copyright header updated to 2026

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

@@ -0,0 +1,147 @@
+= README
+README about the Expressions calculator
+:authors: Celestino Amoroso
+:docinfo: shared
+:encoding: utf-8
+:toc: right
+:toclevels: 4
+//:toc-title: Indice Generale
+:icons: font
+:icon-set: fi
+:numbered:
+//:table-caption: Tabella
+//:figure-caption: Diagramma
+:docinfo1:
+:sectlinks:
+:sectanchors:
+:source-highlighter: rouge
+// :rouge-style: ThankfulEyes
+:rouge-style: gruvbox
+// :rouge-style: colorful
+//:rouge-style: monokay
+
+toc::[]
+
+== Expr
+_Expr_ is a GO package capable of analysing, interpreting and calculating expressions.
+
+A few examples to get started.
+
+.Examples taken from parser_test.go
+[source,go]
+----
+`1.0 / 2`                      // 0.5
+`435 + 105 * 2 - 1`            // 644
+`4 == (3-1)*(10/5)`            // true
+`"uno" * (2+1)`                // `unounouno`
+`2+3 but 5*2`                  // 10 <1>
+`add(add(1+4),3+2,5*(3-2))`    // 15 <2>
+`a=5; b=2; add(a, b*3)`        // 11 <3>
+`two=func(){2}; two()`         // 2  <4>
+`double=func(x){2*x}; a=4+1; two=func() {2}; (double(3+a) + 1) * two()`  // 34
+`import("./test-funcs.expr"); (double(3+a) + 1) * two()`  // 34 <5>
+`[1,2,"hello"]`                // Mixed types list
+`[1,2]+[3]`                    // append list, result: [1,2,3]
+`add([1,[2,2],3,2])`           // Deep list sum, result: 10 <2>
+`[a=1,b=2,c=3] but a+b+c`      // 6
+----
+
+<1> [blue]`but` operator.
+<2> The _add()_ function definition may be changed in the future.
+<3> Multiple expression. Only the last expression value will returned.
+<4> Simple function definition: _two()_ returns 2.
+<5> _import()_ function imports expressions from the specified files. See file _test-funcs.expr_.
+
+
+=== Usage
+
+
+[source,go]
+----
+package main
+
+import (
+	"fmt"
+	"strings"
+	"git.portale-stac.it/go-pkg/expr"
+)
+
+func main() {
+	ctx := expr.NewSimpleVarStore()
+	ctx.SetVar("var", 4)
+
+	source := `(3-1)*(10/5) == var`
+
+	r := strings.NewReader(source)
+	scanner := expr.NewScanner(r, expr.DefaultTranslations())
+	parser := expr.NewParser(ctx)
+
+	if ast, err := parser.Parse(scanner); err == nil {
+		if result, err := ast.Eval(ctx); err == nil {
+			fmt.Printf("%q -> %v [%T]\n", source, result, result)
+		} else {
+			fmt.Println("Error calculating the expression:", err)
+		}
+	} else {
+		fmt.Println("Error parsing the expression:", err)
+	}
+}
+----
+
+The above program is equivalent to the following one.
+
+[source,go]
+----
+package main
+
+import (
+	"fmt"
+	"git.portale-stac.it/go-pkg/expr"
+)
+
+func main() {
+	ctx := expr.NewSimpleVarStore()
+	ctx.SetVar("var", 4)
+
+	source := `(3-1)*(10/5) == var`
+
+	if result, err := expr.EvalString(ctx, source); err == nil {
+		fmt.Printf("%q -> %v [%T]\n", source, result, result)
+	} else {
+		fmt.Println("Error calculating the expression:", err)
+	}
+}
+----
+
+Here is another equivalent version.
+
+[source,go]
+----
+package main
+
+import (
+	"fmt"
+	"git.portale-stac.it/go-pkg/expr"
+)
+
+func main() {
+	source := `(3-1)*(10/5) == var`
+
+	if result, err := expr.EvalStringA(source, expr.Arg{"var", 4}); err == nil {
+		fmt.Printf("%q -> %v [%T]\n", source, result, result)
+	} else {
+		fmt.Println("Error calculating the expression:", err)
+	}
+}
+----
+
+== Context of evaluation
+Unless helpers functions like _expr.EvalStringA()_ are used, a _context_ is required to compute an expession.
+
+A context is an object that implements the _expr.ExprContext_ interface. This interface specifies a set of function to handle variables and functions.
+
+Variables and functions can be added to a context both programmatically and ad an effect of the expression computation.
+
+== Expressions syntax
+
+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

@@ -1,84 +0,0 @@
-// ast.go
-package expr
-
-import (
-	"errors"
-	"fmt"
-	"strings"
-)
-
-//-------- ast
-
-type ast struct {
-	root *term
-}
-
-func NewAst() *ast {
-	return &ast{}
-}
-
-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) {
-	if t := newTerm(tk, nil); t != nil {
-		err = self.addTerm(t)
-	} else {
-		err = fmt.Errorf("No term constructor for 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()
-			subRoot, err = self.insert(last, node)
-			subRoot.setParent(tree)
-		} else {
-			node.setParent(tree)
-		}
-	} else if !node.isLeaf() {
-		root = node
-		tree.setParent(node)
-	} else {
-		err = fmt.Errorf("two adjacent operators: %q and %q", tree, node)
-	}
-	return
-}
-
-func (self *ast) eval(ctx exprContext) (result any, err error) {
-	if self.root != nil {
-		result, err = self.root.compute(ctx)
-	} else {
-		err = errors.New("empty expression")
-	}
-	return
-}

ast_test.go

@@ -1,50 +0,0 @@
-// ast_test.go
-package expr
-
-import (
-	"errors"
-	"testing"
-)
-
-func TestAstString(t *testing.T) {
-	tree := NewAst()
-	if gotResult := tree.String(); gotResult != "(nil)" {
-		t.Errorf(`result: got %q, want "(nil)"`, gotResult)
-	}
-}
-
-func TestAddTokensGood(t *testing.T) {
-	tk1 := NewValueToken(SymInteger, "100", 100)
-	tk2 := NewToken(SymPlus, "+")
-	tk3 := NewValueToken(SymInteger, "50", 500)
-
-	tree := NewAst()
-	if gotErr := tree.addTokens(tk1, tk2, tk3); gotErr != nil {
-		t.Errorf("err: got <%v>, want <nil>", gotErr)
-	}
-}
-
-func TestAddTokensBad(t *testing.T) {
-	tk0 := NewValueToken(SymInteger, "200", 200)
-	tk1 := NewValueToken(SymInteger, "100", 100)
-	tk2 := NewToken(SymPlus, "+")
-	tk3 := NewValueToken(SymInteger, "50", 500)
-
-	wantErr := errors.New(`two adjacent operators: "200" and "100"`)
-
-	tree := NewAst()
-	if gotErr := tree.addTokens(tk0, tk1, tk2, tk3); gotErr != nil && gotErr.Error() != wantErr.Error() {
-		t.Errorf("err: got <%v>, want <nil>", gotErr)
-	}
-}
-
-func TestAddUnknownTokens(t *testing.T) {
-	tk0 := NewToken(SymPercent, "%")
-
-	wantErr := errors.New(`No term constructor for token "%"`)
-
-	tree := NewAst()
-	if gotErr := tree.addToken(tk0); gotErr != nil && gotErr.Error() != wantErr.Error() {
-		t.Errorf("err: got <%v>, want <%v>", gotErr, wantErr)
-	}
-}

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 +1,319 @@
+// 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 unsetFunc(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])
+// 	} else {
+// 		ctx.GetParent().DeleteVar(varName)
+// 		result = nil
+// 	}
+// 	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("unset", kern.NewGolangFunctor(unsetFunc), kern.TypeAny, []kern.ExprFuncParam{
+	// 	kern.NewFuncParam(kern.ParamName),
+	// 	kern.NewFuncParam(kern.ParamValue),
+	// })
+}
+
+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.go

@@ -0,0 +1,151 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const paramHandleOrPath = "handle-or-path"
+const fileReadTextIteratorType = "fileReadTextIterator"
+
+type fileReadTextIterator struct {
+	osReader  *osReader
+	index     int64
+	count     int64
+	line      string
+	autoClose bool
+}
+
+func newReadTextIterator(r *osReader, autoClose bool) *fileReadTextIterator {
+	return &fileReadTextIterator{osReader: r, index: -1, autoClose: autoClose}
+}
+
+func (it *fileReadTextIterator) TypeName() string {
+	return fileReadTextIteratorType
+}
+
+func (it *fileReadTextIterator) String() string {
+	if it.osReader != nil && it.osReader.fh != nil {
+		return fmt.Sprintf("$(%s@%q)", fileReadTextIteratorType, it.osReader.fh.Name())
+	}
+	return fmt.Sprintf("$(%s@<nil>)", fileReadTextIteratorType)
+}
+
+func (it *fileReadTextIterator) Count() int64 {
+	return it.count
+}
+
+func (it *fileReadTextIterator) Next() (item any, err error) { // must return io.EOF after the last item
+	if it.osReader.fh != nil {
+		if it.line, err = it.osReader.reader.ReadString('\n'); err == nil {
+			it.index++
+			it.count++
+			item = it.line[0 : len(it.line)-1]
+		} else if it.autoClose {
+			it.Clean()
+		}
+	}
+	return
+}
+
+func (it *fileReadTextIterator) Current() (item any, err error) {
+	if len(it.line) > 0 {
+		item = it.line[0 : len(it.line)-1]
+	}
+	return
+}
+
+func (it *fileReadTextIterator) Index() int64 {
+	return it.index
+}
+
+func (it *fileReadTextIterator) Reset() (err error) {
+	if _, err = it.osReader.fh.Seek(0, io.SeekStart); err == nil {
+		it.index = -1
+		it.count = 0
+		it.line = ""
+	}
+	return
+}
+
+func (it *fileReadTextIterator) HasOperation(name string) bool {
+	return slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName}, name)
+}
+
+func (it *fileReadTextIterator) Clean() (err error) {
+	if it.osReader.fh != nil {
+		if err = it.osReader.fh.Close(); err == nil {
+			it.osReader = nil
+		}
+	}
+	return nil
+}
+
+func (it *fileReadTextIterator) 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 fileReadIteratorFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle *osReader
+	var invalidFileHandle any
+	var ok, autoClose bool
+
+	result = nil
+	if handle, ok = args[paramHandleOrPath].(*osReader); !ok {
+		if fileName, ok := args[paramHandleOrPath].(string); ok && len(fileName) > 0 {
+			var handleAny any
+			if handleAny, err = openFileFunc(ctx, name, map[string]any{kern.ParamFilepath: fileName}); err != nil {
+				return
+			}
+			if handleAny != nil {
+				handle = handleAny.(*osReader)
+				autoClose = true
+			}
+		} else {
+			invalidFileHandle = args[paramHandleOrPath]
+		}
+	}
+
+	if handle != nil {
+		result = newReadTextIterator(handle, autoClose)
+
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}
+
+// func ImportOsIterFuncs(ctx ExprContext) {
+// 	ctx.RegisterFunc("fileReadIterator", NewGolangFunctor(fileReadIteratorFunc), TypeIterator, []ExprFuncParam{
+// 		NewFuncParam(paramHandleOrPath),
+// 	})
+// }
+
+// func init() {
+// 	RegisterBuiltinModule("os.file", ImportOsIterFuncs, "Operating system file iterator functions")
+// }

builtin-os-file.go

@@ -0,0 +1,263 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const (
+	osLimitCh = "limitCh"
+)
+
+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 kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if filePath, ok := args[kern.ParamFilepath].(string); ok && len(filePath) > 0 {
+		var fh *os.File
+		if fh, err = os.Create(filePath); err == nil {
+			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
+		}
+	} else {
+		err = errMissingFilePath(name)
+	}
+	return
+}
+
+func openFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if filePath, ok := args[kern.ParamFilepath].(string); ok && len(filePath) > 0 {
+		var fh *os.File
+		if fh, err = os.Open(filePath); err == nil {
+			result = &osReader{fh: fh, reader: bufio.NewReader(fh)}
+		}
+	} 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 = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
+		}
+	} else {
+		err = errMissingFilePath(name)
+	}
+	return
+}
+
+func closeFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle osHandle
+	var invalidFileHandle any
+	var ok bool
+
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	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(name, handle)
+	}
+	result = err == nil
+	return
+}
+
+func fileWriteTextFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle osHandle
+	var invalidFileHandle any
+	var ok bool
+
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	if handle != nil {
+		if w, ok := handle.(*osWriter); ok {
+			if v, exists := args[kern.ParamItem]; exists {
+				argv := v.([]any)
+				result, err = fmt.Fprint(w.writer, 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 osHandle
+	var invalidFileHandle any
+	var ok bool
+
+	result = nil
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok || args[kern.ParamHandle] == nil {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	if handle != nil {
+		if r, ok := handle.(*osReader); ok {
+			var limit byte = '\n'
+			var v string
+			if s, ok := args[osLimitCh].(string); ok && len(s) > 0 {
+				limit = s[0]
+			}
+
+			v, err = r.reader.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 osHandle
+	var invalidFileHandle any
+	var ok bool
+
+	result = nil
+	if handle, ok = args[kern.ParamHandle].(osHandle); !ok || args[kern.ParamHandle] == nil {
+		invalidFileHandle = args[kern.ParamHandle]
+	}
+
+	if handle != nil {
+		if r, ok := handle.(*osReader); ok {
+			var b []byte
+			b, err = io.ReadAll(r.reader)
+			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("fileReadIterator", kern.NewGolangFunctor(fileReadIteratorFunc), 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-ring.go

