Expr.doc: more details about the run() function from builtin iterator

1. moved scan/symbol.go to new package sym and adapted all files that reference Symbol type and its values.
2. new type interval defined by begin, end and step values.
3. replaced operator-range.go with operator-interval.go.
4. replaced range operator begin:end with begin..end..step.
5. new implementation of sub-collection extraction based on new interval literal.

array-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // list-iterator.go
@@ -10,10 +10,12 @@ import (
 	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 type ListIterator struct {
-	a     *kern.ListType
+	a     *array.ArrayType
 	count int64
 	index int64
 	start int64
@@ -21,7 +23,7 @@ type ListIterator struct {
 	step  int64
 }
 
-func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
+func NewListIterator(list *array.ArrayType, args []any) (it *ListIterator) {
 	var argc int = 0
 	listLen := int64(len(([]any)(*list)))
 	if args != nil {
@@ -29,21 +31,21 @@ func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
 	}
 	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, err := types.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, err := types.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, err := types.ToGoInt64(args[2], "step"); err == nil {
 					if i < 0 {
 						i = -i
 					}
@@ -60,8 +62,8 @@ func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
 	return
 }
 
-func NewArrayIterator(array []any) (it *ListIterator) {
+func NewArrayIterator(a []any) (it *ListIterator) {
-	it = &ListIterator{a: (*kern.ListType)(&array), count: 0, index: -1, start: 0, stop: int64(len(array)) - 1, step: 1}
+	it = &ListIterator{a: (*array.ArrayType)(&a), count: 0, index: -1, start: 0, stop: int64(len(a)) - 1, step: 1}
 	return
 }
 

bind-expr-functions.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // function.go

builtin-base.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-base.go
@@ -12,6 +12,14 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/float"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 const (
@@ -24,42 +32,47 @@ func isNilFunc(ctx kern.ExprContext, name string, args map[string]any) (result a
 }
 
 func isIntFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsInteger(args[kern.ParamValue])
+	result = types.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])
+	result = float.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])
+	result = boolean.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])
+	result = str.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])
+	result = fract.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])
+	result = fract.IsRational(args[kern.ParamValue])
 	return
 }
 
-func isListFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+func isArrayFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsList(args[kern.ParamValue])
+	result = array.IsArray(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])
+	result = dict.IsDict(args[kern.ParamValue])
+	return
+}
+
+func isListFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = list.IsLinkedList(args[kern.ParamValue])
 	return
 }
 
@@ -67,7 +80,7 @@ func boolFunc(ctx kern.ExprContext, name string, args map[string]any) (result an
 	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = (v != 0)
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v.N() != 0
 	case float64:
 		result = v != 0.0
@@ -75,9 +88,9 @@ func boolFunc(ctx kern.ExprContext, name string, args map[string]any) (result an
 		result = v
 	case string:
 		result = len(v) > 0
-	case *kern.ListType:
+	case *array.ArrayType:
 		result = len(*v) > 0
-	case *kern.DictType:
+	case *dict.DictType:
 		result = len(*v) > 0
 	default:
 		err = kern.ErrCantConvert(name, v, "bool")
@@ -102,7 +115,7 @@ func intFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 		if i, err = strconv.Atoi(v); err == nil {
 			result = int64(i)
 		}
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = int64(v.N() / v.D())
 	default:
 		err = kern.ErrCantConvert(name, v, "int")
@@ -110,7 +123,7 @@ func intFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 	return
 }
 
-func decFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+func floatFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = float64(v)
@@ -127,7 +140,7 @@ func decFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 		if f, err = strconv.ParseFloat(v, 64); err == nil {
 			result = f
 		}
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v.ToFloat()
 	default:
 		err = kern.ErrCantConvert(name, v, "float")
@@ -149,7 +162,7 @@ func stringFunc(ctx kern.ExprContext, name string, args map[string]any) (result
 		}
 	case string:
 		result = v
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v.ToString(0)
 	case kern.Formatter:
 		result = v.ToString(0)
@@ -174,19 +187,19 @@ func fractFunc(ctx kern.ExprContext, name string, args map[string]any) (result a
 		}
 
 		if err == nil {
-			result = kern.NewFraction(v, den)
+			result = fract.NewFraction(v, den)
 		}
 	case float64:
-		result, err = kern.Float64ToFraction(v)
+		result, err = fract.Float64ToFraction(v)
 	case bool:
 		if v {
-			result = kern.NewFraction(1, 1)
+			result = fract.NewFraction(1, 1)
 		} else {
-			result = kern.NewFraction(0, 1)
+			result = fract.NewFraction(0, 1)
 		}
 	case string:
-		result, err = kern.MakeGeneratingFraction(v)
+		result, err = fract.MakeGeneratingFraction(v)
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v
 	default:
 		err = kern.ErrCantConvert(name, v, "float")
@@ -255,24 +268,41 @@ func setFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 	return
 }
 
-// func unsetFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+func charFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-// 	var varName string
+	var ord int
-// 	var ok bool
 
-// 	if varName, ok = args[kern.ParamName].(string); !ok {
+	if n, ok := args[kern.ParamValue].(byte); ok {
-// 		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
+		ord = int(n)
-// 	} else {
+	} else if n, ok := args[kern.ParamValue].(int64); ok {
-// 		ctx.GetParent().DeleteVar(varName)
+		ord = int(n)
-// 		result = nil
+	} else if n, ok := args[kern.ParamValue].(int); ok {
-// 	}
+		ord = n
-// 	return
+	} else {
-// }
+		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
+	}
+	if ord < 0 || ord > 255 {
+		err = kern.ErrFuncInvalidArg(name, fmt.Sprintf("character code must be in range 0-255, got %d", ord))
+	} else {
+		result = string(rune(ord))
+	}
+	return
+}
+
+func seqFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	list := list.NewLinkedList()
+	items := args[kern.ParamValue].([]any)
+	for _, arg := range items {
+		list.PushBack(arg)
+	}
+	result = list
+	return
+}
 
 //// import
 
 func ImportBuiltinsFuncs(ctx kern.ExprContext) {
 	anyParams := []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamValue),
+		kern.NewFuncParam(kern.ParamValue),
 	}
 
 	ctx.RegisterFunc("isNil", kern.NewGolangFunctor(isNilFunc), kern.TypeBoolean, anyParams)
@@ -282,36 +312,40 @@ func ImportBuiltinsFuncs(ctx kern.ExprContext) {
 	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("isArray", kern.NewGolangFunctor(isArrayFunc), kern.TypeBoolean, anyParams)
 	ctx.RegisterFunc("isDict", kern.NewGolangFunctor(isDictionaryFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isList", kern.NewGolangFunctor(isListFunc), 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("float", kern.NewGolangFunctor(floatFunc), kern.TypeFloat, anyParams)
 	ctx.RegisterFunc("string", kern.NewGolangFunctor(stringFunc), kern.TypeString, anyParams)
 	ctx.RegisterFunc("fract", kern.NewGolangFunctor(fractFunc), kern.TypeFraction, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamValue),
+		kern.NewFuncParam(kern.ParamValue),
-		NewFuncParamFlagDef(ParamDenominator, PfDefault, int64(1)),
+		kern.NewFuncParamFlagDef(ParamDenominator, kern.PfDefault, int64(1)),
 	})
 
 	ctx.RegisterFunc("eval", kern.NewGolangFunctor(evalFunc), kern.TypeAny, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
 	})
 
 	ctx.RegisterFunc("var", kern.NewGolangFunctor(varFunc), kern.TypeAny, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamName),
+		kern.NewFuncParam(kern.ParamName),
-		NewFuncParamFlagDef(kern.ParamValue, PfDefault, nil),
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault, nil),
 	})
 
 	ctx.RegisterFunc("set", kern.NewGolangFunctor(setFunc), kern.TypeAny, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamName),
+		kern.NewFuncParam(kern.ParamName),
-		NewFuncParam(kern.ParamValue),
+		kern.NewFuncParam(kern.ParamValue),
 	})
 
-	// ctx.RegisterFunc("unset", kern.NewGolangFunctor(unsetFunc), kern.TypeAny, []kern.ExprFuncParam{
+	ctx.RegisterFunc("char", kern.NewGolangFunctor(charFunc), kern.TypeString, []kern.ExprFuncParam{
-	// 	NewFuncParam(kern.ParamName),
+		kern.NewFuncParam(kern.ParamValue),
-	// 	NewFuncParam(kern.ParamValue),
+	})
-	// })
+
+	ctx.RegisterFunc("seq", kern.NewGolangFunctor(seqFunc), kern.TypeLinkedList, []kern.ExprFuncParam{
+		kern.NewFuncParamFlag(kern.ParamValue, kern.PfRepeat),
+	})
 }
 
 func init() {

builtin-fmt.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-fmt.go
@@ -47,10 +47,10 @@ func printLnFunc(ctx kern.ExprContext, name string, args map[string]any) (result
 
 func ImportFmtFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("print", kern.NewGolangFunctor(printFunc), kern.TypeInt, []kern.ExprFuncParam{
-		NewFuncParamFlag(kern.ParamItem, PfRepeat),
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
 	})
 	ctx.RegisterFunc("println", kern.NewGolangFunctor(printLnFunc), kern.TypeInt, []kern.ExprFuncParam{
-		NewFuncParamFlag(kern.ParamItem, PfRepeat),
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
 	})
 }
 

builtin-import.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-import.go
@@ -10,6 +10,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 func importFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
@@ -47,7 +48,7 @@ func doImport(ctx kern.ExprContext, name string, dirList []string, it kern.Itera
 			var expr *scan.Ast
 			scanner := scan.NewScanner(file, scan.DefaultTranslations())
 			parser := NewParser()
-			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymEos); err == nil {
+			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, sym.SymEos); err == nil {
 				result, err = expr.Eval(ctx)
 			}
 			if err != nil {
@@ -69,10 +70,10 @@ func doImport(ctx kern.ExprContext, name string, dirList []string, it kern.Itera
 
 func ImportImportFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("import", kern.NewGolangFunctor(importFunc), kern.TypeAny, []kern.ExprFuncParam{
-		NewFuncParamFlag(kern.ParamFilepath, PfRepeat),
+		kern.NewFuncParamFlag(kern.ParamFilepath, kern.PfRepeat),
 	})
 	ctx.RegisterFunc("importAll", kern.NewGolangFunctor(importAllFunc), kern.TypeAny, []kern.ExprFuncParam{
-		NewFuncParamFlag(kern.ParamFilepath, PfRepeat),
+		kern.NewFuncParamFlag(kern.ParamFilepath, kern.PfRepeat),
 	})
 }
 

builtin-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-iterator.go
@@ -9,32 +9,39 @@ import (
 	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
 )
 
 const (
 	iterParamOperator = "operator"
 	iterParamVars     = "vars"
 	iterVarStatus     = "status"
+	iterParamStatus   = "status"
+	iterVarAbort      = "__abort"
 )
 
 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]))
+		// err = fmt.Errorf("parameter %q must be an iterator, passed %v [%s]", kern.ParamIterator, args[kern.ParamIterator], kern.TypeName(args[kern.ParamIterator]))
+		err = errBadParamType(kern.ParamIterator, kern.TypeIterator, 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]))
+			// err = fmt.Errorf("parameter %q must be a function, passed %v [%s]", iterParamOperator, args[iterParamOperator], kern.TypeName(args[iterParamOperator]))
+			err = errBadParamType(iterParamOperator, "function", args[iterParamOperator])
 			return
 		}
 	}
 
-	var vars *kern.DictType
+	var vars *dict.DictType
-	if vars, ok = args[iterParamVars].(*kern.DictType); !ok && args[iterParamVars] != nil {
+	if vars, ok = args[iterParamVars].(*dict.DictType); !ok && args[iterParamVars] != nil {
-		err = fmt.Errorf("paramter %q must be a dictionary, passed %v [%s]", iterParamVars, args[iterParamVars], kern.TypeName(args[iterParamVars]))
+		// err = fmt.Errorf("parameter %q must be a dictionary, passed %v [%s]", iterParamVars, args[iterParamVars], kern.TypeName(args[iterParamVars]))
+		err = errBadParamType(iterParamVars, kern.TypeDict, args[iterParamVars])
 		return
 	}
 
@@ -50,12 +57,21 @@ func parseRunArgs(localCtx kern.ExprContext, args map[string]any) (it kern.Itera
 	return
 }
 
+func errBadParamType(paramName, wantedType string, wantedValue any) error {
+	return fmt.Errorf("type of %q must be %s, passed %v [%s]", paramName, wantedType, wantedValue, kern.TypeName(wantedValue))
+}
+
+func abortFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if status, provided := args[iterParamStatus]; provided {
+		ctx.UnsafeSetVar("@"+iterVarStatus, status)
+	}
+	ctx.UnsafeSetVar("@"+iterVarAbort, true)
+	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
 
@@ -66,17 +82,33 @@ func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 		return
 	}
 
+	localCtx.RegisterFunc("abort", kern.NewGolangFunctor(abortFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParamFlagDef(iterParamStatus, kern.PfOptional, "aborted"),
+	})
+
+	params = map[string]any{kern.ParamIndex: 0, kern.ParamItem: nil}
 	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}
+			// params = map[string]any{kern.ParamIndex: it.Index(), kern.ParamItem: item}
-			if v, err = op.InvokeNamed(localCtx, iterParamOperator, params); err != nil {
+			params[kern.ParamIndex] = it.Index()
-				break
+			params[kern.ParamItem] = item
-			} else {
+
-				var success bool
+			localCtx.UnsafeSetVar("_", it.Index())
-				if success, ok = kern.ToBool(v); !success || !ok {
+			localCtx.UnsafeSetVar("__", item)
-					break
+
+			abort := false
+			if _, err = op.InvokeNamed(localCtx, iterParamOperator, params); err != nil {
+				abort = true
+			} else if abortAny, exists := localCtx.GetVar(iterVarAbort); exists {
+				if abort, ok := boolean.ToBool(abortAny); ok && abort {
+					abort = true
 				}
 			}
+			localCtx.DeleteVar("__")
+			localCtx.DeleteVar("_")
+			if abort {
+				break
+			}
 		}
 	}
 
@@ -85,7 +117,7 @@ func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 	}
 	if err == nil {
 		if op == nil {
-			ctx.UnsafeSetVar(iterVarStatus, it.Count())
+			localCtx.UnsafeSetVar(iterVarStatus, it.Count())
 		}
 		result, _ = localCtx.GetVar(iterVarStatus)
 	}
@@ -94,9 +126,9 @@ func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 
 func ImportIterFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("run", kern.NewGolangFunctor(runFunc), kern.TypeAny, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamIterator),
+		kern.NewFuncParam(kern.ParamIterator),
-		NewFuncParamFlag(iterParamOperator, PfOptional),
+		kern.NewFuncParamFlag(iterParamOperator, kern.PfOptional),
-		NewFuncParamFlag(iterParamVars, PfOptional),
+		kern.NewFuncParamFlag(iterParamVars, kern.PfOptional),
 	})
 }
 

builtin-math-arith.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-math-arith.go
@@ -9,10 +9,14 @@ import (
 	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/float"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
 )
 
 func checkNumberParamExpected(funcName string, paramValue any, paramPos, level, subPos int) (err error) {
-	if !(kern.IsNumber(paramValue) || kern.IsFraction(paramValue)) /*|| isList(paramValue)*/ {
+	if !(types.IsNumber(paramValue) || fract.IsFraction(paramValue)) /*|| isArray(paramValue)*/ {
 		err = fmt.Errorf("%s(): param nr %d (%d in %d) has wrong type %T, number expected",
 			funcName, paramPos+1, subPos+1, level, paramValue)
 	}
@@ -23,13 +27,13 @@ func doAdd(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 	var sumAsFloat, sumAsFract bool
 	var floatSum float64 = 0.0
 	var intSum int64 = 0
-	var fractSum *kern.FractionType
+	var fractSum *fract.FractionType
 	var v any
 
 	level++
 
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*kern.ListType); ok {
+		if list, ok := v.(*array.ArrayType); ok {
 			v = NewListIterator(list, nil)
 		}
 		if subIter, ok := v.(kern.Iterator); ok {
@@ -47,29 +51,29 @@ func doAdd(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 		count++
 
 		if !sumAsFloat {
-			if kern.IsFloat(v) {
+			if float.IsFloat(v) {
 				sumAsFloat = true
 				if sumAsFract {
 					floatSum = fractSum.ToFloat()
 				} else {
 					floatSum = float64(intSum)
 				}
-			} else if !sumAsFract && kern.IsFraction(v) {
+			} else if !sumAsFract && fract.IsFraction(v) {
-				fractSum = kern.NewFraction(intSum, 1)
+				fractSum = fract.NewFraction(intSum, 1)
 				sumAsFract = true
 			}
 		}
 
 		if sumAsFloat {
-			floatSum += kern.NumAsFloat(v)
+			floatSum += types.NumAsFloat(v)
 		} else if sumAsFract {
-			var item *kern.FractionType
+			var item *fract.FractionType
 			var ok bool
-			if item, ok = v.(*kern.FractionType); !ok {
+			if item, ok = v.(*fract.FractionType); !ok {
 				iv, _ := v.(int64)
-				item = kern.NewFraction(iv, 1)
+				item = fract.NewFraction(iv, 1)
 			}
-			fractSum = kern.SumFract(fractSum, item)
+			fractSum = fract.SumFract(fractSum, item)
 		} else {
 			iv, _ := v.(int64)
 			intSum += iv
@@ -98,12 +102,12 @@ func doMul(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 	var mulAsFloat, mulAsFract bool
 	var floatProd float64 = 1.0
 	var intProd int64 = 1
-	var fractProd *kern.FractionType
+	var fractProd *fract.FractionType
 	var v any
 
 	level++
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*kern.ListType); ok {
+		if list, ok := v.(*array.ArrayType); ok {
 			v = NewListIterator(list, nil)
 		}
 		if subIter, ok := v.(kern.Iterator); ok {
@@ -123,29 +127,29 @@ func doMul(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 		count++
 
 		if !mulAsFloat {
-			if kern.IsFloat(v) {
+			if float.IsFloat(v) {
 				mulAsFloat = true
 				if mulAsFract {
 					floatProd = fractProd.ToFloat()
 				} else {
 					floatProd = float64(intProd)
 				}
-			} else if !mulAsFract && kern.IsFraction(v) {
+			} else if !mulAsFract && fract.IsFraction(v) {
-				fractProd = kern.NewFraction(intProd, 1)
+				fractProd = fract.NewFraction(intProd, 1)
 				mulAsFract = true
 			}
 		}
 
 		if mulAsFloat {
-			floatProd *= kern.NumAsFloat(v)
+			floatProd *= types.NumAsFloat(v)
 		} else if mulAsFract {
-			var item *kern.FractionType
+			var item *fract.FractionType
 			var ok bool
-			if item, ok = v.(*kern.FractionType); !ok {
+			if item, ok = v.(*fract.FractionType); !ok {
 				iv, _ := v.(int64)
-				item = kern.NewFraction(iv, 1)
+				item = fract.NewFraction(iv, 1)
 			}
-			fractProd = kern.MulFract(fractProd, item)
+			fractProd = fract.MulFract(fractProd, item)
 		} else {
 			iv, _ := v.(int64)
 			intProd *= iv
@@ -172,11 +176,11 @@ func mulFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 
 func ImportMathFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("add", kern.NewGolangFunctor(addFunc), kern.TypeNumber, []kern.ExprFuncParam{
-		NewFuncParamFlagDef(kern.ParamValue, PfDefault|PfRepeat, int64(0)),
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, int64(0)),
 	})
 
 	ctx.RegisterFunc("mul", kern.NewGolangFunctor(mulFunc), kern.TypeNumber, []kern.ExprFuncParam{
-		NewFuncParamFlagDef(kern.ParamValue, PfDefault|PfRepeat, int64(1)),
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, int64(1)),
 	})
 }
 

builtin-os-file-iter-byte.go

@@ -0,0 +1,102 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/file"
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const fileByteIteratorType = "fileByteIterator"
+
+type fileFileByteIterator struct {
+	fileIterBase
+	b byte
+}
+
+func newFileByteIterator(r *file.Reader, autoClose bool) *fileFileByteIterator {
+	return &fileFileByteIterator{
+		fileIterBase: fileIterBase{reader: r, index: -1, count: 0, autoClose: autoClose},
+		b:            0}
+}
+
+func (it *fileFileByteIterator) TypeName() string {
+	return fileByteIteratorType
+}
+
+func (it *fileFileByteIterator) String() string {
+	return it.repr(fileByteIteratorType)
+}
+
+func (it *fileFileByteIterator) Next() (item any, err error) { // must return io.EOF after the last item
+	if it.b, err = it.reader.ReadByte(); err == nil {
+		it.increment()
+		item = it.b
+	} else if it.autoClose {
+		it.Clean()
+	}
+	return
+}
+
+func (it *fileFileByteIterator) Current() (item any, err error) {
+	item = it.b
+	return
+}
+
+func (it *fileFileByteIterator) Reset() (err error) {
+	if err = it.reader.Reset(); err == nil {
+		it.reset()
+		it.b = 0
+	}
+	return
+}
+
+func (it *fileFileByteIterator) Clean() (err error) {
+	if it.reader.Valid() {
+		if err = it.reader.GetFile().Close(); err == nil {
+			it.reader = nil
+		}
+	}
+	// it.reset()
+	// it.b = 0
+	return
+}
+
+func (it *fileFileByteIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	case kern.ResetName:
+		err = it.Reset()
+	case kern.CleanName:
+		err = it.Clean()
+	case kern.IndexName:
+		v = int64(it.Index())
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.count
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func fileByteIteratorFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle *file.Reader
+	var invalidFileHandle any
+	var autoClose bool
+
+	if handle, invalidFileHandle, autoClose, err = initFileHandle(ctx, name, args); err == nil {
+		if handle != nil {
+			result = newFileByteIterator(handle, autoClose)
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}

builtin-os-file-iter-line.go

@@ -0,0 +1,105 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-os-file.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/file"
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
+const fileLineIteratorType = "fileLineIterator"
+
+type fileFileLineIterator struct {
+	fileIterBase
+	line string
+}
+
+func newFileLineIterator(r *file.Reader, autoClose bool) *fileFileLineIterator {
+	return &fileFileLineIterator{
+		fileIterBase: fileIterBase{reader: r, index: -1, count: 0, autoClose: autoClose},
+		line:         "",
+	}
+}
+
+func (it *fileFileLineIterator) TypeName() string {
+	return fileLineIteratorType
+}
+
+func (it *fileFileLineIterator) String() string {
+	return it.repr(fileLineIteratorType)
+}
+
+func (it *fileFileLineIterator) Next() (item any, err error) { // must return io.EOF after the last item
+	if it.line, err = it.reader.ReadString('\n'); err == nil {
+		it.increment()
+		item = it.line[0 : len(it.line)-1]
+	} else if it.autoClose {
+		it.Clean()
+	}
+	return
+}
+
+func (it *fileFileLineIterator) Current() (item any, err error) {
+	if len(it.line) > 0 {
+		item = it.line[0 : len(it.line)-1]
+	}
+	return
+}
+
+func (it *fileFileLineIterator) Reset() (err error) {
+	if err = it.reader.Reset(); err == nil {
+		it.reset()
+		it.line = ""
+	}
+	return
+}
+
+func (it *fileFileLineIterator) Clean() (err error) {
+	if it.reader != nil {
+		if err = it.reader.Close(); err == nil {
+			it.reader = nil
+		}
+	}
+	// it.reset()
+	// it.line = ""
+	return
+}
+
+func (it *fileFileLineIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	case kern.ResetName:
+		err = it.Reset()
+	case kern.CleanName:
+		err = it.Clean()
+	case kern.IndexName:
+		v = int64(it.Index())
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.count
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func fileLineIteratorFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var handle *file.Reader
+	var invalidFileHandle any
+	var autoClose bool
+
+	if handle, invalidFileHandle, autoClose, err = initFileHandle(ctx, name, args); err == nil {
+		if handle != nil {
+			result = newFileLineIterator(handle, autoClose)
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}

builtin-os-file-iter.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-os-file.go
@@ -6,146 +6,66 @@ package expr
 
 import (
 	"fmt"
-	"io"
 	"slices"
 
+	"git.portale-stac.it/go-pkg/expr/file"
 	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 const paramHandleOrPath = "handle-or-path"
-const fileReadTextIteratorType = "fileReadTextIterator"
 
-type fileReadTextIterator struct {
+type fileIterBase struct {
-	osReader  *osReader
+	reader    *file.Reader
 	index     int64
 	count     int64
-	line      string
 	autoClose bool
 }
 
-func newReadTextIterator(r *osReader, autoClose bool) *fileReadTextIterator {
+func (it *fileIterBase) Count() int64 {
-	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
+func (it *fileIterBase) Index() int64 {
-	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) {
+func (it *fileIterBase) HasOperation(name string) bool {
-	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) {
+func (it *fileIterBase) reset() {
-	if it.osReader.fh != nil {
+	it.index = -1
-		if err = it.osReader.fh.Close(); err == nil {
+	it.count = 0
-			it.osReader = nil
-		}
-	}
-	return nil
 }
 
-func (it *fileReadTextIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+func (it *fileIterBase) increment() {
-	switch name {
+	it.index++
-	case kern.NextName:
+	it.count++
-		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) {
+func (it *fileIterBase) repr(typeName string) string {
-	var handle *osReader
+	if it.reader.Valid() {
-	var invalidFileHandle any
+		return fmt.Sprintf("$(%s@%q)", typeName, it.reader.GetName())
-	var ok, autoClose bool
+	}
+	return fmt.Sprintf("$(%s@<nil>)", typeName)
+}
 
-	result = nil
+func initFileHandle(ctx kern.ExprContext, name string, args map[string]any) (handle *file.Reader, invalidFileHandle any, autoClose bool, err error) {
-	if handle, ok = args[paramHandleOrPath].(*osReader); !ok {
+	var ok bool
+
+	if handle, ok = args[paramHandleOrPath].(*file.Reader); !ok {
 		if fileName, ok := args[paramHandleOrPath].(string); ok && len(fileName) > 0 {
 			var handleAny any
 			if handleAny, err = openFileFunc(ctx, name, map[string]any{kern.ParamFilepath: fileName}); err != nil {
 				return
 			}
 			if handleAny != nil {
-				handle = handleAny.(*osReader)
+				handle = handleAny.(*file.Reader)
 				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

@@ -1,15 +1,14 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-os-file.go
 package expr
 
 import (
-	"bufio"
 	"fmt"
 	"io"
-	"os"
 
