (err error) {
+// func _evalFuncCall(ctx ExprContext, opTerm *term) (v any, err error) {
-	if info, exists, owner := GetFuncInfo(ctx, name); exists {
+// 	name, _ := opTerm.Tk.Value.(string)
-		passedCount := len(*varParams)
+// 	params := make([]any, len(opTerm.Children), len(opTerm.Children)+5)
-		if info.MinArgs() > passedCount {
+// 	for i, tree := range opTerm.Children {
-			err = errTooFewParams(name, info.MinArgs(), info.MaxArgs(), passedCount)
+// 		var param any
-		}
+// 		if param, err = tree.Compute(ctx); err != nil {
-		for i, p := range info.Params() {
+// 			break
-			if i >= passedCount {
+// 		}
-				if !p.IsOptional() {
+// 		params[i] = param
-					break
+// 	}
-				}
-				*varParams = append(*varParams, p.DefaultValue())
-			}
-		}
-		if err == nil && info.MaxArgs() >= 0 && info.MaxArgs() < len(*varParams) {
-			err = errTooMuchParams(name, info.MaxArgs(), len(*varParams))
-		}
-		if err == nil && owner != ctx {
-			ctx.RegisterFuncInfo(info)
-		}
-	} else {
-		err = fmt.Errorf("unknown function %s()", name)
-	}
-	return
-}
 
-func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
+// 	if err == nil {
-	ctx := cloneContext(parentCtx)
+// 		v, err = CallFunction(ctx, name, params)
-	name, _ := self.tk.Value.(string)
+// 	}
-	params := make([]any, len(self.children), len(self.children)+5)
+// 	return
-	for i, tree := range self.children {
+// }
-		var param any
-		if param, err = tree.compute(ctx); err != nil {
-			break
-		}
-		params[i] = param
-	}
 
-	if err == nil {
+func evalFuncCall(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-		if err = checkFunctionCall(ctx, name, &params); err == nil {
+	name, _ := opTerm.Tk.Value.(string)
-			if v, err = ctx.Call(name, params); err == nil {
+	v, err = kern.CallFunctionByTerm(ctx, name, opTerm)
-				exportObjects(parentCtx, ctx)
-			}
-		}
-	}
 	return
 }
 
 // -------- function definition term
-func newFuncDefTerm(tk *Token, args []*term) *term {
+func newFuncDefTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
-	return &term{
+	return &scan.Term{
-		tk:       *tk, // value is the expression body
+		Tk:       *tk, // value is the expression body
-		parent:   nil,
+		Parent:   nil,
-		children: args, // function params
+		Children: args, // function params
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalFuncDef,
+		EvalFunc: evalFuncDef,
 	}
 }
 
 // -------- eval func def
-func evalFuncDef(ctx ExprContext, self *term) (v any, err error) {
+func evalFuncDef(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	bodySpec := self.value()
+	bodySpec := opTerm.Value()
-	if expr, ok := bodySpec.(*ast); ok {
+	if ast, ok := bodySpec.(*scan.Ast); ok {
-		paramList := make([]ExprFuncParam, 0, len(self.children))
+		paramList := make([]kern.ExprFuncParam, 0, len(opTerm.Children))
-		for _, param := range self.children {
+		for _, param := range opTerm.Children {
 			var defValue any
-			flags := paramFlags(0)
+			flags := kern.FuncParamFlags(0)
-			if len(param.children) > 0 {
+			if len(param.Children) > 0 {
-				flags |= pfOptional
+				flags |= kern.PfDefault
-				if defValue, err = param.children[0].compute(ctx); err != nil {
+				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

@@ -1,52 +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-iterator.go
 package expr
 
 import (
-	"fmt"
 	"slices"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- iterator term
 
-func newDsIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
+func newIteratorTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
-	tk.Sym = SymIterator
+	tk.Sym = scan.SymIterator
-
+	return &scan.Term{
-	children := make([]*term, 0, 1+len(args))
+		Tk:       *tk,
-	children = append(children, dsTerm)
+		Parent:   nil,
-	children = append(children, args...)
+		Children: args,
-	return &term{
+		Position: scan.PosLeaf,
-		tk:       *tk,
+		Priority: scan.PriValue,
-		parent:   nil,
+		EvalFunc: evalIterator,
-		children: children,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalIterator,
-	}
-}
-
-func newIteratorTerm(tk *Token, args []*term) *term {
-	tk.Sym = SymIterator
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: args,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalIterator,
 	}
 }
 