@@ -1,31 +0,0 @@
-// 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)
-}

context.go

@@ -1,15 +0,0 @@
-// context.go
-package expr
-
-type exprFunc interface {
-	Name() string
-	MinArgs() int
-	MaxArgs() int
-}
-
-type exprContext interface {
-	GetValue(varName string) (value any, exists bool)
-	SetValue(varName string, value any)
-	GetFuncInfo(name string) exprFunc
-	Call(name string, args []any) (result any, err error)
-}

data-cursor.go

@@ -0,0 +1,307 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// data-cursors.go
+package expr
+
+import (
+	"io"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+type dataCursor struct {
+	ds        map[string]kern.Functor
+	ctx       kern.ExprContext
+	initState bool // true if no item has produced yet (this replace di initial Next() call in the contructor)
+	// cursorValid bool // true if resource is nil or if clean has not yet been called
+	index     int64
+	count     int64
+	current   any
+	lastErr   error
+	resource  any
+	nextFunc  kern.Functor
+	cleanFunc kern.Functor
+	resetFunc kern.Functor
+}
+
+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('{')
+// 	for key, _ := range m {
+// 		if sb.Len() > 1 {
+// 			sb.WriteString(fmt.Sprintf(", %q: func(){}", key))
+// 		} else {
+// 			sb.WriteString(fmt.Sprintf("%q: func(){}", key))
+// 		}
+// 	}
+// 	sb.WriteByte('}')
+// 	return sb.String()
+// }
+
+func (dc *dataCursor) String() string {
+	return "$()"
+	/*
+	   var sb strings.Builder
+	   sb.WriteString(fmt.Sprintf(`$(
+	   index: %d,
+	   ds:    %s,
+	   ctx:   `, dc.index, mapToString(dc.ds)))
+	   CtxToBuilder(&sb, dc.ctx, 1)
+	   sb.WriteByte(')')
+	   return sb.String()
+	*/
+}
+
+func (dc *dataCursor) HasOperation(name string) (exists bool) {
+	exists = slices.Contains([]string{kern.CleanName, kern.ResetName, kern.CurrentName, kern.IndexName}, name)
+	if !exists {
+		f, ok := dc.ds[name]
+		exists = ok && kern.IsFunctor(f)
+	}
+	return
+}
+
+func (dc *dataCursor) CallOperation(name string, args map[string]any) (value any, err error) {
+	if name == kern.IndexName {
+		value = int64(dc.Index())
+	} else if name == kern.CleanName {
+		err = dc.Clean()
+	} else if name == kern.ResetName {
+		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 {
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+// 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 {
+		ctx := kern.CloneContext(dc.ctx)
+		actualParams := kern.BindActualParams(dc.resetFunc, []any{dc.resource})
+		_, err = dc.resetFunc.InvokeNamed(ctx, kern.ResetName, actualParams)
+		kern.ExportObjects(dc.ctx, ctx)
+	}
+	dc.index = -1
+	dc.count = 0
+	dc.initState = true
+	dc.current = nil
+	dc.lastErr = nil
+	return
+}
+
+func (dc *dataCursor) Clean() (err error) {
+	if dc.cleanFunc != nil {
+		ctx := kern.CloneContext(dc.ctx)
+		actualParams := kern.BindActualParams(dc.cleanFunc, []any{dc.resource})
+		_, err = dc.cleanFunc.InvokeNamed(ctx, kern.CleanName, actualParams)
+		kern.ExportObjects(dc.ctx, ctx)
+	}
+	dc.lastErr = io.EOF
+	return
+}
+
+// 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
+	dc.init()
+
+	if dc.current != nil {
+		item = dc.current
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (dc *dataCursor) checkFilter(filter kern.Functor, item any) (accepted bool, err error) {
+	var v any
+	var ok bool
+	ctx := kern.CloneContext(dc.ctx)
+
+	actualParams := kern.BindActualParams(filter, []any{item, dc.index})
+	if v, err = filter.InvokeNamed(ctx, kern.FilterName, actualParams); err == nil && v != nil {
+		if accepted, ok = v.(bool); !ok {
+			accepted = true // NOTE: A non-boolean value that is not nil means the item has been accepted
+		}
+	}
+	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})
+		if item, dc.lastErr = dc.nextFunc.InvokeNamed(ctx, kern.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)
+				}
+			}
+		}
+		kern.ExportObjects(dc.ctx, ctx)
+	}
+	dc.current = item
+	if dc.lastErr != nil {
+		dc.index--
+		dc.Clean()
+	}
+	return
+}
+
+// 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
+// 	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
+}

doc/expression-diagram.drawio

@@ -0,0 +1,94 @@
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global-context.go

@@ -0,0 +1,126 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// global-context.go
+package expr
+
+import (
+	"path/filepath"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+//var globalCtx *SimpleStore
+
+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(ctx kern.ExprContext, pattern string) (count int, err error) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		var matched bool
+		for name, mod := range builtinModuleRegister {
+			if matched, err = filepath.Match(pattern, name); err == nil {
+				if matched {
+					count++
+					mod.importFunc(globalCtx)
+					mod.imported = true
+				}
+			} else {
+				break
+			}
+		}
+	}
+	return
+}
+
+func GlobalCtrlSet(ctx kern.ExprContext, name string, newValue any) (currentValue any) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		if !strings.HasPrefix(name, "_") {
+			name = "_" + name
+		}
+
+		currentValue, _ = globalCtx.GetVar(name)
+		globalCtx.SetVar(name, newValue)
+	}
+	return currentValue
+}
+
+func GlobalCtrlGet(ctx kern.ExprContext, name string) (currentValue any) {
+	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+		if !strings.HasPrefix(name, "_") {
+			name = "_" + name
+		}
+		currentValue, _ = globalCtx.GetVar(name)
+	}
+	return currentValue
+}
+
+func CtrlEnable(ctx kern.ExprContext, name string) (currentStatus bool) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + 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) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + 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 v, exists = globalCtx.GetVar(name); exists {
+			s, exists = v.(string)
+		}
+	}
+	return
+}
+
+func InitGlobal() (ctx kern.ExprContext) {
+	ctx = NewSimpleStoreWithoutGlobalContext()
+	kern.InitDefaultVars(ctx)
+	ImportBuiltinsFuncs(ctx)
+	return
+}

go.mod

@@ -0,0 +1,7 @@
+module git.portale-stac.it/go-pkg/expr
+
+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

@@ -0,0 +1,124 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+//go:build graph
+
+// graph.go
+package expr
+
+import (
+	"fmt"
+	"strings"
+)
+
+func BuildGraph(root *term) (g string) {
+	//var sb strings.Builder
+	g = fmt.Sprintf("tree: %v", root)
+
+	r := NewReticle(root)
+	fmt.Println(r)
+	return
+}
+
+type NodeRef struct {
+	node  *term
+	pos   int
+	label string
+}
+
+type Level []*NodeRef
+
+type Reticle struct {
+	levels      []Level
+	left, right int
+	colsWidth   []int
+}
+
+func NewExprReticle(e Expr) *Reticle {
+	tree, _ := e.(*ast)
+	return NewReticle(tree.root)
+}
+
+func NewReticle(tree *term) *Reticle {
+	r := &Reticle{levels: make([]Level, 0)}
+	r.build(tree, 0, 0)
+	r.computeCharWidth()
+	return r
+}
+
+func (r *Reticle) computeCharWidth() {
+	numCol := r.right - r.left + 1
+	r.colsWidth = make([]int, numCol)
+	for _, level := range r.levels {
+		for _, ref := range level {
+			c := ref.pos - r.left
+			if v := ref.node.value(); v != nil {
+				ref.label = fmt.Sprintf("%v", v)
+			} else {
+				ref.label = ref.node.Source()
+			}
+			r.colsWidth[c] = max(r.colsWidth[c], len(ref.label)+2) // +2 to make room for brakets
+		}
+	}
+}
+
+func (r *Reticle) build(node *term, depth, pos int) {
+	var level Level
+	if node == nil {
+		return
+	}
+	if len(r.levels) == depth {
+		level = make(Level, 0)
+		r.levels = append(r.levels, level)
+	} else {
+		level = r.levels[depth]
+	}
+	ref := &NodeRef{node: node, pos: pos}
+	level = append(level, ref)
+	if r.left > pos {
+		r.left = pos
+	}
+	if r.right < pos {
+		r.right = pos
+	}
+	if node.children != nil {
+		halfPos := len(node.children) / 2
+		childPos := pos - halfPos - 1
+		for _, child := range node.children {
+			childPos++
+			if childPos == pos && (len(node.children)&1) == 0 {
+				childPos++
+			}
+			r.build(child, depth+1, childPos)
+		}
+	}
+	r.levels[depth] = level
+}
+
+func (r *Reticle) nodeInLevel(level []*NodeRef, index int) (node *NodeRef) {
+	for _, ref := range level {
+		if ref.pos-r.left == index {
+			node = ref
+			break
+		}
+	}
+	return
+}
+
+func (r *Reticle) String() string {
+	var sb strings.Builder
+	for _, level := range r.levels {
+		for j, w := range r.colsWidth {
+			var label string
+			if ref := r.nodeInLevel(level, j); ref != nil {
+				s := "(" + ref.label + ")"
+				label = fmt.Sprintf("%[1]*s", -w, fmt.Sprintf("%[1]*s", (w+len(s))/2, s))
+			} else {
+				label = strings.Repeat(" ", w)
+			}
+			sb.WriteString(label)
+		}
+		sb.WriteByte('\n')
+	}
+	return sb.String()
+}

helpers.go

@@ -0,0 +1,91 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// helpers.go
+package expr
+
+import (
+	"fmt"
+	"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 kern.ExprContext, source string) (result any, err error) {
+	var tree *scan.Ast
+
+	r := strings.NewReader(source)
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
+	parser := NewParser()
+
+	if tree, err = parser.Parse(scanner); err == nil {
+		result, err = tree.Eval(ctx)
+	}
+	return
+}
+
+type Arg struct {
+	Name  string
+	Value any
+}
+
+func EvalStringA(source string, args ...Arg) (result any, err error) {
+	return EvalStringV(source, args)
+}
+
+func EvalStringV(source string, args []Arg) (result any, err error) {
+	ctx := NewSimpleStoreWithoutGlobalContext()
+	for _, arg := range args {
+		if util.IsFunc(arg.Value) {
+			if f, ok := arg.Value.(kern.FuncTemplate); ok {
+				functor := kern.NewGolangFunctor(f)
+				// ctx.RegisterFunc(arg.Name, functor, 0, -1)
+				ctx.RegisterFunc(arg.Name, functor, kern.TypeAny, []kern.ExprFuncParam{
+					kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, 0),
+				})
+			} else {
+				err = fmt.Errorf("invalid function specification: %q", arg.Name)
+			}
+		} else if integer, ok := kern.AnyInteger(arg.Value); ok {
+			ctx.SetVar(arg.Name, integer)
+		} 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)
+		} else if _, ok := arg.Value.(bool); ok {
+			ctx.SetVar(arg.Name, arg.Value)
+		} else {
+			err = fmt.Errorf("unsupported type %T specified for item %q", arg.Value, arg.Name)
+		}
+	}
+
+	if err == nil {
+		result, err = EvalString(ctx, source)
+	}
+	return
+}
+
+func EvalStream(ctx kern.ExprContext, r io.Reader) (result any, err error) {
+	var tree *scan.Ast
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
+	parser := NewParser()
+
+	if tree, err = parser.Parse(scanner); err == nil {
+		result, err = tree.Eval(ctx)
+	}
+	return
+}
+
+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
+	}
+	defer fh.Close()
+	result, err = EvalStream(ctx, fh)
+	return
+}