+	"git.portale-stac.it/go-pkg/expr/file"
 	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
@@ -17,44 +16,6 @@ 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)
 }
@@ -67,24 +28,26 @@ func errInvalidFileHandle(funcName string, v any) error {
 	}
 }
 
-func createFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+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
+		// var fh *os.File
-		if fh, err = os.Create(filePath); err == nil {
+		// if fh, err = os.Open(filePath); err == nil {
-			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
+		// 	result = file.NewReader(fh)
-		}
+		// }
+		result, err = file.OpenReader(filePath)
 	} else {
 		err = errMissingFilePath(name)
 	}
 	return
 }
 
-func openFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+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
+		// var fh *os.File
-		if fh, err = os.Open(filePath); err == nil {
+		// if fh, err = os.Create(filePath); err == nil {
-			result = &osReader{fh: fh, reader: bufio.NewReader(fh)}
+		// 	result = file.NewWriter(fh)
-		}
+		// }
+		result, err = file.CreateWriter(filePath)
 	} else {
 		err = errMissingFilePath(name)
 	}
@@ -93,10 +56,11 @@ func openFileFunc(ctx kern.ExprContext, name string, args map[string]any) (resul
 
 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
+		// var fh *os.File
-		if fh, err = os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0660); err == nil {
+		// 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)}
+		// 	result = file.NewWriter(fh)
-		}
+		// }
+		result, err = file.AppendWriter(filePath)
 	} else {
 		err = errMissingFilePath(name)
 	}
@@ -104,18 +68,18 @@ func appendFileFunc(ctx kern.ExprContext, name string, args map[string]any) (res
 }
 
 func closeFileFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	var handle osHandle
+	var handle file.Handle
 	var invalidFileHandle any
 	var ok bool
 
-	if handle, ok = args[kern.ParamHandle].(osHandle); !ok {
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok {
 		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
-		if fh := handle.getFile(); fh != nil {
+		if fh := handle.GetFile(); fh != nil {
-			if w, ok := handle.(*osWriter); ok {
+			if w, ok := handle.(*file.Writer); ok {
-				err = w.writer.Flush()
+				err = w.Flush()
 			}
 
 			if err == nil {
@@ -131,19 +95,20 @@ func closeFileFunc(ctx kern.ExprContext, name string, args map[string]any) (resu
 }
 
 func fileWriteTextFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	var handle osHandle
+	var handle file.Handle
 	var invalidFileHandle any
 	var ok bool
 
-	if handle, ok = args[kern.ParamHandle].(osHandle); !ok {
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok {
 		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
-		if w, ok := handle.(*osWriter); ok {
+		if w, ok := handle.(*file.Writer); ok {
 			if v, exists := args[kern.ParamItem]; exists {
 				argv := v.([]any)
-				result, err = fmt.Fprint(w.writer, argv...)
+				// result, err = fmt.Fprint(w.writer, argv...)
+				result, err = w.Write(argv...)
 			}
 		} else {
 			invalidFileHandle = handle
@@ -157,24 +122,24 @@ func fileWriteTextFunc(ctx kern.ExprContext, name string, args map[string]any) (
 }
 
 func fileReadTextFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	var handle osHandle
+	var handle file.Handle
 	var invalidFileHandle any
 	var ok bool
 
 	result = nil
-	if handle, ok = args[kern.ParamHandle].(osHandle); !ok || args[kern.ParamHandle] == nil {
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok || args[kern.ParamHandle] == nil {
 		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
-		if r, ok := handle.(*osReader); ok {
+		if r, ok := handle.(*file.Reader); ok {
 			var limit byte = '\n'
 			var v string
 			if s, ok := args[osLimitCh].(string); ok && len(s) > 0 {
 				limit = s[0]
 			}
 
-			v, err = r.reader.ReadString(limit)
+			v, err = r.ReadString(limit)
 			if err == io.EOF {
 				err = nil
 			}
@@ -197,19 +162,19 @@ func fileReadTextFunc(ctx kern.ExprContext, name string, args map[string]any) (r
 }
 
 func fileReadTextAllFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	var handle osHandle
+	var handle file.Handle
 	var invalidFileHandle any
 	var ok bool
 
 	result = nil
-	if handle, ok = args[kern.ParamHandle].(osHandle); !ok || args[kern.ParamHandle] == nil {
+	if handle, ok = args[kern.ParamHandle].(file.Handle); !ok || args[kern.ParamHandle] == nil {
 		invalidFileHandle = args[kern.ParamHandle]
 	}
 
 	if handle != nil {
-		if r, ok := handle.(*osReader); ok {
+		if r, ok := handle.(*file.Reader); ok {
 			var b []byte
-			b, err = io.ReadAll(r.reader)
+			b, err = r.ReadAll()
 			result = string(b)
 		} else {
 			invalidFileHandle = handle
@@ -224,38 +189,43 @@ func fileReadTextAllFunc(ctx kern.ExprContext, name string, args map[string]any)
 
 func ImportOsFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("fileOpen", kern.NewGolangFunctor(openFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamFilepath),
+		kern.NewFuncParam(kern.ParamFilepath),
 	})
 
 	ctx.RegisterFunc("fileAppend", kern.NewGolangFunctor(appendFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamFilepath),
+		kern.NewFuncParam(kern.ParamFilepath),
 	})
 
 	ctx.RegisterFunc("fileCreate", kern.NewGolangFunctor(createFileFunc), kern.TypeFileHandle, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamFilepath),
+		kern.NewFuncParam(kern.ParamFilepath),
 	})
 
 	ctx.RegisterFunc("fileClose", kern.NewGolangFunctor(closeFileFunc), kern.TypeBoolean, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParam(kern.ParamHandle),
 	})
 
 	ctx.RegisterFunc("fileWriteText", kern.NewGolangFunctor(fileWriteTextFunc), kern.TypeInt, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParam(kern.ParamHandle),
-		NewFuncParamFlagDef(kern.ParamItem, PfDefault|PfRepeat, ""),
+		kern.NewFuncParamFlagDef(kern.ParamItem, kern.PfDefault|kern.PfRepeat, ""),
 	})
 
 	ctx.RegisterFunc("fileReadText", kern.NewGolangFunctor(fileReadTextFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParam(kern.ParamHandle),
-		NewFuncParamFlagDef(osLimitCh, PfDefault, "\n"),
+		kern.NewFuncParamFlagDef(osLimitCh, kern.PfDefault, "\n"),
 	})
 
 	ctx.RegisterFunc("fileReadTextAll", kern.NewGolangFunctor(fileReadTextAllFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParam(kern.ParamHandle),
 	})
 
-	ctx.RegisterFunc("fileReadIterator", kern.NewGolangFunctor(fileReadIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
+	ctx.RegisterFunc("fileLineIterator", kern.NewGolangFunctor(fileLineIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
-		NewFuncParam(paramHandleOrPath),
+		kern.NewFuncParam(paramHandleOrPath),
 	})
+
+	ctx.RegisterFunc("fileByteIterator", kern.NewGolangFunctor(fileByteIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
+		kern.NewFuncParam(paramHandleOrPath),
+	})
+
 }
 
 func init() {

builtin-string.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-string.go
@@ -10,6 +10,8 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 const (
@@ -43,8 +45,8 @@ func joinStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result
 		if v, exists := args[kern.ParamItem]; exists {
 			argv := v.([]any)
 			if len(argv) == 1 {
-				if ls, ok := argv[0].(*kern.ListType); ok {
+				if a, ok := argv[0].(*array.ArrayType); ok {
-					result, err = doJoinStr(name, sep, NewListIterator(ls, nil))
+					result, err = doJoinStr(name, sep, NewListIterator(a, nil))
 				} else if it, ok := argv[0].(kern.Iterator); ok {
 					result, err = doJoinStr(name, sep, it)
 				} else if s, ok := argv[0].(string); ok {
@@ -72,11 +74,11 @@ func subStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result
 		return nil, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 
-	if start, err = kern.ToGoInt(args[kern.ParamStart], name+"()"); err != nil {
+	if start, err = types.ToGoInt(args[kern.ParamStart], name+"()"); err != nil {
 		return
 	}
 
-	if count, err = kern.ToGoInt(args[kern.ParamCount], name+"()"); err != nil {
+	if count, err = types.ToGoInt(args[kern.ParamCount], name+"()"); err != nil {
 		return
 	}
 
@@ -194,11 +196,11 @@ func splitStrFunc(ctx kern.ExprContext, name string, args map[string]any) (resul
 	} else {
 		parts = []string{}
 	}
-	list := make(kern.ListType, len(parts))
+	a := make(array.ArrayType, len(parts))
 	for i, part := range parts {
-		list[i] = part
+		a[i] = part
 	}
-	result = &list
+	result = &a
 	return
 }
 
@@ -225,44 +227,44 @@ func lowerStrFunc(ctx kern.ExprContext, name string, args map[string]any) (resul
 // Import above functions in the context
 func ImportStringFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("strJoin", kern.NewGolangFunctor(joinStrFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSeparator),
+		kern.NewFuncParam(kern.ParamSeparator),
-		NewFuncParamFlag(kern.ParamItem, PfRepeat),
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
 	})
 
 	ctx.RegisterFunc("strSub", kern.NewGolangFunctor(subStrFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
-		NewFuncParamFlagDef(kern.ParamStart, PfDefault, int64(0)),
+		kern.NewFuncParamFlagDef(kern.ParamStart, kern.PfDefault, int64(0)),
-		NewFuncParamFlagDef(kern.ParamCount, PfDefault, int64(-1)),
+		kern.NewFuncParamFlagDef(kern.ParamCount, kern.PfDefault, int64(-1)),
 	})
 
 	ctx.RegisterFunc("strSplit", kern.NewGolangFunctor(splitStrFunc), "list of "+kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
-		NewFuncParamFlagDef(kern.ParamSeparator, PfDefault, ""),
+		kern.NewFuncParamFlagDef(kern.ParamSeparator, kern.PfDefault, ""),
-		NewFuncParamFlagDef(kern.ParamCount, PfDefault, int64(-1)),
+		kern.NewFuncParamFlagDef(kern.ParamCount, kern.PfDefault, int64(-1)),
 	})
 
 	ctx.RegisterFunc("strTrim", kern.NewGolangFunctor(trimStrFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
 	})
 
 	ctx.RegisterFunc("strStartsWith", kern.NewGolangFunctor(startsWithStrFunc), kern.TypeBoolean, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
-		NewFuncParam(kern.ParamPrefix),
+		kern.NewFuncParam(kern.ParamPrefix),
-		NewFuncParamFlag(strParamOther, PfRepeat),
+		kern.NewFuncParamFlag(strParamOther, kern.PfRepeat),
 	})
 
 	ctx.RegisterFunc("strEndsWith", kern.NewGolangFunctor(endsWithStrFunc), kern.TypeBoolean, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
-		NewFuncParam(kern.ParamSuffix),
+		kern.NewFuncParam(kern.ParamSuffix),
-		NewFuncParamFlag(strParamOther, PfRepeat),
+		kern.NewFuncParamFlag(strParamOther, kern.PfRepeat),
 	})
 
 	ctx.RegisterFunc("strUpper", kern.NewGolangFunctor(upperStrFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
 	})
 
 	ctx.RegisterFunc("strLower", kern.NewGolangFunctor(lowerStrFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
 	})
 }
 

builtins-register.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtins-register.go

cmd/ecli/.build.rc

@@ -0,0 +1,14 @@
+# Builder resource file
+# Created on gio 21 mag 2026, 15:35:18, CEST
+
+# Program name
+PROGRAM_NAME="ecli"
+
+# Program version
+PROGRAM_VERSION="$(<version.txt)"
+
+# Preset platform
+platform=("linux/amd64" "darwin/arm64")
+
+#--- end of file ---
+

cmd/ecli/build.bash

@@ -0,0 +1,199 @@
+#!/usr/bin/env bash
+# Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+# All rights reserved.
+
+
+RESOURCE_FILE=".build.rc"
+BUILD_REGISTER=".build_register"
+
+PROGRAM_NAME=""
+PROGRAM_VERSION=""
+
+function usage() {
+	prog=$(basename "${0}")
+	msgln "USAGE:"
+	#msgln "      ${prog} <program-name> <program-version> <os>/<platform>..."
+	msgln "      ${prog} <os>/<platform>..."
+	msgln "      ${prog} --local         Build the local exec"
+	msgln "      ${prog} --init          Create the resource file in the current directory"
+	msgln
+	if [ -r "${RESOURCE_FILE}" ]; then
+		msgln "Resource file '${RESOURCE_FILE}' content:"
+		cat >&2 ${RESOURCE_FILE}
+	else
+		msgln "Resource file '${RESOURCE_FILE}' not found"
+	fi
+}
+
+function msgln() {
+	echo >&2 "${1}"
+}
+
+function exitUsage() {
+	echo >&2 "${1}"
+	usage
+	exit 1
+}
+
+function exitMsg() {
+	echo >&2 "${1}"
+	exit 1
+}
+
+# CMDLINE: help
+if [ "${1}" == "help,," ] || [ "${1,,}" == "--help" ] || [ "${1,,}" == "-h" ]; then
+	usage
+	exit
+fi
+
+# CMDLINE: init
+if [ "${1,,}" == "--init" ]; then
+	cat >"${RESOURCE_FILE}" <<eot
+# Builder resource file
+# Created on $(date)
+
+# Program name
+PROGRAM_NAME="name"
+
+# Program version
+PROGRAM_VERSION="version"
+
+# Preset platform
+platform=("linux/amd64" "darwin/arm64")
+
+#--- end of file ---
+
+eot
+	msgln "Resource file '${RESOURCE_FILE}' create. Edit it to set valid values."
+	#${EDITOR-vi} "${RESOURCE_FILE}"
+	exit
+fi
+
+if [ -r "${RESOURCE_FILE}" ]; then
+	if ! source "${RESOURCE_FILE}"; then
+		exitMsg "Can't load build resource file '${RESOURCE_FILE}'"
+	fi
+fi
+
+if [ -z "${PROGRAM_NAME}" ]; then
+	exitUsage "Missing program name"
+fi
+
+if [ -z "${PROGRAM_VERSION}" ]; then
+	exitUsage "Missing program version"
+fi
+
+
+function getBuildCount() {
+	local reg ver count
+	if [ -r "${BUILD_REGISTER}" ]; then
+		reg=$(<"${BUILD_REGISTER}")
+	else
+		reg="${PROGRAM_VERSION} 0"
+	fi
+	read ver count <<<"${reg}"
+	if [ "${ver}" != "${PROGRAM_VERSION}" ]; then
+		count=0
+	fi
+	count=$((count+1))
+	echo >"${BUILD_REGISTER}" "${PROGRAM_VERSION} ${count}"
+	echo ${count}
+}
+
+function build() {
+	local target=${1} ext cmd
+	IFS=/ read os cpu <<<"${p}"
+	#msgln "OS=${os}; CPU=${cpu}"
+	ext=""
+	if [ "${os}" == 'windows' ]; then
+		ext=".exe"
+	fi
+	cmd="GOOS='${os}' GOARCH='${cpu}' go build -o '${PROGRAM_NAME}_v${PROGRAM_VERSION}_${os}_${cpu}${ext}'"
+	eval "${cmd}"
+}
+
+function buildLocal() {
+	local ext cmd
+	ext=""
+	if [[ "${OSTYPE}" =~ win.* ]]; then
+		ext=".exe"
+	fi
+	cmd="go build -o '${PROGRAM_NAME}${ext}'"
+	eval "${cmd}"
+}
+
+function gitTag() {
+	local gopath gopkg mod
+	local tag
+
+	if ! tag=$(git tag -l --sort=-version:refname "v[0-9]*.[0-9]*.[0-9]*"|head -1) || [ -z "${tag}" ]; then
+		gopath=$(go env GOPATH)
+		gopkg="${gopath}/pkg/mod/git.portale-stac.it/go-pkg"
+		if cd "${gopkg}" 2>/dev/null; then
+			mod=$(ls -1v |grep expr@|tail -1)
+			tag=${mod##*@}
+			cd - >/dev/null
+		fi
+	fi
+	echo ${tag}
+}
+
+function gitTagDate() {
+	local tag_name=${1}
+	local tag_date
+
+	if ! tag_date=$(git show --no-patch --format=%ci "${tag_name}") || [ -z "${tag_date}" ]; then
+		tag_date="n/a"
+	fi
+	echo ${tag_date}
+}
+
+function createVersionSource() {
+	local tag tag_date
+	tag=$(gitTag)
+	if [ -z "${tag}" ]; then
+		tag="n/a"
+	else
+		tag_date=$(gitTagDate "${tag}")
+	fi
+
+	cat >version.go <<eot
+// Copyright (c) 2024-$(date +%Y) Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// version.go
+package main
+
+const (
+	PROGNAME     = "${PROGRAM_NAME}"
+	VERSION      = "v${PROGRAM_VERSION}(build $(getBuildCount)),$(date +"%Y/%m/%d") (celestino.amoroso@portale-stac.it)"
+	EXPR_VERSION = "${tag}"
+	EXPR_DATE    = "${tag_date}"
+)
+eot
+}
+
+## -- TEST -- ##
+
+# echo "Tag: $(gitTag)"
+# echo "Tag Date: $(gitTagDate $(gitTag))"
+# exit 0
+
+## -- MAIN -- ##
+createVersionSource
+
+if [ "${1}" == "--local" ]; then
+	buildLocal
+	exit
+fi
+
+if [ ${#} -gt 0 ]; then
+	for p; do
+		build "${p}"
+	done
+else
+	for p in ${platform[@]}; do
+		build "${p}"
+	done
+fi
+

cmd/ecli/clean-older.bash

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+# Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+# All rights reserved
+
+RESOURCE_FILE=".build.rc"
+BUILD_REGISTER=".build_register"
+
+
+PASSWORD=
+GITEA_USER="camoroso"
+GITEA_PASSWORD_FILE="${HOME}/.gitea_password"
+GITEA_OWNER="go-pkg"
+GITEA_HOST="https://git.portale-stac.it"
+GITEA_BASE_PATH="api/v1/packages"
+GITEA_PKG_TYPE="generic"
+
+
+function msgln() {
+	echo >&2 "${1}"
+}
+
+function exitMsg() {
+	echo >&2 "${1}"
+	exit 1
+}
+
+function readBuildCount() {
+	local reg ver count
+	if [ -r "${BUILD_REGISTER}" ]; then
+		reg=$(<"${BUILD_REGISTER}")
+	else
+		reg="${PROGRAM_VERSION} 0"
+	fi
+	read ver count <<<"${reg}"
+	if [ "${ver}" != "${PROGRAM_VERSION}" ]; then
+		count=0
+	fi
+	echo ${count}
+}
+
+if [ -r "${GITEA_PASSWORD_FILE}" ]; then
+	if ! PASSWORD=$(<"${GITEA_PASSWORD_FILE}"); then
+		exitMsg "Can're password file '${GITEA_PASSWORD_FILE}'"
+	fi
+else
+	exitMsg "Password file '${GITEA_PASSWORD_FILE}' not found"
+fi
+if [ -z "${PASSWORD}" ]; then
+	exitMsg "Empty password. Please, check file '${GITEA_PASSWORD_FILE}'"
+fi
+
+if [ -r "${RESOURCE_FILE}" ]; then
+	source "${RESOURCE_FILE}"
+else
+	exitMsg "resource file '${RESOURCE_FILE}' not found"
+fi
+
+if [ -r "${BUILD_REGISTER}" ]; then
+	BUILD_TAG=$(<"${BUILD_REGISTER}")
+else
+	exitMsg "build register file '${BUILD_REGISTER}' not found"
+fi
+url="${GITEA_HOST}/${GITEA_BASE_PATH}/${GITEA_OWNER}/${GITEA_PKG_TYPE}/${PROGRAM_NAME}/${PROGRAM_VERSION}/files"
+#echo "URL: ${url}"
+#echo $(curl --user "${GITEA_USER}:${PASSWORD}" -X GET ${url}|jq '.[]."name"')
+
+declare -a files=(
+$(curl --no-progress-meter --user "${GITEA_USER}:${PASSWORD}" -X GET ${url}|jq '.[]."name"')
+)
+
+for name in ${files[@]}; do
+	filename=${name:1:${#name}-2}
+	name_terminal=${filename##*_}
+	filever=${name_terminal%%.*}
+
+	if [ "${BUILD_TAG}" != "${PROGRAM_VERSION} ${filever}" ]; then
+		msgln "Deleting ${name}"
+	curl --no-progress-meter --user "${GITEA_USER}:${PASSWORD}" -X DELETE ${GITEA_HOST}/api/packages/${GITEA_OWNER}/${GITEA_PKG_TYPE}/${PROGRAM_NAME}/${PROGRAM_VERSION}/${filename}
+#	else
+#		echo "most recent version"
+	fi
+done
+
+#curl --user "${GITEA_USER}:${PASSWORD}" -X GET https://git.portale-stac.it/api/v1/packages/go-pkg/generic/ecli/1.7.0/files

cmd/ecli/commands.go

@@ -0,0 +1,236 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// commands.go
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr"
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/utils"
+)
+
+type commandFunction func(opt *Options, ctx kern.ExprContext, args []string) (err error)
+
+type command struct {
+	name        string
+	description string
+	code        commandFunction
+}
+
+func (cmd *command) exec(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	return cmd.code(opt, ctx, args)
+}
+
+type commandHandler struct {
+	cmdIndex []string
+	commands map[string]*command
+}
+
+func NewCommandHandler() *commandHandler {
+	return &commandHandler{
+		cmdIndex: make([]string, 0, 20),
+		commands: make(map[string]*command),
+	}
+}
+
+// func (h *commandHandler) setContext(ctx expr.ExprContext) {
+// 	h.ctx = ctx
+// }
+
+func (h *commandHandler) add(name, description string, f commandFunction) {
+	h.cmdIndex = append(h.cmdIndex, name)
+	h.commands[name] = &command{name: name, description: description, code: f}
+}
+
+func (h *commandHandler) get(cmdLine string) (cmd *command, args []string) {
+	if len(cmdLine) > 0 {
+		tokens := strings.Split(cmdLine, " ")
+		name := tokens[0]
+		args = make([]string, 0, len(tokens)-1)
+		if cmd = h.commands[name]; cmd != nil && len(tokens) > 1 {
+			for _, tk := range tokens[1:] {
+				if tk != "" {
+					args = append(args, tk)
+				}
+			}
+		}
+	}
+	return
+}
+
+// ------
+var cmdHandler *commandHandler
+
+func (h *commandHandler) help() {
+	fmt.Fprintln(os.Stderr, `--- REPL commands:`)
+	for _, name := range h.cmdIndex {
+		cmd := h.commands[name]
+		fmt.Fprintf(os.Stderr, "%12s -- %s\n", cmd.name, cmd.description)
+	}
+	fmt.Fprint(os.Stderr, `
+--- Command line options:
+    -b <builtin>       Import builtin modules.
+                       <builtin> can be a list of module names or a glob-pattern.
+                       Use the special value 'all' or the pattern '*' to import all modules.
+    -B, --list-builtins  List all builtin module names
+    -e <expression>    Evaluate <expression> instead of standard-input
+    -i                 Force REPL operation when all -e occurences have been processed
+    -h, --help, help   Show this help menu
+    -m, --modules      List all builtin modules
+    --noout            Disable printing of expression results
+    -p                 Print prefix form
+    -t                 Print tree form
+    -v, --version      Show program version
+`)
+
+}
+
+// --------
+
+func cmdExit(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	return io.EOF
+}
+
+func cmdHelp(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	cmdHandler.help()
+	return
+}
+
+func cmdMultiLine(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	if opt.formOpt&kern.MultiLine == 0 {
+		opt.formOpt |= kern.MultiLine
+	} else {
+		opt.formOpt &= ^kern.MultiLine
+	}
+	return
+}
+
+func cmdTty(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	if opt.formOpt&kern.TTY == 0 {
+		opt.formOpt |= kern.TTY
+	} else {
+		opt.formOpt &= ^kern.TTY
+	}
+	return
+}
+
+func execFile(opt *Options, ctx kern.ExprContext, fileName string) (err error) {
+	var fh *os.File
+	if fh, err = os.Open(fileName); err == nil {
+		goBatch(opt, ctx, fh, false)
+		fh.Close()
+	}
+	return
+}
+
+func cmdSource(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	var target string
+	for _, arg := range args {
+		if len(arg) == 0 {
+			continue
+		}
+		// TODO migliorare questa parte: eventualmente valutare un'espressione
+		if target, err = checkStringLiteral(arg); err != nil {
+			break
+		}
+
+		if target, err = utils.ExpandPath(target); err != nil {
+			break
+		}
+
+		if isPattern(target) {
+			var fileNames []string
+			if fileNames, err = matchPathPattern(target); err == nil {
+				for _, fileName := range fileNames {
+					if err = execFile(opt, ctx, fileName); err != nil {
+						break
+					}
+				}
+			}
+		} else {
+			err = execFile(opt, ctx, target)
+		}
+
+		if err != nil {
+			break
+		}
+	}
+	return
+}
+
+func cmdModules(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	expr.IterateBuiltinModules(func(name, description string, imported bool) bool {
+		var check rune = ' '
+		if imported {
+			check = '*'
+		}
+		fmt.Printf("%c %20q: %s\n", check, name, description)
+		return true
+	})
+	return
+}
+
+func cmdBase(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	if len(args) == 0 {
+		fmt.Println(opt.base)
+	} else if args[0] == "2" {
+		opt.baseVerb = "0b%b"
+		opt.base = 2
+	} else if args[0] == "8" {
+		opt.baseVerb = "0o%o"
+		opt.base = 8
+	} else if args[0] == "10" {
+		opt.baseVerb = "%d"
+		opt.base = 10
+	} else if args[0] == "16" {
+		opt.baseVerb = "0x%x"
+		opt.base = 16
+	} else {
+		err = fmt.Errorf("invalid number base %s", args[0])
+	}
+	return
+}
+
+func cmdOutput(opt *Options, ctx kern.ExprContext, args []string) (err error) {
+	var outputArg string
+	if len(args) == 0 {
+		outputArg = "status"
+	} else {
+		outputArg = strings.ToLower(args[0])
+	}
+	switch outputArg {
+	case "on":
+		opt.output = true
+	case "off":
+		opt.output = false
+	case "status":
+		if opt.output {
+			fmt.Println("on")
+		} else {
+			fmt.Println("off")
+		}
+	default:
+		err = fmt.Errorf("output: unknown option %q", outputArg)
+	}
+	return
+}
+
+//------------------
+
+func setupCommands() {
+	cmdHandler = NewCommandHandler()
+	cmdHandler.add("base", "Set the integer output base: 2, 8, 10, or 16", cmdBase)
+	cmdHandler.add("exit", "Exit the program", cmdExit)
+	cmdHandler.add("help", "Show command list", cmdHelp)
+	cmdHandler.add("ml", "Enable/Disable multi-line output", cmdMultiLine)
+	cmdHandler.add("mods", "List builtin modules", cmdModules)
+	cmdHandler.add("output", "Enable/Disable printing expression results. Options 'on', 'off', 'status'", cmdOutput)
+	cmdHandler.add("source", "Load a file as input", cmdSource)
+	cmdHandler.add("tty", "Enable/Disable ansi output", cmdTty)
+}