 // -------- eval iterator
 
-func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
+func evalTermArray(ctx kern.ExprContext, terms []*scan.Term) (values []any, err error) {
-	values = make([]any, len(a))
+	values = make([]any, len(terms))
-	for i, t := range a {
+	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
@@ -55,27 +41,25 @@ func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
 	return
 }
 
-func evalFirstChild(ctx ExprContext, self *term) (value any, err error) {
+func evalFirstChild(ctx kern.ExprContext, iteratorTerm *scan.Term) (value any, err error) {
-	if len(self.children) < 1 || self.children[0] == nil {
+	if len(iteratorTerm.Children) < 1 || iteratorTerm.Children[0] == nil {
-		err = self.Errorf("missing the data-source parameter")
+		err = iteratorTerm.Errorf("missing the data-source parameter")
 		return
 	}
 
-	value, err = self.children[0].compute(ctx)
+	value, err = iteratorTerm.Children[0].Compute(ctx)
 	return
 }
 
-func getDataSourceDict(ctx ExprContext, self *term, firstChildValue any) (ds map[string]Functor, err error) {
+func getDataSourceDict(iteratorTerm *scan.Term, firstChildValue any) (ds map[string]kern.Functor, err error) {
-	// if dictAny, ok := firstChildValue.(map[any]any); ok {
+	if dictAny, ok := firstChildValue.(*kern.DictType); ok {
-	if dictAny, ok := firstChildValue.(*DictType); ok {
+		requiredFields := []string{kern.NextName}
-		requiredFields := []string{currentName, nextName}
+		fieldsMask := 0b1
-		fieldsMask := 0b11
 		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.(*funcDefFunctor); ok {
+				if functor, ok := item.(kern.Functor); ok {
-				if functor, ok := item.(Functor); ok {
 					ds[key] = functor
 					if index := slices.Index(requiredFields, key); index >= 0 {
 						foundFields |= 1 << index
@@ -91,64 +75,119 @@ func getDataSourceDict(ctx ExprContext, self *term, firstChildValue any) (ds map
 					missingFields = append(missingFields, field)
 				}
 			}
-			err = fmt.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, self *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, self); err != nil {
+	if firstChildValue, err = evalFirstChild(ctx, opTerm); err != nil {
 		return
 	}
 
-	if ds, err = getDataSourceDict(ctx, self, firstChildValue); err != nil {
+	if ds, err = getDataSourceDict(opTerm, firstChildValue); err != nil && ds == nil {
 		return
 	}
+	err = nil
 
 	if ds != nil {
-		dc := newDataCursor(ctx, ds)
+		if len(ds) > 0 {
-		if initFunc, exists := ds[initName]; exists && initFunc != nil {
+			var dc *dataCursor
+			dcCtx := ctx.Clone()
+			if initFunc, exists := ds[kern.InitName]; exists && initFunc != nil {
 				var args []any
-			if len(self.children) > 1 {
+				var resource any
-				if args, err = evalTermArray(ctx, self.children[1:]); err != nil {
+				if len(opTerm.Children) > 1 {
+					if args, err = evalTermArray(ctx, opTerm.Children[1:]); err != nil {
 						return
 					}
 				} else {
 					args = []any{}
 				}
 
-			initCtx := dc.ctx.Clone()
+				actualParams := kern.BindActualParams(initFunc, args)
-			if dc.resource, err = initFunc.Invoke(initCtx, initName, args); err != nil {
+
+				initCtx := ctx.Clone()
+				if resource, err = initFunc.InvokeNamed(initCtx, kern.InitName, actualParams); err != nil {
 					return
 				}
-			exportObjects(dc.ctx, initCtx)
+				kern.ExportObjects(dcCtx, initCtx)
+				dc = NewDataCursor(dcCtx, ds, resource)
+			} else {
+				dc = NewDataCursor(dcCtx, ds, nil)
 			}
 
-		dc.nextFunc, _ = ds[nextName]
-		dc.currentFunc, _ = ds[currentName]
-		dc.cleanFunc, _ = ds[cleanName]
-		dc.resetFunc, _ = ds[resetName]
-
 			v = dc
-	} else if list, ok := firstChildValue.(*ListType); ok {
+		} else {
+			if dictIt, ok := firstChildValue.(*kern.DictType); ok {
 				var args []any
-		if args, err = evalSibling(ctx, self.children, nil); err == nil {
+				if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
-			v = NewListIterator(list, args)
+					v, err = NewDictIterator(dictIt, args)
 				}
 			} else {
-		var list []any
+				err = opTerm.Children[0].Errorf("the data-source must be a dictionary")
-		if list, err = evalSibling(ctx, self.children, firstChildValue); err == nil {
+			}
-			v = NewArrayIterator(list)
+		}
+	} else if list, ok := firstChildValue.(*kern.ListType); ok {
+		var args []any
+		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
+			v = NewListIterator(list, args)
+		}
+	} else if list, ok := firstChildValue.(*kern.LinkedList); ok {
+		var args []any
+		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
+			v = NewLinkedListIterator(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 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
@@ -157,7 +196,7 @@ 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-linked-list.go