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

it-range.go.unused

@@ -0,0 +1,58 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// it-range.go
+package expr
+
+import "io"
+
+type RangeIterator struct {
+	start   int64
+	end     int64
+	step    int64
+	current int64
+	index   int
+}
+
+func NewRangeIterator(start, end, step int64) *RangeIterator {
+	if step == 0 {
+		panic("Range step must be not zero")
+	}
+	if step < 0 && start < end {
+		panic("When the range's step is less than zero, start must be greater than end")
+	}
+	if step > 0 && start > end {
+		panic("When the range's step is greater than zero, start must be less than end")
+	}
+	return &RangeIterator{start: start, end: end, step: step, current: start, index: 0}
+}
+
+func (it *RangeIterator) Reset() {
+	it.index = 0
+	it.current = it.start
+}
+
+func (it *RangeIterator) Next() (item any, err error) {
+	if it.step > 0 {
+		if it.current < it.end {
+			item = it.current
+			it.current += it.step
+			it.index++
+		} else {
+			err = io.EOF
+		}
+	} else {
+		if it.current > it.end {
+			item = it.current
+			it.current += it.step
+			it.index++
+		} else {
+			err = io.EOF
+		}
+	}
+	return
+}
+
+func (it *RangeIterator) Index() int {
+	return it.index - 1
+}

iter-factory.go

@@ -0,0 +1,44 @@
+// 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 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.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 +1,127 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iter-iter.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+type IterIter struct {
+	it       kern.Iterator
+	count    int64
+	index    int64
+	ctx      kern.ExprContext
+	exprList []*scan.Term
+	current  any
+}
+
+func NewIterIter(it kern.Iterator, ctx kern.ExprContext, exprs []*scan.Term) (iter kern.Iterator, err error) {
+	iter = &IterIter{it: it, count: 0, index: -1, ctx: ctx, exprList: exprs, current: nil}
+	return
+}
+
+func (it *IterIter) String() string {
+	return fmt.Sprintf("$(%s)", it.it)
+}
+
+func (it *IterIter) TypeName() string {
+	return "IterIter"
+}
+
+func (it *IterIter) HasOperation(name string) bool {
+	return HasIterStandardOperations(name)
+}
+
+func (it *IterIter) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	case kern.ResetName:
+		err = it.Reset()
+	case kern.CleanName:
+		err = it.Clean()
+	case kern.IndexName:
+		v = int64(it.Index())
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.count
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func (it *IterIter) Current() (item any, err error) {
+	if it.current != nil {
+		item = it.current
+	} else if len(it.exprList) > 0 {
+		// Evaluate the expression list and use the result as the current item
+		var exprValue any
+		for _, expr := range it.exprList {
+			if exprValue, err = expr.Compute(it.ctx); err != nil {
+				break
+			}
+			it.ctx.UnsafeSetVar(kern.ControlLastResult, exprValue)
+		}
+		if err == nil {
+			item = exprValue
+		}
+	} else {
+		var exists bool
+		if it.current, exists = it.ctx.GetVar("_"); !exists {
+			err = fmt.Errorf("current item not available")
+		} else {
+			item = it.current
+		}
+	}
+	return
+}
+
+func (it *IterIter) Next() (item any, err error) {
+	var src any
+
+	it.current = nil
+	ctx := it.ctx
+	for src, err = it.it.Next(); src == nil && err == nil; src, err = it.it.Next() {
+	}
+
+	if err == nil {
+		if src == nil {
+			err = io.EOF
+		} else {
+			ctx.UnsafeSetVar("_", src)
+			ctx.UnsafeSetVar("__", it.it.Index())
+			ctx.UnsafeSetVar("_#", it.it.Count())
+			item, err = it.Current()
+			ctx.DeleteVar("_#")
+			ctx.DeleteVar("__")
+			ctx.DeleteVar("_")
+		}
+	}
+	return
+}
+
+func (it *IterIter) Index() int64 {
+	return it.index
+}
+
+func (it *IterIter) Count() int64 {
+	return it.count
+}
+
+func (it *IterIter) Reset() error {
+	it.index = -1
+	it.count = 0
+	return nil
+}
+
+func (it *IterIter) Clean() error {
+	return nil
+}

kern/bind-go-functions.go

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

kern/bool.go

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

kern/common-errors.go

@@ -0,0 +1,91 @@
+// 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)
+}
+
+// --- 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 +1,23 @@
+// 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"
+)

kern/compare.go

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

kern/context-helpers.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// context-helpers.go
+package kern
+
+func CloneContext(sourceCtx ExprContext) (clonedCtx ExprContext) {
+	if sourceCtx != nil {
+		clonedCtx = sourceCtx.Clone()
+	}
+	return
+}
+
+func exportVar(ctx ExprContext, name string, value any) {
+	if name[0] == '@' {
+		name = name[1:]
+	}
+	ctx.UnsafeSetVar(name, value)
+}
+
+func exportFunc(ctx ExprContext, name string, info ExprFunc) {
+	if name[0] == '@' {
+		name = name[1:]
+	}
+	ctx.RegisterFunc(name, info.Functor(), info.ReturnType(), info.Params())
+}
+
+func ExportObjects(destCtx, sourceCtx ExprContext) {
+	exportAll := CtrlIsEnabled(sourceCtx, ControlExportAll)
+	// fmt.Printf("Exporting from sourceCtx [%p] to destCtx [%p] -- exportAll=%t\n", sourceCtx, destCtx, exportAll)
+	// Export variables
+	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return (exportAll || name[0] == '@') && !(name[0] == '_') }) {
+		// fmt.Printf("\tExporting %q\n", refName)
+		refValue, _ := sourceCtx.GetVar(refName)
+		exportVar(destCtx, refName, refValue)
+	}
+	// Export functions
+	for _, refName := range sourceCtx.EnumFuncs(func(name string) bool { return exportAll || name[0] == '@' }) {
+		if info, _ := sourceCtx.GetFuncInfo(refName); info != nil {
+			exportFunc(destCtx, refName, info)
+		}
+	}
+}
+
+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 +1,193 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// dict-type.go
+package kern
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+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.WriteString(string('"') + key + string('"'))
+			} else {
+				sb.WriteString(fmt.Sprintf("%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 {
+				sb.WriteString(fmt.Sprintf("%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.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) SetItem(key any, value any) {
+	(*dict)[key] = value
+}
+
+func (dict *DictType) GetItem(key any) (value any, exists bool) {
+	value, exists = (*dict)[key]
+	return
+}
+
+func (dict *DictType) Clone() (c *DictType) {
+	c = newDict(nil)
+	for k, v := range *dict {
+		(*c)[k] = v
+	}
+	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 +1,31 @@
+// 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)
+}

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

@@ -0,0 +1,79 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// formatter.go
+package kern
+
+import "fmt"
+
+type FmtOpt uint32 // lower 16 bits hold a bit-mask, higher 16 bits hold an indentation number
+
+const (
+	TTY FmtOpt = 1 << iota
+	MultiLine
+	Truncate
+	Base2
+	Base8
+	Base10
+	Base16
+)
+
+const (
+	TruncateEllipsis = "(...)"
+	MinTruncateSize  = 10
+	TruncateSize     = MinTruncateSize + 15
+)
+
+func TruncateString(s string) (trunc string) {
+	finalPart := len(s) - (MinTruncateSize - len(TruncateEllipsis))
+	trunc = s[0:len(s)-MinTruncateSize] + TruncateEllipsis + s[finalPart:]
+	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) {
+	if v == nil {
+		text = "(nil)"
+	} else if s, ok := v.(string); ok {
+		text = s
+	} else if formatter, ok := v.(Formatter); ok {
+		text = formatter.ToString(opt)
+	} else {
+		text = fmt.Sprintf("%v", v)
+	}
+	return
+}
+
+type Typer interface {
+	TypeName() string
+}
+
+func TypeName(v any) (name string) {
+	if v == nil {
+		name = "nil"
+	} else if typer, ok := v.(Typer); ok {
+		name = typer.TypeName()
+	} else if IsInteger(v) {
+		name = "integer"
+	} else if IsFloat(v) {
+		name = "float"
+	} else {
+		name = fmt.Sprintf("%T", v)
+	}
+	return
+}

kern/fraction-type.go

@@ -0,0 +1,384 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// fraction-type.go
+package kern
+
+//https://www.youmath.it/lezioni/algebra-elementare/lezioni-di-algebra-e-aritmetica-per-scuole-medie/553-dalle-frazioni-a-numeri-decimali.html
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+)
+
+type FractionType struct {
+	num, den int64
+}
+
+func NewFraction(num, den int64) *FractionType {
+	num, den = simplifyIntegers(num, den)
+	return &FractionType{num, den}
+}
+
+func Float64ToFraction(f float64) (fract *FractionType, err error) {
+	var sign string
+	intPart, decPart := math.Modf(f)
+	if decPart < 0.0 {
+		sign = "-"
+		intPart = -intPart
+		decPart = -decPart
+	}
+	dec := fmt.Sprintf("%.12f", decPart)
+	s := fmt.Sprintf("%s%.f%s", sign, intPart, dec[1:])
+	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) {
+	var num, den int64
+	var sign int64 = 1
+	var parts []string
+	if len(s) == 0 {
+		goto exit
+	}
+	if s[0] == '-' {
+		sign = int64(-1)
+		s = s[1:]
+	} else if s[0] == '+' {
+		s = s[1:]
+	}
+	//	if strings.HasSuffix(s, "()") {
+	//		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)
+	} else if len(parts) == 2 {
+		subParts := strings.SplitN(parts[1], "(", 2)
+		if len(subParts) == 1 {
+			den = 1
+			dec := parts[1]
+			lsd := len(dec)
+			for i := lsd - 1; i >= 0 && dec[i] == '0'; i-- {
+				lsd--
+			}
+			for _, c := range dec[0:lsd] {
+				if c < '0' || c > '9' {
+					return nil, ErrExpectedGot("fract", "digit", c)
+				}
+				num = num*10 + int64(c-'0')
+				den = den * 10
+			}
+			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)
+				}
+				num = num*10 + int64(c-'0')
+				sub = sub*10 + int64(c-'0')
+				mul *= 10
+			}
+			if len(subParts) == 2 {
+				if s[len(s)-1] != ')' {
+					goto exit
+				}
+				p := subParts[1][0 : len(subParts[1])-1]
+				for _, c := range p {
+					if c < '0' || c > '9' {
+						return nil, ErrExpectedGot("fract", "digit", c)
+					}
+					num = num*10 + int64(c-'0')
+					den = den*10 + 9
+				}
+				den *= mul
+			}
+			num -= sub
+			f = NewFraction(sign*num, den)
+		}
+	}
+exit:
+	if f == nil {
+		err = errors.New("bad syntax")
+	}
+	return
+}
+
+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)
+}
+
+func (f *FractionType) String() string {
+	return f.ToString(0)
+}
+
+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))
+	} else {
+		var sign, num string
+		if f.num < 0 && opt&TTY == 0 {
+			num = strconv.FormatInt(-f.num, 10)
+			sign = "-"
+		} else {
+			num = strconv.FormatInt(f.num, 10)
+		}
+		den := strconv.FormatInt(f.den, 10)
+		size := max(len(num), len(den))
+		if opt&TTY != 0 {
+			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(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(sign) > 0 {
+				sb.WriteString(sign)
+				sb.WriteByte(' ')
+			}
+			sb.WriteString(strings.Repeat("-", size))
+			sb.WriteByte('\n')
+			if len(sign) > 0 {
+				sb.WriteString("  ")
+			}
+		}
+		sDen := fmt.Sprintf("%[1]*s", size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den))
+		sb.WriteString(sDen)
+	}
+
+	return sb.String()
+}
+
+func (f *FractionType) TypeName() string {
+	return "fraction"
+}
+
+// -------- fraction utility functions
+
+// greatest common divider
+func Gcd(a, b int64) (g int64) {
+	if a < 0 {
+		a = -a
+	}
+	if b < 0 {
+		b = -b
+	}
+	if a < b {
+		a, b = b, a
+	}
+	r := a % b
+	for r > 0 {
+		a, b = b, r
+		r = a % b
+	}
+	g = b
+	return
+}
+
+// lower common multiple
+func lcm(a, b int64) (l int64) {
+	g := Gcd(a, b)
+	l = a * b / g
+	return
+}
+
+// Sum two fractions
+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)
+	return
+}
+
+// Multiply two fractions
+func MulFract(f1, f2 *FractionType) (prod *FractionType) {
+	prod = NewFraction(f1.num*f2.num, f1.den*f2.den)
+	return
+}
+
+func anyToFract(v any) (f *FractionType, err error) {
+	var ok bool
+	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)
+		}
+	}
+	return
+}
+
+func anyPairToFract(v1, v2 any) (f1, f2 *FractionType, err error) {
+	if f1, err = anyToFract(v1); err != nil {
+		return
+	}
+	if f2, err = anyToFract(v2); err != nil {
+		return
+	}
+	return
+}
+
+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)
+	if f.num == 0 {
+		sum = 0
+	} else {
+		sum = simplifyFraction(f)
+	}
+	return
+}
+
+// Returns
+//
+//		 <0 if af1 < af2
+//		 =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) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	result = cmpFract(f1, f2)
+	return
+}
+
+// Returns
+//
+//	<0 if af1 < af2
+//	=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)
+		if f.num < 0 {
+			result = -1
+		} else if f.num > 0 {
+			result = 1
+		} else {
+			result = 0
+		}
+	}
+	return
+}
+
+func SubAnyFract(af1, af2 any) (sum any, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	f2.num = -f2.num
+	f := SumFract(f1, f2)
+	if f.num == 0 {
+		sum = 0
+	} else {
+		sum = simplifyFraction(f)
+	}
+	return
+}
+
+func MulAnyFract(af1, af2 any) (prod any, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	if f1.num == 0 || f2.num == 0 {
+		prod = 0
+	} else {
+		f := &FractionType{f1.num * f2.num, f1.den * f2.den}
+		prod = simplifyFraction(f)
+	}
+	return
+}
+
+func DivAnyFract(af1, af2 any) (quot any, err error) {
+	var f1, f2 *FractionType
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	if f2.num == 0 {
+		err = errors.New("division by zero")
+		return
+	}
+	if f1.num == 0 || f2.den == 0 {
+		quot = 0
+	} else {
+		f := &FractionType{f1.num * f2.den, f1.den * f2.num}
+		quot = simplifyFraction(f)
+	}
+	return
+}
+
+func simplifyFraction(f *FractionType) (v any) {
+	f.num, f.den = simplifyIntegers(f.num, f.den)
+	if f.den == 1 {
+		v = f.num
+	} else {
+		v = &FractionType{f.num, f.den}
+	}
+	return v
+}
+
+func simplifyIntegers(num, den int64) (a, b int64) {
+	if num == 0 {
+		return 0, 1
+	}
+	if den == 0 {
+		panic("fraction with denominator == 0")
+	}
+	if den < 0 {
+		den = -den
+		num = -num
+	}
+	g := Gcd(num, den)
+	a = num / g
+	b = den / g
+	return
+}
+
+func intToFraction(n int64) *FractionType {
+	return &FractionType{n, 1}
+}
+
+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 +1,52 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iterator.go
+package kern
+
+import (
+	// "errors"
+	"fmt"
+)
+
+// 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
+}

