alias operators: '<<' same as '<+', '>>' same as '+>'. Insert and append operation optimized with linked lists

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
@@ -12,7 +12,7 @@ import (
 type exprFunctor struct {
 	kern.BaseFunctor
 	params []kern.ExprFuncParam
-	expr   Expr
+	expr   kern.Expr
 	defCtx kern.ExprContext
 }
 
@@ -20,7 +20,7 @@ func (functor *exprFunctor) GetParams() (params []kern.ExprFuncParam) {
 	return functor.params
 }
 
-func newExprFunctor(e Expr, params []kern.ExprFuncParam, ctx kern.ExprContext) *exprFunctor {
+func newExprFunctor(e kern.Expr, params []kern.ExprFuncParam, ctx kern.ExprContext) *exprFunctor {
 	var defCtx kern.ExprContext
 	if ctx != nil {
 		defCtx = ctx

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
@@ -11,6 +11,7 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 const (
@@ -199,7 +200,7 @@ func fractFunc(ctx kern.ExprContext, name string, args map[string]any) (result a
 
 func evalFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	if source, ok := args[kern.ParamSource].(string); ok {
-		var ast Expr
+		var ast kern.Expr
 
 		parser := NewParser()
 		if ctx == nil {
@@ -207,7 +208,7 @@ func evalFunc(ctx kern.ExprContext, name string, args map[string]any) (result an
 		}
 
 		r := strings.NewReader(source)
-		scanner := NewScanner(r, DefaultTranslations())
+		scanner := scan.NewScanner(r, scan.DefaultTranslations())
 
 		if ast, err = parser.Parse(scanner); err == nil {
 			CtrlEnable(ctx, kern.ControlExportAll)
@@ -254,24 +255,31 @@ 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) {
-// 	var varName string
-// 	var ok bool
+func charFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	var ord int
 
-// 	if varName, ok = args[kern.ParamName].(string); !ok {
-// 		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
-// 	} else {
-// 		ctx.GetParent().DeleteVar(varName)
-// 		result = nil
-// 	}
-// 	return
-// }
+	if n, ok := args[kern.ParamValue].(byte); ok {
+		ord = int(n)
+	} else if n, ok := args[kern.ParamValue].(int64); ok {
+		ord = int(n)
+	} else if n, ok := args[kern.ParamValue].(int); ok {
+		ord = n
+	} else {
+		return nil, kern.ErrWrongParamType(name, kern.ParamName, kern.TypeString, args[kern.ParamName])
+	}
+	if ord < 0 || ord > 255 {
+		err = kern.ErrFuncInvalidArg(name, fmt.Sprintf("character code must be in range 0-255, got %d", ord))
+	} else {
+		result = string(rune(ord))
+	}
+	return
+}
 
 //// 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)
@@ -289,28 +297,27 @@ func ImportBuiltinsFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("dec", kern.NewGolangFunctor(decFunc), kern.TypeFloat, anyParams)
 	ctx.RegisterFunc("string", kern.NewGolangFunctor(stringFunc), kern.TypeString, anyParams)
 	ctx.RegisterFunc("fract", kern.NewGolangFunctor(fractFunc), kern.TypeFraction, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamValue),
-		NewFuncParamFlagDef(ParamDenominator, PfDefault, int64(1)),
+		kern.NewFuncParam(kern.ParamValue),
+		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),
-		NewFuncParamFlagDef(kern.ParamValue, PfDefault, nil),
+		kern.NewFuncParam(kern.ParamName),
+		kern.NewFuncParamFlagDef(kern.ParamValue, kern.PfDefault, nil),
 	})
 
 	ctx.RegisterFunc("set", kern.NewGolangFunctor(setFunc), kern.TypeAny, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamName),
-		NewFuncParam(kern.ParamValue),
+		kern.NewFuncParam(kern.ParamName),
+		kern.NewFuncParam(kern.ParamValue),
 	})
 