@@ -0,0 +1,43 @@
+// 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 newLinkedListTermA(args ...*scan.Term) *scan.Term {
+// 	return newLinkedListTerm(0, 0, args)
+// }
+
+func newLinkedListTerm(row, col int, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(row, col, scan.SymLinkedList, "[<>]", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalLinkedList,
+	}
+}
+
+// -------- list func
+func evalLinkedList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	list, _ := opTerm.Value().([]*scan.Term)
+	items := kern.NewLinkedList()
+	for _, tree := range list {
+		var param any
+		if param, err = tree.Compute(ctx); err != nil {
+			break
+		}
+		items.PushBack(param)
+	}
+	if err == nil {
+		v = items
+	}
+	return
+}

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 {
+func newListTerm(row, col int, args []*scan.Term) *scan.Term {
-	return &term{
+	return &scan.Term{
-		tk:       *NewValueToken(row, col, SymList, "[]", args),
+		Tk:       *scan.NewValueToken(row, col, scan.SymList, "[]", args),
-		parent:   nil,
+		Parent:   nil,
-		children: nil,
+		Children: nil,
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalList,
+		EvalFunc: evalList,
 	}
 }
 
 // -------- list func
-func evalList(ctx ExprContext, self *term) (v any, err error) {
+func evalList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	list, _ := self.value().([]*term)
+	list, _ := opTerm.Value().([]*scan.Term)
-	items := make(ListType, len(list))
+	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 {
+func newLiteralTerm(tk *scan.Token) *scan.Term {
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		parent:   nil,
+		Parent:   nil,
-		children: nil,
+		Children: nil,
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalLiteral,
+		EvalFunc: evalLiteral,
 	}
 }
 
 // -------- eval func
-func evalLiteral(ctx ExprContext, self *term) (v any, err error) {
+func evalLiteral(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	v = self.tk.Value
+	v = opTerm.Tk.Value
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymString, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymString, newLiteralTerm)
-	registerTermConstructor(SymInteger, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymInteger, newLiteralTerm)
-	registerTermConstructor(SymFloat, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFloat, newLiteralTerm)
-	registerTermConstructor(SymFraction, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFraction, newLiteralTerm)
-	registerTermConstructor(SymBool, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymBool, newLiteralTerm)
-	registerTermConstructor(SymKwNil, 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
+	filterList *scan.Term
-	caseExpr   Expr
+	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 {
+func newSelectorCaseTerm(row, col int, filterList *scan.Term, caseExpr kern.Expr) *scan.Term {
-	tk := NewValueToken(row, col, SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
+	tk := scan.NewValueToken(row, col, scan.SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		parent:   nil,
+		Parent:   nil,
-		children: nil,
+		Children: nil,
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalSelectorCase,
+		EvalFunc: evalSelectorCase,
 	}
 }
 
 // -------- eval selector case
-func evalSelectorCase(ctx ExprContext, self *term) (v any, err error) {
+func evalSelectorCase(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var ok bool
-	if v, ok = self.value().(*selectorCase); !ok {
+	if v, ok = opTerm.Value().(*selectorCase); !ok {
-		err = fmt.Errorf("selector-case expected, got %T", self.value())
+		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 {
+func newVarTerm(tk *scan.Token) *scan.Term {
-	t := &term{
+	t := &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		parent:   nil,
+		Parent:   nil,
-		children: nil,
+		Children: nil,
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalVar,
+		EvalFunc: evalVar,
 	}
-	t.tk.Sym = SymVariable
+	t.Tk.Sym = scan.SymVariable
 	return t
 }
 
 // -------- eval func
-func evalVar(ctx ExprContext, self *term) (v any, err error) {
+func evalVar(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var exists bool
-	name := self.source()
+	name := opTerm.Source()
-	if v, exists = GetVar(ctx, name); !exists {
+	if v, exists = ctx.GetVar(name); !exists {
-		if info, exists, _ := GetFuncInfo(ctx, 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, self *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymIdentifier, newVarTerm)
+	scan.RegisterTermConstructor(scan.SymIdentifier, newVarTerm)
 }

operator-assign.go

@@ -1,34 +1,60 @@
-// 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) {
+func newAssignTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		children: make([]*term, 0, 2),
+		Children: make([]*scan.Term, 0, 2),
-		position: posInfix,
+		Position: scan.PosInfix,
-		priority: priAssign,
+		Priority: scan.PriAssign,
-		evalFunc: evalAssign,
+		EvalFunc: evalAssign,
 	}
 }
 