kern/list-type.go

@@ -0,0 +1,202 @@
+// 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 (dict *ListType) ToString(opt FmtOpt) (s string) {
+	indent := GetFormatIndent(opt)
+	flags := GetFormatFlags(opt)
+
+	var sb strings.Builder
+	sb.WriteByte('[')
+	if len(*dict) > 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(*dict) {
+			if i > 0 {
+				if flags&MultiLine != 0 {
+					sb.WriteString(",\n")
+					sb.WriteString(nest)
+				} else {
+					sb.WriteString(", ")
+				}
+			}
+			if s, ok := item.(string); ok {
+				sb.WriteByte('"')
+				sb.WriteString(s)
+				sb.WriteByte('"')
+			} else if formatter, ok := item.(Formatter); ok {
+				sb.WriteString(formatter.ToString(innerOpt))
+			} else {
+				sb.WriteString(fmt.Sprintf("%v", item))
+			}
+		}
+		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 (dict *ListType) String() string {
+	return dict.ToString(0)
+}
+
+func (dict *ListType) TypeName() string {
+	return "list"
+}
+
+func (dict *ListType) Contains(t *ListType) (answer bool) {
+	if len(*dict) >= len(*t) {
+		answer = true
+		for _, item := range *t {
+			if answer = dict.IndexDeepSameCmp(item) >= 0; !answer {
+				break
+			}
+		}
+	}
+	return
+}
+
+func (ls1 *ListType) Equals(ls2 ListType) (answer bool) {
+	if ls2 != nil && len(*ls1) == len(ls2) {
+		answer = true
+		for index, i1 := range *ls1 {
+			// if !reflect.DeepEqual(i1, ls2[index]) {
+			// 	answer = false
+			// 	break
+			// }
+			if !Equal(i1, ls2[index]) {
+				answer = false
+				break
+			}
+		}
+	}
+	return
+}
+
+func (dict *ListType) IndexDeepSameCmp(target any) (index int) {
+	var eq bool
+	var err error
+	index = -1
+	for i, item := range *dict {
+		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 (dict *ListType) SetItem(index int64, value any) (err error) {
+	if index >= 0 && index < int64(len(*dict)) {
+		(*dict)[index] = value
+	} else {
+		err = fmt.Errorf("index %d out of bounds (0, %d)", index, len(*dict)-1)
+	}
+	return
+}
+
+func (dict *ListType) AppendItem(value any) {
+	*dict = append(*dict, value)
+}

kern/number.go

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

kern/string.go

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

kern/term.go

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

lib-ext-darwin.go

@@ -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"

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
+}

operand-const.go

@@ -1,72 +0,0 @@
-// operand-const.go
-package expr
-
-// -------- bool const term
-func newBoolTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		class:    classConst,
-		kind:     kindBool,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- integer const term
-func newIntegerTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		class:    classConst,
-		kind:     kindInteger,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- float const term
-func newFloatTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		class:    classConst,
-		kind:     kindFloat,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- string const term
-func newStringTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		class:    classConst,
-		kind:     kindString,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- eval func
-func evalConst(ctx exprContext, self *term) (v any, err error) {
-	v = self.tk.Value
-	return
-}
-
-// init
-func init() {
-	registerTermConstructor(SymString, newStringTerm)
-	registerTermConstructor(SymInteger, newIntegerTerm)
-	registerTermConstructor(SymFloat, newFloatTerm)
-	registerTermConstructor(SymBool, newBoolTerm)
-}

operand-dict.go

@@ -0,0 +1,39 @@
+// 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]*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(0, 0, scan.SymDict, "{}", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalDict,
+	}
+}
+
+// -------- dict func
+func evalDict(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	dict, _ := opTerm.Value().(map[any]*scan.Term)
+	items := make(kern.DictType, len(dict))
+	for key, tree := range dict {
+		var param any
+		if param, err = tree.Compute(ctx); err != nil {
+			break
+		}
+		items[key] = param
+	}
+	if err == nil {
+		v = &items
+	}
+	return
+}

operand-expr.go

@@ -0,0 +1,35 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-expr.go
+package expr
+
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+// -------- expr term
+func newExprTerm(root *scan.Term) *scan.Term {
+	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymExpression, root.Source(), root)
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalExpr,
+	}
+}
+
+// -------- eval expr
+func evalExpr(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	if ast, ok := opTerm.Value().(*scan.Term); ok {
+		v, err = ast.Compute(ctx)
+	} else {
+		err = fmt.Errorf("expression expected, got %T", opTerm.Value())
+	}
+	return
+}

operand-func.go

@@ -1,33 +1,88 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // operand-func.go
 package expr
 
-// -------- function term
-func newFuncTerm(tk *Token, args []*term) *term {
-	return &term{
-		tk:       *tk,
-		class:    classVar,
-		kind:     kindUnknown,
-		parent:   nil,
-		children: args,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalFunc,
+import (
+	"errors"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+// -------- function call term
+func newFuncCallTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	var pos scan.TermPosition = scan.PosLeaf
+	if len(args) > 0 {
+		pos = scan.PosMultifix
+	}
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: args,
+		Position: pos,
+		Priority: scan.PriValue,
+		EvalFunc: evalFuncCall,
 	}
 }
 
-// -------- eval func
-func evalFunc(ctx exprContext, self *term) (v any, err error) {
-	name, _ := self.tk.Value.(string)
-	params := make([]any, len(self.children))
-	for i, tree := range self.children {
-		var param any
-		if param, err = tree.compute(ctx); err != nil {
-			break
+// -------- eval func call
+// func _evalFuncCall(ctx ExprContext, opTerm *term) (v any, err error) {
+// 	name, _ := opTerm.Tk.Value.(string)
+// 	params := make([]any, len(opTerm.Children), len(opTerm.Children)+5)
+// 	for i, tree := range opTerm.Children {
+// 		var param any
+// 		if param, err = tree.Compute(ctx); err != nil {
+// 			break
+// 		}
+// 		params[i] = param
+// 	}
+
+// 	if err == nil {
+// 		v, err = CallFunction(ctx, name, params)
+// 	}
+// 	return
+// }
+
+func evalFuncCall(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	name, _ := opTerm.Tk.Value.(string)
+	v, err = kern.CallFunctionByTerm(ctx, name, opTerm)
+	return
+}
+
+// -------- function definition term
+func newFuncDefTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk, // value is the expression body
+		Parent:   nil,
+		Children: args, // function params
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalFuncDef,
 	}
-		params[i] = param
+}
+
+// -------- eval func def
+func evalFuncDef(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	bodySpec := opTerm.Value()
+	if ast, ok := bodySpec.(*scan.Ast); ok {
+		paramList := make([]kern.ExprFuncParam, 0, len(opTerm.Children))
+		for _, param := range opTerm.Children {
+			var defValue any
+			flags := kern.FuncParamFlags(0)
+			if len(param.Children) > 0 {
+				flags |= kern.PfDefault
+				if defValue, err = param.Children[0].Compute(ctx); err != nil {
+					return
 				}
-	if err == nil {
-		v, err = ctx.Call(name, params)
+			}
+			info := kern.NewFuncParamFlagDef(param.Source(), flags, defValue)
+			paramList = append(paramList, info)
+		}
+		v = newExprFunctor(ast, paramList, ctx)
+	} else {
+		err = errors.New("invalid function definition: the body specification must be an expression")
 	}
 	return
 }

operand-iterator.go

@@ -0,0 +1,203 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-iterator.go
+package expr
+
+import (
+	"slices"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+// -------- iterator term
+
+func newIteratorTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	tk.Sym = scan.SymIterator
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: args,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalIterator,
+	}
+}
+
+// -------- eval iterator
+
+func evalTermArray(ctx kern.ExprContext, terms []*scan.Term) (values []any, err error) {
+	values = make([]any, len(terms))
+	for i, t := range terms {
+		var value any
+		if value, err = t.Compute(ctx); err == nil {
+			values[i] = value
+		} else {
+			break
+		}
+	}
+	return
+}
+
+func evalFirstChild(ctx kern.ExprContext, iteratorTerm *scan.Term) (value any, err error) {
+	if len(iteratorTerm.Children) < 1 || iteratorTerm.Children[0] == nil {
+		err = iteratorTerm.Errorf("missing the data-source parameter")
+		return
+	}
+
+	value, err = iteratorTerm.Children[0].Compute(ctx)
+	return
+}
+
+func getDataSourceDict(iteratorTerm *scan.Term, firstChildValue any) (ds map[string]kern.Functor, err error) {
+	if dictAny, ok := firstChildValue.(*kern.DictType); ok {
+		requiredFields := []string{kern.NextName}
+		fieldsMask := 0b1
+		foundFields := 0
+		ds = make(map[string]kern.Functor)
+		for keyAny, item := range *dictAny {
+			if key, ok := keyAny.(string); ok {
+				if functor, ok := item.(kern.Functor); ok {
+					ds[key] = functor
+					if index := slices.Index(requiredFields, key); index >= 0 {
+						foundFields |= 1 << index
+					}
+				}
+			}
+		}
+		// check required functions
+		if foundFields != fieldsMask {
+			missingFields := make([]string, 0, len(requiredFields))
+			for index, field := range requiredFields {
+				if (foundFields & (1 << index)) == 0 {
+					missingFields = append(missingFields, field)
+				}
+			}
+			err = iteratorTerm.Children[0].Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
+		}
+	}
+	return
+}
+
+func evalIterator(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var firstChildValue any
+	var ds map[string]kern.Functor
+
+	if firstChildValue, err = evalFirstChild(ctx, opTerm); err != nil {
+		return
+	}
+
+	if ds, err = getDataSourceDict(opTerm, firstChildValue); err != nil && ds == nil {
+		return
+	}
+	err = nil
+
+	if ds != nil {
+		if len(ds) > 0 {
+			var dc *dataCursor
+			dcCtx := ctx.Clone()
+			if initFunc, exists := ds[kern.InitName]; exists && initFunc != nil {
+				var args []any
+				var resource any
+				if len(opTerm.Children) > 1 {
+					if args, err = evalTermArray(ctx, opTerm.Children[1:]); err != nil {
+						return
+					}
+				} else {
+					args = []any{}
+				}
+
+				actualParams := kern.BindActualParams(initFunc, args)
+
+				initCtx := ctx.Clone()
+				if resource, err = initFunc.InvokeNamed(initCtx, kern.InitName, actualParams); err != nil {
+					return
+				}
+				kern.ExportObjects(dcCtx, initCtx)
+				dc = NewDataCursor(dcCtx, ds, resource)
+			} else {
+				dc = NewDataCursor(dcCtx, ds, nil)
+			}
+
+			v = dc
+		} else {
+			if dictIt, ok := firstChildValue.(*kern.DictType); ok {
+				var args []any
+				if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
+					v, err = NewDictIterator(dictIt, args)
+				}
+			} else {
+				err = opTerm.Children[0].Errorf("the data-source must be a dictionary")
+			}
+		}
+	} 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 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 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
+		if i == 0 {
+			if firstChildValue == nil {
+				continue
+			}
+			param = firstChildValue
+		} else if param, err = tree.Compute(ctx); err != nil {
+			break
+		}
+		items = append(items, param)
+	}
+	if err == nil {
+		list = items
+	}
+	return
+}