cmd/ecli/ecli.adoc

@@ -0,0 +1,339 @@
+= Ecli
+Expression Calculator Interactive Tool
+:authors: Celestino Amoroso
+:email: celestino.amoroso@gmail.com
+:docinfo: shared
+:encoding: utf-8
+:toc: right
+:toclevels: 4
+:icons: font
+:icon-set: fi
+:numbered:
+:data-uri:
+:docinfo1:
+:sectlinks:
+:sectanchors:
+:source-highlighter: rouge
+:rouge-style: manni
+:stylesdir: /home/share/s3-howto/styles
+:stylesheet: adoc-colony.css
+
+// Workaround to manage double-column in back-tick quotes
+:2c: ::
+// Workaround to manage double-plus in back-tick quotes
+:plusplus: ++
+// Workaround to manage asterisk in back-tick quotes
+:star: *
+
+#Generated by Copilot#
+
+== Overview
+
+`ecli` (Expression Calculator Interactive Tool) is an interactive REPL (Read-Eval-Print Loop) application for evaluating expressions using the Expr package. It provides a powerful command-line interface for expression evaluation with support for multiple builtin modules, file operations, and interactive scripting.
+
+The tool combines the expression evaluation capabilities of the Expr package with an interactive shell environment, making it ideal for:
+
+- Interactive expression testing and prototyping
+- Command history survival across sessions
+- Batch expression evaluation from scripts
+- Data processing and transformation
+- Mathematical computations with fractions and complex operators
+
+== Getting Started
+
+=== Installation
+
+To build and install `ecli`:
+
+[source,bash]
+----
+cd cmd/ecli
+./build.bash
+----
+
+The compiled binary will be available as `ecli` in the current directory.
+
+=== Basic Usage
+
+Start the interactive REPL:
+
+[source,bash]
+----
+./ecli
+----
+
+You'll see the prompt `>>>` where you can enter expressions to evaluate.
+
+=== Command Line Options
+
+[cols="1,4", options="header"]
+|===
+| Option | Description
+
+| `-e <expression>` | Evaluate an expression directly without entering REPL mode
+| `-i` | Force REPL operation after processing all `-e` options
+| `-b <builtin>` | Import builtin modules (comma-separated list, glob patterns, or 'all')
+| `-B, --list-builtins` | List all available builtin module names
+| `-m, --modules` | List all builtin modules
+| `-p` | Print expressions in prefix form
+| `-t` | Print expressions in tree form
+| `--noout` | Disable printing of expression results
+| `-h, --help` | Show help message
+| `-v, --version` | Show program version
+|===
+
+== Interactive Commands
+
+Within the REPL, you can use the following commands:
+
+[cols="2,5", options="header"]
+|===
+| Command | Description
+
+| `base [2\|8\|10\|16]` | Set the integer output base. Use without arguments to show current base
+| `exit` | Exit the REPL
+| `help` | Display available commands and command-line options
+| `ml` | Enable/Disable multi-line input mode for complex expressions
+| `mods` | List all builtin modules (with `*` marking imported ones)
+| `output [on\|off\|status]` | Enable/Disable printing of expression results
+| `source <file>` | Load and execute expressions from a file
+| `tty` | Enable/Disable ANSI terminal output
+|===
+
+== Features
+
+=== Expression Evaluation
+
+`ecli` supports the full expression language provided by the Expr package, including:
+
+- **Arithmetic Operations**: Addition, subtraction, multiplication, division, modulo
+- **Bitwise Operations**: AND, OR, XOR, NOT, shift operations
+- **Boolean Logic**: AND, OR, NOT operations
+- **Relational Operators**: Comparison and equality operators
+- **String Operations**: Concatenation and string manipulation
+- **Iterators**: Range, list, and custom iterators
+- **Functions**: Builtin and user-defined functions
+- **Collections**: Lists, dictionaries, and linked lists
+- **Fractions**: Support for fractional arithmetic
+
+=== Builtin Modules
+
+`ecli` provides access to various builtin modules through the `-b` option:
+
+[cols="1,4", options="header"]
+|===
+| Module | Functionality
+
+| `base` | Core expression evaluation functions
+| `fmt` | String formatting and output functions
+| `string` | String manipulation functions
+| `math-arith` | Mathematical and arithmetic operations
+| `iterator` | Iterator-related functions
+| `os-file` | File I/O operations
+| `import` | Module import functionality
+|===
+
+Use `-B` or `--list-builtins` to see all available modules:
+
+[source,bash]
+----
+./ecli --list-builtins
+----
+
+== Examples
+
+=== Basic Arithmetic
+
+[source,bash]
+----
+>>> 2 + 3 * 4
+14
+>>> (2 + 3) * 4
+20
+----
+
+=== String Operations
+
+[source,bash]
+----
+>>> "hello" + " " + "world"
+hello world
+----
+
+=== Using Iterators
+
+[source,bash]
+----
+>>> it = [1, 2, 3, 4, 5] map $_ * 2
+$($([#5]))
+>>> $$(it)
+[<
+  2,
+  4,
+  6,
+  8,
+  10
+>]
+----
+
+=== Evaluating from Command Line
+
+[source,bash]
+----
+./ecli -e "2 + 2"
+4
+----
+
+=== Loading Builtin Modules
+
+[source,bash]
+----
+./ecli -b "math-arith,string"
+----
+
+=== Loading Expressions from Files
+
+Inside the REPL:
+
+[source]
+----
+>>> source "expressions.expr"
+----
+
+Or from command line:
+
+[source,bash]
+----
+./ecli -e "@expressions.expr"
+----
+
+== Configuration
+
+=== Resource Files
+
+`ecli` supports startup resource files:
+
+- `.ecli.rc` - Main configuration file
+- `.ecli.rc.d/` - Directory for modular configuration files
+
+These files are automatically loaded at startup if they exist in the current directory or home directory.
+
+== Building from Source
+
+=== Prerequisites
+
+- Go 1.18 or later
+- Make or bash shell
+
+=== Build Steps
+
+[source,bash]
+----
+cd cmd/ecli
+./build.bash
+----
+
+=== Build Artifacts
+
+The build process generates:
+
+- `ecli` - The main executable
+- `version.txt` - Version information
+- Platform-specific binaries (e.g., `ecli_v1.17.0_linux_amd64`, `ecli_v1.17.0_darwin_arm64`)
+
+== Advanced Usage
+
+=== Multi-line Input
+
+For complex expressions, split operations across multiple lines terminating with a backslash (`\`):
+
+[source]
+----
+>>> ml
+>>> result = [1, 2, 3, 4, 5] \
+...   filter $_ > 2 \
+...   map $_ * 2
+>>> $$(result)
+[<6, 8, 10>
+----
+
+=== Script Execution
+
+Create a file `calculations.expr`:
+
+[source]
+----
+x = 10
+y = 20
+result = x + y * 2
+----
+
+Execute it:
+
+[source,bash]
+----
+./ecli -e '@calculations.expr' -e 'result'
+50
+----
+
+=== Other Iterator Examples
+
+[source]
+----
+>>> data = [{"name": "alice", "age": 30}, {"name": "bob", "age": 25}]
+
+// Extract names using map iterator
+>>> $$(data map ($_).name)
+[<
+  "alice",
+  "bob"
+>]
+
+// Filter ages greater than 28
+>>> $$(data filter ($_).age > 28 map ($_).name)
+[<
+  "alice"
+>]
+
+----
+
+== Troubleshooting
+
+=== Expression Parsing Errors
+
+If you encounter parsing errors, check:
+
+- Bracket matching and quotation marks
+- Operator precedence
+- Variable and function names
+
+=== Module Loading Issues
+
+Verify available modules:
+
+[source,bash]
+----
+./ecli --list-builtins
+----
+
+=== File Not Found Errors
+
+Ensure file paths are:
+
+- Properly quoted in expressions
+- Relative to the current working directory or absolute paths
+- Readable by the current user
+
+== Related Documentation
+
+- link:../../../README.adoc[Expr Package Documentation]
+- Expr Expression Language Syntax
+- Builtin Modules Reference
+
+== Version History
+
+For version information and changes, see the link:version.txt[version file].
+
+== License
+
+Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com). All rights reserved.

cmd/ecli/go.mod

@@ -0,0 +1,15 @@
+module ecli
+
+go 1.24.0
+
+require (
+	git.portale-stac.it/go-pkg/expr v0.33.0
+	git.portale-stac.it/go-pkg/utils v0.3.0
+	github.com/ergochat/readline v0.1.3
+)
+
+require (
+	golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6 // indirect
+	golang.org/x/sys v0.38.0 // indirect
+	golang.org/x/text v0.31.0 // indirect
+)

cmd/ecli/go.sum

@@ -0,0 +1,36 @@
+git.portale-stac.it/go-pkg/expr v0.1.0 h1:7xGEuUhdh6RRFaRbRnLVqVJBmHJWHfqjDBm2K0fIW2s=
+git.portale-stac.it/go-pkg/expr v0.1.0/go.mod h1:kUFEQkUMCJ1IiUKkL0P5/vznaAIzFI26Xf5P0rTXqR0=
+git.portale-stac.it/go-pkg/expr v0.2.0 h1:AAaVsV0uaC4EikKU91VuubIpbIN7wuya7t4avyFgg+0=
+git.portale-stac.it/go-pkg/expr v0.2.0/go.mod h1:DZqqZ3A9h4qEOs7yMvG4VZq7B/xhFsYqC3IKd3M2VKc=
+git.portale-stac.it/go-pkg/expr v0.17.0 h1:4ANGwJfwJO3AmnKka4Cf1AO9/ckGLMj8RIWeoDFKawQ=
+git.portale-stac.it/go-pkg/expr v0.17.0/go.mod h1:DZqqZ3A9h4qEOs7yMvG4VZq7B/xhFsYqC3IKd3M2VKc=
+git.portale-stac.it/go-pkg/expr v0.32.0 h1:ikXqHjJslIGkD79G1/51xe+c25TFi2CslJ6nu8mOuJY=
+git.portale-stac.it/go-pkg/expr v0.32.0/go.mod h1:R2TYIahLtD8YDgNEHtgHCQdoEUZ7yCQsMHyJXhJijmw=
+git.portale-stac.it/go-pkg/expr v0.33.0 h1:GJ7PPgA1689GSC/cUWGYm08jn7qMmkp0FMQf/As5sCw=
+git.portale-stac.it/go-pkg/expr v0.33.0/go.mod h1:R2TYIahLtD8YDgNEHtgHCQdoEUZ7yCQsMHyJXhJijmw=
+git.portale-stac.it/go-pkg/utils v0.2.0 h1:2l4IVUhElzjaIUJlahPG2DZTGb9x7OXuFTO4z1K6LmY=
+git.portale-stac.it/go-pkg/utils v0.2.0/go.mod h1:PebQ45Qbe89aMTd3wcbcx1bkpNRW4/frNLnpuyZYovU=
+git.portale-stac.it/go-pkg/utils v0.3.0 h1:kCJ3+XcekV7in/SieJjiswdtJKMBS0RTJMlG2fW5mK0=
+git.portale-stac.it/go-pkg/utils v0.3.0/go.mod h1:PebQ45Qbe89aMTd3wcbcx1bkpNRW4/frNLnpuyZYovU=
+github.com/ergochat/readline v0.1.0 h1:KEIiAnyH9qGZB4K8oq5mgDcExlEKwmZDcyyocgJiABc=
+github.com/ergochat/readline v0.1.0/go.mod h1:o3ux9QLHLm77bq7hDB21UTm6HlV2++IPDMfIfKDuOgY=
+github.com/ergochat/readline v0.1.1 h1:C8Uuo3ybB23GWOt0uxmHbGzKM9owmtXary6Clrj84s0=
+github.com/ergochat/readline v0.1.1/go.mod h1:o3ux9QLHLm77bq7hDB21UTm6HlV2++IPDMfIfKDuOgY=
+github.com/ergochat/readline v0.1.3 h1:/DytGTmwdUJcLAe3k3VJgowh5vNnsdifYT6uVaf4pSo=
+github.com/ergochat/readline v0.1.3/go.mod h1:o3ux9QLHLm77bq7hDB21UTm6HlV2++IPDMfIfKDuOgY=
+golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6 h1:zfMcR1Cs4KNuomFFgGefv5N0czO2XZpUbxGUy8i8ug0=
+golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6/go.mod h1:46edojNIoXTNOhySWIWdix628clX9ODXwPsQuG6hsK0=
+golang.org/x/sys v0.15.0 h1:h48lPFYpsTvQJZF4EKyI4aLHaev3CxivZmv7yZig9pc=
+golang.org/x/sys v0.15.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.21.0 h1:rF+pYz3DAGSQAxAu1CbC7catZg4ebC4UIeIhKxBZvws=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.38.0 h1:3yZWxaJjBmCWXqhN1qh02AkOnCQ1poK6oF+a7xWL6Gc=
+golang.org/x/sys v0.38.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
+golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
+golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
+golang.org/x/text v0.9.0 h1:2sjJmO8cDvYveuX97RDLsxlyUxLl+GHoLxBiRdHllBE=
+golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
+golang.org/x/text v0.16.0 h1:a94ExnEXNtEwYLGJSIUxnWoxoRz/ZcCsV63ROupILh4=
+golang.org/x/text v0.16.0/go.mod h1:GhwF1Be+LQoKShO3cGOHzqOgRrGaYc9AvblQOmPVHnI=
+golang.org/x/text v0.31.0 h1:aC8ghyu4JhP8VojJ2lEHBnochRno1sgL6nEi9WGFGMM=
+golang.org/x/text v0.31.0/go.mod h1:tKRAlv61yKIjGGHX/4tP1LTbc13YSec1pxVEWXzfoeM=

cmd/ecli/graph.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+//go:build graph
+
+// NOTE: Enable this build tag to print the graph of the expression instead of evaluating it.
+//       go run -tags graph cmd/ecli/main.go
+
+// graph.go
+package main
+
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr"
+)
+
+func printGraph() {
+	r := expr.NewExprReticle(ast)
+	fmt.Println(r.String())
+}

cmd/ecli/main.go

@@ -0,0 +1,418 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// main.go
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr"
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/str"
+	"git.portale-stac.it/go-pkg/utils"
+
+	// https://pkg.go.dev/github.com/ergochat/readline#section-readme
+	"github.com/ergochat/readline"
+)
+
+const (
+	intro = PROGNAME + ` -- Expressions calculator ` + VERSION + `
+	Based on the Expr package ` + EXPR_VERSION + ` (` + EXPR_DATE + `) 
+	Type help to get the list of available commands
+	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
+`
+	mainPrompt = ">>> "
+	contPrompt = "... "
+
+	historyFile = "~/.expr_history"
+)
+
+// ------
+
+func errOptValueRequired(opt string) error {
+	return fmt.Errorf("option %q requires a value", opt)
+}
+
+func about() string {
+	return PROGNAME + " -- " + VERSION + "; Expr package " + EXPR_VERSION
+}
+
+func importBuiltins(ctx kern.ExprContext, opt *Options) (err error) {
+	for _, spec := range opt.builtin {
+		if moduleSpec, ok := spec.(string); ok {
+			if moduleSpec == "all" {
+				moduleSpec = "*"
+			}
+			_, err = expr.ImportInContextByGlobPattern(ctx, moduleSpec)
+		} else if moduleSpec, ok := spec.([]string); ok {
+			notFoundList := make([]string, 0)
+			for _, name := range moduleSpec {
+				if !expr.ImportInContext(ctx, name) {
+					notFoundList = append(notFoundList, name)
+				}
+			}
+			if len(notFoundList) > 0 {
+				err = fmt.Errorf("not found modules: %s", strings.Join(notFoundList, ","))
+			}
+		}
+	}
+	return
+}
+
+func initReadlineConfig(cfg *readline.Config) {
+	if histfile, err := utils.ExpandPath(historyFile); err == nil {
+		cfg.HistoryFile = histfile
+	}
+	cfg.Undo = true
+	cfg.DisableAutoSaveHistory = true
+
+}
+
+func goInteractiveReadline(opt *Options, ctx kern.ExprContext, r io.Reader) {
+	var sb strings.Builder
+	var cfg readline.Config
+	initReadlineConfig(&cfg)
+	rl, err := readline.NewFromConfig(&cfg)
+	if err != nil {
+		goInteractive(opt, ctx, r)
+		return
+	}
+	defer rl.Close()
+
+	fmt.Print(intro)
+	rl.SetPrompt(mainPrompt)
+	for line, err := rl.ReadLine(); err == nil; line, err = rl.ReadLine() {
+		if continuation(&sb, line) {
+			rl.SetPrompt(contPrompt)
+			continue
+		}
+
+		rl.SetPrompt(mainPrompt)
+		sb.WriteString(line)
+		source := strings.TrimSpace(sb.String())
+		if source != "" && !strings.HasPrefix(source, "//") {
+			if cmd, args := cmdHandler.get(source); cmd != nil {
+				rl.SaveToHistory(source)
+				if err = cmd.exec(opt, ctx, args); err != nil {
+					if err == io.EOF {
+						err = nil
+						break
+					} else {
+						fmt.Fprintln(os.Stderr, "Eval Error:", err)
+						break
+					}
+				}
+			} else {
+				rl.SaveToHistory(source)
+				r := strings.NewReader(source)
+				compute(opt, ctx, r, true)
+			}
+		}
+		sb.Reset()
+	}
+	fmt.Println()
+}
+
+func goInteractive(opt *Options, ctx kern.ExprContext, r io.Reader) {
+	var sb strings.Builder
+	fmt.Print(intro)
+	fmt.Print(mainPrompt)
+	reader := bufio.NewReaderSize(r, 1024)
+	for line, err := reader.ReadString('\n'); err == nil && line != "exit\n"; line, err = reader.ReadString('\n') {
+		if continuation(&sb, line) {
+			continue
+		}
+
+		sb.WriteString(line)
+		source := strings.TrimSpace(sb.String())
+		// fmt.Printf("source=%q\n", source)
+		if source != "" && !strings.HasPrefix(source, "//") {
+			if cmd, args := cmdHandler.get(source); cmd != nil {
+				if err = cmd.exec(opt, ctx, args); err != nil {
+					break
+				}
+			} else {
+				r := strings.NewReader(source)
+				compute(opt, ctx, r, true)
+			}
+		}
+		sb.Reset()
+		fmt.Print(mainPrompt)
+	}
+	fmt.Println()
+}
+
+func continuation(sb *strings.Builder, line string) (cont bool) {
+	line = strings.TrimSpace(line)
+	if strings.HasSuffix(line, "\\") {
+		sb.WriteString(line[0 : len(line)-1])
+		cont = true
+	} else if strings.HasSuffix(line, ";") {
+		sb.WriteString(line)
+		cont = true
+	} else if len(line) > 0 {
+		if scan.StringEndsWithOperator(line) {
+			sb.WriteString(line)
+			cont = true
+		} else {
+			fullInput := sb.String() + line
+			if strings.Count(fullInput, "(") > strings.Count(fullInput, ")") ||
+				strings.Count(fullInput, "[") > strings.Count(fullInput, "]") ||
+				strings.Count(fullInput, "{") > strings.Count(fullInput, "}") {
+				sb.WriteString(line)
+				cont = true
+			}
+		}
+	}
+
+	return
+}
+
+func goBatch(opt *Options, ctx kern.ExprContext, r io.Reader, outputEnabled bool) {
+	var sb strings.Builder
+	reader := bufio.NewReaderSize(r, 1024)
+	for line, err := reader.ReadString('\n'); err == nil && line != "exit\n"; line, err = reader.ReadString('\n') {
+		if continuation(&sb, line) {
+			continue
+		}
+		sb.WriteString(line)
+		source := strings.TrimSpace(sb.String())
+		// fmt.Printf("source=%q\n", source)
+		if source != "" && !strings.HasPrefix(source, "//") {
+			if cmd, args := cmdHandler.get(source); cmd != nil {
+				if err = cmd.exec(opt, ctx, args); err != nil {
+					fmt.Fprintln(os.Stderr, "Eval Error:", err)
+					break
+				}
+			} else {
+				r := strings.NewReader(source)
+				compute(opt, ctx, r, outputEnabled)
+			}
+		}
+		sb.Reset()
+	}
+}
+
+func compute(opt *Options, ctx kern.ExprContext, r io.Reader, outputEnabled bool) {
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
+	parser := expr.NewParser()
+
+	if ast, err := parser.Parse(scanner); err == nil {
+		if opt.printPrefix {
+			fmt.Println(ast)
+		}
+		if opt.printTree {
+			printGraph()
+		}
+
+		if result, err := ast.Eval(ctx); err == nil {
+			if outputEnabled && opt.output {
+				printResult(opt, result)
+			}
+		} else {
+			fmt.Fprintln(os.Stderr, "Eval Error:", err)
+		}
+	} else {
+		fmt.Fprintln(os.Stderr, "Parse Error:", err)
+	}
+}
+
+func printResult(opt *Options, result any) {
+	if f, ok := result.(kern.Formatter); ok {
+		fmt.Println(f.ToString(opt.formOpt))
+	} else if types.IsInteger(result) {
+		fmt.Printf(opt.baseVerb, result)
+		fmt.Println()
+	} else if str.IsString(result) {
+		fmt.Printf("\"%s\"\n", result)
+	} else {
+		fmt.Println(result)
+	}
+}
+
+func isReaderTerminal(r io.Reader) bool {
+	if fh, ok := r.(*os.File); ok {
+		return utils.StreamIsTerminal(fh)
+	}
+	return false
+}
+
+func registerLocalFunctions(ctx kern.ExprContext) {
+	const (
+		devParamProp   = "prop"
+		devParamDigits = "digits"
+	)
+
+	aboutFunc := func(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+		result = about()
+		return
+	}
+
+	ctrlListFunc := func(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+		vars := ctx.EnumVars(func(name string) bool {
+			return len(name) > 0 && name[0] == '_'
+		})
+		result = array.ArrayFromStrings(vars)
+		return
+	}
+
+	ctrlFunc := func(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+		varName, _ := args[devParamProp].(string)
+		if len(args) == 1 {
+			result = expr.GlobalCtrlGet(ctx, varName)
+		} else {
+			result = expr.GlobalCtrlSet(ctx, varName, args[kern.ParamValue])
+		}
+		return
+	}
+
+	envSetFunc := func(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+		var varName, value string
+		var ok bool
+		if varName, ok = args[kern.ParamName].(string); !ok {
+			err = kern.ErrExpectedGot(name, kern.TypeString, args[kern.ParamName])
+			return
+		}
+		if value, ok = args[kern.ParamValue].(string); !ok {
+			err = kern.ErrExpectedGot(name, kern.TypeString, args[kern.ParamValue])
+			return
+		}
+		if err = os.Setenv(varName, value); err == nil {
+			result = value
+		}
+		return
+	}
+
+	envGetFunc := func(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 {
+			err = kern.ErrExpectedGot(name, kern.TypeString, args[kern.ParamName])
+			return
+		}
+
+		if result, ok = os.LookupEnv(varName); !ok {
+			err = fmt.Errorf("environment variable %q does not exist", varName)
+		}
+		return
+	}
+
+	envListFunc := func(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+		env := os.Environ()
+		vars := make([]string, 0, len(env))
+		for _, e := range env {
+			name, _, _ := strings.Cut(e, "=")
+			vars = append(vars, name)
+		}
+		result = array.ArrayFromStrings(vars)
+		return
+	}
+
+	binFunc := func(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+		var value, digits int64
+		var ok bool
+		var sb strings.Builder
+
+		if value, ok = args[kern.ParamValue].(int64); !ok {
+			err = kern.ErrExpectedGot(name, kern.TypeInt, args[kern.ParamValue])
+			return
+		}
+		if digits, ok = args[devParamDigits].(int64); !ok {
+			err = kern.ErrExpectedGot(name, kern.TypeInt, args[devParamDigits])
+			return
+		}
+		if digits != 64 && digits != 32 && digits != 16 && digits != 8 {
+			err = fmt.Errorf("%s param allows 8, 16, 32, or 64 values only", devParamDigits)
+			return
+		}
+
+		mask := uint64(0)
+		for i := 0; i < int(digits); i++ {
+			mask |= (1 << i)
+		}
+		maskedValue := uint64(value) & mask
+		// if maskedValue != uint64(value) {
+		// 	err = fmt.Errorf("%s param (%d) is not compatible with the value (%d) of %s param", expr.ParamValue, value, digits, devParamDigits)
+		// 	return
+		// }
+
+		for i := int(digits) - 1; i >= 0; i-- {
+			if maskedValue&(1<<i) == 0 {
+				sb.WriteByte('0')
+			} else {
+				sb.WriteByte('1')
+			}
+		}
+
+		result = sb.String()
+		return
+	}
+
+	ctx.RegisterFunc("about", kern.NewGolangFunctor(aboutFunc), kern.TypeString, []kern.ExprFuncParam{})
+	ctx.RegisterFunc("ctrlList", kern.NewGolangFunctor(ctrlListFunc), kern.TypeListOfStrings, []kern.ExprFuncParam{})
+	ctx.RegisterFunc("ctrl", kern.NewGolangFunctor(ctrlFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParam(devParamProp),
+		kern.NewFuncParamFlag(kern.ParamValue, kern.PfOptional),
+	})
+	ctx.RegisterFunc("envSet", kern.NewGolangFunctor(envSetFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamName),
+		kern.NewFuncParam(kern.ParamValue),
+	})
+	ctx.RegisterFunc("envGet", kern.NewGolangFunctor(envGetFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamName),
+	})
+	ctx.RegisterFunc("envList", kern.NewGolangFunctor(envListFunc), kern.TypeListOfStrings, []kern.ExprFuncParam{})
+
+	ctx.RegisterFunc("bin", kern.NewGolangFunctor(binFunc), kern.TypeInt, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamValue),
+		kern.NewFuncParamFlagDef(devParamDigits, kern.PfOptional|kern.PfDefault, int64(8)),
+	})
+}
+
+func main() {
+	setupCommands()
+	opt := NewOptions()
+	opt.loadRc()
+	if err := opt.parseArgs(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	ctx := expr.NewSimpleStore()
+
+	if err := importBuiltins(ctx, opt); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
+	registerLocalFunctions(ctx)
+
+	if len(opt.expressions) == opt.rcCount || opt.forceInteractive {
+		opt.expressions = append(opt.expressions, os.Stdin)
+	}
+
+	for _, input := range opt.expressions {
+		if isReaderTerminal(input) {
+			goInteractiveReadline(opt, ctx, input)
+		} else {
+			_, enableOutput := input.(*strings.Reader)
+			goBatch(opt, ctx, input, enableOutput)
+			if f, ok := input.(*os.File); ok {
+				f.Close()
+			}
+		}
+	}
+
+	// TODO: why did I added these lines?
+	// if opt.output {
+	// 	printResult(opt, ctx.GetLast())
+	// }
+}