-func assignCollectionItem(ctx ExprContext, collectionTerm, keyListTerm *term, value any) (err error) {
+func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	v, err = generalEvalAssign(ctx, opTerm, false)
+	return
+}
+
+func newDeepCopyAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAssign,
+		EvalFunc: evalDeepCopyAssign,
+	}
+}
+
+func evalDeepCopyAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	v, err = generalEvalAssign(ctx, opTerm, true)
+	return
+}
+
+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 {
+	} else if keyList, ok = keyListValue.(*kern.ListType); !ok || len(*keyList) != 1 {
-		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, typeName(keyListValue))
+		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, kern.TypeName(keyListValue))
 		return
 	}
 	if keyValue = (*keyList)[0]; keyValue == nil {
@@ -37,56 +63,99 @@ 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:
+	case *kern.DictType:
-		err = collection.setItem(keyValue, value)
+		collection.SetItem(keyValue, value)
 	default:
 		err = collectionTerm.Errorf("collection expected")
 	}
 	return
 }
 
-func assignValue(ctx ExprContext, leftTerm *term, v any) (err error) {
+func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any, deepCopy bool) (err error) {
-	if leftTerm.symbol() == SymIndex {
+	if leftTerm.Symbol() == scan.SymIndex {
-		err = assignCollectionItem(ctx, leftTerm.children[0], leftTerm.children[1], v)
+		err = assignCollectionItem(ctx, leftTerm.Children[0], leftTerm.Children[1], v)
 	} else {
-		ctx.UnsafeSetVar(leftTerm.source(), v)
+		if deepCopy {
+			v = kern.Clone(v)
+		}
+		ctx.UnsafeSetVar(leftTerm.Source(), v)
 	}
 	return
 }
 
-func evalAssign(ctx ExprContext, self *term) (v any, err error) {
+func evalAssignDictItem(ctx kern.ExprContext, dotTerm *scan.Term, valueTerm kern.Term) (v any, err error) {
-	if err = self.checkOperands(); err != nil {
+	var ok bool
+	var dictAny, dotKey any
+	var dict *kern.DictType
+
+	if err = dotTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := self.children[0]
+	dotLeftTerm := dotTerm.GetChild(0)
-	leftSym := leftTerm.symbol()
+	if dictAny, err = dotLeftTerm.Compute(ctx); err != nil {
-	if leftSym != SymVariable && leftSym != SymIndex {
+		return
-		err = leftTerm.tk.Errorf("left operand of %q must be a variable or a collection's item", self.tk.source)
+	}
+	if dict, ok = dictAny.(*kern.DictType); !ok {
+		err = dotTerm.Tk.ErrorExpectedGot(kern.DictTypeName)
 		return
 	}
 
-	rightChild := self.children[1]
+	dotRightTerm := dotTerm.Children[1]
+	dotRightSym := dotRightTerm.Symbol()
+	if dotRightSym == scan.SymVariable || dotRightSym == scan.SymString {
+		dotKey = util.UnquoteString(dotRightTerm.Source())
+	} else if dotKey, err = dotRightTerm.Compute(ctx); err != nil {
+		return
+	}
 
-	if v, err = rightChild.compute(ctx); err == nil {
+	if v, err = valueTerm.Compute(ctx); err != nil {
-		if functor, ok := v.(Functor); ok {
+		return
+	}
+
+	dict.SetItem(dotKey, v)
+	return
+}
+
+func generalEvalAssign(ctx kern.ExprContext, opTerm *scan.Term, deepCopy bool) (v any, err error) {
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	leftTerm := opTerm.Children[0]
+	leftSym := leftTerm.Symbol()
+	if leftSym == scan.SymDot {
+		return evalAssignDictItem(ctx, opTerm.Children[0], opTerm.GetChild(1))
+	} else 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]
+
+	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 = self.Errorf("unknown function %s()", rightChild.source())
+					err = opTerm.Errorf("unknown function %s()", rightChild.Source())
 				}
 			} else {
-			err = assignValue(ctx, leftTerm, v)
+				err = assignValue(ctx, leftTerm, v, deepCopy)
+			}
+		} else {
+			err = assignValue(ctx, leftTerm, v, deepCopy)
 		}
 	}
 	if err != nil {
@@ -95,7 +164,123 @@ func evalAssign(ctx ExprContext, self *term) (v any, err error) {
 	return
 }
 