operand-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 newListTermA(args ...*scan.Term) *scan.Term {
+	return newListTerm(0, 0, args)
+}
+
+func newListTerm(row, col int, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(row, col, scan.SymList, "[]", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalList,
+	}
+}
+
+// -------- list func
+func evalList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	list, _ := opTerm.Value().([]*scan.Term)
+	items := make(kern.ListType, len(list))
+	for i, tree := range list {
+		var param any
+		if param, err = tree.Compute(ctx); err != nil {
+			break
+		}
+		items[i] = param
+	}
+	if err == nil {
+		v = &items
+	}
+	return
+}

operand-literal.go

@@ -0,0 +1,38 @@
+// 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 *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalLiteral,
+	}
+}
+
+// -------- eval func
+func evalLiteral(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	v = opTerm.Tk.Value
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymString, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymInteger, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFloat, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFraction, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymBool, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymKwNil, newLiteralTerm)
+}

operand-selector-case.go

@@ -0,0 +1,53 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-selector-case.go
+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 *scan.Term
+	caseExpr   kern.Expr
+}
+
+func (sc *selectorCase) String() string {
+	var sb strings.Builder
+	if sc.filterList != nil {
+		sc.filterList.ToString(&sb)
+		sb.WriteByte(' ')
+	}
+	sb.WriteByte('{')
+	sb.WriteString(sc.caseExpr.String())
+	sb.WriteByte('}')
+	return sb.String()
+}
+
+func newSelectorCaseTerm(row, col int, filterList *scan.Term, caseExpr kern.Expr) *scan.Term {
+	tk := scan.NewValueToken(row, col, scan.SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalSelectorCase,
+	}
+}
+
+// -------- eval selector case
+func evalSelectorCase(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var ok bool
+	if v, ok = opTerm.Value().(*selectorCase); !ok {
+		err = fmt.Errorf("selector-case expected, got %T", opTerm.Value())
+	}
+	return
+}

operand-var.go

@@ -1,32 +1,45 @@
+// 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 {
-	return &term{
-		tk:       *tk,
-		class:    classVar,
-		kind:     kindUnknown,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalVar,
+func newVarTerm(tk *scan.Token) *scan.Term {
+	t := &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalVar,
 	}
+	t.Tk.Sym = 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
-	if v, exists = ctx.GetValue(self.tk.source); !exists {
-		err = fmt.Errorf("undefined variable %q", self.tk.source)
+	name := opTerm.Source()
+	if v, exists = ctx.GetVar(name); !exists {
+		if info, exists := ctx.GetFuncInfo(name); exists {
+			v = info.Functor()
+		} else {
+			err = fmt.Errorf("undefined variable or function %q", name)
+		}
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymIdentifier, newVarTerm)
+	scan.RegisterTermConstructor(scan.SymIdentifier, newVarTerm)
 }

operator-assign.go

@@ -0,0 +1,226 @@
+// 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 *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAssign,
+		EvalFunc: evalAssign,
+	}
+}
+
+func assignCollectionItem(ctx 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 {
+			err = collection.SetItem(index, value)
+		} else {
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
+		}
+	case *kern.DictType:
+		collection.SetItem(keyValue, value)
+	default:
+		err = collectionTerm.Errorf("collection expected")
+	}
+	return
+}
+
+func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any) (err error) {
+	if leftTerm.Symbol() == scan.SymIndex {
+		err = assignCollectionItem(ctx, leftTerm.Children[0], leftTerm.Children[1], v)
+	} else {
+		ctx.UnsafeSetVar(leftTerm.Source(), v)
+	}
+	return
+}
+
+func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	leftTerm := opTerm.Children[0]
+	leftSym := leftTerm.Symbol()
+	if leftSym != 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())
+				} else if funcDef, ok := functor.(*exprFunctor); ok {
+					paramSpecs := util.ForAll(funcDef.params, func(p kern.ExprFuncParam) kern.ExprFuncParam { return p })
+
+					ctx.RegisterFunc(leftTerm.Source(), functor, kern.TypeAny, paramSpecs)
+				} else {
+					err = opTerm.Errorf("unknown function %s()", rightChild.Source())
+				}
+			} else {
+				err = assignValue(ctx, leftTerm, v)
+			}
+		} else {
+			err = assignValue(ctx, leftTerm, v)
+		}
+	}
+	if err != nil {
+		v = nil
+	}
+	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)
+			}
+		}
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymEqual, newAssignTerm)
+	scan.RegisterTermConstructor(scan.SymPlusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymMinusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymStarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymSlashEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymPercEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleLessEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleGreaterEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymAmpersandEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymVertBarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymCaretEqual, newOpAssignTerm)
+}

operator-bitwise.go

@@ -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

@@ -1,106 +1,181 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // operator-bool.go
 package expr
 
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- NOT term
 
-func newNotTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priNot,
-		evalFunc: evalNot,
+func newNotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriNot,
+		EvalFunc: evalNot,
 	}
 }
 
-func evalNot(ctx exprContext, 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) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priAnd,
-		evalFunc: evalAnd,
+func newAndTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAnd,
+		EvalFunc: evalAnd,
 	}
 }
 
-func evalAnd(ctx exprContext, self *term) (v any, err error) {
+func evalAnd(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
+	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
+		v, err = evalAndWithShortcut(ctx, self)
+	} else {
+		v, err = evalAndWithoutShortcut(ctx, self)
+	}
+	return
+}
+
+func evalAndWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var leftBool, rightBool bool
 	var lok, rok bool
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = self.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	leftBool, lok = toBool(leftValue)
-	rightBool, rok = toBool(rightValue)
+	leftBool, lok = kern.ToBool(leftValue)
+	rightBool, rok = kern.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool && rightBool
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = self.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func evalAndWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if err = self.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = self.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if leftBool, lok := kern.ToBool(leftValue); !lok {
+		// err = fmt.Errorf("got %s as left operand type of 'AND' operator, it must be bool", expr.TypeName(leftValue))
+		// return
+		err = self.ErrIncompatibleType(leftValue, "left")
+	} else if !leftBool {
+		v = false
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
+		if rightBool, rok := kern.ToBool(rightValue); rok {
+			v = rightBool
+		} else {
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
+		}
 	}
 	return
 }
 
 //-------- OR term
 
-func newOrTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priOr,
-		evalFunc: evalOr,
+func newOrTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriOr,
+		EvalFunc: evalOr,
 	}
 }
 
-func evalOr(ctx exprContext, self *term) (v any, err error) {
+func evalOr(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
+	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
+		v, err = evalOrWithShortcut(ctx, self)
+	} else {
+		v, err = evalOrWithoutShortcut(ctx, self)
+	}
+	return
+}
+
+func evalOrWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var leftBool, rightBool bool
 	var lok, rok bool
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = self.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	leftBool, lok = toBool(leftValue)
-	rightBool, rok = toBool(rightValue)
+	leftBool, lok = kern.ToBool(leftValue)
+	rightBool, rok = kern.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool || rightBool
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = self.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func evalOrWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if err = self.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = self.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if leftBool, lok := kern.ToBool(leftValue); !lok {
+		err = fmt.Errorf("got %s as left operand type of 'OR' operator, it must be bool", kern.TypeName(leftValue))
+		return
+	} else if leftBool {
+		v = true
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
+		if rightBool, rok := kern.ToBool(rightValue); rok {
+			v = rightBool
+		} else {
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
+		}
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymNot, newNotTerm)
-	registerTermConstructor(SymAnd, newAndTerm)
-	registerTermConstructor(SymOr, newOrTerm)
+	scan.RegisterTermConstructor(scan.SymNot, newNotTerm)
+	scan.RegisterTermConstructor(scan.SymAnd, newAndTerm)
+	scan.RegisterTermConstructor(scan.SymOr, newOrTerm)
 }

operator-builtin.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-builtin.go
+package expr
+
+import (
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- builtin term
+
+func newBuiltinTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalBuiltin,
+	}
+}
+
+func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
+		return
+	}
+
+	count := 0
+	if kern.IsString(childValue) {
+		module, _ := childValue.(string)
+		count, err = ImportInContextByGlobPattern(ctx, module)
+	} else {
+		var moduleSpec any
+		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(ctx, module) {
+					count++
+				} else {
+					err = opTerm.Errorf("unknown builtin module %q", module)
+					break
+				}
+			} else {
+				err = opTerm.Errorf("expected string at item nr %d, got %s", it.Index()+1, kern.TypeName(moduleSpec))
+				break
+			}
+		}
+		if err == io.EOF {
+			err = nil
+		}
+	}
+	if err == nil {
+		v = int64(count)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwBuiltin, newBuiltinTerm)
+}

operator-but.go

@@ -0,0 +1,32 @@
+// 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 *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBut,
+		EvalFunc: evalBut,
+	}
+}
+
+func evalBut(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	_, v, err = opTerm.EvalInfix(ctx)
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwBut, newButTerm)
+}

operator-context.go

@@ -0,0 +1,65 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-context-value.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- context term
+
+func newContextTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalContextValue,
+	}
+}
+
+func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var childValue any
+
+	var sourceCtx kern.ExprContext
+	if len(opTerm.Children) == 0 {
+		sourceCtx = ctx
+	} else if opTerm.Children[0].Symbol() == scan.SymVariable && opTerm.Children[0].Source() == "global" {
+		sourceCtx = ctx.GetGlobal()
+	} else if childValue, err = opTerm.EvalPrefix(ctx); err == nil {
+		if dc, ok := childValue.(*dataCursor); ok {
+			sourceCtx = dc.ctx
+		}
+	}
+
+	if sourceCtx != nil {
+		if formatter, ok := sourceCtx.(kern.DictFormat); ok {
+			v = formatter.ToDict()
+		} else if formatter, ok := sourceCtx.(kern.Formatter); ok {
+			v = formatter.ToString(0)
+		} else {
+			// keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+			keys := sourceCtx.EnumVars(nil)
+			d := make(map[string]any)
+			for _, key := range keys {
+				d[key], _ = sourceCtx.GetVar(key)
+			}
+			keys = sourceCtx.EnumFuncs(func(name string) bool { return true })
+			for _, key := range keys {
+				d[key], _ = sourceCtx.GetFuncInfo(key)
+			}
+			v = d
+		}
+	} else {
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymDoubleDollar, newContextTerm)
+}

operator-ctrl.go

@@ -0,0 +1,32 @@
+// 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 *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalExportAll,
+	}
+}
+
+func evalExportAll(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	CtrlEnable(ctx, kern.ControlExportAll)
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymDoubleAt, newExportAllTerm)
+}

operator-default.go

@@ -0,0 +1,129 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-default.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- default term
+
+func newDefaultTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalDefault,
+	}
+}
+
+func evalDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var rightValue any
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
+		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
+		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
+		return
+	}
+
+	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists {
+		v = leftValue
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+		v = rightValue
+	}
+	return
+}
+
+//-------- alternate term
+
+func newAlternateTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalAlternate,
+	}
+}
+
+func evalAlternate(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var rightValue any
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
+		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
+		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
+		return
+	}
+
+	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists && leftValue != nil {
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			v = rightValue
+		}
+	} else {
+		v = leftValue
+	}
+	return
+}
+
+//-------- default assign term
+
+func newDefaultAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalAssignDefault,
+	}
+}
+
+func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var rightValue any
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
+		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
+		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
+		return
+	}
+
+	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists {
+		v = leftValue
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+		if functor, ok := rightValue.(kern.Functor); ok {
+			//ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
+			ctx.RegisterFunc(leftTerm.Source(), functor, kern.TypeAny, []kern.ExprFuncParam{
+				kern.NewFuncParamFlag(kern.ParamValue, kern.PfDefault|kern.PfRepeat),
+			})
+		} else {
+			v = rightValue
+			ctx.UnsafeSetVar(leftTerm.Source(), rightValue)
+		}
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymDoubleQuestion, newDefaultTerm)
+	scan.RegisterTermConstructor(scan.SymQuestionEqual, newDefaultAssignTerm)
+	scan.RegisterTermConstructor(scan.SymQuestionExclam, newAlternateTerm)
+}

operator-digest.go

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

operator-dot.go

@@ -0,0 +1,75 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-dot.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+// -------- dot term
+func newDotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDot,
+		EvalFunc: evalDot,
+	}
+}
+
+func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	indexTerm := opTerm.Children[1]
+
+	switch unboxedValue := leftValue.(type) {
+	case kern.ExtIterator:
+		if indexTerm.Tk.Sym == scan.SymVariable /*|| indexTerm.Tk.Sym == scan.SymString */ {
+			opName := indexTerm.Source()
+			if unboxedValue.HasOperation(opName) {
+				v, err = unboxedValue.CallOperation(opName, map[string]any{})
+			} else {
+				err = indexTerm.Errorf("this iterator do not support the %q command", opName)
+				v = false
+			}
+		} else {
+			err = indexTerm.Tk.ErrorExpectedGot("identifier")
+		}
+	case *kern.DictType:
+		var ok bool
+		s := opTerm.Children[1].Tk.Sym
+		if s == scan.SymVariable || s == scan.SymString {
+			src := opTerm.Children[1].Source()
+			if len(src) > 1 && src[0] == '"' && src[len(src)-1] == '"' {
+				src = src[1 : len(src)-1]
+			}
+			if v, ok = unboxedValue.GetItem(src); !ok {
+				err = opTerm.Errorf("key %q not found", src)
+			}
+		} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			if v, ok = unboxedValue.GetItem(rightValue); !ok {
+				err = opTerm.Errorf("key %q not found", rightValue)
+			}
+		}
+	default:
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			err = opTerm.Errorf("incompatible types: %s and %s", kern.TypeName(leftValue), kern.TypeName(rightValue))
+		}
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymDot, newDotTerm)
+}

operator-fact.go

@@ -1,30 +1,36 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // operator-fact.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
 