cmd/ecli/match.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// match.go
+package main
+
+import (
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+)
+
+func matchFilePattern(dirName string, pattern string, join bool) (fileList []string, err error) {
+	var entries []os.DirEntry
+	if entries, err = os.ReadDir(dirName); err == nil {
+		for _, entry := range entries {
+			if entry.Type().IsRegular() {
+				var match bool
+				if match, err =filepath.Match(pattern, entry.Name()); err != nil {
+					fileList = nil
+					break
+				}
+				if match {
+					if fileList == nil {
+						fileList = make([]string, 0, 1)
+					}
+					if join {
+						fileList = append(fileList, path.Join(dirName, entry.Name()))
+					} else {
+						fileList = append(fileList, entry.Name())
+					}
+				}
+			}
+		}
+	}
+	return
+}
+
+func matchPathPattern(pathPattern string) (fileList []string, err error) {
+	dirName := path.Dir(pathPattern)
+	pattern := path.Base(pathPattern)
+	return matchFilePattern(dirName, pattern, true) 
+}
+
+
+func isPattern(name string) bool{
+	return strings.ContainsAny(name, "*?[]")
+} 

cmd/ecli/match_test.go

@@ -0,0 +1,36 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// main.go
+package main
+
+import (
+	"path"
+	"slices"
+	"testing"
+)
+
+func TestIsPattern(t *testing.T) {
+	target := "non-pattern"
+	if isPattern(target) {
+		t.Errorf("%q recognized as a pattern", target)
+	}
+
+	target = "pattern/*.expr"
+	if !isPattern(target) {
+		t.Errorf("%q not recognized as a pattern", target)
+	}
+}
+
+func TestMatchFilePattern(t *testing.T) {
+	target := "./go.*sum"
+	dirName := path.Dir(target)
+	pattern := path.Base(target)
+	if matchedFiles, err := matchFilePattern(dirName, pattern, true); err == nil {
+		if slices.Compare(matchedFiles, []string{"go.sum", "go.work.sum"}) != 0 {
+			t.Errorf("Matched file list is not correct: %v", matchedFiles)
+		}
+	} else {
+		t.Errorf("Got error: %v", err)
+	}
+}

cmd/ecli/options.go

@@ -0,0 +1,140 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// options.go
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr"
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/utils"
+)
+
+type Options struct {
+	printTree        bool
+	printPrefix      bool
+	forceInteractive bool
+	builtin          []any
+	expressions      []io.Reader
+	formOpt          kern.FmtOpt
+	baseVerb         string
+	base             int
+	output           bool
+	rcCount          int
+}
+
+func NewOptions() *Options {
+	return &Options{
+		expressions: make([]io.Reader, 0),
+		builtin:     make([]any, 0),
+		formOpt:     kern.Base10,
+		baseVerb:    "%d",
+		base:        10,
+		output:      true,
+		rcCount:     0,
+	}
+}
+
+func (opt *Options) loadRc() {
+	var rcPath string
+	var fh *os.File
+	var err error
+
+	rcList := []string{
+		".ecli.rc",
+		"~/.ecli.rc",
+		"~/.config/expr/ecli.rc",
+		"~/.dev-expr.rc", // OBSOLETE, to be removed in future releases
+	}
+	for _, rcFile := range rcList {
+		if rcPath, err = utils.ExpandPath(rcFile); err != nil {
+			return
+		}
+		if fh, err = os.Open(rcPath); err == nil {
+			opt.expressions = append(opt.expressions, fh) // rc should be the first source to be read
+			opt.rcCount++
+			break
+		}
+	}
+}
+
+func listBuiltins() {
+	expr.IterateBuiltinModules(func(name, description string, imported bool) bool {
+		if imported {
+			name = "*" + name
+		}
+		fmt.Printf("%20q: %s\n", name, description)
+		return true
+	})
+}
+
+func (opt *Options) parseArgs() (err error) {
+	for i := 1; i < len(os.Args) && err == nil; i++ {
+		arg := os.Args[i]
+		switch arg {
+		case "-i":
+			opt.forceInteractive = true
+		case "-t":
+			opt.printTree = true
+		case "-p":
+			opt.printPrefix = true
+		case "-e":
+			if i+1 < len(os.Args) {
+				i++
+				spec := os.Args[i]
+				if strings.HasPrefix(spec, "@") {
+					var f *os.File
+					if f, err = os.Open(spec[1:]); err == nil {
+						opt.expressions = append(opt.expressions, f)
+					} else {
+						return
+					}
+				} else {
+					if len(spec) > 0 && spec[len(spec)-1] != '\n' {
+						spec += "\n"
+					}
+					opt.expressions = append(opt.expressions, strings.NewReader(spec))
+				}
+			} else {
+				err = errOptValueRequired(arg)
+			}
+		case "-b":
+			if i+1 < len(os.Args) {
+				i++
+				specs := strings.Split(os.Args[i], ",")
+				if len(specs) == 1 {
+					opt.builtin = append(opt.builtin, specs[0])
+				} else {
+					opt.builtin = append(opt.builtin, specs)
+				}
+			} else {
+				err = errOptValueRequired(arg)
+			}
+		case "-B", "--list-builtins":
+			listBuiltins()
+			os.Exit(0)
+		case "-m", "--modules":
+			expr.IterateBuiltinModules(func(name, description string, _ bool) bool {
+				fmt.Printf("%20q: %s\n", name, description)
+				return true
+			})
+			os.Exit(0)
+		case "--noout":
+			opt.output = false
+		case "-h", "--help", "help":
+			cmdHandler.help()
+			os.Exit(0)
+		case "-v", "--version", "version", "about":
+			fmt.Println(about())
+			os.Exit(0)
+		default:
+			err = fmt.Errorf("invalid option nr %d %q", i+1, arg)
+		}
+	}
+	return
+}

cmd/ecli/publish.bash

@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+# Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+# All rights reserved.
+
+RESOURCE_FILE=".build.rc"
+BUILD_REGISTER=".build_register"
+PASSWORD=
+GITEA_USER="camoroso"
+GITEA_PASSWORD_FILE="${HOME}/.gitea_password"
+GITEA_OWNER="go-pkg"
+GITEA_HOST="https://git.portale-stac.it"
+GITEA_BASE_PATH="api/packages"
+GITEA_PKG_TYPE="generic"
+
+function exitMsg() {
+	echo >&2 "${1}"
+	exit 1
+}
+
+function readBuildCount() {
+	local reg ver count
+	if [ -r "${BUILD_REGISTER}" ]; then
+		reg=$(<"${BUILD_REGISTER}")
+	else
+		reg="${PROGRAM_VERSION} 0"
+	fi
+	read ver count <<<"${reg}"
+	if [ "${ver}" != "${PROGRAM_VERSION}" ]; then
+		count=0
+	fi
+	echo ${count}
+}
+
+if [ -r "${GITEA_PASSWORD_FILE}" ]; then
+	if ! PASSWORD=$(<"${GITEA_PASSWORD_FILE}"); then
+		exitMsg "Can're password file '${GITEA_PASSWORD_FILE}'"
+	fi
+else
+	exitMsg "Password file '${GITEA_PASSWORD_FILE}' not found"
+fi
+if [ -z "${PASSWORD}" ]; then
+	exitMsg "Empty password. Please, check file '${GITEA_PASSWORD_FILE}'"
+fi
+
+if ! ./build.bash; then
+	exitMsg "Build program failed"
+fi
+
+if ! source "${RESOURCE_FILE}"; then
+	exitMsg "Loading resource file failed"
+fi
+
+if ! exeList=$(echo 2>/dev/null ${PROGRAM_NAME}_v${PROGRAM_VERSION}_*); then
+	exitMsg "No executable found"
+fi
+
+buildCount=$(readBuildCount)
+fileCount=0
+for exe in ${exeList}; do
+	if [ "${exe/tar.gz/}" != "${exe}" ]; then
+		continue
+	fi
+	((fileCount++))
+	dir="${exe}_${buildCount}"
+	dist="${dir}.tar.gz"
+	rm -f "${dist}"
+	printf "%2d: %-30s  -->  %s\n" "${fileCount}" "${exe}" "${dist}"
+	mkdir "${dir}"
+	cp "${exe}" "${dir}/${PROGRAM_NAME}"
+	tar czf "${dist}" "${dir}"
+	rm -fR "${dir}"
+
+	url="${GITEA_HOST}/${GITEA_BASE_PATH}/${GITEA_OWNER}/${GITEA_PKG_TYPE}/${PROGRAM_NAME}/${PROGRAM_VERSION}/${dist}"
+#	echo "${url}"
+	curl --user "${USER}:${PASSWORD}" --upload-file "${dist}" "${url}"
+
+	rm -f "${dist}"
+done
+

cmd/ecli/util-string.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// util-string.go
+package main
+
+import (
+	"fmt"
+)
+
+func checkStringLiteral(literal string) (value string, err error) {
+	length := len(literal)
+	if length >= 2 {
+		if (literal[0] == '"' && literal[length-1] == '"') || literal[0] == '\'' && literal[length-1] == '\'' {
+			value = literal[1 : length-1]
+		} else {
+			err = fmt.Errorf("unquoted or partially quoted string literal: `%s`", literal)
+		}
+	} else {
+		err = fmt.Errorf("invalid string literal: `%s`", literal)
+	}
+	return
+}

cmd/ecli/version.txt

@@ -0,0 +1 @@
+1.17.0

data-cursor.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // data-cursors.go

dict-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // dict-iterator.go
@@ -11,6 +11,9 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 type dictIterMode int
@@ -22,7 +25,7 @@ const (
 )
 
 type DictIterator struct {
-	a        *kern.DictType
+	a        *dict.DictType
 	count    int64
 	index    int64
 	keys     []any
@@ -67,7 +70,7 @@ func (it *DictIterator) makeKeys(m map[any]any, sort sortType) {
 	}
 }
 
-func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err error) {
+func NewDictIterator(dict *dict.DictType, args []any) (it *DictIterator, err error) {
 	var sortType = sortTypeNone
 	var s string
 	var argAny any
@@ -78,7 +81,7 @@ func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err err
 	} else {
 		argAny = "default"
 	}
-	if s, err = kern.ToGoString(argAny, "sort type"); err == nil {
+	if s, err = str.ToGoString(argAny, "sort type"); err == nil {
 		switch strings.ToLower(s) {
 		case "a", "asc":
 			sortType = sortTypeAsc
@@ -99,7 +102,7 @@ func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err err
 				argAny = "default"
 			}
 
-			if s, err = kern.ToGoString(argAny, "iteration mode"); err == nil {
+			if s, err = str.ToGoString(argAny, "iteration mode"); err == nil {
 				switch strings.ToLower(s) {
 				case "k", "key", "keys":
 					dictIt.iterMode = dictIterModeKeys
@@ -116,12 +119,15 @@ func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err err
 		}
 	}
 
-	dictIt.makeKeys(*dict, sortType)
+	if err == nil {
-	return dictIt, err
+		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 = &DictIterator{a: (*dict.DictType)(&m), count: 0, index: -1, keys: nil}
 	it.makeKeys(m, sortTypeNone)
 	return
 }
@@ -139,7 +145,6 @@ func (it *DictIterator) TypeName() string {
 }
 
 func (it *DictIterator) HasOperation(name string) bool {
-	// yes := name == NextName || name == ResetName || name == IndexName || name == CountName || name == CurrentName
 	yes := slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName, kern.KeyName, kern.ValueName}, name)
 	return yes
 }
@@ -188,7 +193,7 @@ func (it *DictIterator) Current() (item any, err error) {
 		case dictIterModeItems:
 			a := *(it.a)
 			pair := []any{it.keys[it.index], a[it.keys[it.index]]}
-			item = kern.NewList(pair)
+			item = array.NewArray(pair)
 		}
 	} else {
 		err = io.EOF

doc/Expr.html

@@ -581,7 +581,11 @@ pre.rouge .ss {
 <li><a href="#_operator">4.1. <code class="blue">;</code> operator</a></li>
 <li><a href="#_but_operator">4.2. <code class="blue">but</code> operator</a></li>
 <li><a href="#_assignment_operator">4.3. Assignment operator <code class="blue">=</code></a></li>
-<li><a href="#_selector_operator">4.4. Selector operator <code class="blue">? : ::</code></a></li>
+<li><a href="#_selector_operator">4.4. Selector operator <code class="blue">? : ::</code></a>
+<ul class="sectlevel3">
+<li><a href="#_triple_special_case_of_the_selector_operator">4.4.1. Triple special case of the selector operator</a></li>
+</ul>
+</li>
 <li><a href="#_variable_default_value_and">4.5. Variable default value <code class="blue">??</code>, <code class="blue">?=</code>, and <code class="blue">?!</code></a></li>
 </ul>
 </li>
@@ -613,8 +617,10 @@ pre.rouge .ss {
 <li><a href="#_dec">dec()</a></li>
 <li><a href="#_string">string()</a></li>
 <li><a href="#_fract">fract()</a></li>
+<li><a href="#_char">char()</a></li>
 <li><a href="#_eval">eval()</a></li>
 <li><a href="#_var">var()</a></li>
+<li><a href="#_set">set</a></li>
 </ul>
 </li>
 <li><a href="#_module_fmt">7.1.2. Module "fmt"</a>
@@ -649,6 +655,8 @@ pre.rouge .ss {
 <li><a href="#_filewritetext">fileWriteText()</a></li>
 <li><a href="#_filereadtext">fileReadText()</a></li>
 <li><a href="#_filereadtextall">fileReadTextAll()</a></li>
+<li><a href="#_filebyteiterator">fileByteIterator()</a></li>
+<li><a href="#_filelineiterator">fileLineIterator()</a></li>
 </ul>
 </li>
 <li><a href="#_module_string">7.1.7. Module "string"</a>
@@ -674,7 +682,15 @@ pre.rouge .ss {
 <li><a href="#_named_operators">8.1.1. Named operators</a></li>
 </ul>
 </li>
-<li><a href="#_iterator_over_custom_data_sources">8.2. Iterator over custom data-sources</a></li>
+<li><a href="#_infixed_operators_on_iterators">8.2. Infixed operators on iterators</a>
+<ul class="sectlevel3">
+<li><a href="#_cat_operator">8.2.1. <code class="blue">cat</code> operator</a></li>
+<li><a href="#_filter_operator">8.2.2. <code class="blue">filter</code> operator</a></li>
+<li><a href="#_groupby_operator">8.2.3. <code class="blue">groupby</code> operator</a></li>
+<li><a href="#_map_operator">8.2.4. <code class="blue">map</code> operator</a></li>
+</ul>
+</li>
+<li><a href="#_iterator_over_custom_data_sources">8.3. Iterator over custom data-sources</a></li>
 </ul>
 </li>
 <li><a href="#_plugins">9. Plugins</a></li>
@@ -686,7 +702,7 @@ pre.rouge .ss {
 <div class="sectionbody">
 <!-- toc disabled -->
 <div class="paragraph">
-<p><mark>TODO: Work in progress (last update on 2026/04/15, 6:02 p.m.)</mark></p>
+<p><mark>TODO: Work in progress (last update on 2026/05/08)</mark></p>
 </div>
 </div>
 </div>
@@ -788,7 +804,26 @@ pre.rouge .ss {
 <code class="green">}</code></p>
 </div>
 <div class="paragraph">
-<p>In order to inspect the global context issue the <code class="blue">$$global</code> operator.</p>
+<p>In order to inspect the global context issue the <code class="blue">$$ global</code> operation.</p>
+</div>
+<div class="paragraph">
+<div class="title">Example: list all functions whose name starts with "str"</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">builtin "string</code>  <em class="gray">// most function in the builtin module <strong>string</strong> have names starting with "str".</em><br>
+<code class="green">1</code></p>
+</div>
+<div class="paragraph">
+<p><code>&gt;&gt;&gt;</code> <code class="blue">($$$global).functions) filter strStartsWith($_, "str"</code><br>
+<code class="green">[</code><br>
+<code class="green">&#160;&#160;"strEndsWith",</code><br>
+<code class="green">&#160;&#160;"strJoin",</code><br>
+<code class="green">&#160;&#160;"strLower",</code><br>
+<code class="green">&#160;&#160;"strSplit",</code><br>
+<code class="green">&#160;&#160;"strStartsWith",</code><br>
+<code class="green">&#160;&#160;"strSub",</code><br>
+<code class="green">&#160;&#160;"strTrim",</code><br>
+<code class="green">&#160;&#160;"strUpper",</code><br>
+<code class="green">&#160;&#160;"string"</code><br>
+<code class="green">]</code></p>
 </div>
 </div>
 </div>
@@ -1880,10 +1915,10 @@ Technically <code class="blue">;</code> is not treated as a real operator. It ac
 <p>The <em>selector operator</em> is very similar to the <em>switch/case/default</em> statement available in many programming languages.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 13. Selector literal Syntax</div>
+<div class="title">Example 13. Selector literal syntax</div>
 <div class="content">
 <div class="paragraph">
-<p><em>selector-operator</em> = <em>select-expression</em> "<strong>?</strong>" <em>selector-case</em> { "<strong>:</strong>" <em>selector-case</em> } ["<strong>::</strong>" <em>default-multi-expression</em>]<br>
+<p><strong><em>selector-operator</em></strong> = <em>select-expression</em> "<strong>?</strong>" <em>selector-case</em> { "<strong>:</strong>" <em>selector-case</em> } ["<strong>::</strong>" <em>default-multi-expression</em>]<br>
 <em>selector-case</em> = [<em>match-list</em>] <em>case-value</em><br>
 <em>match-list</em> = "<strong>[</strong>" <em>item</em> {"<strong>,</strong>" <em>items</em>} "<strong>]</strong>"<br>
 <em>item</em> = <em>expression</em><br>
@@ -1931,11 +1966,45 @@ Technically <code class="blue">;</code> is not treated as a real operator. It ac
 <p><code>&gt;&gt;&gt;</code> <code class="blue">10 ? {"a"} : {"b"}</code><br>
 <code class="red">Eval Error: [1:3] no case catches the value (10) of the selection expression</code></p>
 </div>
+<div class="sect3">
+<h4 id="_triple_special_case_of_the_selector_operator"><a class="anchor" href="#_triple_special_case_of_the_selector_operator"></a><a class="link" href="#_triple_special_case_of_the_selector_operator">4.4.1. Triple special case of the selector operator</a></h4>
+<div class="paragraph">
+<p>If the <em>select-expression</em> is a boolean expression, the selector operator can be used as a sort of <em>if-then-else</em> statement. In this case, the first case is evaluated if the <em>select-expression</em> is true, and the second case is evaluated if the <em>select-expression</em> is false. In this special case, the <em>match-list</em> of both cases must be empty.</p>
+</div>
+<div class="paragraph">
+<div class="title">Example</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">(true) ? {"T"}: {"F"}</code><br>
+<code class="green">T</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">(2 &gt; 1) ? {"a"} : {"b"}</code><br>
+<code class="green">a</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">(2 &lt; 1) ? {"a"} : {"b"}</code><br>
+<code class="green">b</code></p>
+</div>
+<div class="admonitionblock warning">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-warning" title="Warning"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>The triple special case of the selector operator is very useful, but it only works with boolean expressions.</p>
+</div>
+<div class="paragraph">
+<div class="title">Example of confusion</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">int(true) ? {"T"}: {"F"}</code><br>
+<code class="green">F</code></p>
+</div>
+</td>
+</tr>
+</table>
+</div>
+</div>
 </div>
 <div class="sect2">
 <h3 id="_variable_default_value_and"><a class="anchor" href="#_variable_default_value_and"></a><a class="link" href="#_variable_default_value_and">4.5. Variable default value <code class="blue">??</code>, <code class="blue">?=</code>, and <code class="blue">?!</code></a></h3>
 <div class="paragraph">
-<p>The left operand of the first two operators, <code class="blue">??</code> and <code class="blue">?=</code>, must be a variable. The right operator can be any expression. They return the value of the variable if this is defined; otherwise they return the value of the right expression.</p>
+<p>The left operand of the first two operators, <code class="blue">??</code> and <code class="blue">?=</code>, must be a variable. The right operatand can be any expression. They return the value of the variable if this is defined; otherwise they return the value of the right expression.</p>
 </div>
 <div class="admonitionblock important">
 <table>
@@ -1953,7 +2022,7 @@ If the left variable is defined, the right expression is not evaluated at all.
 <p>The <code class="blue">??</code> operator do not change the status of the left variable.</p>
 </div>
 <div class="paragraph">
-<p>The <code class="blue">?=</code> assigns the calculated value of the right expression to the left variable.</p>
+<p>The <code class="blue">?=</code> assigns the calculated value of the right expression to the variable on the left side.</p>
 </div>
 <div class="paragraph">
 <p>The third one, <code class="blue">?!</code>, is the alternate operator. If the variable on the left size is not defined, it returns <em class="blue">nil</em>. Otherwise it returns the result of the expressione on the right side.</p>
@@ -1965,7 +2034,7 @@ If the left variable is defined, the right expression is not evaluated at all.
 <i class="fa icon-important" title="Important"></i>
 </td>
 <td class="content">
-If the left variable is NOT defined, the right expression is not evaluated at all.
+If the variable <code class="blue">?!</code> is NOT defined, the expression is not evaluated at all.
 </td>
 </tr>
 </table>
@@ -2371,7 +2440,7 @@ These operators have a high priority, in particular higher than the operator <co
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>identifier</em> <code>=</code> <em>any</em> &#8594; <em>any</em></p></td>
 </tr>
 <tr>
-<td class="tableblock halign-center valign-top" colspan="4"><p class="tableblock"><em>See also the table of special allocation operators below</em></p></td>
+<td class="tableblock halign-center valign-top" colspan="4"><p class="tableblock"><em>See also the table of special assignment operators below</em></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><strong>BUT</strong></p></td>
@@ -2381,6 +2450,40 @@ These operators have a high priority, in particular higher than the operator <co
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>any</em> <code>but</code> <em>any</em> &#8594; <em>any</em></p></td>
 </tr>
 <tr>
+<td class="tableblock halign-center valign-top" rowspan="6"><p class="tableblock"><strong>ITER-OP</strong></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">digest</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Item-digesting</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>iterable</em> <code>digest</code> <em>expr</em> &#8594; <em>any</em></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">filter</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Item-filtering</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>iterable</em> <code>filter</code> <em>expr</em> &#8594; <em>list</em></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">groupby</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Dict-grouping</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>iterable</em> <code>groupby</code> <em>key-expr</em> &#8594; <em>dict</em></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">cat</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Item-concatenation</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>iterable</em> `cat ` <em>iterable</em> &#8594; <em>list</em></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">map</code></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>Item-mapping</em></p></td>
+<td class="tableblock halign-center valign-top"><p class="tableblock"><em>iterable</em> <code>map</code> <em>-expr</em> &#8594; <em>list</em></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-center valign-top" colspan="4"><p class="tableblock"><em>See iterators section for examples</em></p></td>
+</tr>
+<tr>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><strong>RANGE</strong></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><code class="blue">:</code></p></td>
 <td class="tableblock halign-center valign-top"><p class="tableblock"><em>Infix</em></p></td>
@@ -2536,14 +2639,14 @@ short for<br>
 </div>
 <div class="paragraph">
 <p><code>&gt;&gt;&gt;</code> <em class="gray">// Required and optional parameters</em><br>
-<code>&gt;&gt;&gt;</code> <code class="blue">measure = func(value, unit="meter"){ value + " " + unit + (value &gt; 1) ? [true] {"s"} :: {""}}</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">measure = func(value, unit="meter"){ value + " " + unit + (value &gt; 1) ? {"s"} :: {""}}</code><br>
 <code class="green">measure(value, unit="meter"):any{}</code></p>
 </div>
 </div>
 <div class="sect2">
 <h3 id="_golang_function_definition"><a class="anchor" href="#_golang_function_definition"></a><a class="link" href="#_golang_function_definition">6.2. <em>Golang</em> function definition</a></h3>
 <div class="paragraph">
-<p>Description of how to define Golang functions and how to bind them to <em>Expr</em> are topics covered in another document that I&#8217;ll write, one day, maybe.</p>
+<p>Description of how to define Golang functions and how to bind them to <em>Expr</em> are topics covered in another documents that I&#8217;ll write, one day, maybe.</p>
 </div>
 </div>
 <div class="sect2">
@@ -2642,7 +2745,7 @@ short for<br>
 <div class="title">Example</div>
 <p><code>&gt;&gt;&gt;</code> <code class="blue">f = func() { @x = 3; x = 5 }</code> <em class="gray">// f() declares two <strong>different</strong> local variables: <code>@x</code> and <code>x</code></em><br>
 <code class="green">f():any{}</code><br>
-<code>&gt;&gt;&gt;</code> <code class="blue">f()</code> <em class="gray">// The multi-expression (two) in f() is calculated and the last result is returned</em><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">f()</code> <em class="gray">// The multi-expression (two expressions) in f() is calculated and the last result is returned</em><br>
 <code class="green">5</code><br>
 <code>&gt;&gt;&gt;</code> <code class="blue">x</code> <em class="gray">// The <code>x</code> variable was not defined in the main context before the f() invocation. It appears in the main context by cloning the <code>@x</code> variable, local to f() after its termnation.</em><br>
 <code class="green">3</code></p>
@@ -2727,7 +2830,7 @@ The clone modifier <code class="blue">@</code> does not make a variable a refere
 <div class="title">Example 16. Builtin activation syntax</div>
 <div class="content">
 <div class="paragraph">
-<p><strong><em>builtin-activation</em></strong> = <code class="blue">BUILTIN</code> (<em>builtin-name</em> | <em>list-of-builtin-names</em>)<br>
+<p><strong><em>builtin-activation</em></strong> = <code class="blue">BUILTIN</code> (<em>builtin-name</em> | <em>list-of-builtin-names</em> | <strong>"*"</strong>)<br>
 <em>builtin-name</em> = <em>string</em><br>
 <em>list-of-builtin-names</em> = <strong>[</strong> <em>string</em> { "<strong>,</strong>" <em>string</em> } <strong>]</strong></p>
 </div>
@@ -2815,9 +2918,15 @@ To avoid the need to activate builtin modules one by one, it is possible to acti
 <div class="title">Other functions</div>
 <ul>
 <li>
+<p><a href="#_char">char()</a></p>
+</li>
+<li>
 <p><a href="#_eval">eval()</a></p>
 </li>
 <li>
+<p><a href="#_set">set()</a></p>
+</li>
+<li>
 <p><a href="#_var">var()</a></p>
 </li>
 </ul>
@@ -2833,7 +2942,9 @@ Returns <em>true</em> if the value type of <em>&lt;expr&gt;</em> is boolean, fal
 <p><code>&gt;&gt;&gt;</code> <code class="blue">isBool(true)</code><br>
 <code class="green">true</code><br>
 <code>&gt;&gt;&gt;</code> <code class="blue">isBool(3==2)</code><br>
-<code class="green">true</code></p>
+<code class="green">true</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">isBool(3 + 2)</code><br>
+<code class="green">false</code></p>
 </div>
 </div>
 <div class="sect4">
@@ -2938,7 +3049,7 @@ Returns <em>true</em> if the value type of <em>&lt;expr&gt;</em> is fraction or
 <h5 id="_isstring"><a class="anchor" href="#_isstring"></a><a class="link" href="#_isstring">isString()</a></h5>
 <div class="paragraph">
 <p>Syntax: <code>isString(&lt;expr&gt;) &#8594; bool</code><br>
-Returns a boolean value , false otherwise.</p>
+Returns <em>true</em> if the value type of <em>&lt;expr&gt;</em> is string, false otherwise.</p>
 </div>
 <div class="paragraph">
 <div class="title">Examples</div>
@@ -2954,7 +3065,7 @@ Returns a boolean value , false otherwise.</p>
 <h5 id="_bool"><a class="anchor" href="#_bool"></a><a class="link" href="#_bool">bool()</a></h5>
 <div class="paragraph">
 <p>Syntax: <code>bool(&lt;expr&gt;) &#8594; bool</code><br>
-Returns a <em>boolean</em> value consisent to the value of the expression.</p>
+Returns a <em>boolean</em> value consisent with the value of the expression.</p>
 </div>
 <div class="paragraph">
 <div class="title">Examples</div>
@@ -3077,6 +3188,20 @@ Returns a <em>fraction</em> value consistent with the value of the expression.</
 </div>
 </div>
 <div class="sect4">
+<h5 id="_char"><a class="anchor" href="#_char"></a><a class="link" href="#_char">char()</a></h5>
+<div class="paragraph">
+<p>Syntax: <code>char(&lt;intexpr&gt;) &#8594; string</code><br>
+Returns the character whose ASCII (soon Unicode too) code point is specified by the integer expression.</p>
+</div>
+<div class="paragraph">
+<div class="title">Examples</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">char(65)</code><br>
+<code class="green">"A"</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">char(97)</code><br>
+<code class="green">"a"</code></p>
+</div>
+</div>
+<div class="sect4">
 <h5 id="_eval"><a class="anchor" href="#_eval"></a><a class="link" href="#_eval">eval()</a></h5>
 <div class="paragraph">
 <p>Syntax: <code>eval(&lt;string-expr&gt;) &#8594; any</code><br>
@@ -3096,13 +3221,13 @@ Computes and returns the value of the <span class="underline">string</span> expr
  <code>&#160;&#160;&#160;&#160;var(&lt;string-expr&gt;) &#8594; any</code></p>
 </div>
 <div class="paragraph">
-<p>This function allows you to define variables whose names must include special characters. The first form of the function allows you to define a variable with a name specified by the first parameter and assign it the value of the second parameter. The second form only returns the value of the variable with the specified name.</p>
+<p>This function allows you to define variables whose names can include special characters. The first form of the function allows you to define a variable with a name specified by the first parameter and assign it the value of the second parameter. The second form only returns the value of the variable with the specified name.</p>
 </div>
 <div class="paragraph">
 <div class="title">Examples</div>
 <p><code>&gt;&gt;&gt;</code> <code class="blue">var("$x", 3+9)</code><br>
 <code class="green">12</code><br>
-<code>&gt;&gt;&gt;</code> <code class="blue">var("$x")</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">var("$"+"x")</code><br>
 <code class="green">12</code><br>
 <code>&gt;&gt;&gt;</code> <code class="blue">var("gain%", var("$x"))</code><br>
 <code class="green">12</code><br>
@@ -3110,9 +3235,32 @@ Computes and returns the value of the <span class="underline">string</span> expr
 <code class="green">13</code></p>
 </div>
 </div>
+<div class="sect4">
+<h5 id="_set"><a class="anchor" href="#_set"></a><a class="link" href="#_set">set</a></h5>
+<div class="paragraph">
+<p>Syntax:<br>
+ <code>&#160;&#160;&#160;&#160;set(&lt;string-expr&gt;, &lt;expr&gt;) &#8594; any</code></p>
+</div>
+<div class="paragraph">
+<p>This function allows you to set the value of a variable whose name can include special characters. The first parameter is the name of the variable and the second parameter is the new value to assign to that variable.</p>
+</div>
+<div class="paragraph">
+<p>It is equivalent to the first form of the var() function, but it is more explicit about the intent of changing the value of an existing variable.</p>
+</div>
+<div class="paragraph">
+<div class="title">Examples</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">set("$x", 100)</code><br>
+<code class="green">100</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">var("$x")</code><br>
+<code class="green">100</code><br></p>
+</div>
+</div>
 </div>
 <div class="sect3">
 <h4 id="_module_fmt"><a class="anchor" href="#_module_fmt"></a><a class="link" href="#_module_fmt">7.1.2. Module "fmt"</a></h4>
+<div class="paragraph">
+<p><mark>to-do</mark></p>
+</div>
 <div class="sect4">
 <h5 id="_print"><a class="anchor" href="#_print"></a><a class="link" href="#_print">print()</a></h5>
 