-	// ctx.RegisterFunc("unset", kern.NewGolangFunctor(unsetFunc), kern.TypeAny, []kern.ExprFuncParam{
-	// 	NewFuncParam(kern.ParamName),
-	// 	NewFuncParam(kern.ParamValue),
-	// })
+	ctx.RegisterFunc("char", kern.NewGolangFunctor(charFunc), kern.TypeString, []kern.ExprFuncParam{
+		kern.NewFuncParam(kern.ParamValue),
+	})
 }
 
 func init() {

builtin-fmt.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-fmt.go
@@ -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
@@ -9,6 +9,7 @@ import (
 	"os"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 func importFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
@@ -43,10 +44,10 @@ func doImport(ctx kern.ExprContext, name string, dirList []string, it kern.Itera
 		var file *os.File
 		if file, err = os.Open(sourceFilepath); err == nil {
 			defer file.Close()
-			var expr *ast
-			scanner := NewScanner(file, DefaultTranslations())
+			var expr *scan.Ast
+			scanner := scan.NewScanner(file, scan.DefaultTranslations())
 			parser := NewParser()
-			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, SymEos); err == nil {
+			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymEos); err == nil {
 				result, err = expr.Eval(ctx)
 			}
 			if err != nil {
@@ -68,10 +69,10 @@ 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
@@ -94,9 +94,9 @@ 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),
-		NewFuncParamFlag(iterParamOperator, PfOptional),
-		NewFuncParamFlag(iterParamVars, PfOptional),
+		kern.NewFuncParam(kern.ParamIterator),
+		kern.NewFuncParamFlag(iterParamOperator, kern.PfOptional),
+		kern.NewFuncParamFlag(iterParamVars, kern.PfOptional),
 	})
 }
 

builtin-math-arith.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // builtin-math-arith.go
@@ -172,11 +172,11 @@ 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 {
-	osReader  *osReader
+type fileIterBase struct {
+	reader    *file.Reader
 	index     int64
 	count     int64
-	line      string
 	autoClose bool
 }
 
-func newReadTextIterator(r *osReader, autoClose bool) *fileReadTextIterator {
-	return &fileReadTextIterator{osReader: r, index: -1, autoClose: autoClose}
-}
-
-func (it *fileReadTextIterator) TypeName() string {
-	return fileReadTextIteratorType
-}
-
-func (it *fileReadTextIterator) String() string {
-	if it.osReader != nil && it.osReader.fh != nil {
-		return fmt.Sprintf("$(%s@%q)", fileReadTextIteratorType, it.osReader.fh.Name())
-	}
-	return fmt.Sprintf("$(%s@<nil>)", fileReadTextIteratorType)
-}
-
-func (it *fileReadTextIterator) Count() int64 {
+func (it *fileIterBase) Count() int64 {
 	return it.count
 }
 
-func (it *fileReadTextIterator) Next() (item any, err error) { // must return io.EOF after the last item
-	if it.osReader.fh != nil {
-		if it.line, err = it.osReader.reader.ReadString('\n'); err == nil {
-			it.index++
-			it.count++
-			item = it.line[0 : len(it.line)-1]
-		} else if it.autoClose {
-			it.Clean()
-		}
-	}
-	return
-}
-
-func (it *fileReadTextIterator) Current() (item any, err error) {
-	if len(it.line) > 0 {
-		item = it.line[0 : len(it.line)-1]
-	}
-	return
-}
-
-func (it *fileReadTextIterator) Index() int64 {
+func (it *fileIterBase) Index() int64 {
 	return it.index
 }
 
-func (it *fileReadTextIterator) Reset() (err error) {
-	if _, err = it.osReader.fh.Seek(0, io.SeekStart); err == nil {
-		it.index = -1
-		it.count = 0
-		it.line = ""
-	}
-	return
-}
-
-func (it *fileReadTextIterator) HasOperation(name string) bool {
+func (it *fileIterBase) HasOperation(name string) bool {
 	return slices.Contains([]string{kern.NextName, kern.ResetName, kern.IndexName, kern.CountName, kern.CurrentName, kern.CleanName}, name)
 }
 
-func (it *fileReadTextIterator) Clean() (err error) {
-	if it.osReader.fh != nil {
-		if err = it.osReader.fh.Close(); err == nil {
-			it.osReader = nil
-		}
-	}
-	return nil
+func (it *fileIterBase) reset() {
+	it.index = -1
+	it.count = 0
 }
 
-func (it *fileReadTextIterator) CallOperation(name string, args map[string]any) (v any, err error) {
-	switch name {
-	case kern.NextName:
-		v, err = it.Next()
-	case kern.ResetName:
-		err = it.Reset()
-	case kern.CleanName:
-		err = it.Clean()
-	case kern.IndexName:
-		v = int64(it.Index())
-	case kern.CurrentName:
-		v, err = it.Current()
-	case kern.CountName:
-		v = it.count
-	default:
-		err = kern.ErrNoOperation(name)
-	}
-	return
+func (it *fileIterBase) increment() {
+	it.index++
+	it.count++
 }
 