 //-------- fact term
 
-func newFactTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindInteger,
-		children: make([]*term, 0, 1),
-		position: posPostfix,
-		priority: priFact,
-		evalFunc: evalFact,
+func newFactTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPostfix,
+		Priority: scan.PriFact,
+		EvalFunc: evalFact,
 	}
 }
 
-func evalFact(ctx exprContext, self *term) (v any, err error) {
+func evalFact(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue any
 
-	if leftValue, err = self.evalPrefix(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if isInteger(leftValue) {
+	if kern.IsInteger(leftValue) {
 		if i, _ := leftValue.(int64); i >= 0 {
 			f := int64(1)
 			for k := int64(1); k <= i; k++ {
@@ -35,12 +41,12 @@ func evalFact(ctx exprContext, self *term) (v any, err error) {
 			err = fmt.Errorf("factorial of a negative integer (%d) is not allowed", i)
 		}
 	} else {
-		err = self.errIncompatibleType(leftValue)
+		err = opTerm.Errorf("incompatible type for factorial: %s", kern.TypeName(leftValue))
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymExclamation, newFactTerm)
+	scan.RegisterTermConstructor(scan.SymExclamation, newFactTerm)
 }

operator-filter.go

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

operator-fraction.go

@@ -0,0 +1,75 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-fraction.go
+package expr
+
+//https://www.youmath.it/lezioni/algebra-elementare/lezioni-di-algebra-e-aritmetica-per-scuole-medie/553-dalle-frazioni-a-numeri-decimali.html
+
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+// -------- fraction term
+func newFractionTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriFraction,
+		EvalFunc: evalFraction,
+	}
+}
+
+// -------- eval func
+func evalFraction(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var numValue, denValue any
+	var num, den int64
+	var ok bool
+
+	if numValue, denValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+	if num, ok = numValue.(int64); !ok {
+		err = fmt.Errorf("numerator must be integer, got %T (%v)", numValue, numValue)
+		return
+	}
+	if den, ok = denValue.(int64); !ok {
+		err = fmt.Errorf("denominator must be integer, got %T (%v)", denValue, denValue)
+		return
+	}
+	if den == 0 {
+		err = opTerm.Errorf("division by zero")
+		return
+	}
+
+	if den < 0 {
+		den = -den
+		num = -num
+	}
+	if num != 0 {
+		if g := kern.Gcd(num, den); g != 1 {
+			num = num / g
+			den = den / g
+		}
+		if den == 1 {
+			v = num
+		} else {
+			// v = &expr.FractionType{num, den}
+			v = kern.NewFraction(num, den)
+		}
+	} else {
+		// v = &FractionType{0, den}
+		v = kern.NewFraction(0, den)
+	}
+	return
+}
+
+// init
+func init() {
+	// registerTermConstructor(SymVertBar, newFractionTerm)
+	scan.RegisterTermConstructor(scan.SymColon, newFractionTerm)
+}

operator-groupby.go

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

operator-in.go

@@ -0,0 +1,51 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-in.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- in term
+
+func newInTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalIn,
+	}
+}
+
+// func hasKey(d map[any]any, target any) (ok bool) {
+// 	_, ok = d[target]
+// 	return
+// }
+
+func evalIn(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	if kern.IsList(rightValue) {
+		list, _ := rightValue.(*kern.ListType)
+		v = list.IndexDeepSameCmp(leftValue) >= 0
+	} else if kern.IsDict(rightValue) {
+		dict, _ := rightValue.(*kern.DictType)
+		v = dict.HasKey(leftValue)
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwIn, newInTerm)
+}

operator-include.go

@@ -0,0 +1,65 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-include.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- include term
+
+func newIncludeTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalInclude,
+	}
+}
+
+func evalInclude(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
+		return
+	}
+
+	count := 0
+	if kern.IsList(childValue) {
+		list, _ := childValue.(*kern.ListType)
+		for i, filePathSpec := range *list {
+			if filePath, ok := filePathSpec.(string); ok {
+				if v, err = EvalFile(ctx, filePath); err == nil {
+					count++
+				} else {
+					err = opTerm.Errorf("can't load file %q", filePath)
+					break
+				}
+			} else {
+				err = opTerm.Errorf("expected string at item nr %d, got %T", i+1, filePathSpec)
+				break
+			}
+		}
+	} else if kern.IsString(childValue) {
+		filePath, _ := childValue.(string)
+		if v, err = EvalFile(ctx, filePath); err == nil {
+			count++
+		}
+	} else {
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
+	}
+	if err != nil {
+		//v = count
+		v = nil
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwInclude, newIncludeTerm)
+}

operator-index.go

@@ -0,0 +1,143 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-index.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+// -------- index term
+func newIndexTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDot,
+		EvalFunc: evalIndex,
+	}
+}
+
+func verifyKey(indexList *kern.ListType) (index any, err error) {
+	index = (*indexList)[0]
+	return
+}
+
+func verifyIndex(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (index int, err error) {
+	var v int
+
+	if v, err = kern.ToGoInt((*indexList)[0], "index expression"); err == nil {
+		if v < 0 && v >= -maxValue {
+			v = maxValue + v
+		}
+		if v >= 0 && v < maxValue {
+			index = v
+		} else {
+			err = indexTerm.Errorf("index %d out of bounds", v)
+		}
+	}
+	return
+}
+
+func verifyRange(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (startIndex, endIndex int, err error) {
+	v, _ := ((*indexList)[0]).(*intPair)
+	startIndex = v.a
+	endIndex = v.b
+	if endIndex == kern.ConstLastIndex {
+		endIndex = maxValue
+	}
+	if startIndex < 0 && startIndex >= -maxValue {
+		startIndex = maxValue + startIndex
+	}
+	if endIndex < 0 && endIndex >= -maxValue {
+		endIndex = maxValue + endIndex
+	}
+	if startIndex < 0 || startIndex > maxValue {
+		err = indexTerm.Errorf("range start-index %d is out of bounds", startIndex)
+	} else if endIndex < 0 || endIndex > maxValue {
+		err = indexTerm.Errorf("range end-index %d is out of bounds", endIndex)
+	} else if startIndex > endIndex {
+		err = indexTerm.Errorf("range start-index %d must not be greater than end-index %d", startIndex, endIndex)
+	}
+	return
+}
+
+func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var indexList *kern.ListType
+	var ok bool
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	indexTerm := opTerm.Children[1]
+	if indexList, ok = rightValue.(*kern.ListType); !ok {
+		err = opTerm.Errorf("invalid index expression")
+		return
+	} else if len(*indexList) != 1 {
+		err = indexTerm.Errorf("one index only is allowed")
+		return
+	}
+
+	if kern.IsInteger((*indexList)[0]) {
+		switch unboxedValue := leftValue.(type) {
+		case *kern.ListType:
+			var index int
+			if index, err = verifyIndex(indexTerm, indexList, len(*unboxedValue)); err == nil {
+				v = (*unboxedValue)[index]
+			}
+		case string:
+			var index int
+			if index, err = verifyIndex(indexTerm, indexList, len(unboxedValue)); err == nil {
+				v = string(unboxedValue[index])
+			}
+		case *kern.DictType:
+			v, err = getDictItem(unboxedValue, indexTerm, indexList, rightValue)
+		default:
+			err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+		}
+	} else if isIntPair((*indexList)[0]) {
+		switch unboxedValue := leftValue.(type) {
+		case *kern.ListType:
+			var start, end int
+			if start, end, err = verifyRange(indexTerm, indexList, len(*unboxedValue)); err == nil {
+				sublist := kern.ListType((*unboxedValue)[start:end])
+				v = &sublist
+			}
+		case string:
+			var start, end int
+			if start, end, err = verifyRange(indexTerm, indexList, len(unboxedValue)); err == nil {
+				v = unboxedValue[start:end]
+			}
+		default:
+			err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+		}
+	} else if kern.IsDict(leftValue) {
+		d := leftValue.(*kern.DictType)
+		v, err = getDictItem(d, indexTerm, indexList, rightValue)
+	} else {
+		rightChild := opTerm.Children[1]
+		err = rightChild.Errorf("invalid index type: %v", (*indexList)[0])
+	}
+	return
+}
+
+func getDictItem(d *kern.DictType, indexTerm *scan.Term, indexList *kern.ListType, rightValue any) (v any, err error) {
+	var ok bool
+	var indexValue any
+
+	if indexValue, err = verifyKey(indexList); err == nil {
+		if v, ok = (*d)[indexValue]; !ok {
+			err = indexTerm.Errorf("key %v does not belong to the dictionary", rightValue)
+		}
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymIndex, newIndexTerm)
+}

operator-insert.go

@@ -0,0 +1,96 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-insert.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- prepend term
+
+func newPrependTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriInsert,
+		EvalFunc: evalPrepend,
+	}
+}
+
+func newAppendTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriInsert,
+		EvalFunc: evalAppend,
+	}
+}
+
+func evalPrepend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	if kern.IsList(rightValue) {
+		list, _ := rightValue.(*kern.ListType)
+		newList := append(kern.ListType{leftValue}, *list...)
+		v = &newList
+		if opTerm.Children[1].Symbol() == scan.SymVariable {
+			ctx.UnsafeSetVar(opTerm.Children[1].Source(), v)
+		}
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func evalAppend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	if kern.IsList(leftValue) {
+		list, _ := leftValue.(*kern.ListType)
+		newList := append(*list, rightValue)
+		v = &newList
+		if opTerm.Children[0].Symbol() == scan.SymVariable {
+			ctx.UnsafeSetVar(opTerm.Children[0].Source(), v)
+		}
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// func evalAssignAppend(ctx ExprContext, self *term) (v any, err error) {
+// 	var leftValue, rightValue any
+
+// 	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+// 		return
+// 	}
+
+// 	if IsList(leftValue) {
+// 		list, _ := leftValue.(*ListType)
+// 		newList := append(*list, rightValue)
+// 		v = &newList
+// 		if
+// 	} else {
+// 		err = self.errIncompatibleTypes(leftValue, rightValue)
+// 	}
+// 	return
+// }
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymPlusGreater, newPrependTerm)
+	scan.RegisterTermConstructor(scan.SymLessPlus, newAppendTerm)
+}

operator-iter-value.go

@@ -0,0 +1,43 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-iter-value.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- iter value term
+
+func newIterValueTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriDereference,
+		EvalFunc: evalIterValue,
+	}
+}
+
+func evalIterValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
+		return
+	}
+
+	if it, ok := childValue.(kern.Iterator); ok {
+		v, err = it.Current()
+	} else {
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	//	registerTermConstructor(SymOpenClosedRound, newIterValueTerm)
+	scan.RegisterTermConstructor(scan.SymDereference, newIterValueTerm)
+}

operator-join.go

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

operator-length.go

@@ -0,0 +1,57 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-length.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- length term
+
+func newLengthTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalLength,
+	}
+}
+
+func evalLength(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
+		return
+	}
+
+	if kern.IsList(childValue) {
+		ls, _ := childValue.(*kern.ListType)
+		v = int64(len(*ls))
+	} else if kern.IsString(childValue) {
+		s, _ := childValue.(string)
+		v = int64(len(s))
+	} else if kern.IsDict(childValue) {
+		m, _ := childValue.(*kern.DictType)
+		v = int64(len(*m))
+	} else if it, ok := childValue.(kern.Iterator); ok {
+		v = int64(it.Count())
+		// if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(CountName) {
+		// 	count, _ := extIt.CallOperation(CountName, nil)
+		// 	v, _ = ToGoInt(count, "")
+		// } else {
+		// 	v = int64(it.Index() + 1)
+		// }
+	} else {
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymHash, newLengthTerm)
+}

operator-map.go

@@ -0,0 +1,74 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-map.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- map term
+
+func newMapTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalMap,
+	}
+}
+
+func evalMap(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var it kern.Iterator
+	var item any
+	var ok bool
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if it, ok = leftValue.(kern.Iterator); !ok {
+		if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
+	}
+
+	values := kern.NewListA()
+	for item, err = it.Next(); err == nil; item, err = it.Next() {
+		ctx.SetVar("_", item)
+		ctx.SetVar("__", it.Index())
+		ctx.SetVar("_#", it.Count())
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			values.AppendItem(rightValue)
+		}
+		ctx.DeleteVar("_#")
+		ctx.DeleteVar("__")
+		ctx.DeleteVar("_")
+		if err != nil {
+			break
+		}
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	if err == nil {
+		v = values
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwMap, newMapTerm)
+}

operator-plugin.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-plugin.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- plugin term
+
+func newPluginTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalPlugin,
+	}
+}
+
+func evalPlugin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var childValue any
+	var count int
+
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
+		return
+	}
+
+	if count, err = importPluginFromSearchPath(ctx, childValue); err == nil {
+		v = int64(count)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwPlugin, newPluginTerm)
+}

operator-post-inc-dec.go

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

operator-pre-inc-dec.go

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

operator-prod.go

@@ -1,95 +1,203 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // operator-prod.go
 package expr
 
 import (
-	"errors"
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- multiply term
 