@@ -3124,10 +3272,18 @@ Computes and returns the value of the <span class="underline">string</span> expr
 </div>
 <div class="sect3">
 <h4 id="_module_import"><a class="anchor" href="#_module_import"></a><a class="link" href="#_module_import">7.1.3. Module "import"</a></h4>
+<div class="paragraph">
+<p>Module activation:<br>
+<code>&#160;&#160;&#160;&#160;BUILTIN "import"</code></p>
+</div>
 <div class="sect4">
 <h5 id="_import"><a class="anchor" href="#_import"></a><a class="link" href="#_import"><em>import()</em></a></h5>
 <div class="paragraph">
-<p><em class="blue">import(<span class="grey">&lt;source-file&gt;</span>)</em>&#8201;&#8212;&#8201;loads the multi-expression contained in the specified source and returns its value.</p>
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;import(&lt;source-file&gt;)</code></p>
+</div>
+<div class="paragraph">
+<p>Loads the multi-expression contained in the specified source and returns its value.</p>
 </div>
 </div>
 <div class="sect4">
@@ -3137,16 +3293,40 @@ Computes and returns the value of the <span class="underline">string</span> expr
 </div>
 <div class="sect3">
 <h4 id="_module_iterator"><a class="anchor" href="#_module_iterator"></a><a class="link" href="#_module_iterator">7.1.4. Module "iterator"</a></h4>
+<div class="paragraph">
+<p>Module activation:<br>
+<code>&#160;&#160;&#160;&#160;BUILTIN "iterator"</code></p>
+</div>
 <div class="sect4">
 <h5 id="_run"><a class="anchor" href="#_run"></a><a class="link" href="#_run">run()</a></h5>
-
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;run(&lt;iterator&gt;, &lt;operator&gt;, &lt;vars&gt;) &#8594; any</code></p>
+</div>
+<div class="paragraph">
+<p>Iterates over the specified iterator and applies the specified operator to the current value of the iterator.</p>
+</div>
 </div>
 </div>
 <div class="sect3">
 <h4 id="_module_math_arith"><a class="anchor" href="#_module_math_arith"></a><a class="link" href="#_module_math_arith">7.1.5. Module "math.arith"</a></h4>
 <div class="paragraph">
+<p>Module activation:<br>
+<code>&#160;&#160;&#160;&#160;BUILTIN "math.arith"</code></p>
+</div>
+<div class="paragraph">
 <p>Currently, the "math.arith" module provides two functions, add() and mul(), that perform addition and multiplication of an arbitrary number of parameters. More functions will be added in the future.</p>
 </div>
+<div class="ulist">
+<ul>
+<li>
+<p><a href="#_add">add()</a></p>
+</li>
+<li>
+<p><a href="#_mul">mul()</a></p>
+</li>
+</ul>
+</div>
 <div class="sect4">
 <h5 id="_add"><a class="anchor" href="#_add"></a><a class="link" href="#_add">add()</a></h5>
 <div class="paragraph">
@@ -3202,37 +3382,213 @@ Computes and returns the value of the <span class="underline">string</span> expr
 </div>
 <div class="sect3">
 <h4 id="_module_os_file"><a class="anchor" href="#_module_os_file"></a><a class="link" href="#_module_os_file">7.1.6. Module "os.file"</a></h4>
+<div class="paragraph">
+<p>Module activation:<br>
+<code>&#160;&#160;&#160;&#160;BUILTIN "os.file"</code></p>
+</div>
+<div class="paragraph">
+<p>The "os.file" module provides functions for working with files.</p>
+</div>
+<div class="ulist">
+<div class="title">File related functions</div>
+<ul>
+<li>
+<p><a href="#_fileOpen">fileOpen()</a></p>
+</li>
+<li>
+<p><a href="#_fileAppend">fileAppend()</a></p>
+</li>
+<li>
+<p><a href="#_fileCreate">fileCreate()</a></p>
+</li>
+<li>
+<p><a href="#_fileClose">fileClose()</a></p>
+</li>
+<li>
+<p><a href="#_fileWriteText">fileWriteText()</a></p>
+</li>
+<li>
+<p><a href="#_fileReadText">fileReadText()</a></p>
+</li>
+<li>
+<p><a href="#_fileReadTextAll">fileReadTextAll()</a></p>
+</li>
+</ul>
+</div>
+<div class="ulist">
+<div class="title">Iterator functions for files</div>
+<ul>
+<li>
+<p><a href="#_fileByteIterator">fileByteIterator()</a></p>
+</li>
+<li>
+<p><a href="#_fileLineIterator">fileLineIterator()</a></p>
+</li>
+</ul>
+</div>
+<div class="paragraph">
+<p>More functions will be added in the future.</p>
+</div>
+<hr>
 <div class="sect4">
 <h5 id="_fileopen"><a class="anchor" href="#_fileopen"></a><a class="link" href="#_fileopen">fileOpen()</a></h5>
-
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;fileOpen(&lt;file-path&gt;) &#8594; file-handle</code></p>
+</div>
+<div class="paragraph">
+<p>Returns a file handle for the specified file path. The file is opened in read-write mode. If the file does not exist, it is created.</p>
+</div>
 </div>
 <div class="sect4">
 <h5 id="_fileappend"><a class="anchor" href="#_fileappend"></a><a class="link" href="#_fileappend">fileAppend()</a></h5>
-
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;fileAppend(&lt;file-path&gt;) &#8594; any</code></p>
+</div>
+<div class="paragraph">
+<p>Like <a href="#_fileCreate">fileCreate()</a> but write operations happen at the end of the file.</p>
+</div>
 </div>
 <div class="sect4">
 <h5 id="_filecreate"><a class="anchor" href="#_filecreate"></a><a class="link" href="#_filecreate">fileCreate()</a></h5>
-
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;fileCreate(&lt;file-path&gt;) &#8594; file-handle</code></p>
+</div>
+<div class="paragraph">
+<p>Creates or truncates the named <em>&lt;file-path&gt;</em>. If the file already exists, it is truncated. If the file does not exist, it is created with mode 0o666 (before umask). The associated file descriptor has mode [O_RDWR]. The directory containing the file must already exist.</p>
+</div>
 </div>
 <div class="sect4">
 <h5 id="_fileclose"><a class="anchor" href="#_fileclose"></a><a class="link" href="#_fileclose">fileClose()</a></h5>
-
+<div class="paragraph">
+<p><mark>to-do</mark></p>
+</div>
 </div>
 <div class="sect4">
 <h5 id="_filewritetext"><a class="anchor" href="#_filewritetext"></a><a class="link" href="#_filewritetext">fileWriteText()</a></h5>
-
+<div class="paragraph">
+<p><mark>to-do</mark></p>
+</div>
 </div>
 <div class="sect4">
 <h5 id="_filereadtext"><a class="anchor" href="#_filereadtext"></a><a class="link" href="#_filereadtext">fileReadText()</a></h5>
-
+<div class="paragraph">
+<p><mark>to-do</mark></p>
+</div>
 </div>
 <div class="sect4">
 <h5 id="_filereadtextall"><a class="anchor" href="#_filereadtextall"></a><a class="link" href="#_filereadtextall">fileReadTextAll()</a></h5>
-
+<div class="paragraph">
+<p><mark>to-do</mark></p>
+</div>
+</div>
+<div class="sect4">
+<h5 id="_filebyteiterator"><a class="anchor" href="#_filebyteiterator"></a><a class="link" href="#_filebyteiterator">fileByteIterator()</a></h5>
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;fileByteIterator(handle-or-path) &#8594; iterator</code></p>
+</div>
+<div class="paragraph">
+<p>Returns an iterator that produces the bytes of the specified file. The parameter can be either a file handle or a file path. If a file path is provided, the file is opened and closed automatically by the iterator.</p>
+</div>
+<div class="paragraph">
+<div class="title">Examples</div>
+<p>&gt;&gt;&gt; builtin "os.file"<br>
+<code class="green">1</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">fileByteIterator("test-file.txt") map $_</code><br>
+<code class="green">[
+  117,
+  110,
+  111,
+  10,
+  100,
+  117,
+  101,
+  10
+]</code></p>
+</div>
+<div class="paragraph">
+<p>&gt;&gt;&gt; builtin ["os.file", "string"]<br>
+<code class="green">2</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">fileByteIterator("test-file.txt") map char($_)</code><br>
+<code class="green">[
+  "u",
+  "n",
+  "o",
+  "
+",
+  "d",
+  "u",
+  "e",
+  "
+",
+]</code></p>
+</div>
+</div>
+<div class="sect4">
+<h5 id="_filelineiterator"><a class="anchor" href="#_filelineiterator"></a><a class="link" href="#_filelineiterator">fileLineIterator()</a></h5>
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;fileLineIterator(handle-or-path) &#8594; iterator</code></p>
+</div>
+<div class="paragraph">
+<p>Returns an iterator that produces the lines of the specified file. The parameter can be either a file handle or a file path. If a file path is provided, the file is opened and closed automatically by the iterator.</p>
+</div>
+<div class="paragraph">
+<div class="title">Examples</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">builtin "os.file"</code><br>
+<code class="green">1</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">fileLineIterator("test-file.txt") map $_</code><br>
+<code class="green">[
+  "uno",
+  "due"
+]</code></p>
+</div>
 </div>
 </div>
 <div class="sect3">
 <h4 id="_module_string"><a class="anchor" href="#_module_string"></a><a class="link" href="#_module_string">7.1.7. Module "string"</a></h4>
+<div class="paragraph">
+<p>Module activation:<br>
+<code>&#160;&#160;&#160;&#160;BUILTIN "string"</code></p>
+</div>
+<div class="paragraph">
+<p>This module provides functions for working with strings.</p>
+</div>
+<div class="paragraph">
+<p>Currently available functions:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><a href="#_strJoin">strJoin()</a></p>
+</li>
+<li>
+<p><a href="#_strSub">strSub()</a></p>
+</li>
+<li>
+<p><a href="#_strSplit">strSplit()</a></p>
+</li>
+<li>
+<p><a href="#_strTrim">strTrim()</a></p>
+</li>
+<li>
+<p><a href="#_strStartsWith">strStartsWith()</a></p>
+</li>
+<li>
+<p><a href="#_strEndsWith">strEndsWith()</a></p>
+</li>
+<li>
+<p><a href="#_strUpper">strUpper()</a></p>
+</li>
+<li>
+<p><a href="#_strLower">strLower()</a></p>
+</li>
+</ul>
+</div>
+<hr>
 <div class="sect4">
 <h5 id="_strjoin"><a class="anchor" href="#_strjoin"></a><a class="link" href="#_strjoin">strJoin()</a></h5>
 <div class="paragraph">
@@ -3589,7 +3945,81 @@ Iterators built on custom data-sources can provide additional named operators, d
 </div>
 </div>
 <div class="sect2">
-<h3 id="_iterator_over_custom_data_sources"><a class="anchor" href="#_iterator_over_custom_data_sources"></a><a class="link" href="#_iterator_over_custom_data_sources">8.2. Iterator over custom data-sources</a></h3>
+<h3 id="_infixed_operators_on_iterators"><a class="anchor" href="#_infixed_operators_on_iterators"></a><a class="link" href="#_infixed_operators_on_iterators">8.2. Infixed operators on iterators</a></h3>
+<div class="paragraph">
+<p>There are also some infixed operators that can be used with iterators. They are defined as follows.</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><a href="#_cat">cat operator</a></p>
+</li>
+<li>
+<p><a href="#_diget">digest operator</a></p>
+</li>
+<li>
+<p><a href="#_filter">filter operator</a></p>
+</li>
+<li>
+<p><a href="#_groupby">groupby operator</a></p>
+</li>
+<li>
+<p><a href="#_map">map operator</a></p>
+</li>
+</ul>
+</div>
+<hr>
+<div class="sect3">
+<h4 id="_cat_operator"><a class="anchor" href="#_cat_operator"></a><a class="link" href="#_cat_operator">8.2.1. <code class="blue">cat</code> operator</a></h4>
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;&lt;iterable&gt; cat &lt;iterable&gt; &#8594; &lt;iterator&gt;&#160;&#160;&#160;&#160;</code></p>
+</div>
+<div class="paragraph">
+<p><code class="blue">cat</code> operator takes two iterators or iterables and returns a new iterator that produces the elements of the first iterator followed by the elements of the second iterator.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="_filter_operator"><a class="anchor" href="#_filter_operator"></a><a class="link" href="#_filter_operator">8.2.2. <code class="blue">filter</code> operator</a></h4>
+<div class="paragraph">
+<div class="title">Examples</div>
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;&lt;iterable&gt; filter &lt;expr&gt; &#8594; &lt;iterator&gt;&#160;&#160;&#160;&#160;</code></p>
+</div>
+<div class="paragraph">
+<p><code class="blue">filter</code> applies a boolean expression to each element of the iterator and returns a list of the elements for which the expression evaluates to true.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="_groupby_operator"><a class="anchor" href="#_groupby_operator"></a><a class="link" href="#_groupby_operator">8.2.3. <code class="blue">groupby</code> operator</a></h4>
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;&lt;dict&gt; groupby &lt;key&gt; &#8594; &lt;dict&gt;&#160;&#160;&#160;&#160;</code></p>
+</div>
+<div class="paragraph">
+<p><code class="blue">groupby</code> operator groups the elements of the iterator based on the value of a specified expression and returns a dictionary where the keys are the group values and the values are lists of the elements in each group.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="_map_operator"><a class="anchor" href="#_map_operator"></a><a class="link" href="#_map_operator">8.2.4. <code class="blue">map</code> operator</a></h4>
+<div class="paragraph">
+<p>Syntax:<br>
+<code>&#160;&#160;&#160;&#160;&lt;iterable&gt; map &lt;expr&gt; &#8594; &lt;list&gt;&#160;&#160;&#160;&#160;</code></p>
+</div>
+<div class="paragraph">
+<p><code class="blue">map</code> operator iterates over the elements of the iterator and evaluates the expressions provided on the right side for each element. Its result is a list of the computed values of the that expression. The current element of the iterator is available in the expression as the variable <code>$_</code>.</p>
+</div>
+<div class="paragraph">
+<div class="title">Example: using the <code class="blue">map</code> operator</div>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">it = $(["one", "two", "three"])</code><br>
+<code class="green">$(#3)</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">it map $_ + "!"</code><br>
+<code class="green">["one!", "two!", "three!"]</code></p>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="_iterator_over_custom_data_sources"><a class="anchor" href="#_iterator_over_custom_data_sources"></a><a class="link" href="#_iterator_over_custom_data_sources">8.3. Iterator over custom data-sources</a></h3>
 <div class="paragraph">
 <p>It is possible to create iterators over custom data-sources by defining a dictionary that has the key <code>next</code> whose value is a function that returns the next element of the collection and updates the state of the iterator. The syntax for creating an iterator over a custom data-source is as follows.</p>
 </div>
@@ -3610,7 +4040,7 @@ Iterators built on custom data-sources can provide additional named operators, d
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2026-04-21 06:35:14 +0200
+Last updated 2026-05-12 16:25:27 +0200
 </div>
 </div>
 </body>

file/coverage.html

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

file/file.go

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

file/reader.go

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

file/t_reader_test.go

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

file/t_writer_test.go

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

file/writer.go

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

function.go

@@ -1,388 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// function.go
-package expr
-
-import (
-	"fmt"
-	"strings"
-
-	"git.portale-stac.it/go-pkg/expr/kern"
-	"git.portale-stac.it/go-pkg/expr/scan"
-)
-
-// ---- Function template
-// type FuncTemplate func(ctx expr.ExprContext, name string, args map[string]any) (result any, err error)
-
-// ---- Common functor definition
-type BaseFunctor struct {
-	info kern.ExprFunc
-}
-
-func (functor *BaseFunctor) ToString(opt kern.FmtOpt) (s string) {
-	if functor.info != nil {
-		s = functor.info.ToString(opt)
-	} else {
-		s = "func(){}"
-	}
-	return s
-}
-
-func (functor *BaseFunctor) GetParams() (params []kern.ExprFuncParam) {
-	if functor.info != nil {
-		return functor.info.Params()
-	} else {
-		return []kern.ExprFuncParam{}
-	}
-}
-
-func (functor *BaseFunctor) SetFunc(info kern.ExprFunc) {
-	functor.info = info
-}
-
-func (functor *BaseFunctor) GetFunc() kern.ExprFunc {
-	return functor.info
-}
-
-func (functor *BaseFunctor) GetDefinitionContext() kern.ExprContext {
-	return nil
-}
-
-// ---- Function Parameters
-type paramFlags uint16
-
-const (
-	PfDefault paramFlags = 1 << iota
-	PfOptional
-	PfRepeat
-)
-
-type funcParamInfo struct {
-	name         string
-	flags        paramFlags
-	defaultValue any
-}
-
-func NewFuncParam(name string) kern.ExprFuncParam {
-	return &funcParamInfo{name: name}
-}
-
-func NewFuncParamFlag(name string, flags paramFlags) kern.ExprFuncParam {
-	return &funcParamInfo{name: name, flags: flags}
-}
-
-func NewFuncParamFlagDef(name string, flags paramFlags, defValue any) *funcParamInfo {
-	return &funcParamInfo{name: name, flags: flags, defaultValue: defValue}
-}
-
-func (param *funcParamInfo) Name() string {
-	return param.name
-}
-
-func (param *funcParamInfo) Type() string {
-	return kern.TypeAny
-}
-
-func (param *funcParamInfo) IsDefault() bool {
-	return (param.flags & PfDefault) != 0
-}
-
-func (param *funcParamInfo) IsOptional() bool {
-	return (param.flags & PfOptional) != 0
-}
-
-func (param *funcParamInfo) IsRepeat() bool {
-	return (param.flags & PfRepeat) != 0
-}
-
-func (param *funcParamInfo) DefaultValue() any {
-	return param.defaultValue
-}
-
-// --- Functions
-
-// funcInfo implements expr.ExprFunc
-type funcInfo struct {
-	name         string
-	minArgs      int
-	maxArgs      int
-	functor      kern.Functor
-	formalParams []kern.ExprFuncParam
-	returnType   string
-}
-
-func newFuncInfo(name string, functor kern.Functor, returnType string, params []kern.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() []kern.ExprFuncParam {
-	return info.formalParams
-}
-
-func (info *funcInfo) ReturnType() string {
-	return info.returnType
-}
-
-func (info *funcInfo) ToString(opt kern.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(kern.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() kern.Functor {
-	return info.functor
-}
-
-func (info *funcInfo) AllocContext(parentCtx kern.ExprContext) (ctx kern.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) kern.ExprFuncParam {
-	for _, spec := range info.formalParams {
-		if spec.Name() == paramName {
-			return spec
-		}
-	}
-	return nil
-}
-
-func initActualParams(ctx kern.ExprContext, info kern.ExprFunc, callTerm *scan.Term) (actualParams map[string]any, err error) {
-	var varArgs []any
-	var varName string
-
-	namedParamsStarted := false
-
-	formalParams := info.Params()
-	actualParams = make(map[string]any, len(formalParams))
-	if callTerm == nil {
-		return
-	}
-
-	for i, tree := range callTerm.Children {
-		var paramValue any
-		paramCtx := ctx.Clone()
-		if paramValue, err = tree.Compute(paramCtx); err != nil {
-			break
-		}
-		if paramName, namedParam := kern.GetAssignVarName(tree); namedParam {
-			if info.ParamSpec(paramName) == nil {
-				err = fmt.Errorf("%s(): unknown param %q", info.Name(), paramName)
-				break
-			}
-			actualParams[paramName] = paramValue
-			namedParamsStarted = true
-		} else if !namedParamsStarted {
-			if varArgs != nil {
-				varArgs = append(varArgs, paramValue)
-			} else if i < len(formalParams) {
-				spec := formalParams[i]
-				if spec.IsRepeat() {
-					varArgs = make([]any, 0, len(callTerm.Children)-i)
-					varArgs = append(varArgs, paramValue)
-					varName = spec.Name()
-				} else {
-					actualParams[spec.Name()] = paramValue
-				}
-			} else {
-				err = kern.ErrTooManyParams(info.Name(), len(formalParams), len(callTerm.Children))
-				break
-			}
-		} else {
-			err = fmt.Errorf("%s(): positional param nr %d not allowed after named params", info.Name(), i+1)
-			break
-		}
-	}
-	if err == nil {
-		if varArgs != nil {
-			actualParams[varName] = varArgs
-		}
-	}
-	return
-}
-
-func (info *funcInfo) PrepareCall(name string, actualParams map[string]any) (err error) {
-	passedCount := len(actualParams)
-	if info.MinArgs() > passedCount {
-		err = kern.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 = kern.ErrTooManyParams(name, info.MaxArgs(), len(actualParams))
-	}
-	return
-}
-
-// ----- Call a function ---
-
-// func getAssignVarName(t *term) (name string, ok bool) {
-// 	if ok = t.symbol() == SymEqual; ok {
-// 		name = t.children[0].source()
-// 	}
-// 	return
-// }
-
-// func CallFunctionByTerm(parentCtx expr.ExprContext, name string, callTerm *term) (result any, err error) {
-// 	var actualParams map[string]any
-// 	if info, exists := GetFuncInfo(parentCtx, name); exists {
-// 		if actualParams, err = initActualParams(parentCtx, info, callTerm); err == nil {
-// 			ctx := info.AllocContext(parentCtx)
-// 			if err = info.PrepareCall(name, actualParams); err == nil {
-// 				functor := info.Functor()
-// 				result, err = functor.InvokeNamed(ctx, name, actualParams)
-// 				exportObjectsToParent(ctx)
-// 			}
-// 		}
-// 	} else {
-// 		err = fmt.Errorf("unknown function %s()", name)
-// 	}
-// 	return
-// }
-
-// func CallFunctionByArgs(parentCtx expr.ExprContext, name string, args []any) (result any, err error) {
-// 	var actualParams map[string]any
-// 	if info, exists := GetFuncInfo(parentCtx, name); exists {
-// 		functor := info.Functor()
-// 		actualParams = bindActualParams(functor, args)
-// 		ctx := info.AllocContext(parentCtx)
-// 		if err = info.PrepareCall(name, actualParams); err == nil {
-// 			result, err = functor.InvokeNamed(ctx, name, actualParams)
-// 			exportObjectsToParent(ctx)
-// 		}
-// 	} else {
-// 		err = fmt.Errorf("unknown function %s()", name)
-// 	}
-// 	return
-// }
-
-// func CallFunctionByParams(parentCtx expr.ExprContext, name string, actualParams map[string]any) (result any, err error) {
-// 	//var actualParams map[string]any
-// 	if info, exists := GetFuncInfo(parentCtx, name); exists {
-// 		functor := info.Functor()
-// 		ctx := info.AllocContext(parentCtx)
-// 		if err = info.PrepareCall(name, actualParams); err == nil {
-// 			result, err = functor.InvokeNamed(ctx, name, actualParams)
-// 			exportObjectsToParent(ctx)
-// 		}
-// 	} else {
-// 		err = fmt.Errorf("unknown function %s()", name)
-// 	}
-// 	return
-// }
-
-// func GetParam(args map[string]any, paramName string, paramNum int) (value any, exists bool) {
-// 	if value, exists = args[paramName]; !exists {
-// 		if paramNum > 0 && paramNum <= len(args) {
-// 			value, exists = args["arg"+strconv.Itoa(paramNum)]
-// 		}
-// 	}
-// 	return
-// }
-
-// func bindActualParams(functor Functor, args []any) (actualParams map[string]any) {
-// 	formalParams := functor.GetParams()
-// 	actualParams = make(map[string]any, len(args))
-// 	for i, arg := range args {
-// 		if i < len(formalParams) {
-// 			actualParams[formalParams[i].Name()] = arg
-// 		} else {
-// 			actualParams["arg"+strconv.Itoa(i+1)] = arg
-// 		}
-// 	}
-// 	return
-// }

global-context.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // global-context.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
 )
 