-func fileReadIteratorFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	var handle *osReader
-	var invalidFileHandle any
-	var ok, autoClose bool
+func (it *fileIterBase) repr(typeName string) string {
+	if it.reader.Valid() {
+		return fmt.Sprintf("$(%s@%q)", typeName, it.reader.GetName())
+	}
+	return fmt.Sprintf("$(%s@<nil>)", typeName)
+}
 
-	result = nil
-	if handle, ok = args[paramHandleOrPath].(*osReader); !ok {
+func initFileHandle(ctx kern.ExprContext, name string, args map[string]any) (handle *file.Reader, invalidFileHandle any, autoClose bool, err error) {
+	var ok bool
+
+	if handle, ok = args[paramHandleOrPath].(*file.Reader); !ok {
 		if fileName, ok := args[paramHandleOrPath].(string); ok && len(fileName) > 0 {
 			var handleAny any
 			if handleAny, err = openFileFunc(ctx, name, map[string]any{kern.ParamFilepath: fileName}); err != nil {
 				return
 			}
 			if handleAny != nil {
-				handle = handleAny.(*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
-		if fh, err = os.Create(filePath); err == nil {
-			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
-		}
+		// var fh *os.File
+		// if fh, err = os.Open(filePath); err == nil {
+		// 	result = file.NewReader(fh)
+		// }
+		result, err = file.OpenReader(filePath)
 	} else {
 		err = errMissingFilePath(name)
 	}
 	return
 }
 
-func 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
-		if fh, err = os.Open(filePath); err == nil {
-			result = &osReader{fh: fh, reader: bufio.NewReader(fh)}
-		}
+		// var fh *os.File
+		// if fh, err = os.Create(filePath); err == nil {
+		// 	result = file.NewWriter(fh)
+		// }
+		result, err = file.CreateWriter(filePath)
 	} else {
 		err = errMissingFilePath(name)
 	}
@@ -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
-		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)}
-		}
+		// var fh *os.File
+		// if fh, err = os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0660); err == nil {
+		// 	result = file.NewWriter(fh)
+		// }
+		result, err = file.AppendWriter(filePath)
 	} else {
 		err = errMissingFilePath(name)
 	}
@@ -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 w, ok := handle.(*osWriter); ok {
-				err = w.writer.Flush()
+		if fh := handle.GetFile(); fh != nil {
+			if w, ok := handle.(*file.Writer); ok {
+				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),
-		NewFuncParamFlagDef(kern.ParamItem, PfDefault|PfRepeat, ""),
+		kern.NewFuncParam(kern.ParamHandle),
+		kern.NewFuncParamFlagDef(kern.ParamItem, kern.PfDefault|kern.PfRepeat, ""),
 	})
 
 	ctx.RegisterFunc("fileReadText", kern.NewGolangFunctor(fileReadTextFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamHandle),
-		NewFuncParamFlagDef(osLimitCh, PfDefault, "\n"),
+		kern.NewFuncParam(kern.ParamHandle),
+		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{
-		NewFuncParam(paramHandleOrPath),
+	ctx.RegisterFunc("fileLineIterator", kern.NewGolangFunctor(fileLineIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
+		kern.NewFuncParam(paramHandleOrPath),
 	})
+
+	ctx.RegisterFunc("fileByteIterator", kern.NewGolangFunctor(fileByteIteratorFunc), kern.TypeIterator, []kern.ExprFuncParam{
+		kern.NewFuncParam(paramHandleOrPath),
+	})
+
 }
 
 func init() {

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
@@ -225,44 +225,44 @@ 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),
-		NewFuncParamFlag(kern.ParamItem, PfRepeat),
+		kern.NewFuncParam(kern.ParamSeparator),
+		kern.NewFuncParamFlag(kern.ParamItem, kern.PfRepeat),
 	})
 
 	ctx.RegisterFunc("strSub", kern.NewGolangFunctor(subStrFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
-		NewFuncParamFlagDef(kern.ParamStart, PfDefault, int64(0)),
-		NewFuncParamFlagDef(kern.ParamCount, PfDefault, int64(-1)),
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParamFlagDef(kern.ParamStart, kern.PfDefault, int64(0)),
+		kern.NewFuncParamFlagDef(kern.ParamCount, kern.PfDefault, int64(-1)),
 	})
 