-func newMultiplyTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindUnknown,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalMultiply,
+func newMultiplyTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalMultiply,
 	}
 }
 
-func evalMultiply(ctx exprContext, self *term) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
-		return
-	}
-
-	if isString(leftValue) && isInteger(rightValue) {
+func mulValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsString(leftValue) && kern.IsInteger(rightValue) {
 		s, _ := leftValue.(string)
 		n, _ := rightValue.(int64)
 		v = strings.Repeat(s, int(n))
-	} else if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
-			v = numAsFloat(leftValue) * numAsFloat(rightValue)
+	} else if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) * kern.NumAsFloat(rightValue)
+		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+			v, err = kern.MulAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt * rightInt
 		}
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
+func evalMultiply(ctx kern.ExprContext, prodTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = prodTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	return mulValues(prodTerm, leftValue, rightValue)
+}
+
 //-------- divide term
 
-func newDivideTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindUnknown,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalDivide,
+func newDivideTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalDivide,
 	}
 }
 
-func evalDivide(ctx exprContext, self *term) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
-		return
-	}
-
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
-			d := numAsFloat(rightValue)
+func divValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			d := kern.NumAsFloat(rightValue)
 			if d == 0.0 {
-				err = errors.New("division by zero")
+				err = opTerm.ErrDivisionByZero()
 			} else {
-				v = numAsFloat(leftValue) / d
+				v = kern.NumAsFloat(leftValue) / d
 			}
+		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+			v, err = kern.DivAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			if rightInt, _ := rightValue.(int64); rightInt == 0 {
-				err = errors.New("division by zero")
+				err = opTerm.ErrDivisionByZero()
 			} else {
 				v = leftInt / rightInt
 			}
 		}
+	} else if kern.IsString(leftValue) && kern.IsString(rightValue) {
+		source := leftValue.(string)
+		sep := rightValue.(string)
+		v = kern.ListFromStrings(strings.Split(source, sep))
+	} else if kern.IsString(leftValue) && kern.IsInteger(rightValue) {
+		source := leftValue.(string)
+		partSize := int(rightValue.(int64))
+		if partSize == 0 {
+			err = opTerm.ErrDivisionByZero()
 		} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+			partCount := len(source) / partSize
+			remainder := len(source) % partSize
+			listSize := partCount
+			if remainder > 0 {
+				listSize++
+			}
+			parts := make([]any, 0, listSize)
+			for i := 0; i < partCount; i++ {
+				parts = append(parts, source[i*partSize:(i+1)*partSize])
+			}
+			if remainder > 0 {
+				parts = append(parts, source[len(source)-remainder:])
+			}
+			v = kern.NewList(parts)
+		}
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
+func evalDivide(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	return divValues(opTerm, leftValue, rightValue)
+}
+
+//-------- divide as float term
+
+func newDivideAsFloatTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalDivideAsFloat,
+	}
+}
+
+func evalDivideAsFloat(ctx kern.ExprContext, floatDivTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = floatDivTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		d := kern.NumAsFloat(rightValue)
+		if d == 0.0 {
+			err = floatDivTerm.ErrDivisionByZero()
+		} else {
+			v = kern.NumAsFloat(leftValue) / d
+		}
+	} else {
+		err = floatDivTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+//-------- reminder term
+
+func newRemainderTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalRemainder,
+	}
+}
+func remainderValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
+		rightInt, _ := rightValue.(int64)
+		if rightInt == 0 {
+			err = opTerm.ErrDivisionByZero()
+		} else {
+			leftInt, _ := leftValue.(int64)
+			v = leftInt % rightInt
+		}
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func evalRemainder(ctx kern.ExprContext, remainderTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = remainderTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	return remainderValues(remainderTerm, leftValue, rightValue)
+}
+
 // init
 func init() {
-	registerTermConstructor(SymStar, newMultiplyTerm)
-	registerTermConstructor(SymSlash, newDivideTerm)
+	scan.RegisterTermConstructor(scan.SymStar, newMultiplyTerm)
+	scan.RegisterTermConstructor(scan.SymSlash, newDivideTerm)
+	scan.RegisterTermConstructor(scan.SymDotSlash, newDivideAsFloatTerm)
+	scan.RegisterTermConstructor(scan.SymPercent, newRemainderTerm)
 }

operator-range.go

@@ -0,0 +1,87 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-range.go
+package expr
+
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+// -------- range term
+type intPair struct {
+	a, b int
+}
+
+func (p *intPair) TypeName() string {
+	return kern.TypePair
+}
+
+func (p *intPair) ToString(opt kern.FmtOpt) string {
+	return fmt.Sprintf("(%d, %d)", p.a, p.b)
+}
+
+func isIntPair(v any) bool {
+	_, ok := v.(*intPair)
+	return ok
+}
+
+func newRangeTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRange,
+		EvalFunc: evalRange,
+	}
+}
+
+func changeColonToRange(t *scan.Term) {
+	if t.Tk.IsSymbol(scan.SymColon) {
+		t.Tk.Sym = scan.SymRange
+		t.EvalFunc = evalRange
+	}
+}
+
+func evalRange(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if len(opTerm.Children) == 0 {
+		leftValue = int64(0)
+		rightValue = int64(-1)
+	} else if len(opTerm.Children) == 1 {
+		if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+			return
+		}
+		rightValue = int64(kern.ConstLastIndex)
+	} else if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+	if !(kern.IsInteger(leftValue) && kern.IsInteger(rightValue)) {
+		// err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = errRangeInvalidSpecification(opTerm)
+		return
+	}
+
+	startIndex, _ := leftValue.(int64)
+	endIndex, _ := rightValue.(int64)
+
+	v = &intPair{int(startIndex), int(endIndex)}
+	return
+}
+
+func errRangeInvalidSpecification(t *scan.Term) error {
+	return t.Errorf("invalid range specification")
+}
+
+func errRangeUnexpectedExpression(t *scan.Term) error {
+	return t.Errorf("unexpected range expression")
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymRange, newRangeTerm)
+}

operator-rel.go

@@ -1,220 +1,228 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // operator-rel.go
 package expr
 
+import (
+	"reflect"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- equal term
 
-func newEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalEqual,
+func newEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalEqual,
 	}
 }
 
-func evalEqual(ctx exprContext, self *term) (v any, err error) {
+// type deepFuncTemplate func(a, b any) (eq bool, err error)
+
+func equals(a, b any, deepCmp kern.DeepFuncTemplate) (eq bool, err error) {
+	if kern.IsNumOrFract(a) && kern.IsNumOrFract(b) {
+		if kern.IsNumber(a) && kern.IsNumber(b) {
+			if kern.IsInteger(a) && kern.IsInteger(b) {
+				li, _ := a.(int64)
+				ri, _ := b.(int64)
+				eq = li == ri
+			} else {
+				eq = kern.NumAsFloat(a) == kern.NumAsFloat(b)
+			}
+		} else {
+			var cmp int
+			if cmp, err = kern.CmpAnyFract(a, b); err == nil {
+				eq = cmp == 0
+			}
+		}
+	} else if deepCmp != nil && kern.IsList(a) && kern.IsList(b) {
+		eq, err = deepCmp(a, b)
+	} else {
+		eq = reflect.DeepEqual(a, b)
+	}
+
+	return
+}
+
+func evalEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isInteger(leftValue) && isInteger(rightValue) {
-			li, _ := leftValue.(int64)
-			ri, _ := rightValue.(int64)
-			v = li == ri
-		} else {
-			v = numAsFloat(leftValue) == numAsFloat(rightValue)
-		}
-	} else if isString(leftValue) && isString(rightValue) {
-		ls, _ := leftValue.(string)
-		rs, _ := rightValue.(string)
-		v = ls == rs
-	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
-	}
+	v, err = equals(leftValue, rightValue, nil)
 	return
 }
 
 //-------- not equal term
 
-func newNotEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalNotEqual,
+func newNotEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalNotEqual,
 	}
 }
 
-func evalNotEqual(ctx exprContext, self *term) (v any, err error) {
-	if v, err = evalEqual(ctx, self); err == nil {
-		b, _ := toBool(v)
+func evalNotEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	if v, err = evalEqual(ctx, opTerm); err == nil {
+		b, _ := kern.ToBool(v)
 		v = !b
 	}
 	return
 }
 
-// func evalNotEqual(ctx exprContext, self *term) (v any, err error) {
-// 	var leftValue, rightValue any
-
-// 	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
-// 		return
-// 	}
-
-// 	if isNumber(leftValue) && isNumber(rightValue) {
-// 		if isInteger(leftValue) && isInteger(rightValue) {
-// 			li, _ := leftValue.(int64)
-// 			ri, _ := rightValue.(int64)
-// 			v = li != ri
-// 		} else {
-// 			v = numAsFloat(leftValue) != numAsFloat(rightValue)
-// 		}
-// 	} else if isString(leftValue) && isString(rightValue) {
-// 		ls, _ := leftValue.(string)
-// 		rs, _ := rightValue.(string)
-// 		v = ls != rs
-// 	} else {
-// 		err = self.errIncompatibleTypes(leftValue, rightValue)
-// 	}
-// 	return
-// }
-
 //-------- less term
 
-func newLessTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalLess,
+func newLessTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalLess,
 	}
 }
 
-func evalLess(ctx exprContext, self *term) (v any, err error) {
+func lessThan(self *scan.Term, a, b any) (isLess bool, err error) {
+	if kern.IsNumOrFract(a) && kern.IsNumOrFract(b) {
+		if kern.IsNumber(a) && kern.IsNumber(b) {
+			if kern.IsInteger(a) && kern.IsInteger(b) {
+				li, _ := a.(int64)
+				ri, _ := b.(int64)
+				isLess = li < ri
+			} else {
+				isLess = kern.NumAsFloat(a) < kern.NumAsFloat(b)
+			}
+		} else {
+			var cmp int
+			if cmp, err = kern.CmpAnyFract(a, b); err == nil {
+				isLess = cmp < 0
+			}
+		}
+	} else if kern.IsString(a) && kern.IsString(b) {
+		ls, _ := a.(string)
+		rs, _ := b.(string)
+		isLess = ls < rs
+		// Inclusion test
+	} else if kern.IsList(a) && kern.IsList(b) {
+		aList, _ := a.(*kern.ListType)
+		bList, _ := b.(*kern.ListType)
+		isLess = len(*aList) < len(*bList) && bList.Contains(aList)
+	} else {
+		err = self.ErrIncompatibleTypes(a, b)
+	}
+	return
+}
+
+func evalLess(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
-
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isInteger(leftValue) && isInteger(rightValue) {
-			li, _ := leftValue.(int64)
-			ri, _ := rightValue.(int64)
-			v = li < ri
-		} else {
-			v = numAsFloat(leftValue) < numAsFloat(rightValue)
-		}
-	} else if isString(leftValue) && isString(rightValue) {
-		ls, _ := leftValue.(string)
-		rs, _ := rightValue.(string)
-		v = ls < rs
-	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
-	}
+	v, err = lessThan(opTerm, leftValue, rightValue)
 	return
 }
 