 //var globalCtx *SimpleStore
@@ -42,12 +43,16 @@ func ImportInContextByGlobPattern(ctx kern.ExprContext, pattern string) (count i
 	return
 }
 
+func fixCtrlVar(name string) string {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	return name
+}
+
 func GlobalCtrlSet(ctx kern.ExprContext, name string, newValue any) (currentValue any) {
 	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
-		if !strings.HasPrefix(name, "_") {
+		name = fixCtrlVar(name)
-			name = "_" + name
-		}
-
 		currentValue, _ = globalCtx.GetVar(name)
 		globalCtx.SetVar(name, newValue)
 	}
@@ -56,19 +61,15 @@ func GlobalCtrlSet(ctx kern.ExprContext, name string, newValue any) (currentValu
 
 func GlobalCtrlGet(ctx kern.ExprContext, name string) (currentValue any) {
 	if globalCtx := ctx.GetGlobal(); globalCtx != nil {
-		if !strings.HasPrefix(name, "_") {
+		name = fixCtrlVar(name)
-			name = "_" + name
-		}
 		currentValue, _ = globalCtx.GetVar(name)
 	}
 	return currentValue
 }
 
 func CtrlEnable(ctx kern.ExprContext, name string) (currentStatus bool) {
-	if !strings.HasPrefix(name, "_") {
+	name = fixCtrlVar(name)
-		name = "_" + name
+	if v, exists := ctx.GetVar(name); exists && boolean.IsBool(v) {
-	}
-	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
 		currentStatus, _ = v.(bool)
 	}
 
@@ -77,10 +78,8 @@ func CtrlEnable(ctx kern.ExprContext, name string) (currentStatus bool) {
 }
 
 func CtrlDisable(ctx kern.ExprContext, name string) (currentStatus bool) {
-	if !strings.HasPrefix(name, "_") {
+	name = fixCtrlVar(name)
-		name = "_" + name
+	if v, exists := ctx.GetVar(name); exists && boolean.IsBool(v) {
-	}
-	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
 		currentStatus, _ = v.(bool)
 	}
 

go.sum

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

graph.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 //go:build graph

helpers.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // helpers.go
@@ -12,6 +12,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/float"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -45,14 +47,14 @@ func EvalStringV(source string, args []Arg) (result any, err error) {
 				functor := kern.NewGolangFunctor(f)
 				// ctx.RegisterFunc(arg.Name, functor, 0, -1)
 				ctx.RegisterFunc(arg.Name, functor, kern.TypeAny, []kern.ExprFuncParam{
-					NewFuncParamFlagDef(kern.ParamValue, PfDefault|PfRepeat, 0),
+					kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault|kern.PfRepeat, 0),
 				})
 			} else {
 				err = fmt.Errorf("invalid function specification: %q", arg.Name)
 			}
-		} else if integer, ok := kern.AnyInteger(arg.Value); ok {
+		} else if integer, ok := types.AnyInteger(arg.Value); ok {
 			ctx.SetVar(arg.Name, integer)
-		} else if float, ok := kern.AnyFloat(arg.Value); ok {
+		} else if float, ok := float.AnyFloat(arg.Value); ok {
 			ctx.SetVar(arg.Name, float)
 		} else if _, ok := arg.Value.(string); ok {
 			ctx.SetVar(arg.Name, arg.Value)

import-utils.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // import-utils.go
@@ -13,6 +13,7 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -22,7 +23,7 @@ const (
 )
 
 func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(kern.IsString(paramValue) /*|| isList(paramValue)*/) {
+	if !(str.IsString(paramValue) /*|| isArray(paramValue)*/) {
 		err = fmt.Errorf("%s(): param nr %d has wrong type %s, string expected", funcName, paramPos+1, kern.TypeName(paramValue))
 	}
 	return
@@ -89,16 +90,17 @@ func searchAmongPath(filename string, dirList []string) (filePath string) {
 		if dir, err = util.ExpandPath(dir); err != nil {
 			continue
 		}
-		if fullPath := path.Join(dir, filename); isFile(fullPath) {
+		fullPath := path.Join(dir, filename)
+		if isFile(fullPath) {
 			filePath = fullPath
 			break
 		}
 
-		subdir := strings.TrimSuffix(filename, suffix)
+		// subdir := strings.TrimSuffix(filename, suffix)
-		if fullPath := path.Join(dir, subdir, filename); isFile(fullPath) {
+		// if fullPath := path.Join(dir, subdir, filename); isFile(fullPath) {
-			filePath = fullPath
+		// 	filePath = fullPath
-			break
+		// 	break
-		}
+		// }
 	}
 	return
 }

int-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // int-iterator.go
@@ -10,14 +10,32 @@ import (
 	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
 )
 
 type IntIterator struct {
-	count int64
+	count   int64
-	index int64
+	index   int64
-	start int64
+	next    int64
-	stop  int64
+	current any
-	step  int64
+	start   int64
+	stop    int64
+	step    int64
+}
+
+func NewIntIteratorFromInterval(p *interval.IntervalType) (it *IntIterator, err error) {
+	b := p.Begin()
+	e := p.End()
+	s := p.Step()
+	if b > e {
+		s = -s
+	}
+	return NewIntIteratorA(b, e, s)
+}
+
+func NewIntIteratorA(args ...any) (it *IntIterator, err error) {
+	return NewIntIterator(args)
 }
 
 func NewIntIterator(args []any) (it *IntIterator, err error) {
@@ -27,16 +45,16 @@ func NewIntIterator(args []any) (it *IntIterator, err error) {
 	}
 	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 {
+		if it.stop, err = types.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 {
+			if it.stop, err = types.ToGoInt64(args[1], "stop index"); err != nil {
 				return
 			}
 			if argc >= 3 {
-				if it.step, err = kern.ToGoInt64(args[2], "step"); err != nil {
+				if it.step, err = types.ToGoInt64(args[2], "step"); err != nil {
 					return
 				}
 			} else if it.start > it.stop {
@@ -94,26 +112,23 @@ func (it *IntIterator) CallOperation(name string, args map[string]any) (v any, e
 }
 
 func (it *IntIterator) Current() (item any, err error) {
-	if it.start <= it.stop {
+	return it.current, nil
-		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
+	item = it.next
-	if item, err = it.Current(); err != io.EOF {
+	if it.step > 0 {
+		if it.next+it.step > it.stop {
+			err = io.EOF
+		}
+	} else if it.next+it.step < it.stop {
+		err = io.EOF
+	}
+	if err == nil {
+		it.index++
 		it.count++
+		it.next += it.step
+		it.current = item
 	}
 	return
 }
@@ -127,7 +142,9 @@ func (it *IntIterator) Count() int64 {
 }
 
 func (it *IntIterator) Reset() error {
-	it.index = it.start - it.step
+	it.index = -1
+	it.next = it.start
+	it.current = nil
 	it.count = 0
 	return nil
 }

iter-factory.go

@@ -1,29 +1,58 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // iter-factory.go
 package expr
 
 import (
+	"slices"
+
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
-func NewIterator(value any) (it kern.Iterator, err error) {
+func NewFormalIterator(value any) (it kern.Iterator) {
+	if value == nil {
+		it = NewArrayIterator([]any{})
+	} else {
+		it = NewArrayIterator([]any{value})
+	}
+	return
+}
+
+func NewIterator(ctx kern.ExprContext, value any, ops []*scan.Term) (it kern.Iterator, err error) {
 	if value == nil {
 		return NewArrayIterator([]any{}), nil
 	}
 
 	switch v := value.(type) {
-	case *kern.ListType:
+	case *array.ArrayType:
 		it = NewListIterator(v, nil)
-	case *kern.DictType:
+	case *list.LinkedList:
+		it = NewLinkedListIterator(v, nil)
+	case *dict.DictType:
 		it, err = NewDictIterator(v, nil)
 	case []any:
 		it = NewArrayIterator(v)
 	case kern.Iterator:
-		it = v
+		// var exprs []*scan.Term
+		it, err = NewIterIter(v, ctx, ops)
 	default:
 		it = NewArrayIterator([]any{value})
 	}
 	return
 }
+
+func HasIterStandardOperations(name string) bool {
+	return slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName}, name)
+}
+
+// func HasIterOperations(name string, ops ...string) bool {
+// 	return slices.Contains([]string{
+// 		kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName,
+// 	}, name) ||
+// 		slices.Contains(ops, name)
+// }

iter-iter.go

@@ -0,0 +1,135 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iter-iter.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+const iterIterType = "IterIter"
+
+type IterIter struct {
+	it       kern.Iterator
+	count    int64
+	index    int64
+	ctx      kern.ExprContext
+	exprList []*scan.Term
+	current  any
+}
+
+func NewIterIter(it kern.Iterator, ctx kern.ExprContext, exprs []*scan.Term) (iter kern.Iterator, err error) {
+	if ctx == nil {
+		err = fmt.Errorf("context is required for %s", iterIterType)
+	} else if it == nil {
+		err = fmt.Errorf("source iterator is required for %s", iterIterType)
+	} else {
+		iter = &IterIter{it: it, count: 0, index: -1, ctx: ctx, exprList: exprs, current: nil}
+	}
+	return
+}
+
+func (it *IterIter) String() string {
+	return fmt.Sprintf("$(%s)", it.it)
+}
+
+func (it *IterIter) TypeName() string {
+	return iterIterType
+}
+
+func (it *IterIter) HasOperation(name string) bool {
+	return HasIterStandardOperations(name)
+}
+
+func (it *IterIter) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	case kern.ResetName:
+		err = it.Reset()
+	case kern.CleanName:
+		err = it.Clean()
+	case kern.IndexName:
+		v = int64(it.Index())
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.count
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func (it *IterIter) Current() (item any, err error) {
+	if it.current != nil {
+		item = it.current
+	} else if len(it.exprList) > 0 {
+		// Evaluate the expression list and use the result as the current item
+		var exprValue any
+		for _, expr := range it.exprList {
+			if exprValue, err = expr.Compute(it.ctx); err != nil {
+				break
+			}
+			it.ctx.UnsafeSetVar(kern.ControlLastResult, exprValue)
+		}
+		if err == nil {
+			item = exprValue
+		}
+	} else {
+		var exists bool
+		if it.current, exists = it.ctx.GetVar("_"); !exists {
+			err = fmt.Errorf("current item not available")
+		} else {
+			item = it.current
+		}
+	}
+	return
+}
+
+func (it *IterIter) Next() (item any, err error) {
+	var src any
+
+	it.current = nil
+	ctx := it.ctx
+	for src, err = it.it.Next(); src == nil && err == nil; src, err = it.it.Next() {
+	}
+
+	if err == nil {
+		if src == nil {
+			err = io.EOF
+		} else {
+			ctx.UnsafeSetVar("_", src)
+			ctx.UnsafeSetVar("__", it.it.Index())
+			ctx.UnsafeSetVar("_#", it.it.Count())
+			item, err = it.Current()
+			ctx.DeleteVar("_#")
+			ctx.DeleteVar("__")
+			ctx.DeleteVar("_")
+		}
+	}
+	return
+}
+
+func (it *IterIter) Index() int64 {
+	return it.index
+}
+
+func (it *IterIter) Count() int64 {
+	return it.count
+}
+
+func (it *IterIter) Reset() error {
+	it.index = -1
+	it.count = 0
+	return nil
+}
+
+func (it *IterIter) Clean() error {
+	return nil
+}

kern/bind-go-functions.go

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

kern/cloner.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// cloner.go
+package kern
+
+type Cloner interface {
+	Clone() Cloner
+}
+
+func IsCloner(v any) (ok bool) {
+	_, ok = v.(Cloner)
+	return
+}
+
+func Clone(a any) (clone any) {
+	if IsCloner(a) {
+		clone = a.(Cloner).Clone()
+	} else {
+		clone = a
+	}
+	return
+}

kern/common-errors.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // common-errors.go
@@ -84,6 +84,10 @@ func ErrUnknownVar(funcName, varName string) error {
 	return fmt.Errorf("%s(): unknown variable %q", funcName, varName)
 }
 
+func ErrFuncInvalidArg(funcName, details string) error {
+	return fmt.Errorf("%s(): invalid argument -- %s", funcName, details)
+}
+
 // --- Operator errors
 
 func ErrLeftOperandMustBeVariable(leftTerm, opTerm Term) error {

kern/common-params.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // common-params.go

kern/common-type-names.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // common-type-names.go
@@ -6,6 +6,7 @@ package kern
 
 const (
 	TypeAny           = "any"
+	TypeArray         = "array"
 	TypeNil           = "nil"
 	TypeBoolean       = "boolean"
 	TypeFloat         = "float"
@@ -15,9 +16,10 @@ const (
 	TypeItem          = "item"
 	TypeIterator      = "iterator"
 	TypeNumber        = "number"
-	TypePair          = "pair"
+	TypeIntPair       = "int-pair"
 	TypeString        = "string"
 	TypeDict          = "dict"
 	TypeListOf        = "list-of-"
 	TypeListOfStrings = "list-of-strings"
+	TypeLinkedList    = "linked-list"
 )

kern/compare.go

@@ -1,37 +0,0 @@
-// 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/consts.go

@@ -0,0 +1,7 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// consts.go
+package kern
+
+const MaxUint64Allowed = uint64(9_223_372_036_854_775_807)

kern/context-helpers.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // context-helpers.go

kern/control.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // control.go

kern/equaler.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// equaler.go
+package kern
+
+type Equaler interface {
+	EqualTo(other Equaler) bool
+}
+
+func IsEqualer(v any) (ok bool) {
+	_, ok = v.(Equaler)
+	return
+}
+
+func Equal(a, b any) (equal bool) {
+	if IsEqualer(a) && IsEqualer(b) {
+		equal = a.(Equaler).EqualTo(b.(Equaler))
+	} else {
+		equal = a == b
+	}
+	return
+}

kern/expr-context.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr-context.go
@@ -28,4 +28,7 @@ type ExprContext interface {
 	Call(name string, args map[string]any) (result any, err error)
 	RegisterFuncInfo(info ExprFunc)
 	RegisterFunc(name string, f Functor, returnType string, param []ExprFuncParam) (funcInfo ExprFunc, err error)
+
+	ToDict() (dict any) // must be a *DictType
+	ToString(opt FmtOpt) string
 }

kern/expr-function.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr-function.go
@@ -37,3 +37,8 @@ type ExprFunc interface {
 	PrepareCall(name string, actualParams map[string]any) (err error)
 	AllocContext(parentCtx ExprContext) (ctx ExprContext)
 }
+
+func IsFunctor(v any) (ok bool) {
+	_, ok = v.(Functor)
+	return
+}

kern/expr.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr.go

kern/formatter.go

@@ -1,10 +1,13 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // formatter.go
 package kern
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 type FmtOpt uint32 // lower 16 bits hold a bit-mask, higher 16 bits hold an indentation number
 
@@ -18,6 +21,10 @@ const (
 	Base16
 )
 
+type Formatter interface {
+	ToString(options FmtOpt) string
+}
+
 const (
 	TruncateEllipsis = "(...)"
 	MinTruncateSize  = 10
@@ -42,8 +49,16 @@ func GetFormatIndent(opt FmtOpt) int {
 	return int(opt >> 16)
 }
 
-type Formatter interface {
+func Format(sb *strings.Builder, item any, opt FmtOpt) {
-	ToString(options FmtOpt) string
+	if s, ok := item.(string); ok {
+		sb.WriteByte('"')
+		sb.WriteString(s)
+		sb.WriteByte('"')
+	} else if formatter, ok := item.(Formatter); ok {
+		sb.WriteString(formatter.ToString(opt))
+	} else {
+		fmt.Fprintf(sb, "%v", item)
+	}
 }
 
 func GetFormatted(v any, opt FmtOpt) (text string) {
@@ -58,22 +73,3 @@ func GetFormatted(v any, opt FmtOpt) (text string) {
 	}
 	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/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

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // function.go
@@ -14,11 +14,6 @@ type FuncTemplate func(ctx ExprContext, name string, args map[string]any) (resul
 
 type DeepFuncTemplate func(a, b any) (eq bool, err error)
 
-func IsFunctor(v any) (ok bool) {
-	_, ok = v.(Functor)
-	return
-}
-
 // ---- Common functor definition
 type BaseFunctor struct {
 	info ExprFunc
@@ -54,17 +49,17 @@ func (functor *BaseFunctor) GetDefinitionContext() ExprContext {
 }
 
 // ---- Function Parameters
-type paramFlags uint16
+type FuncParamFlags uint16
 
 const (
-	PfDefault paramFlags = 1 << iota
+	PfDefault FuncParamFlags = 1 << iota
 	PfOptional
 	PfRepeat
 )
 
 type funcParamInfo struct {
 	name         string
-	flags        paramFlags
+	flags        FuncParamFlags
 	defaultValue any
 }
 
@@ -72,11 +67,11 @@ func NewFuncParam(name string) ExprFuncParam {
 	return &funcParamInfo{name: name}
 }
 
-func NewFuncParamFlag(name string, flags paramFlags) ExprFuncParam {
+func NewFuncParamFlag(name string, flags FuncParamFlags) ExprFuncParam {
 	return &funcParamInfo{name: name, flags: flags}
 }
 
-func NewFuncParamFlagDef(name string, flags paramFlags, defValue any) *funcParamInfo {
+func NewFuncParamFlagDef(name string, flags FuncParamFlags, defValue any) *funcParamInfo {
 	return &funcParamInfo{name: name, flags: flags, defaultValue: defValue}
 }
 

kern/iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // iterator.go
@@ -7,6 +7,7 @@ package kern
 import (
 	// "errors"
 	"fmt"
+	"slices"
 )
 
 // Operator names
@@ -50,3 +51,45 @@ func IsIterator(v any) (ok bool) {
 	_, ok = v.(Iterator)
 	return
 }
+
+type IteratorBase struct {
+	ItemIndex int64
+	ItemCount int64
+	current   any
+}
+
+func (it *IteratorBase) Current() (item any, err error) {
+	return it.current, nil
+}
+
+func (it *IteratorBase) Index() int64 {
+	return it.ItemIndex
+}
+
+func (it *IteratorBase) Count() int64 {
+	return it.ItemCount
+}
+
+func (it *IteratorBase) HasOperation(name string) bool {
+	return slices.Contains([]string{NextName, IndexName, CountName, CurrentName}, name)
+}
+
+func (it *IteratorBase) Clean() (err error) {
+	return
+}
+
+func (it *IteratorBase) Reset() (err error) {
+	it.ItemIndex = -1
+	it.ItemCount = 0
+	it.current = nil
+	return
+}
+
+func (it *IteratorBase) Increment() {
+	it.ItemIndex++
+	it.ItemCount++
+}
+
+func (it *IteratorBase) SetCurrent(v any) {
+	it.current = v
+}

kern/list-type.go

@@ -1,202 +0,0 @@
-// Copyright (c) 2024 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/term.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // term.go
@@ -6,6 +6,8 @@ package kern
 
 import (
 	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 type Term interface {
@@ -15,7 +17,16 @@ type Term interface {
 	GetChildCount() (count int)
 	GetChild(index int) Term
 	GetChildSource(index int) string
-	Compute(ctx ExprContext) (result any, err error)
+	GetLeftChild() (c Term)
+	GetRightChild() (c Term)
+	Symbol() (symbol sym.Symbol)
+	IsSymbol(symbol sym.Symbol) bool
+	IsOneOf(symbols ...sym.Symbol) bool
 	IsAssign() bool
+	IsVar() bool
+	SetSymbol(symbol sym.Symbol)
+	Compute(ctx ExprContext) (result any, err error)
+	EvalInfix(ctx ExprContext) (leftValue, rightValue any, err error)
 	Errorf(template string, args ...any) (err error)
+	ErrIncompatibleTypes(leftValue, rightValue any) error
 }

kern/typer.go

@@ -0,0 +1,26 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// typer.go
+package kern
+
+import "fmt"
+
+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 _, ok := v.(int64); ok {
+		name = "integer"
+	} else if _, ok := v.(float64); ok {
+		name = "float"
+	} else {
+		name = fmt.Sprintf("%T", v)
+	}
+	return
+}

kern/util.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// util.go
+package kern
+
+func FixAnyNumber(v any) (fixed any) {
+	switch unboxed := v.(type) {
+	case int:
+		fixed = int64(unboxed)
+	case int8:
+		fixed = int64(unboxed)
+	case int16:
+		fixed = int64(unboxed)
+	case int32:
+		fixed = int64(unboxed)
+	case uint:
+		fixed = int64(unboxed)
+	case uint8:
+		fixed = int64(unboxed)
+	case uint16:
+		fixed = int64(unboxed)
+	case uint32:
+		fixed = int64(unboxed)
+	case uint64:
+		if unboxed <= MaxUint64Allowed {
+			fixed = int64(unboxed)
+		} else {
+			fixed = float64(unboxed)
+		}
+	case float32:
+		fixed = float64(unboxed)
+	default:
+		fixed = v
+	}
+	return
+}

lib-ext-darwin.go

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

lib-ext-linux.go

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

lib-ext-windows.go

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

linked-list-iterator.go

@@ -0,0 +1,103 @@
+// 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"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+)
+
+type LinkedListIterator struct {
+	a       *list.LinkedList
+	count   int64
+	index   int64
+	current *list.ListNode
+}
+
+func NewLinkedListIterator(list *list.LinkedList, args []any) (it *LinkedListIterator) {
+	it = &LinkedListIterator{a: list, count: 0, index: -1, current: list.FirstNode()}
+	return
+}
+
+func (it *LinkedListIterator) String() string {
+	var l = int64(0)
+	if it.a != nil {
+		l = int64(it.a.Len())
+	}
+	return fmt.Sprintf("$([<#%d>])", l)
+}
+
+func (it *LinkedListIterator) TypeName() string {
+	return "LinkedListIterator"
+}
+
+func (it *LinkedListIterator) HasOperation(name string) bool {
+	yes := slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName}, name)
+	return yes
+}
+
+func (it *LinkedListIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	case kern.ResetName:
+		err = it.Reset()
+	case kern.CleanName:
+		err = it.Clean()
+	case kern.IndexName:
+		v = int64(it.Index())
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.count
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+func (it *LinkedListIterator) Current() (item any, err error) {
+	if it.current != nil {
+		item = it.current.Data()
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (it *LinkedListIterator) Next() (item any, err error) {
+	if it.current != nil {
+		item = it.current.Data()
+		it.current = it.current.Next()
+		it.index++
+		it.count++
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (it *LinkedListIterator) Index() int64 {
+	return it.index
+}
+
+func (it *LinkedListIterator) Count() int64 {
+	return it.count
+}
+
+func (it *LinkedListIterator) Reset() error {
+	it.current = it.a.FirstNode()
+	it.index = -1
+	it.count = 0
+	return nil
+}
+
+func (it *LinkedListIterator) Clean() error {
+	return nil
+}

operand-dict.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-dict.go
@@ -7,12 +7,16 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 // -------- dict term
 func newDictTerm(args map[any]*scan.Term) *scan.Term {
 	return &scan.Term{
-		Tk:       *scan.NewValueToken(0, 0, scan.SymDict, "{}", args),
+		Tk:       *scan.NewValueToken(0, 0, sym.SymDict, "{}", args),
 		Parent:   nil,
 		Children: nil,
 		Position: scan.PosLeaf,
@@ -23,14 +27,21 @@ func newDictTerm(args map[any]*scan.Term) *scan.Term {
 