 	ctx.RegisterFunc("strSplit", kern.NewGolangFunctor(splitStrFunc), "list of "+kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
-		NewFuncParamFlagDef(kern.ParamSeparator, PfDefault, ""),
-		NewFuncParamFlagDef(kern.ParamCount, PfDefault, int64(-1)),
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParamFlagDef(kern.ParamSeparator, kern.PfDefault, ""),
+		kern.NewFuncParamFlagDef(kern.ParamCount, kern.PfDefault, int64(-1)),
 	})
 
 	ctx.RegisterFunc("strTrim", kern.NewGolangFunctor(trimStrFunc), kern.TypeString, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSource),
 	})
 
 	ctx.RegisterFunc("strStartsWith", kern.NewGolangFunctor(startsWithStrFunc), kern.TypeBoolean, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
-		NewFuncParam(kern.ParamPrefix),
-		NewFuncParamFlag(strParamOther, PfRepeat),
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamPrefix),
+		kern.NewFuncParamFlag(strParamOther, kern.PfRepeat),
 	})
 
 	ctx.RegisterFunc("strEndsWith", kern.NewGolangFunctor(endsWithStrFunc), kern.TypeBoolean, []kern.ExprFuncParam{
-		NewFuncParam(kern.ParamSource),
-		NewFuncParam(kern.ParamSuffix),
-		NewFuncParamFlag(strParamOther, PfRepeat),
+		kern.NewFuncParam(kern.ParamSource),
+		kern.NewFuncParam(kern.ParamSuffix),
+		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

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
@@ -116,8 +116,11 @@ func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err err
 		}
 	}
 
-	dictIt.makeKeys(*dict, sortType)
-	return dictIt, err
+	if err == nil {
+		dictIt.makeKeys(*dict, sortType)
+		it = dictIt
+	}
+	return
 }
 
 func NewMapIterator(m map[any]any) (it *DictIterator) {
@@ -139,7 +142,6 @@ 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
 }

doc/Expr.adoc

@@ -34,7 +34,7 @@ Expressions calculator
 
 toc::[]
 
-#TODO: Work in progress (last update on 2026/04/21, 6:49 p.m.)#
+#TODO: Work in progress (last update on 2026/05/08)#
 
 == Expr
 _Expr_ is a GO package that can analyze, interpret and calculate expressions.
@@ -698,9 +698,9 @@ The value on the left side of [blue]`=` must be a variable identifier or an expr
 === Selector operator [blue]`? : ::`
 The _selector operator_ is very similar to the _switch/case/default_ statement available in many programming languages.
 
-.Selector literal Syntax
+.Selector literal syntax
 ====
-_selector-operator_ = _select-expression_ "*?*" _selector-case_ { "*:*" _selector-case_ } ["*::*" _default-multi-expression_] +
+*_selector-operator_* = _select-expression_ "*?*" _selector-case_ { "*:*" _selector-case_ } ["*::*" _default-multi-expression_] +
 _selector-case_ = [_match-list_] _case-value_ +
 _match-list_ = "*[*" _item_ {"*,*" _items_} "*]*" +
 _item_ = _expression_ +
@@ -737,19 +737,38 @@ The [blue]`:` symbol (colon) is the separator of the selector-cases. Note that i
 `>>>` [blue]`10 ? {"a"} : {"b"}` +
 [red]`Eval Error: [1:3] no case catches the value (10) of the selection expression`
 
+==== Triple special case of the selector operator
+If the _select-expression_ is a boolean expression, the selector operator can be used as a sort of _if-then-else_ statement. In this case, the first case is evaluated if the _select-expression_ is true, and the second case is evaluated if the _select-expression_ is false. In this special case, the _match-list_ of both cases must be empty.
+
+.Example
+`>>>` [blue]`(true) ? {"T"}: {"F"}` +
+[green]`T` +
+`>>>` [blue]`(2 > 1) ? {"a"} : {"b"}` +
+[green]`a` +
+`>>>` [blue]`(2 < 1) ? {"a"} : {"b"}` +
+[green]`b`
+
+[WARNING]
+====
+The triple special case of the selector operator is very useful, but it only works with boolean expressions.
+
+.Example of confusion
+`>>>` [blue]`int(true) ? {"T"}: {"F"}` +
+[green]`F`
+====
 
 === Variable default value [blue]`??`, [blue]`?=`, and [blue]`?!`
-The left operand of the first two operators, [blue]`??` and [blue]`?=`, 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.
+The left operand of the first two operators, [blue]`??` and [blue]`?=`, 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.
 