 //-------- less or equal term
 
-func newLessEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindUnknown,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalLessEqual,
+func newLessEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalLessEqual,
 	}
 }
 
-func evalLessEqual(ctx exprContext, self *term) (v any, err error) {
+func lessThanOrEqual(self *scan.Term, a, b any) (isLessEq bool, err error) {
+	if isLessEq, err = lessThan(self, a, b); err == nil {
+		if !isLessEq {
+			if kern.IsList(a) && kern.IsList(b) {
+				isLessEq, err = kern.SameContent(a, b)
+			} else {
+				isLessEq, err = equals(a, b, nil)
+			}
+		}
+	}
+	return
+}
+
+func evalLessEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isInteger(leftValue) && isInteger(rightValue) {
-			li, _ := leftValue.(int64)
-			ri, _ := rightValue.(int64)
-			v = li <= ri
-		} else {
-			v = numAsFloat(leftValue) <= numAsFloat(rightValue)
-		}
-	} else if isString(leftValue) && isString(rightValue) {
-		ls, _ := leftValue.(string)
-		rs, _ := rightValue.(string)
-		v = ls <= rs
-	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
-	}
+	v, err = lessThanOrEqual(opTerm, leftValue, rightValue)
+
 	return
 }
 
 //-------- greater term
 
-func newGreaterTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalGreater,
+func newGreaterTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalGreater,
 	}
 }
 
-func evalGreater(ctx exprContext, self *term) (v any, err error) {
-	if v, err = evalLessEqual(ctx, self); err == nil {
-		b, _ := toBool(v)
-		v = !b
+func evalGreater(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
 	}
+
+	v, err = lessThan(opTerm, rightValue, leftValue)
 	return
 }
 
 //-------- greater or equal term
 
-func newGreaterEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindBool,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalGreaterEqual,
+func newGreaterEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalGreaterEqual,
 	}
 }
 
-func evalGreaterEqual(ctx exprContext, self *term) (v any, err error) {
-	if v, err = evalLess(ctx, self); err == nil {
-		b, _ := toBool(v)
-		v = !b
+func evalGreaterEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
 	}
+
+	v, err = lessThanOrEqual(opTerm, rightValue, leftValue)
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleEqual, newEqualTerm)
-	registerTermConstructor(SymNotEqual, newNotEqualTerm)
-	registerTermConstructor(SymLess, newLessTerm)
-	registerTermConstructor(SymLessOrEqual, newLessEqualTerm)
-	registerTermConstructor(SymGreater, newGreaterTerm)
-	registerTermConstructor(SymGreaterOrEqual, newGreaterEqualTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleEqual, newEqualTerm)
+	scan.RegisterTermConstructor(scan.SymNotEqual, newNotEqualTerm)
+	scan.RegisterTermConstructor(scan.SymLess, newLessTerm)
+	scan.RegisterTermConstructor(scan.SymLessOrEqual, newLessEqualTerm)
+	scan.RegisterTermConstructor(scan.SymGreater, newGreaterTerm)
+	scan.RegisterTermConstructor(scan.SymGreaterOrEqual, newGreaterEqualTerm)
 }

operator-selector.go

@@ -0,0 +1,86 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-selector.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- selector term
+
+func newSelectorTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 3),
+		Position: scan.PosInfix,
+		Priority: scan.PriSelector,
+		EvalFunc: evalSelector,
+	}
+}
+
+func trySelectorCase(ctx kern.ExprContext, exprValue, caseSel any, caseIndex int) (match bool, selectedValue any, err error) {
+	caseData, _ := caseSel.(*selectorCase)
+	if caseData.filterList == nil {
+		selectedValue, err = caseData.caseExpr.Eval(ctx)
+		match = true
+	} else if filterList, ok := caseData.filterList.Value().([]*scan.Term); ok {
+		if len(filterList) == 0 {
+			var valueAsInt = int64(0)
+			if b, ok := exprValue.(bool); ok {
+				if !b {
+					valueAsInt = 1
+				}
+			} else if valueAsInt, ok = exprValue.(int64); !ok {
+				return
+			}
+			if valueAsInt == int64(caseIndex) {
+				selectedValue, err = caseData.caseExpr.Eval(ctx)
+				match = true
+			}
+		} else {
+			var caseValue any
+			for _, caseTerm := range filterList {
+				if caseValue, err = caseTerm.Compute(ctx); err != nil || caseValue == exprValue {
+					selectedValue, err = caseData.caseExpr.Eval(ctx)
+					match = true
+					break
+				}
+			}
+		}
+	}
+	return
+}
+
+func evalSelector(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var exprValue any
+	var match bool
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+	exprTerm := opTerm.Children[0]
+	if exprValue, err = exprTerm.Compute(ctx); err != nil {
+		return
+	}
+
+	caseListTerm := opTerm.Children[1]
+	caseList, _ := caseListTerm.Value().([]*scan.Term)
+	for i, caseTerm := range caseList {
+		caseSel := caseTerm.Value()
+		if match, v, err = trySelectorCase(ctx, exprValue, caseSel, i); err != nil || match {
+			break
+		}
+	}
+	if err == nil && !match {
+		err = exprTerm.Tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymSelector, newSelectorTerm)
+}

operator-shift.go

@@ -0,0 +1,82 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-shift.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- bit right shift term
+
+func newRightShiftTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBinShift,
+		EvalFunc: evalRightShift,
+	}
+}
+
+func bitRightShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
+		leftInt := leftValue.(int64)
+		rightInt := rightValue.(int64)
+		v = leftInt >> rightInt
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func evalRightShift(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	v, err = bitRightShift(opTerm, leftValue, rightValue)
+	return
+}
+
+func newLeftShiftTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBinShift,
+		EvalFunc: evalLeftShift,
+	}
+}
+
+func bitLeftShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
+		leftInt := leftValue.(int64)
+		rightInt := rightValue.(int64)
+		v = leftInt << rightInt
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func evalLeftShift(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	v, err = bitLeftShift(opTerm, leftValue, rightValue)
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymDoubleGreater, newRightShiftTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleLess, newLeftShiftTerm)
+}

operator-sign.go

@@ -1,61 +1,65 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // operator-sign.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
 //-------- plus sign term
 
-func newPlusSignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindUnknown,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalSign,
+func newPlusSignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalSign,
 	}
 }
 
-func newMinusSignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindUnknown,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalSign,
+func newMinusSignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalSign,
 	}
 }
 
-func evalSign(ctx exprContext, self *term) (v any, err error) {
+func evalSign(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 isFloat(rightValue) {
-		if self.tk.Sym == SymChangeSign {
+	if kern.IsFloat(rightValue) {
+		if opTerm.Tk.Sym == scan.SymChangeSign {
 			f, _ := rightValue.(float64)
 			v = -f
 		} else {
 			v = rightValue
 		}
-	} else if isInteger(rightValue) {
-		if self.tk.Sym == SymChangeSign {
+	} else if kern.IsInteger(rightValue) {
+		if opTerm.Tk.Sym == scan.SymChangeSign {
 			i, _ := rightValue.(int64)
 			v = -i
 		} else {
 			v = rightValue
 		}
 	} else {
-		err = self.errIncompatibleType(rightValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymUnchangeSign, newPlusSignTerm)
-	registerTermConstructor(SymChangeSign, newMinusSignTerm)
+	scan.RegisterTermConstructor(scan.SymUnchangeSign, newPlusSignTerm)
+	scan.RegisterTermConstructor(scan.SymChangeSign, newMinusSignTerm)
 }

operator-sum.go

@@ -1,84 +1,130 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // operator-sum.go
 package expr
 
 import (
 	"fmt"
+	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- plus term
 
-func newPlusTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindUnknown,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priSum,
-		evalFunc: evalPlus,
+func newPlusTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriSum,
+		EvalFunc: evalPlus,
 	}
 }
 
-func evalPlus(ctx exprContext, self *term) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
-		return
-	}
-
-	if (isString(leftValue) && isNumberString(rightValue)) || (isString(rightValue) && isNumberString(leftValue)) {
+func sumValues(plusTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if (kern.IsString(leftValue) && kern.IsNumberString(rightValue)) || (kern.IsString(rightValue) && kern.IsNumberString(leftValue)) {
 		v = fmt.Sprintf("%v%v", leftValue, rightValue)
-	} else if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
-			v = numAsFloat(leftValue) + numAsFloat(rightValue)
+	} else if kern.IsNumber(leftValue) && kern.IsNumber(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) + kern.NumAsFloat(rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt + rightInt
 		}
+	} else if kern.IsList(leftValue) && kern.IsList(rightValue) {
+		var leftList, rightList *kern.ListType
+		leftList, _ = leftValue.(*kern.ListType)
+		rightList, _ = rightValue.(*kern.ListType)
+
+		sumList := make(kern.ListType, 0, len(*leftList)+len(*rightList))
+		sumList = append(sumList, *leftList...)
+		sumList = append(sumList, *rightList...)
+		v = &sumList
+	} else if (kern.IsFraction(leftValue) && kern.IsNumber(rightValue)) || (kern.IsFraction(rightValue) && kern.IsNumber(leftValue)) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) + kern.NumAsFloat(rightValue)
 		} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+			v, err = kern.SumAnyFract(leftValue, rightValue)
 		}
+	} else if kern.IsDict(leftValue) && kern.IsDict(rightValue) {
+		leftDict, _ := leftValue.(*kern.DictType)
+		rightDict, _ := rightValue.(*kern.DictType)
+		c := leftDict.Clone()
+		c.Merge(rightDict)
+		v = c
+	} else if kern.IsFraction(leftValue) && kern.IsFraction(rightValue) {
+		v, err = kern.SumAnyFract(leftValue, rightValue)
+	} else {
+		err = plusTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return v, err
+}
+
+func evalPlus(ctx kern.ExprContext, plusTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = plusTerm.EvalInfix(ctx); err != nil {
 		return
+	}
+
+	return sumValues(plusTerm, leftValue, rightValue)
 }
 
 //-------- minus term
 
-func newMinusTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		class:    classOperator,
-		kind:     kindUnknown,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priSum,
-		evalFunc: evalMinus,
+func newMinusTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriSum,
+		EvalFunc: evalMinus,
 	}
 }
 
-func evalMinus(ctx exprContext, self *term) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
-		return
-	}
-
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
-			v = numAsFloat(leftValue) - numAsFloat(rightValue)
+func diffValues(minusTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
+	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+			v = kern.NumAsFloat(leftValue) - kern.NumAsFloat(rightValue)
+		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+			v, err = kern.SubAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt - rightInt
 		}
+	} else if kern.IsList(leftValue) && kern.IsList(rightValue) {
+		leftList, _ := leftValue.(*kern.ListType)
+		rightList, _ := rightValue.(*kern.ListType)
+		diffList := make(kern.ListType, 0, len(*leftList)-len(*rightList))
+		for _, item := range *leftList {
+			if slices.Index(*rightList, item) < 0 {
+				diffList = append(diffList, item)
+			}
+		}
+		v = &diffList
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = minusTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
+func evalMinus(ctx kern.ExprContext, minusTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = minusTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	return diffValues(minusTerm, leftValue, rightValue)
+}
+
 // init
 func init() {
-	registerTermConstructor(SymPlus, newPlusTerm)
-	registerTermConstructor(SymMinus, newMinusTerm)
+	scan.RegisterTermConstructor(scan.SymPlus, newPlusTerm)
+	scan.RegisterTermConstructor(scan.SymMinus, newMinusTerm)
 }

operator-unset.go

@@ -0,0 +1,74 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-unset.go
+package expr
+
+import (
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- unset term
+
+func newUnsetTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalUnset,
+	}
+}
+
+func deleteContextItem(ctx kern.ExprContext, opTerm *scan.Term, item any) (deleted bool, err error) {
+	if name, ok := item.(string); ok {
+		var size int
+		if strings.HasSuffix(name, "()") {
+			size = ctx.FuncCount()
+			ctx.DeleteFunc(strings.TrimRight(name, "()"))
+			deleted = ctx.FuncCount() < size
+		} else {
+			size = ctx.VarCount()
+			ctx.DeleteVar(name)
+			deleted = ctx.VarCount() < size
+		}
+	} else {
+		err = opTerm.ErrIncompatiblePrefixPostfixType(item)
+	}
+	return
+}
+
+func evalUnset(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var childValue any
+	var deleted bool
+
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
+		return
+	}
+
+	count := 0
+	if kern.IsList(childValue) {
+		list, _ := childValue.(*kern.ListType)
+		for _, item := range *list {
+			if deleted, err = deleteContextItem(ctx, opTerm, item); err != nil {
+				break
+			} else if deleted {
+				count++
+			}
+		}
+	} else if deleted, err = deleteContextItem(ctx, opTerm, childValue); err == nil && deleted {
+		count++
+	}
+	if err == nil {
+		v = int64(count)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwUnset, newUnsetTerm)
+}