 // -------- dict func
 func evalDict(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	dict, _ := opTerm.Value().(map[any]*scan.Term)
+	dt, _ := opTerm.Value().(map[any]*scan.Term)
-	items := make(kern.DictType, len(dict))
+	items := make(dict.DictType, len(dt))
-	for key, tree := range dict {
+	for key, tree := range dt {
 		var param any
 		if param, err = tree.Compute(ctx); err != nil {
 			break
 		}
-		items[key] = param
+		var keyValue any
+		if keyValue, err = (key.(*scan.Term)).Compute(ctx); err == nil {
+			if types.IsInteger(keyValue) || str.IsString(keyValue) {
+				items[keyValue] = param
+			} else {
+				err = key.(*scan.Term).Errorf("dict key can be integer or string, got %s", kern.TypeName(keyValue))
+			}
+		}
 	}
 	if err == nil {
 		v = &items

operand-expr.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-expr.go
@@ -9,11 +9,12 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 // -------- expr term
 func newExprTerm(root *scan.Term) *scan.Term {
-	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymExpression, root.Source(), root)
+	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), sym.SymExpression, root.Source(), root)
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,

operand-func.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-func.go
@@ -70,14 +70,14 @@ func evalFuncDef(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		paramList := make([]kern.ExprFuncParam, 0, len(opTerm.Children))
 		for _, param := range opTerm.Children {
 			var defValue any
-			flags := paramFlags(0)
+			flags := kern.FuncParamFlags(0)
 			if len(param.Children) > 0 {
-				flags |= PfDefault
+				flags |= kern.PfDefault
 				if defValue, err = param.Children[0].Compute(ctx); err != nil {
 					return
 				}
 			}
-			info := NewFuncParamFlagDef(param.Source(), flags, defValue)
+			info := kern.NewFuncParamFlagDef(param.Source(), flags, defValue)
 			paramList = append(paramList, info)
 		}
 		v = newExprFunctor(ast, paramList, ctx)

operand-iterator.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-iterator.go
@@ -10,12 +10,17 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 // -------- iterator term
 
 func newIteratorTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
-	tk.Sym = scan.SymIterator
+	tk.Sym = sym.SymIterator
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,
@@ -52,7 +57,7 @@ func evalFirstChild(ctx kern.ExprContext, iteratorTerm *scan.Term) (value any, e
 }
 
 func getDataSourceDict(iteratorTerm *scan.Term, firstChildValue any) (ds map[string]kern.Functor, err error) {
-	if dictAny, ok := firstChildValue.(*kern.DictType); ok {
+	if dictAny, ok := firstChildValue.(*dict.DictType); ok {
 		requiredFields := []string{kern.NextName}
 		fieldsMask := 0b1
 		foundFields := 0
@@ -123,35 +128,73 @@ func evalIterator(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 			v = dc
 		} else {
-			if dictIt, ok := firstChildValue.(*kern.DictType); ok {
+			if dictIt, ok := firstChildValue.(*dict.DictType); ok {
 				var args []any
-				if args, err = evalSibling(ctx, opTerm.Children, nil); err == nil {
+				if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
 					v, err = NewDictIterator(dictIt, args)
 				}
 			} else {
 				err = opTerm.Children[0].Errorf("the data-source must be a dictionary")
 			}
 		}
-	} else if list, ok := firstChildValue.(*kern.ListType); ok {
+	} else if a, ok := firstChildValue.(*array.ArrayType); ok {
 		var args []any
-		if args, err = evalSibling(ctx, opTerm.Children, nil); err == nil {
+		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
-			v = NewListIterator(list, args)
+			v = NewListIterator(a, args)
 		}
-	} else if intVal, ok := firstChildValue.(int64); ok {
+	} else if ll, ok := firstChildValue.(*list.LinkedList); ok {
 		var args []any
-		if args, err = evalSibling(ctx, opTerm.Children, intVal); err == nil {
+		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
-			v, err = NewIntIterator(args)
+			v = NewLinkedListIterator(ll, args)
 		}
+	} else if intervalVal, ok := firstChildValue.(*interval.IntervalType); ok {
+		v, err = NewIntIteratorFromInterval(intervalVal)
+		// } else if intVal, ok := firstChildValue.(int64); ok {
+		// 	var args []any
+		// 	if args, err = evalSiblings(ctx, opTerm.Children, intVal); err == nil {
+		// 		v, err = NewIntIterator(args)
+		// 	}
+	} else if it, ok := firstChildValue.(kern.Iterator); ok {
+		v, err = NewIterIter(it, ctx, opTerm.Children[1:])
 	} else {
-		var list []any
+		var siblings []any
-		if list, err = evalSibling(ctx, opTerm.Children, firstChildValue); err == nil {
+		if siblings, err = evalSiblings(ctx, opTerm.Children, firstChildValue); err == nil {
-			v = NewArrayIterator(list)
+			v = NewArrayIterator(siblings)
 		}
 	}
 	return
 }
 
-func evalSibling(ctx kern.ExprContext, terms []*scan.Term, firstChildValue any) (list []any, err error) {
+// func evalIterIter(ctx kern.ExprContext, firstChildValue any, siblings []any) (v any, err error) {
+// 	var op kern.Functor
+// 	var args map[string]any
+
+// 	if it, ok := firstChildValue.(kern.Iterator); ok {
+// 		if len(siblings) > 1 {
+// 			if op, ok = siblings[1].(kern.Functor); ok {
+// 				args = make(map[string]any, len(siblings)-2)
+// 				for i, arg := range siblings[2:] {
+// 					switch a := arg.(type) {
+// 					case *kern.DictType:
+// 						for keyAny, item := range *a {
+// 							if key, ok := keyAny.(string); ok {
+// 								args[key] = item
+// 							}
+// 						}
+// 					default:
+// 						args["arg"+strconv.Itoa(i+1)] = arg
+// 					}
+// 				}
+// 			} else if op == nil {
+// 				return nil, fmt.Errorf("the first sibling parameter must be a functor to be used as operation for the iterator")
+// 			}
+// 		}
+// 		v, err = NewIterIter(it, ctx, op, args)
+// 	}
+// 	return
+// }
+
+func evalSiblings(ctx kern.ExprContext, terms []*scan.Term, firstChildValue any) (list []any, err error) {
 	items := make([]any, 0, len(terms))
 	for i, tree := range terms {
 		var param any

operand-linked-list.go

@@ -0,0 +1,45 @@
+// 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"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+)
+
+// -------- list term
+// func newLinkedListTermA(args ...*scan.Term) *scan.Term {
+// 	return newLinkedListTerm(0, 0, args)
+// }
+
+func newLinkedListTerm(row, col int, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(row, col, sym.SymLinkedList, "[<>]", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalLinkedList,
+	}
+}
+
+// -------- list func
+func evalLinkedList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	listTerm, _ := opTerm.Value().([]*scan.Term)
+	items := list.NewLinkedList()
+	for _, tree := range listTerm {
+		var param any
+		if param, err = tree.Compute(ctx); err != nil {
+			break
+		}
+		items.PushBack(param)
+	}
+	if err == nil {
+		v = items
+	}
+	return
+}

operand-list.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-list.go
@@ -7,6 +7,8 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 // -------- list term
@@ -16,7 +18,7 @@ func newListTermA(args ...*scan.Term) *scan.Term {
 
 func newListTerm(row, col int, args []*scan.Term) *scan.Term {
 	return &scan.Term{
-		Tk:       *scan.NewValueToken(row, col, scan.SymList, "[]", args),
+		Tk:       *scan.NewValueToken(row, col, sym.SymList, "[]", args),
 		Parent:   nil,
 		Children: nil,
 		Position: scan.PosLeaf,
@@ -28,7 +30,7 @@ func newListTerm(row, col int, args []*scan.Term) *scan.Term {
 // -------- 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))
+	items := make(array.ArrayType, len(list))
 	for i, tree := range list {
 		var param any
 		if param, err = tree.Compute(ctx); err != nil {

operand-literal.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-literal.go
@@ -7,10 +7,22 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
 )
 
 // -------- literal term
 func newLiteralTerm(tk *scan.Token) *scan.Term {
+
+	if tk.Sym == sym.SymFraction {
+		if v, isString := tk.Value.(string); isString {
+			var err error
+			if tk.Value, err = fract.MakeGeneratingFraction(v); err != nil {
+				return nil
+			}
+		}
+	}
+
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,
@@ -29,10 +41,10 @@ func evalLiteral(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymString, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymString, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymInteger, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymInteger, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymFloat, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymFloat, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymFraction, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymFraction, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymBool, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymBool, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymKwNil, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymKwNil, newLiteralTerm)
 }

operand-selector-case.go

@@ -1,15 +1,13 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-selector-case.go
 package expr
 
 import (
-	"fmt"
-	"strings"
-
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 // -------- selector case term
@@ -19,20 +17,20 @@ type selectorCase struct {
 	caseExpr   kern.Expr
 }
 
-func (sc *selectorCase) String() string {
+// func (sc *selectorCase) String() string {
-	var sb strings.Builder
+// 	var sb strings.Builder
-	if sc.filterList != nil {
+// 	if sc.filterList != nil {
-		sc.filterList.ToString(&sb)
+// 		sc.filterList.ToString(&sb)
-		sb.WriteByte(' ')
+// 		sb.WriteByte(' ')
-	}
+// 	}
-	sb.WriteByte('{')
+// 	sb.WriteByte('{')
-	sb.WriteString(sc.caseExpr.String())
+// 	sb.WriteString(sc.caseExpr.String())
-	sb.WriteByte('}')
+// 	sb.WriteByte('}')
-	return sb.String()
+// 	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})
+	tk := scan.NewValueToken(row, col, sym.SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,
@@ -45,9 +43,14 @@ func newSelectorCaseTerm(row, col int, filterList *scan.Term, caseExpr kern.Expr
 
 // -------- eval selector case
 func evalSelectorCase(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	var ok bool
+	v, _ = opTerm.Value().(*selectorCase)
-	if v, ok = opTerm.Value().(*selectorCase); !ok {
-		err = fmt.Errorf("selector-case expected, got %T", opTerm.Value())
-	}
 	return
 }
+
+// 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

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-var.go
@@ -9,6 +9,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 // -------- variable term
@@ -21,7 +22,7 @@ func newVarTerm(tk *scan.Token) *scan.Term {
 		Priority: scan.PriValue,
 		EvalFunc: evalVar,
 	}
-	t.Tk.Sym = scan.SymVariable
+	t.Tk.Sym = sym.SymVariable
 	return t
 }
 
@@ -41,5 +42,5 @@ func evalVar(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymIdentifier, newVarTerm)
+	scan.RegisterTermConstructor(sym.SymIdentifier, newVarTerm)
 }

operator-assign.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserightChilded.
 
 // operator-assign.go
@@ -7,6 +7,10 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -22,9 +26,29 @@ func newAssignTerm(tk *scan.Token) (inst *scan.Term) {
 	}
 }
 
+func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	v, err = generalEvalAssign(ctx, opTerm, false)
+	return
+}
+
+func newDeepCopyAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAssign,
+		EvalFunc: evalDeepCopyAssign,
+	}
+}
+
+func evalDeepCopyAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	v, err = generalEvalAssign(ctx, opTerm, true)
+	return
+}
+
 func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term, value any) (err error) {
 	var collectionValue, keyListValue, keyValue any
-	var keyList *kern.ListType
+	var keyList *array.ArrayType
 	var ok bool
 
 	if collectionValue, err = collectionTerm.Compute(ctx); err != nil {
@@ -33,7 +57,7 @@ func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *sca
 
 	if keyListValue, err = keyListTerm.Compute(ctx); err != nil {
 		return
-	} else if keyList, ok = keyListValue.(*kern.ListType); !ok || len(*keyList) != 1 {
+	} else if keyList, ok = keyListValue.(*array.ArrayType); !ok || len(*keyList) != 1 {
 		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, kern.TypeName(keyListValue))
 		return
 	}
@@ -43,37 +67,82 @@ func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *sca
 	}
 
 	switch collection := collectionValue.(type) {
-	case *kern.ListType:
+	case *array.ArrayType:
 		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:
+	case *dict.DictType:
 		collection.SetItem(keyValue, value)
+	case *list.LinkedList:
+		if index, ok := keyValue.(int64); ok {
+			err = collection.SetItem(index, value)
+		} else {
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
+		}
 	default:
 		err = collectionTerm.Errorf("collection expected")
 	}
 	return
 }
 
-func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any) (err error) {
+func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any, deepCopy bool) (err error) {
-	if leftTerm.Symbol() == scan.SymIndex {
+	if leftTerm.Symbol() == sym.SymIndex {
 		err = assignCollectionItem(ctx, leftTerm.Children[0], leftTerm.Children[1], v)
 	} else {
+		if deepCopy {
+			v = kern.Clone(v)
+		}
 		ctx.UnsafeSetVar(leftTerm.Source(), v)
 	}
 	return
 }
 
-func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+func evalAssignDictItem(ctx kern.ExprContext, dotTerm *scan.Term, valueTerm kern.Term) (v any, err error) {
+	var ok bool
+	var dictAny, dotKey any
+	var dt *dict.DictType
+
+	if err = dotTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	dotLeftTerm := dotTerm.GetChild(0)
+	if dictAny, err = dotLeftTerm.Compute(ctx); err != nil {
+		return
+	}
+	if dt, ok = dictAny.(*dict.DictType); !ok {
+		err = dotTerm.Tk.ErrorExpectedGot(dict.DictTypeName)
+		return
+	}
+
+	dotRightTerm := dotTerm.Children[1]
+	dotRightSym := dotRightTerm.Symbol()
+	if dotRightSym == sym.SymVariable || dotRightSym == sym.SymString {
+		dotKey = util.UnquoteString(dotRightTerm.Source())
+	} else if dotKey, err = dotRightTerm.Compute(ctx); err != nil {
+		return
+	}
+
+	if v, err = valueTerm.Compute(ctx); err != nil {
+		return
+	}
+
+	dt.SetItem(dotKey, v)
+	return
+}
+
+func generalEvalAssign(ctx kern.ExprContext, opTerm *scan.Term, deepCopy bool) (v any, err error) {
 	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
 	leftTerm := opTerm.Children[0]
 	leftSym := leftTerm.Symbol()
-	if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+	if leftSym == sym.SymDot {
+		return evalAssignDictItem(ctx, opTerm.Children[0], opTerm.GetChild(1))
+	} else if leftSym != sym.SymVariable && leftSym != sym.SymIndex {
 		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
@@ -82,7 +151,7 @@ func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 	if v, err = rightChild.Compute(ctx); err == nil {
 		if functor, ok := v.(kern.Functor); ok {
-			if leftSym == scan.SymVariable {
+			if leftSym == sym.SymVariable {
 				if info := functor.GetFunc(); info != nil {
 					ctx.RegisterFunc(leftTerm.Source(), info.Functor(), info.ReturnType(), info.Params())
 				} else if funcDef, ok := functor.(*exprFunctor); ok {
@@ -93,10 +162,10 @@ func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 					err = opTerm.Errorf("unknown function %s()", rightChild.Source())
 				}
 			} else {
-				err = assignValue(ctx, leftTerm, v)
+				err = assignValue(ctx, leftTerm, v, deepCopy)
 			}
 		} else {
-			err = assignValue(ctx, leftTerm, v)
+			err = assignValue(ctx, leftTerm, v, deepCopy)
 		}
 	}
 	if err != nil {
@@ -119,7 +188,7 @@ func newOpAssignTerm(tk *scan.Token) (inst *scan.Term) {
 
 func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term) (value any, err error) {
 	var collectionValue, keyListValue, keyValue any
-	var keyList *kern.ListType
+	var keyList *array.ArrayType
 	var ok bool
 
 	if collectionValue, err = collectionTerm.Compute(ctx); err != nil {
@@ -128,7 +197,7 @@ func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *s
 
 	if keyListValue, err = keyListTerm.Compute(ctx); err != nil {
 		return
-	} else if keyList, ok = keyListValue.(*kern.ListType); !ok || len(*keyList) != 1 {
+	} else if keyList, ok = keyListValue.(*array.ArrayType); !ok || len(*keyList) != 1 {
 		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, kern.TypeName(keyListValue))
 		return
 	}
@@ -138,13 +207,13 @@ func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *s
 	}
 
 	switch collection := collectionValue.(type) {
-	case *kern.ListType:
+	case *array.ArrayType:
 		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:
+	case *dict.DictType:
 		value = (*collection)[keyValue]
 	default:
 		err = collectionTerm.Errorf("collection expected")
@@ -153,7 +222,7 @@ func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *s
 }
 
 func getAssignValue(ctx kern.ExprContext, leftTerm *scan.Term) (value any, err error) {
-	if leftTerm.Symbol() == scan.SymIndex {
+	if leftTerm.Symbol() == sym.SymIndex {
 		value, err = getCollectionItemValue(ctx, leftTerm.Children[0], leftTerm.Children[1])
 	} else {
 		value, _ = ctx.GetVar(leftTerm.Source())
@@ -169,7 +238,7 @@ func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 	leftTerm := opTerm.Children[0]
 	leftSym := leftTerm.Symbol()
-	if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+	if leftSym != sym.SymVariable && leftSym != sym.SymIndex {
 		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
@@ -179,31 +248,31 @@ func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	if rightValue, err = rightChild.Compute(ctx); err == nil {
 		if leftValue, err = getAssignValue(ctx, leftTerm); err == nil {
 			switch opTerm.Symbol() {
-			case scan.SymPlusEqual:
+			case sym.SymPlusEqual:
 				v, err = sumValues(opTerm, leftValue, rightValue)
-			case scan.SymMinusEqual:
+			case sym.SymMinusEqual:
 				v, err = diffValues(opTerm, leftValue, rightValue)
-			case scan.SymStarEqual:
+			case sym.SymStarEqual:
 				v, err = mulValues(opTerm, leftValue, rightValue)
-			case scan.SymSlashEqual:
+			case sym.SymSlashEqual:
 				v, err = divValues(opTerm, leftValue, rightValue)
-			case scan.SymPercEqual:
+			case sym.SymPercEqual:
 				v, err = remainderValues(opTerm, leftValue, rightValue)
-			case scan.SymAmpersandEqual:
+			case sym.SymAmpersandEqual:
 				v, err = bitwiseAnd(opTerm, leftValue, rightValue)
-			case scan.SymVertBarEqual:
+			case sym.SymVertBarEqual:
 				v, err = bitwiseOr(opTerm, leftValue, rightValue)
-			case scan.SymCaretEqual:
+			case sym.SymCaretEqual:
 				v, err = bitwiseXor(opTerm, leftValue, rightValue)
-			case scan.SymDoubleLessEqual:
+			case sym.SymDoubleLessEqual:
 				v, err = bitLeftShift(opTerm, leftValue, rightValue)
-			case scan.SymDoubleGreaterEqual:
+			case sym.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)
+				err = assignValue(ctx, leftTerm, v, false)
 			}
 		}
 	}
@@ -212,15 +281,16 @@ func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymEqual, newAssignTerm)
+	scan.RegisterTermConstructor(sym.SymEqual, newAssignTerm)
-	scan.RegisterTermConstructor(scan.SymPlusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymColonEqual, newDeepCopyAssignTerm)
-	scan.RegisterTermConstructor(scan.SymMinusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymPlusEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymStarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymMinusEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymSlashEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymStarEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymPercEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymSlashEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymDoubleLessEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymPercEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymDoubleGreaterEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleLessEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymAmpersandEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleGreaterEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymVertBarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymAmpersandEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymCaretEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymVertBarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymCaretEqual, newOpAssignTerm)
 }

operator-at.go

@@ -0,0 +1,68 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-at.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/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+)
+
+//-------- at term
+
+func newAtTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalAt,
+	}
+}
+
+// func hasKey(d map[any]any, target any) (ok bool) {
+// 	_, ok = d[target]
+// 	return
+// }
+
+func evalAt(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 = int64(-1) // default value if not found
+	if array.IsArray(rightValue) {
+		a, _ := rightValue.(*array.ArrayType)
+		if index := a.IndexDeepSameCmp(leftValue); index >= 0 {
+			v = index
+		}
+	} else if dict.IsDict(rightValue) {
+		dict, _ := rightValue.(*dict.DictType)
+		if k, exists := dict.FindKey(leftValue); exists {
+			v = k
+		} else {
+			v = nil
+		}
+	} else if list.IsLinkedList(rightValue) {
+		ls, _ := rightValue.(*list.LinkedList)
+		if index := ls.Index(leftValue); index >= 0 {
+			v = index
+		}
+	} else {
+		v = nil
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(sym.SymKwAt, newAtTerm)
+}

operator-bitwise.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-bitwise.go
@@ -7,6 +7,8 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
 )
 
 //-------- Bitwise NOT term
@@ -28,7 +30,7 @@ func evalBitwiseNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error)
 		return
 	}
 
-	if kern.IsInteger(value) {
+	if types.IsInteger(value) {
 		i, _ := value.(int64)
 		v = ^i
 	} else {
@@ -152,8 +154,8 @@ func evalBitwiseXor(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error)
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymTilde, newBitwiseNotTerm)
+	scan.RegisterTermConstructor(sym.SymTilde, newBitwiseNotTerm)
-	scan.RegisterTermConstructor(scan.SymAmpersand, newBitwiseAndTerm)
+	scan.RegisterTermConstructor(sym.SymAmpersand, newBitwiseAndTerm)
-	scan.RegisterTermConstructor(scan.SymVertBar, newBitwiseOrTerm)
+	scan.RegisterTermConstructor(sym.SymVertBar, newBitwiseOrTerm)
-	scan.RegisterTermConstructor(scan.SymCaret, newBitwiseXorTerm)
+	scan.RegisterTermConstructor(sym.SymCaret, newBitwiseXorTerm)
 }

operator-bool.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-bool.go
@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
 )
 
 //-------- NOT term
@@ -30,7 +32,7 @@ func evalNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if b, ok := kern.ToBool(rightValue); ok {
+	if b, ok := boolean.ToBool(rightValue); ok {
 		v = !b
 	} else {
 		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
@@ -68,8 +70,8 @@ func evalAndWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err e
 		return
 	}
 
-	leftBool, lok = kern.ToBool(leftValue)
+	leftBool, lok = boolean.ToBool(leftValue)
-	rightBool, rok = kern.ToBool(rightValue)
+	rightBool, rok = boolean.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool && rightBool
@@ -90,14 +92,14 @@ func evalAndWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err erro
 		return
 	}
 
-	if leftBool, lok := kern.ToBool(leftValue); !lok {
+	if leftBool, lok := boolean.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 {
+		if rightBool, rok := boolean.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
 			err = self.ErrIncompatibleTypes(leftValue, rightValue)
@@ -136,8 +138,8 @@ func evalOrWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err er
 		return
 	}
 
-	leftBool, lok = kern.ToBool(leftValue)
+	leftBool, lok = boolean.ToBool(leftValue)
-	rightBool, rok = kern.ToBool(rightValue)
+	rightBool, rok = boolean.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool || rightBool
@@ -158,13 +160,13 @@ func evalOrWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error
 		return
 	}
 
-	if leftBool, lok := kern.ToBool(leftValue); !lok {
+	if leftBool, lok := boolean.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 {
+		if rightBool, rok := boolean.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
 			err = self.ErrIncompatibleTypes(leftValue, rightValue)
@@ -175,7 +177,7 @@ func evalOrWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymNot, newNotTerm)
+	scan.RegisterTermConstructor(sym.SymNot, newNotTerm)
-	scan.RegisterTermConstructor(scan.SymAnd, newAndTerm)
+	scan.RegisterTermConstructor(sym.SymAnd, newAndTerm)
-	scan.RegisterTermConstructor(scan.SymOr, newOrTerm)
+	scan.RegisterTermConstructor(sym.SymOr, newOrTerm)
 }

operator-builtin.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-builtin.go
@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- builtin term
@@ -31,13 +33,13 @@ func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	count := 0
-	if kern.IsString(childValue) {
+	if str.IsString(childValue) {
 		module, _ := childValue.(string)
 		count, err = ImportInContextByGlobPattern(ctx, module)
 	} else {
 		var moduleSpec any
 		var it kern.Iterator
-		if it, err = NewIterator(childValue); err != nil {
+		if it, err = NewIterator(ctx, childValue, nil); err != nil {
 			return
 		}
 		for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
@@ -65,5 +67,5 @@ func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwBuiltin, newBuiltinTerm)
+	scan.RegisterTermConstructor(sym.SymKwBuiltin, newBuiltinTerm)
 }

operator-but.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-but.go
@@ -7,6 +7,7 @@ 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/sym"
 )
 