 IMPORTANT: If the left variable is defined, the right expression is not evaluated at all.
 
 The [blue]`??` operator do not change the status of the left variable.
 
-The [blue]`?=` assigns the calculated value of the right expression to the left variable.
+The [blue]`?=` assigns the calculated value of the right expression to the variable on the left side.
 
 The third one, [blue]`?!`, is the alternate operator. If the variable on the left size is not defined, it returns [blue]_nil_. Otherwise it returns the result of the expressione on the right side.
 
-IMPORTANT: If the left variable is NOT defined, the right expression is not evaluated at all.
+IMPORTANT: If the variable [blue]`?!` is NOT defined, the expression is not evaluated at all.
 
 .Examples
 `>>>` [blue]`var ?? (1+2)` +
@@ -836,8 +855,14 @@ The table below shows all supported operators by decreasing priorities.
 .2+|*INSERT*| [blue]`+>` | _Infix_ | _Prepend_ | _any_ `+>` _list_ -> _list_
 | [blue]`<+` | _Infix_ | _Append_ | _list_ `<+` _any_ -> _list_
 .2+|*ASSIGN*| [blue]`=` | _Infix_ | _Assignment_ | _identifier_ `=` _any_ -> _any_
-4+| _See also the table of special allocation operators below_
+4+| _See also the table of special assignment operators below_
 .1+|*BUT*| [blue]`but` | _Infix_ | _But_ | _any_ `but` _any_ -> _any_
+.6+|*ITER-OP*| [blue]`digest` | _Infix_ | _Item-digesting_ | _iterable_ `digest` _expr_ -> _any_
+| [blue]`filter` | _Infix_ | _Item-filtering_ | _iterable_ `filter` _expr_ -> _list_
+| [blue]`groupby` | _Infix_ | _Dict-grouping_ | _iterable_ `groupby` _key-expr_ -> _dict_
+| [blue]`join` | _Infix_ | _Item-joining_ | _iterable_ `join` _iterable_ -> _list_
+| [blue]`map` | _Infix_ | _Item-mapping_ | _iterable_ `map` _-expr_ -> _list_
+4+| _See iterators section for examples_
 .1+|*RANGE*| [blue]`:` | _Infix_ | _Index-range_ | _integer_ `:` _integer_ -> _integer-pair_
 |===
 
@@ -921,12 +946,12 @@ _param-name_ = _identifier_
 [green]`fib(n):any{}`
 
 `>>>` [gray]_// Required and optional parameters_ +
-`>>>` [blue]`measure = func(value, unit="meter"){ value + " " + unit + (value > 1) ? [true] {"s"} :: {""}}` +
+`>>>` [blue]`measure = func(value, unit="meter"){ value + " " + unit + (value > 1) ? {"s"} :: {""}}` +
 [green]`measure(value, unit="meter"):any{}`
 
 
 === _Golang_ function definition
-Description of how to define Golang functions and how to bind them to _Expr_ are topics covered in another document that I'll write, one day, maybe.
+Description of how to define Golang functions and how to bind them to _Expr_ are topics covered in another documents that I'll write, one day, maybe.
 
 === Function calls
 To call a function, either Expr or Golang type, it is necessary to specify its name and, at least, its required parameters.
@@ -1010,7 +1035,7 @@ Clone variables are normal local variables. The only diffence will appear when t
 .Example
 `>>>` [blue]`f = func() { @x = 3; x = 5 }` [gray]_// f() declares two *different* local variables: ``@x`` and ``x``_ +
 [green]`f():any{}` +
-`>>>` [blue]`f()` [gray]_// The multi-expression (two) in f() is calculated and the last result is returned_ +
+`>>>` [blue]`f()` [gray]_// The multi-expression (two expressions) in f() is calculated and the last result is returned_ +
 [green]`5` +
 `>>>` [blue]`x` [gray]_// The `x` variable was not defined in the main context before the f() invocation. It appears in the main context by cloning the `@x` variable, local to f() after its termnation._ +
 [green]`3`
@@ -1048,7 +1073,7 @@ Builtins activation is done by using the [blue]`BUILTIN` operator. All modules e
 