+//-------- assign term
+
+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 kern.ExprContext, collectionTerm, keyListTerm *scan.Term) (value any, err error) {
+	var collectionValue, keyListValue, keyValue any
+	var keyList *kern.ListType
+	var ok bool
+
+	if collectionValue, err = collectionTerm.Compute(ctx); err != nil {
+		return
+	}
+
+	if keyListValue, err = keyListTerm.Compute(ctx); err != nil {
+		return
+	} 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 {
+		err = keyListTerm.Errorf("index/key is nil")
+		return
+	}
+
+	switch collection := collectionValue.(type) {
+	case *kern.ListType:
+		if index, ok := keyValue.(int64); ok {
+			value = (*collection)[index]
+		} else {
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
+		}
+	case *kern.DictType:
+		value = (*collection)[keyValue]
+	default:
+		err = collectionTerm.Errorf("collection expected")
+	}
+	return
+}
+
+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())
+	}
+	return
+}
+
+func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var rightValue, leftValue any
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	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]
+
+	if rightValue, err = rightChild.Compute(ctx); err == nil {
+		if leftValue, err = getAssignValue(ctx, leftTerm); err == nil {
+			switch opTerm.Symbol() {
+			case scan.SymPlusEqual:
+				v, err = sumValues(opTerm, leftValue, rightValue)
+			case scan.SymMinusEqual:
+				v, err = diffValues(opTerm, leftValue, rightValue)
+			case scan.SymStarEqual:
+				v, err = mulValues(opTerm, leftValue, rightValue)
+			case scan.SymSlashEqual:
+				v, err = divValues(opTerm, leftValue, rightValue)
+			case scan.SymPercEqual:
+				v, err = remainderValues(opTerm, leftValue, rightValue)
+			case scan.SymAmpersandEqual:
+				v, err = bitwiseAnd(opTerm, leftValue, rightValue)
+			case scan.SymVertBarEqual:
+				v, err = bitwiseOr(opTerm, leftValue, rightValue)
+			case scan.SymCaretEqual:
+				v, err = bitwiseXor(opTerm, leftValue, rightValue)
+			case scan.SymDoubleLessEqual:
+				v, err = bitLeftShift(opTerm, leftValue, rightValue)
+			case scan.SymDoubleGreaterEqual:
+				v, err = bitRightShift(opTerm, leftValue, rightValue)
+			default:
+				err = opTerm.Errorf("unsupported assign operator %q", opTerm.Source())
+			}
+			if err == nil {
+				err = assignValue(ctx, leftTerm, v, false)
+			}
+		}
+	}
+	return
+}
+
 // init
 func init() {
-	registerTermConstructor(SymEqual, newAssignTerm)
+	scan.RegisterTermConstructor(scan.SymEqual, newAssignTerm)
+	scan.RegisterTermConstructor(scan.SymColonEqual, newDeepCopyAssignTerm)
+	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

@@ -0,0 +1,159 @@
+// 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 *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 kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var value any
+
+	if value, err = opTerm.EvalPrefix(ctx); err != nil {
+		return
+	}
+
+	if kern.IsInteger(value) {
+		i, _ := value.(int64)
+		v = ^i
+	} else {
+		err = opTerm.ErrIncompatiblePrefixPostfixType(value)
+	}
+	return
+}
+
+//-------- Bitwise AND term
+
+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 *scan.Term, leftValue, rightValue any) (v any, err error) {
+	var leftInt, rightInt int64
+	var lok, rok bool
+
+	leftInt, lok = leftValue.(int64)
+	rightInt, rok = rightValue.(int64)
+
+	if lok && rok {
+		v = leftInt & rightInt
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+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 {
+		return
+	}
+	v, err = bitwiseAnd(opTerm, leftValue, rightValue)
+	return
+}
+
+//-------- Bitwise OR term
+
+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 *scan.Term, leftValue, rightValue any) (v any, err error) {
+	var leftInt, rightInt int64
+	var lok, rok bool
+
+	leftInt, lok = leftValue.(int64)
+	rightInt, rok = rightValue.(int64)
+
+	if lok && rok {
+		v = leftInt | rightInt
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+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 {
+		return
+	}
+
+	v, err = bitwiseOr(opTerm, leftValue, rightValue)
+	return
+}
+
+//-------- Bitwise XOR term
+
+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 *scan.Term, leftValue, rightValue any) (v any, err error) {
+	var leftInt, rightInt int64
+	var lok, rok bool
+
+	leftInt, lok = leftValue.(int64)
+	rightInt, rok = rightValue.(int64)
+
+	if lok && rok {
+		v = leftInt ^ rightInt
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+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 {
+		return
+	}
+
+	v, err = bitwiseXor(opTerm, leftValue, rightValue)
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymTilde, newBitwiseNotTerm)
+	scan.RegisterTermConstructor(scan.SymAmpersand, newBitwiseAndTerm)
+	scan.RegisterTermConstructor(scan.SymVertBar, newBitwiseOrTerm)
+	scan.RegisterTermConstructor(scan.SymCaret, newBitwiseXorTerm)
+}