 //-------- but term
@@ -28,5 +29,5 @@ func evalBut(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwBut, newButTerm)
+	scan.RegisterTermConstructor(sym.SymKwBut, newButTerm)
 }

operator-cat.go

@@ -0,0 +1,152 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-cat.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+)
+
+//-------- cat term
+
+func newCatTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalCat,
+	}
+}
+
+func evalCat(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var itLeft, itRight kern.Iterator
+	// var item any
+	var ok bool
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
+		return
+	}
+
+	if itLeft, ok = leftValue.(kern.Iterator); !ok {
+		if itLeft, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of JOIN must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
+	}
+
+	if itRight, ok = rightValue.(kern.Iterator); !ok {
+		if itRight, err = NewIterator(ctx, rightValue, nil); err != nil {
+			return nil, fmt.Errorf("right operand of JOIN must be an iterable data-source; got %s", kern.TypeName(rightValue))
+		}
+	}
+
+	// values := kern.NewListA()
+	// for _, it := range []kern.Iterator{itLeft, itRight} {
+	// 	for item, err = it.Next(); err == nil; item, err = it.Next() {
+	// 		values.AppendItem(item)
+	// 	}
+	// }
+	// if err == io.EOF {
+	// 	err = nil
+	// }
+	// v = values
+	v = newCatIterator(itLeft, itRight)
+	return
+}
+
+const catIteratorType = "cat"
+
+type catIterator struct {
+	kern.IteratorBase
+	itLeft    kern.Iterator
+	itRight   kern.Iterator
+	itCurrent kern.Iterator
+}
+
+func newCatIterator(itLeft, itRight kern.Iterator) (it *catIterator) {
+	it = &catIterator{
+		IteratorBase: kern.IteratorBase{},
+		itLeft:       itLeft,
+		itRight:      itRight,
+		itCurrent:    itLeft,
+	}
+	it.Reset()
+	return
+}
+
+func (it *catIterator) TypeName() string {
+	return catIteratorType
+}
+
+func (it *catIterator) String() string {
+	return fmt.Sprintf("$(%s %s %s)", it.itLeft, catIteratorType, it.itRight)
+}
+
+func (it *catIterator) Next() (item any, err error) {
+	if it.itCurrent == nil {
+		err = io.EOF
+	} else {
+		if item, err = it.itCurrent.Next(); err == nil {
+			it.Increment()
+		} else if err == io.EOF {
+			if it.itCurrent == it.itLeft {
+				it.itCurrent = it.itRight
+			} else {
+				return
+			}
+			if item, err = it.itCurrent.Next(); err == nil {
+				it.Increment()
+			} else {
+				it.itCurrent = nil
+			}
+		}
+	}
+	it.SetCurrent(item)
+	return
+}
+
+// func (it *catIterator) Reset() (err error) {
+// 	err = it.itLeft.Reset()
+// 	it.IteratorBase.Reset()
+// 	return
+// }
+
+func (it *catIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	// case kern.ResetName:
+	// 	err = it.Reset()
+	// case kern.CleanName:
+	// 	err = it.Clean()
+	case kern.IndexName:
+		v = it.Index()
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.Count()
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(sym.SymKwCat, newCatTerm)
+}

operator-context.go

@@ -1,12 +1,16 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-context-value.go
 package expr
 
 import (
+	"io"
+
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 //-------- context term
@@ -23,35 +27,37 @@ func newContextTerm(tk *scan.Token) (inst *scan.Term) {
 
 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" {
+	} else if opTerm.Children[0].Symbol() == sym.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
 		}
+	} else {
+		return
 	}
 
 	if sourceCtx != nil {
-		if formatter, ok := sourceCtx.(kern.DictFormat); ok {
+		v = sourceCtx.ToDict()
-			v = formatter.ToDict()
+	} else if childValue != nil {
-		} else if formatter, ok := sourceCtx.(kern.Formatter); ok {
+		it, ok := childValue.(kern.Iterator)
-			v = formatter.ToString(0)
+		if !ok {
-		} else {
+			it, err = NewIterator(ctx, childValue, nil)
-			// keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+		}
-			keys := sourceCtx.EnumVars(nil)
+		if err == nil {
-			d := make(map[string]any)
+			var item any
-			for _, key := range keys {
+			values := list.NewLinkedListA()
-				d[key], _ = sourceCtx.GetVar(key)
+			for item, err = it.Next(); err == nil; item, err = it.Next() {
+				values.PushBack(item)
 			}
-			keys = sourceCtx.EnumFuncs(func(name string) bool { return true })
+			if err == io.EOF {
-			for _, key := range keys {
+				err = nil
-				d[key], _ = sourceCtx.GetFuncInfo(key)
+				v = values
 			}
-			v = d
 		}
 	} else {
 		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
@@ -61,5 +67,5 @@ func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleDollar, newContextTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleDollar, newContextTerm)
 }

operator-ctrl.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-ctrl.go
@@ -7,6 +7,7 @@ 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/sym"
 )
 
 //-------- export all term
@@ -28,5 +29,5 @@ func evalExportAll(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleAt, newExportAllTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleAt, newExportAllTerm)
 }

operator-default.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-default.go
@@ -7,6 +7,7 @@ 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/sym"
 )
 
 //-------- default term
@@ -29,7 +30,7 @@ func evalDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	leftTerm := opTerm.Children[0]
-	if leftTerm.Tk.Sym != scan.SymVariable {
+	if leftTerm.Tk.Sym != sym.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -63,7 +64,7 @@ func evalAlternate(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	leftTerm := opTerm.Children[0]
-	if leftTerm.Tk.Sym != scan.SymVariable {
+	if leftTerm.Tk.Sym != sym.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -99,7 +100,7 @@ func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err erro
 	}
 
 	leftTerm := opTerm.Children[0]
-	if leftTerm.Tk.Sym != scan.SymVariable {
+	if leftTerm.Tk.Sym != sym.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -111,7 +112,7 @@ func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err erro
 		if functor, ok := rightValue.(kern.Functor); ok {
 			//ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
 			ctx.RegisterFunc(leftTerm.Source(), functor, kern.TypeAny, []kern.ExprFuncParam{
-				NewFuncParamFlag(kern.ParamValue, PfDefault|PfRepeat),
+				kern.NewFuncParamFlag(kern.ParamValue, kern.PfDefault|kern.PfRepeat),
 			})
 		} else {
 			v = rightValue
@@ -123,7 +124,7 @@ func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err erro
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleQuestion, newDefaultTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleQuestion, newDefaultTerm)
-	scan.RegisterTermConstructor(scan.SymQuestionEqual, newDefaultAssignTerm)
+	scan.RegisterTermConstructor(sym.SymQuestionEqual, newDefaultAssignTerm)
-	scan.RegisterTermConstructor(scan.SymQuestionExclam, newAlternateTerm)
+	scan.RegisterTermConstructor(sym.SymQuestionExclam, newAlternateTerm)
 }

operator-digest.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-digest.go
@@ -10,6 +10,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- digest term
@@ -37,7 +38,7 @@ func evalDigest(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
+	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))
 	}
 
@@ -45,15 +46,16 @@ func evalDigest(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	for item, err = it.Next(); err == nil; item, err = it.Next() {
 		ctx.SetVar("_", item)
 		ctx.SetVar("__", it.Index())
-		ctx.SetVar("_#", it.Count())
+		ctx.SetVar("#", it.Count())
 		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 			if rightValue == nil {
-				break
+				err = io.EOF
 			} else {
 				lastValue = rightValue
+				ctx.SetVar(kern.ControlLastResult, lastValue)
 			}
 		}
-		ctx.DeleteVar("_#")
+		ctx.DeleteVar("#")
 		ctx.DeleteVar("__")
 		ctx.DeleteVar("_")
 		if err != nil {
@@ -69,5 +71,5 @@ func evalDigest(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwDigest, newDigestTerm)
+	scan.RegisterTermConstructor(sym.SymKwDigest, newDigestTerm)
 }

operator-dot.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-dot.go
@@ -7,6 +7,9 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/util"
 )
 
 // -------- dot term
@@ -34,7 +37,7 @@ func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 	switch unboxedValue := leftValue.(type) {
 	case kern.ExtIterator:
-		if indexTerm.Tk.Sym == scan.SymVariable /*|| indexTerm.Tk.Sym == scan.SymString */ {
+		if indexTerm.Symbol() == sym.SymVariable /*|| indexTerm.Tk.Sym == sym.SymString */ {
 			opName := indexTerm.Source()
 			if unboxedValue.HasOperation(opName) {
 				v, err = unboxedValue.CallOperation(opName, map[string]any{})
@@ -45,22 +48,8 @@ func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		} else {
 			err = indexTerm.Tk.ErrorExpectedGot("identifier")
 		}
-	case *kern.DictType:
+	case *dict.DictType:
-		var ok bool
+		v, err = dotGetDictItemValue(ctx, unboxedValue, opTerm.Children[1])
-		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))
@@ -69,7 +58,35 @@ func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	return
 }
 
+func dotGetDictItemValue(ctx kern.ExprContext, d *dict.DictType, rightTerm *scan.Term) (v any, err error) {
+	var ok bool
+	var rightValue any
+	s := rightTerm.Symbol()
+	if s == sym.SymVariable || s == sym.SymString {
+		// src := rightTerm.Source()
+		// if len(src) > 1 && src[0] == '"' && src[len(src)-1] == '"' {
+		// 	src = src[1 : len(src)-1]
+		// }
+		src := util.UnquoteString(rightTerm.Source())
+		if v, ok = d.GetItem(src); !ok {
+			err = errDictKeyNotFound(rightTerm, src)
+		}
+	} else if rightValue, err = rightTerm.Compute(ctx); err == nil {
+		if v, ok = d.GetItem(rightValue); !ok {
+			err = errDictKeyNotFound(rightTerm, rightValue)
+		}
+	}
+	return
+}
+
+func errDictKeyNotFound(term *scan.Term, key any) error {
+	if s, ok := key.(string); ok {
+		return term.Errorf("key %q not found", s)
+	}
+	return term.Errorf("key %v not found", key)
+}
+
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDot, newDotTerm)
+	scan.RegisterTermConstructor(sym.SymDot, newDotTerm)
 }

operator-fact.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-fact.go
@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
 )
 
 //-------- fact term
@@ -30,7 +32,7 @@ func evalFact(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsInteger(leftValue) {
+	if types.IsInteger(leftValue) {
 		if i, _ := leftValue.(int64); i >= 0 {
 			f := int64(1)
 			for k := int64(1); k <= i; k++ {
@@ -48,5 +50,5 @@ func evalFact(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymExclamation, newFactTerm)
+	scan.RegisterTermConstructor(sym.SymExclamation, newFactTerm)
 }

operator-filter.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-filter.go
@@ -6,10 +6,11 @@ package expr
 
 import (
 	"fmt"
-	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
 )
 
 //-------- map term
@@ -25,9 +26,11 @@ func newFilterTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 func evalFilter(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	var leftValue, rightValue any
+	// var leftValue, rightValue any
+	var leftValue any
 	var it kern.Iterator
-	var item any
+	// var item any
+	var ok bool
 
 	if err = opTerm.CheckOperands(); err != nil {
 		return
@@ -37,39 +40,130 @@ func evalFilter(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
+	if it, ok = leftValue.(kern.Iterator); !ok {
-		return nil, fmt.Errorf("left operand of FILTER must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		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()
+	// values := kern.NewListA()
-	for item, err = it.Next(); err == nil; item, err = it.Next() {
+	// for item, err = it.Next(); err == nil; item, err = it.Next() {
-		ctx.SetVar("_", item)
+	// 	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
+
+	v = newFilerIterator(ctx, it, opTerm.Children[1])
+	return
+}
+
+const filterIteratorType = "filter"
+
+type filterIterator struct {
+	kern.IteratorBase
+	ctx   kern.ExprContext
+	itSrc kern.Iterator
+	expr  *scan.Term
+}
+
+func newFilerIterator(ctx kern.ExprContext, itSrc kern.Iterator, filterExpr *scan.Term) (it *filterIterator) {
+	it = &filterIterator{
+		IteratorBase: kern.IteratorBase{},
+		ctx:          ctx,
+		itSrc:        itSrc,
+		expr:         filterExpr,
+	}
+	it.IteratorBase.Reset()
+	return
+}
+
+func (it *filterIterator) TypeName() string {
+	return filterIteratorType
+}
+
+func (it *filterIterator) String() string {
+	return fmt.Sprintf("$(%s %s bool-expr)", it.itSrc, filterIteratorType)
+}
+
+func (it *filterIterator) Next() (item any, err error) {
+	var attempt, result any
+
+	ctx := it.ctx
+
+	for attempt, err = it.itSrc.Next(); err == nil; attempt, err = it.itSrc.Next() {
+		ctx.SetVar("_", attempt)
 		ctx.SetVar("__", it.Index())
-		ctx.SetVar("_#", it.Count())
+		ctx.SetVar("#", it.Count())
-		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+		result, err = it.expr.Compute(ctx)
-			if success, valid := kern.ToBool(rightValue); valid {
+		ctx.DeleteVar("#")
-				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 {
+			if success, valid := boolean.ToBool(result); valid {
+				if success {
+					item = attempt
+					break
+				}
+			} else {
+				err = fmt.Errorf("filter expression must return a boolean or a castable to boolean, got %v [%T]", result, result)
+			}
+		}
 		if err != nil {
 			break
 		}
 	}
-	if err == io.EOF {
+
-		err = nil
+	it.SetCurrent(item)
+	return
+}
+
+// func (it *filterIterator) Reset() (err error) {
+// 	err = it.itLeft.Reset()
+// 	it.IteratorBase.Reset()
+// 	return
+// }
+
+func (it *filterIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	// case kern.ResetName:
+	// 	err = it.Reset()
+	// case kern.CleanName:
+	// 	err = it.Clean()
+	case kern.IndexName:
+		v = it.Index()
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.Count()
+	default:
+		err = kern.ErrNoOperation(name)
 	}
-	v = values
 	return
 }
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwFilter, newFilterTerm)
+	scan.RegisterTermConstructor(sym.SymKwFilter, newFilterTerm)
 }

operator-fraction.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-fraction.go
@@ -11,6 +11,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
 )
 
 // -------- fraction term
@@ -51,7 +53,7 @@ func evalFraction(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		num = -num
 	}
 	if num != 0 {
-		if g := kern.Gcd(num, den); g != 1 {
+		if g := fract.Gcd(num, den); g != 1 {
 			num = num / g
 			den = den / g
 		}
@@ -59,11 +61,11 @@ func evalFraction(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 			v = num
 		} else {
 			// v = &expr.FractionType{num, den}
-			v = kern.NewFraction(num, den)
+			v = fract.NewFraction(num, den)
 		}
 	} else {
 		// v = &FractionType{0, den}
-		v = kern.NewFraction(0, den)
+		v = fract.NewFraction(0, den)
 	}
 	return
 }
@@ -71,5 +73,5 @@ func evalFraction(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 // init
 func init() {
 	// registerTermConstructor(SymVertBar, newFractionTerm)
-	scan.RegisterTermConstructor(scan.SymColon, newFractionTerm)
+	scan.RegisterTermConstructor(sym.SymColon, newFractionTerm)
 }

operator-groupby.go

@@ -11,6 +11,10 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- group by term
@@ -31,6 +35,7 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var item any
 	var sKey string
 	var keyByIndex bool
+	var ok bool
 
 	if err = opTerm.CheckOperands(); err != nil {
 		return
@@ -40,35 +45,41 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
+	if it, ok = leftValue.(kern.Iterator); !ok {
-		return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		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() == "__" {
+	if rightTk.IsSymbol(sym.SymVariable) && rightTk.Source() == "__" {
 		keyByIndex = true
 	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
 		return
-	} else if kern.IsString(rightValue) {
+	} else if str.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()
+	values := dict.MakeDict()
 	for item, err = it.Next(); err == nil; item, err = it.Next() {
 		ctx.SetVar("_", item)
 		ctx.SetVar("__", it.Index())
-		ctx.SetVar("_#", it.Count())
+		ctx.SetVar("#", it.Count())
 
 		var sItemKey string
 
-		if d, ok := item.(*kern.DictType); ok {
+		if d, ok := item.(*dict.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)
+					if s, ok := keyValue.(string); ok {
+						sItemKey = s
+					} else {
+						sItemKey = fmt.Sprintf("%v", keyValue)
+					}
 				} else {
 					sItemKey = "_"
 				}
@@ -79,17 +90,17 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 			sItemKey = strconv.Itoa(int(it.Index()))
 		}
 
-		var ls *kern.ListType
+		var ls *array.ArrayType
 		if lsAny, exists := values.GetItem(sItemKey); exists && lsAny != nil {
-			ls = lsAny.(*kern.ListType)
+			ls = lsAny.(*array.ArrayType)
 		}
 		if ls == nil {
-			ls = kern.NewListA()
+			ls = array.NewArrayA()
 		}
 		ls.AppendItem(item)
 		values.SetItem(sItemKey, ls)
 
-		ctx.DeleteVar("_#")
+		ctx.DeleteVar("#")
 		ctx.DeleteVar("__")
 		ctx.DeleteVar("_")
 	}
@@ -102,5 +113,5 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwGroupBy, newGroupByTerm)
+	scan.RegisterTermConstructor(sym.SymKwGroupBy, newGroupByTerm)
 }

operator-in.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-in.go
@@ -7,6 +7,10 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 //-------- in term
@@ -33,12 +37,15 @@ func evalIn(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsList(rightValue) {
+	if array.IsArray(rightValue) {
-		list, _ := rightValue.(*kern.ListType)
+		a, _ := rightValue.(*array.ArrayType)
-		v = list.IndexDeepSameCmp(leftValue) >= 0
+		v = a.IndexDeepSameCmp(leftValue) >= 0
-	} else if kern.IsDict(rightValue) {
+	} else if dict.IsDict(rightValue) {
-		dict, _ := rightValue.(*kern.DictType)
+		dict, _ := rightValue.(*dict.DictType)
 		v = dict.HasKey(leftValue)
+	} else if list.IsLinkedList(rightValue) {
+		ls, _ := rightValue.(*list.LinkedList)
+		v = ls.HasValue(leftValue)
 	} else {
 		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
@@ -47,5 +54,5 @@ func evalIn(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwIn, newInTerm)
+	scan.RegisterTermConstructor(sym.SymKwIn, newInTerm)
 }

operator-include.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-include.go
@@ -7,6 +7,9 @@ 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/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- include term
@@ -29,9 +32,9 @@ func evalInclude(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	count := 0
-	if kern.IsList(childValue) {
+	if array.IsArray(childValue) {
-		list, _ := childValue.(*kern.ListType)
+		a, _ := childValue.(*array.ArrayType)
-		for i, filePathSpec := range *list {
+		for i, filePathSpec := range *a {
 			if filePath, ok := filePathSpec.(string); ok {
 				if v, err = EvalFile(ctx, filePath); err == nil {
 					count++
@@ -44,7 +47,7 @@ func evalInclude(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 				break
 			}
 		}
-	} else if kern.IsString(childValue) {
+	} else if str.IsString(childValue) {
 		filePath, _ := childValue.(string)
 		if v, err = EvalFile(ctx, filePath); err == nil {
 			count++
@@ -61,5 +64,5 @@ func evalInclude(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwInclude, newIncludeTerm)
+	scan.RegisterTermConstructor(sym.SymKwInclude, newIncludeTerm)
 }

operator-index.go

@@ -1,12 +1,20 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-index.go
 package expr
 
 import (
+	"strings"
+
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 // -------- index term
@@ -20,15 +28,15 @@ func newIndexTerm(tk *scan.Token) (inst *scan.Term) {
 	}
 }
 
-func verifyKey(indexList *kern.ListType) (index any, err error) {
+func verifyKey(indexList *array.ArrayType) (index any, err error) {
 	index = (*indexList)[0]
 	return
 }
 
-func verifyIndex(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (index int, err error) {
+func verifyIndex(indexTerm kern.Term, indexList *array.ArrayType, maxValue int64) (index int64, err error) {
-	var v int
+	var v int64
 
-	if v, err = kern.ToGoInt((*indexList)[0], "index expression"); err == nil {
+	if v, err = types.ToGoInt64((*indexList)[0], "index expression"); err == nil {
 		if v < 0 && v >= -maxValue {
 			v = maxValue + v
 		}
@@ -41,32 +49,32 @@ func verifyIndex(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (
 	return
 }
 
-func verifyRange(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (startIndex, endIndex int, err error) {
+// func verifyInterval(indexTerm kern.Term, indexList *array.ArrayType, maxValue int64) (startIndex, endIndex int64, err error) {
-	v, _ := ((*indexList)[0]).(*intPair)
+// 	v, _ := ((*indexList)[0]).(*interval.IntervalType)
-	startIndex = v.a
+// 	startIndex = v.Begin()
-	endIndex = v.b
+// 	endIndex = v.End()
-	if endIndex == kern.ConstLastIndex {
+// 	if endIndex == kern.ConstLastIndex {
-		endIndex = maxValue
+// 		endIndex = int64(maxValue)
-	}
+// 	}
-	if startIndex < 0 && startIndex >= -maxValue {
+// 	if startIndex < 0 && startIndex >= -maxValue {
-		startIndex = maxValue + startIndex
+// 		startIndex = int64(maxValue) + startIndex
-	}
+// 	}
-	if endIndex < 0 && endIndex >= -maxValue {
+// 	if endIndex < 0 && endIndex >= -maxValue {
-		endIndex = maxValue + endIndex
+// 		endIndex = int64(maxValue) + endIndex
-	}
+// 	}
-	if startIndex < 0 || startIndex > maxValue {
+// 	if startIndex < 0 || startIndex > maxValue {
-		err = indexTerm.Errorf("range start-index %d is out of bounds", startIndex)
+// 		err = indexTerm.Errorf("%s start-index %d is out of bounds", interval.TypeName, startIndex)
-	} else if endIndex < 0 || endIndex > maxValue {
+// 	} else if endIndex < 0 || endIndex > maxValue {
-		err = indexTerm.Errorf("range end-index %d is out of bounds", endIndex)
+// 		err = indexTerm.Errorf("%s end-index %d is out of bounds", interval.TypeName, endIndex)
-	} else if startIndex > endIndex {
+// 	} else if startIndex > endIndex {
-		err = indexTerm.Errorf("range start-index %d must not be greater than end-index %d", startIndex, endIndex)
+// 		err = indexTerm.Errorf("%s start-index %d must not be greater than end-index %d", interval.TypeName, startIndex, endIndex)
-	}
+// 	}
-	return
+// 	return
-}
+// }
 
 func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
-	var indexList *kern.ListType
+	var indexList *array.ArrayType
 	var ok bool
 
 	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
@@ -74,7 +82,7 @@ func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	indexTerm := opTerm.Children[1]
-	if indexList, ok = rightValue.(*kern.ListType); !ok {
+	if indexList, ok = rightValue.(*array.ArrayType); !ok {
 		err = opTerm.Errorf("invalid index expression")
 		return
 	} else if len(*indexList) != 1 {
@@ -82,41 +90,12 @@ func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsInteger((*indexList)[0]) {
+	if types.IsInteger((*indexList)[0]) {
-		switch unboxedValue := leftValue.(type) {
+		v, err = collectionItemByIndex(opTerm, leftValue, rightValue, indexList)
-		case *kern.ListType:
+	} else if interval.IsInterval((*indexList)[0]) {
-			var index int
+		v, err = subCollectionByIndex(opTerm, leftValue, rightValue, indexList)
-			if index, err = verifyIndex(indexTerm, indexList, len(*unboxedValue)); err == nil {
+	} else if dict.IsDict(leftValue) {
-				v = (*unboxedValue)[index]
+		d := leftValue.(*dict.DictType)
-			}
-		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]
@@ -125,7 +104,126 @@ func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	return
 }
 
-func getDictItem(d *kern.DictType, indexTerm *scan.Term, indexList *kern.ListType, rightValue any) (v any, err error) {
+func collectionItemByIndex(opTerm kern.Term, leftValue, rightValue any, indexList *array.ArrayType) (v any, err error) {
+	indexTerm := opTerm.GetChild(1)
+	switch unboxedValue := leftValue.(type) {
+	case *array.ArrayType:
+		var index int64
+		if index, err = verifyIndex(indexTerm, indexList, int64(len(*unboxedValue))); err == nil {
+			v = (*unboxedValue)[index]
+		}
+	case *list.LinkedList:
+		var index int64
+		if index, err = verifyIndex(indexTerm, indexList, int64(unboxedValue.Len())); err == nil {
+			v, err = unboxedValue.At(index)
+		}
+	case string:
+		var index int64
+		if index, err = verifyIndex(indexTerm, indexList, int64(len(unboxedValue))); err == nil {
+			v = string(unboxedValue[index])
+		}
+	case *dict.DictType:
+		v, err = getDictItem(unboxedValue, indexTerm, indexList, rightValue)
+	default:
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func subCollectionByIndex(opTerm kern.Term, leftValue, rightValue any, indexList *array.ArrayType) (v any, err error) {
+	triple := (*indexList)[0].(*interval.IntervalType)
+	switch unboxedValue := leftValue.(type) {
+	case *array.ArrayType:
+		v = intervalSubArray(unboxedValue, triple)
+	case *list.LinkedList:
+		v = intervalSubLinkedList(unboxedValue, triple)
+	case string:
+		v = intervalSubString(unboxedValue, triple)
+	default:
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func fixInterval(p *interval.IntervalType, maxLength int) (b, e, s int) {
+	b, e, s = p.ToIntTriple()
+	if b < 0 {
+		b = maxLength + b
+	}
+	if e < 0 {
+		e = maxLength + e //+ 1
+	}
+	return
+}
+
+func intervalSubString(source string, p *interval.IntervalType) (result string) {
+	b, e, s := fixInterval(p, len(source))
+	if b <= e {
+		e = min(e, len(source))
+		if s == 1 {
+			result = source[b:e]
+		} else {
+			var sb strings.Builder
+			for i := b; i < e; i += s {
+				sb.WriteByte(source[i])
+			}
+			result = sb.String()
+		}
+	} else {
+		var sb strings.Builder
+		for i := b; i >= e; i -= s {
+			sb.WriteByte(source[i])
+		}
+		result = sb.String()
+	}
+	return
+}
+
+func intervalSubArray(source *array.ArrayType, p *interval.IntervalType) (result *array.ArrayType) {
+	var a array.ArrayType
+	b, e, s := fixInterval(p, len(*source))
+	if b <= e {
+		e = min(e, len(*source))
+		if s == 1 {
+			a = (*source)[b:e]
+		} else {
+			size := (e-b)/s + 1
+			a = make(array.ArrayType, 0, size)
+			for i := b; i < e; i += s {
+				a = append(a, (*source)[i])
+			}
+		}
+	} else {
+		size := (b-e)/s + 1
+		a = make(array.ArrayType, 0, size)
+		for i := b; i > e; i -= s {
+			a = append(a, (*source)[i])
+		}
+	}
+	result = &a
+	return
+}
+
+func intervalSubLinkedList(source *list.LinkedList, p *interval.IntervalType) (result *list.LinkedList) {
+	b, e, s := fixInterval(p, source.Len())
+	revert := b > e
+	if revert {
+		b, e = e, b
+		source = source.Revert()
+	}
+	e = min(e, source.Len())
+	if s == 1 {
+		result = source.Sub(int64(b), int64(e))
+	} else {
+		result = source.SubStep(int64(b), int64(e), int64(s))
+	}
+	if revert {
+		source = source.Revert()
+	}
+	return
+}
+
+func getDictItem(d *dict.DictType, indexTerm kern.Term, indexList *array.ArrayType, rightValue any) (v any, err error) {
 	var ok bool
 	var indexValue any
 
@@ -139,5 +237,5 @@ func getDictItem(d *kern.DictType, indexTerm *scan.Term, indexList *kern.ListTyp
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymIndex, newIndexTerm)
+	scan.RegisterTermConstructor(sym.SymIndex, newIndexTerm)
 }