 .Builtin activation syntax
 ====
-*_builtin-activation_* = [blue]`BUILTIN` (_builtin-name_ | _list-of-builtin-names_) +
+*_builtin-activation_* = [blue]`BUILTIN` (_builtin-name_ | _list-of-builtin-names_ | **"*"**) +
 _builtin-name_ = _string_ +
 _list-of-builtin-names_ = **[** _string_ { "**,**" _string_ } **]**
 ====
@@ -1086,9 +1111,9 @@ The "base" builtin module provides functions for type checking and type conversi
 * <<_fract,fract()>>
 
 .Other functions
+* <<_char,char()>>
 * <<_eval,eval()>>
 * <<_set,set()>>
-* <<_unset,unset()>>
 * <<_var,var()>>
 
 
@@ -1100,7 +1125,9 @@ Returns _true_ if the value type of _<expr>_ is boolean, false otherwise.
 `>>>` [blue]`isBool(true)` +
 [green]`true` +
 `>>>` [blue]`isBool(3==2)` +
-[green]`true`
+[green]`true` +
+`>>>` [blue]`isBool(3 + 2)` +
+[green]`false`
 
 ===== isDict()
 Syntax: `isDict(<expr>) -> bool` +
@@ -1178,7 +1205,7 @@ Returns _true_ if the value type of _<expr>_ is fraction or int, false otherwise
 
 ===== isString()
 Syntax: `isString(<expr>) -> bool` +
-Returns a boolean value , false otherwise.
+Returns _true_ if the value type of _<expr>_ is string, false otherwise.
 
 .Examples
 `>>>` [blue]`isString("ciao")` +
@@ -1190,7 +1217,7 @@ Returns a boolean value , false otherwise.
 
 ===== bool()
 Syntax: `bool(<expr>) -> bool` +
-Returns a _boolean_ value consisent to the value of the expression.
+Returns a _boolean_ value consisent with the value of the expression.
 
 .Examples
 `>>>` [blue]`bool(1)` +
@@ -1295,6 +1322,16 @@ Returns a _fraction_ value consistent with the value of the expression.
 `>>>` [blue]`fract(true)` +
 [green]`1:1`
 
+===== char()
+Syntax: `char(<intexpr>) -> string` +
+Returns the character whose ASCII (soon Unicode too) code point is specified by the integer expression.
+
+.Examples
+`>>>` [blue]`char(65)` +
+[green]`"A"` +
+`>>>` [blue]`char(97)` +
+[green]`"a"`
+
 ===== eval()
 Syntax: `eval(<string-expr>) -> any` +
 Computes and returns the value of the [.underline]#string# expression.
@@ -1308,12 +1345,12 @@ Syntax: +
  `{4sp}var(<string-expr>, <expr>) -> any` +
  `{4sp}var(<string-expr>) -> any`
 
-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.
+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.
 
 .Examples
 `>>>` [blue]`var("$x", 3+9)` +
 [green]`12` +
-`>>>` [blue]`var("$x")` +
+`>>>` [blue]`var("$"+"x")` +
 [green]`12` +
 `>>>` [blue]`var("gain%", var("$x"))` +
 [green]`12` +
@@ -1334,26 +1371,17 @@ It is equivalent to the first form of the var() function, but it is more explici
 `>>>` [blue]`var("$x")` +
 [green]`100` +
 
-===== unset()
-Syntax: +
- `{4sp}unset(<string-expr>) -> any`
-
-This function allows you to unset a variable whose name can include special characters. The parameter is the name of the variable to unset.
-
-.Examples
-`>>>` [blue]`unset("$x")` +
-[green]`nil` +
-`>>>` [blue]`var("$x")` +
-[red]`Eval Error: var(): unknown variable "$x"`
 
 ==== Module "fmt"
+#to-do#
 
 ===== print()
 
 ===== println()
 
 ==== Module "import"
-Module actiovation: +
+Module activation: +
+`{4sp}BUILTIN "import"`
 
 ===== _import()_
 Syntax: +
@@ -1364,6 +1392,8 @@ Loads the multi-expression contained in the specified source and returns its val
 ===== _importAll()_
 
 ==== Module "iterator"
+Module activation: +
+`{4sp}BUILTIN "iterator"`
 
 ===== run()
 Syntax: +
@@ -1372,6 +1402,9 @@ Syntax: +
 Iterates over the specified iterator and applies the specified operator to the current value of the iterator.
 