operator-bool.go

@@ -1,54 +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) {
+func newNotTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		children: make([]*term, 0, 1),
+		Children: make([]*scan.Term, 0, 1),
-		position: posPrefix,
+		Position: scan.PosPrefix,
-		priority: priNot,
+		Priority: scan.PriNot,
-		evalFunc: evalNot,
+		EvalFunc: evalNot,
 	}
 }
 
-func evalNot(ctx ExprContext, self *term) (v any, err error) {
+func evalNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if rightValue, err = self.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 = self.errIncompatibleType(rightValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
 	}
 	return
 }
 
 //-------- AND term
 
-func newAndTerm(tk *Token) (inst *term) {
+func newAndTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk: *tk,
+		Tk:       *tk,
-		// class:    classOperator,
+		Children: make([]*scan.Term, 0, 2),
-		// kind:     kindBool,
+		Position: scan.PosInfix,
-		children: make([]*term, 0, 2),
+		Priority: scan.PriAnd,
-		position: posInfix,
+		EvalFunc: evalAnd,
-		priority: priAnd,
-		evalFunc: evalAnd,
 	}
 }
 
-func evalAnd(ctx ExprContext, self *term) (v any, err error) {
+func evalAnd(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
-	if isEnabled(ctx, ControlBoolShortcut) {
+	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
 		v, err = evalAndWithShortcut(ctx, self)
 	} else {
 		v, err = evalAndWithoutShortcut(ctx, self)
@@ -56,47 +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)
+	leftBool, lok = kern.ToBool(leftValue)
-	rightBool, rok = toBool(rightValue)
+	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 {
+	if leftBool, lok := kern.ToBool(leftValue); !lok {
-		err = fmt.Errorf("got %T as left operand type of 'and' operator, it must be bool", leftBool)
+		// err = fmt.Errorf("got %s as left operand type of 'AND' operator, it must be bool", expr.TypeName(leftValue))
-		return
+		// return
+		err = self.ErrIncompatibleType(leftValue, "left")
 	} else if !leftBool {
 		v = false
-	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
-		if rightBool, rok := toBool(rightValue); rok {
+		if rightBool, rok := kern.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
-			err = self.errIncompatibleTypes(leftValue, rightValue)
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	}
 	return
@@ -104,20 +108,18 @@ func evalAndWithShortcut(ctx ExprContext, self *term) (v any, err error) {
 
 //-------- OR term
 
-func newOrTerm(tk *Token) (inst *term) {
+func newOrTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk: *tk,
+		Tk:       *tk,
-		// class:    classOperator,
+		Children: make([]*scan.Term, 0, 2),
-		// kind:     kindBool,
+		Position: scan.PosInfix,
-		children: make([]*term, 0, 2),
+		Priority: scan.PriOr,
-		position: posInfix,
+		EvalFunc: evalOr,
-		priority: priOr,
-		evalFunc: evalOr,
 	}
 }
 
-func evalOr(ctx ExprContext, self *term) (v any, err error) {
+func evalOr(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
-	if isEnabled(ctx, ControlBoolShortcut) {
+	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
 		v, err = evalOrWithShortcut(ctx, self)
 	} else {
 		v, err = evalOrWithoutShortcut(ctx, self)
@@ -125,47 +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)
+	leftBool, lok = kern.ToBool(leftValue)
-	rightBool, rok = toBool(rightValue)
+	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 {
+	if leftBool, lok := kern.ToBool(leftValue); !lok {
-		err = fmt.Errorf("got %T as left operand type of 'or' operator, it must be bool", leftBool)
+		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 {
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
-		if rightBool, rok := toBool(rightValue); rok {
+		if rightBool, rok := kern.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
-			err = self.errIncompatibleTypes(leftValue, rightValue)
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	}
 	return
@@ -173,7 +175,7 @@ func evalOrWithShortcut(ctx ExprContext, self *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymNot, newNotTerm)
+	scan.RegisterTermConstructor(scan.SymNot, newNotTerm)
-	registerTermConstructor(SymAnd, newAndTerm)
+	scan.RegisterTermConstructor(scan.SymAnd, newAndTerm)
-	registerTermConstructor(SymOr, newOrTerm)
+	scan.RegisterTermConstructor(scan.SymOr, newOrTerm)
 }

operator-builtin.go

@@ -1,47 +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) {
+func newBuiltinTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		children: make([]*term, 0, 1),
+		Children: make([]*scan.Term, 0, 1),
-		position: posPrefix,
+		Position: scan.PosPrefix,
-		priority: priSign,
+		Priority: scan.PriSign,
-		evalFunc: evalBuiltin,
+		EvalFunc: evalBuiltin,
 	}
 }
 
-func evalBuiltin(ctx ExprContext, self *term) (v any, err error) {
+func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = self.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
-		it := NewAnyIterator(childValue)
+		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 = self.Errorf("unknown module %q", module)
+					err = opTerm.Errorf("unknown builtin module %q", module)
 					break
 				}
 			} else {
-				err = self.Errorf("expected string at item nr %d, got %T", it.Index()+1, moduleSpec)
+				err = opTerm.Errorf("expected string at item nr %d, got %s", it.Index()+1, kern.TypeName(moduleSpec))
 				break
 			}
 		}
@@ -57,5 +65,5 @@ func evalBuiltin(ctx ExprContext, self *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) {
+func newButTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		children: make([]*term, 0, 2),
+		Children: make([]*scan.Term, 0, 2),
-		position: posInfix,
+		Position: scan.PosInfix,
-		priority: priBut,
+		Priority: scan.PriBut,
-		evalFunc: evalBut,
+		EvalFunc: evalBut,
 	}
 }
 
-func evalBut(ctx ExprContext, self *term) (v any, err error) {
+func evalBut(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	_, v, err = self.evalInfix(ctx)
+	_, v, err = opTerm.EvalInfix(ctx)
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymKwBut, newButTerm)
+	scan.RegisterTermConstructor(scan.SymKwBut, newButTerm)
 }

operator-cat.go

@@ -0,0 +1,151 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-cat.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- cat term
+
+func newCatTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalCat,
+	}
+}
+
+func evalCat(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
+	v = newCatIterator(itLeft, itRight)
+	return
+}
+
+const catIteratorType = "cat"
+
+type catIterator struct {
+	kern.IteratorBase
+	itLeft    kern.Iterator
+	itRight   kern.Iterator
+	itCurrent kern.Iterator
+}
+
+func newCatIterator(itLeft, itRight kern.Iterator) (it *catIterator) {
+	it = &catIterator{
+		IteratorBase: kern.IteratorBase{},
+		itLeft:       itLeft,
+		itRight:      itRight,
+		itCurrent:    itLeft,
+	}
+	it.Reset()
+	return
+}
+
+func (it *catIterator) TypeName() string {
+	return catIteratorType
+}
+
+func (it *catIterator) String() string {
+	return fmt.Sprintf("$(%s %s %s)", it.itLeft, catIteratorType, it.itRight)
+}
+
+func (it *catIterator) Next() (item any, err error) {
+	if it.itCurrent == nil {
+		err = io.EOF
+	} else {
+		if item, err = it.itCurrent.Next(); err == nil {
+			it.Increment()
+		} else if err == io.EOF {
+			if it.itCurrent == it.itLeft {
+				it.itCurrent = it.itRight
+			} else {
+				return
+			}
+			if item, err = it.itCurrent.Next(); err == nil {
+				it.Increment()
+			} else {
+				it.itCurrent = nil
+			}
+		}
+	}
+	it.SetCurrent(item)
+	return
+}
+
+// func (it *catIterator) Reset() (err error) {
+// 	err = it.itLeft.Reset()
+// 	it.IteratorBase.Reset()
+// 	return
+// }
+
+func (it *catIterator) 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 = it.Index()
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.Count()
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwCat, newCatTerm)
+}

operator-coalesce.go

@@ -1,85 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// operator-coalesce.go
-package expr
-
-//-------- null coalesce term
-
-func newNullCoalesceTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priCoalesce,
-		evalFunc: evalNullCoalesce,
-	}
-}
-
-func evalNullCoalesce(ctx ExprContext, self *term) (v any, err error) {
-	var rightValue any
-
-	if err = self.checkOperands(); err != nil {
-		return
-	}
-
-	leftTerm := self.children[0]
-	if leftTerm.tk.Sym != SymVariable {
-		err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
-		return
-	}
-
-	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
-		v = leftValue
-	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		v = rightValue
-	}
-	return
-}
-
-//-------- coalesce assign term
-
-func newCoalesceAssignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priCoalesce,
-		evalFunc: evalAssignCoalesce,
-	}
-}
-
-func evalAssignCoalesce(ctx ExprContext, self *term) (v any, err error) {
-	var rightValue any
-
-	if err = self.checkOperands(); err != nil {
-		return
-	}
-
-	leftTerm := self.children[0]
-	if leftTerm.tk.Sym != SymVariable {
-		err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
-		return
-	}
-
-	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
-		v = leftValue
-	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if functor, ok := rightValue.(Functor); ok {
-			//ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
-			ctx.RegisterFunc(leftTerm.source(), functor, typeAny, []ExprFuncParam{
-				newFuncParamFlag(paramValue, pfOptional|pfRepeat),
-			})
-		} else {
-			v = rightValue
-			ctx.UnsafeSetVar(leftTerm.source(), rightValue)
-		}
-	}
-	return
-}
-
-// init
-func init() {
-	registerTermConstructor(SymDoubleQuestion, newNullCoalesceTerm)
-	registerTermConstructor(SymQuestionEqual, newCoalesceAssignTerm)
-}

operator-context.go

@@ -1,57 +1,69 @@
-// 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 (
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- context term
 
-func newContextTerm(tk *Token) (inst *term) {
+func newContextTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		children: make([]*term, 0, 1),
+		Children: make([]*scan.Term, 0, 1),
-		position: posPrefix,
+		Position: scan.PosPrefix,
-		priority: priIncDec,
+		Priority: scan.PriIncDec,
-		evalFunc: evalContextValue,
+		EvalFunc: evalContextValue,
 	}
 }
 
-func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
+func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
+	var sourceCtx kern.ExprContext
 
-	var sourceCtx ExprContext
+	if len(opTerm.Children) == 0 {
-	if self.children == nil || len(self.children) == 0 {
 		sourceCtx = ctx
-	} else if self.children[0].symbol() == SymVariable && self.children[0].source() == "global" {
+	} else if opTerm.Children[0].Symbol() == scan.SymVariable && opTerm.Children[0].Source() == "global" {
-		sourceCtx = globalCtx
+		sourceCtx = ctx.GetGlobal()
-	} else if childValue, err = self.evalPrefix(ctx); err == nil {
+	} else if childValue, err = opTerm.EvalPrefix(ctx); err == nil {
 		if dc, ok := childValue.(*dataCursor); ok {
 			sourceCtx = dc.ctx
 		}
+	} else {
+		return
 	}
 
 	if sourceCtx != nil {
-		if formatter, ok := sourceCtx.(Formatter); ok {
+		v = sourceCtx.ToDict()
-			v = formatter.ToString(0)
+	} else if childValue != nil {
-		} else {
+		it, ok := childValue.(kern.Iterator)
-			keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+		if !ok {
-			d := make(map[string]any)
+			it, err = NewIterator(ctx, childValue, nil)
-			for _, key := range keys {
-				d[key], _ = sourceCtx.GetVar(key)
 		}
-			keys = sourceCtx.EnumFuncs(func(name string) bool { return true })
+		if err == nil {
-			for _, key := range keys {
+			var item any
-				d[key], _ = sourceCtx.GetFuncInfo(key)
+			values := kern.NewLinkedListA()
+			for item, err = it.Next(); err == nil; item, err = it.Next() {
+				values.PushBack(item)
+			}
+			if err == io.EOF {
+				err = nil
+				v = values
 			}
-			v = d
 		}
 	} else {
-		err = self.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) {
+func newExportAllTerm(tk *scan.Token) (inst *scan.Term) {
-	return &term{
+	return &scan.Term{
-		tk:       *tk,
+		Tk:       *tk,
-		children: nil,
+		Children: nil,
-		position: posLeaf,
+		Position: scan.PosLeaf,
-		priority: priValue,
+		Priority: scan.PriValue,
-		evalFunc: evalExportAll,
+		EvalFunc: evalExportAll,
 	}
 }
 
-func evalExportAll(ctx ExprContext, self *term) (v any, err error) {
+func evalExportAll(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	enable(ctx, control_export_all)
+	CtrlEnable(ctx, kern.ControlExportAll)
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleAt, newExportAllTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleAt, newExportAllTerm)
 }