 ==== Module "math.arith"
+Module activation: +
+`{4sp}BUILTIN "math.arith"`
+
 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.
 
 * <<_add,add()>>
@@ -1421,13 +1454,12 @@ Same as <<_add,add()>> but returns the product of the values of the parameters.
 [green]`24`
 
 ==== Module "os.file"
+Module activation: +
+`{4sp}BUILTIN "os.file"`
+
 The "os.file" module provides functions for working with files.
 
-Activation: +
-`{4sp}builtin "os.file"`
-
-Currently available functions:
-
+.File related functions
 * <<_fileOpen,fileOpen()>>
 * <<_fileAppend,fileAppend()>>
 * <<_fileCreate,fileCreate()>>
@@ -1436,6 +1468,10 @@ Currently available functions:
 * <<_fileReadText,fileReadText()>>
 * <<_fileReadTextAll,fileReadTextAll()>>
 
+.Iterator functions for files
+* <<_fileByteIterator,fileByteIterator()>>
+* <<_fileLineIterator,fileLineIterator()>>
+
 More functions will be added in the future.
 
 ---
@@ -1447,6 +1483,10 @@ Syntax: +
 Returns a file handle for the specified file path. The file is opened in read-write mode. If the file does not exist, it is created.
 
 ===== fileAppend()
+Syntax: +
+`{4sp}fileAppend(<file-path>) -> any`
+
+Like <<_fileCreate,fileCreate()>> but write operations happen at the end of the file.
 
 ===== fileCreate()
 Syntax: +
@@ -1455,21 +1495,30 @@ Syntax: +
 Creates or truncates the named _<file-path>_. If the file already exists, it is truncated. If the file does not exist, it is created with mode 0o666 (before umask). The associated file descriptor has mode [O_RDWR]. The directory containing the file must already exist.
 
 ===== fileClose()
+#to-do#
 
 ===== fileWriteText()
+#to-do#
 
 ===== fileReadText()
+#to-do#
 
 ===== fileReadTextAll()
+#to-do#
+
+===== fileByteIterator()
+#to-do#
+
+===== fileLineIterator()
+#to-do#
 
 
 ==== Module "string"
+Module activation: +
+`{4sp}BUILTIN "string"`
+
 This module provides functions for working with strings.
 
-Activation: +
-`{4sp}builtin "string"`
-
-
 Currently available functions:
 
 * <<_strJoin,strJoin()>>

expr.go

@@ -1,16 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// expr.go
-package expr
-
-import (
-	kern "git.portale-stac.it/go-pkg/expr/kern"
-)
-
-// ----Expression interface
-type Expr interface {
-	kern.Typer
-	Eval(ctx kern.ExprContext) (result any, err error)
-	String() string
-}

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

@@ -1,387 +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"
-)
-
-// ---- 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 *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

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
@@ -11,14 +11,15 @@ 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/util"
 )
 
 func EvalString(ctx kern.ExprContext, source string) (result any, err error) {
-	var tree *ast
+	var tree *scan.Ast
 
 	r := strings.NewReader(source)
-	scanner := NewScanner(r, DefaultTranslations())
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
 	parser := NewParser()
 
 	if tree, err = parser.Parse(scanner); err == nil {
@@ -44,7 +45,7 @@ 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)
@@ -69,8 +70,8 @@ func EvalStringV(source string, args []Arg) (result any, err error) {
 }
 
 func EvalStream(ctx kern.ExprContext, r io.Reader) (result any, err error) {
-	var tree *ast
-	scanner := NewScanner(r, DefaultTranslations())
+	var tree *scan.Ast
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
 	parser := NewParser()
 
 	if tree, err = parser.Parse(scanner); err == nil {

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

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

iter-factory.go

@@ -1,14 +1,17 @@
-// 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"
 )
 
-func NewIterator(value any) (it kern.Iterator, err error) {
+func NewIterator(ctx kern.ExprContext, value any, ops []*scan.Term) (it kern.Iterator, err error) {
 	if value == nil {
 		return NewArrayIterator([]any{}), nil
 	}
@@ -21,9 +24,21 @@ func NewIterator(value any) (it kern.Iterator, err error) {
 	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 {
-	return &golangFunctor{f: f}
+func NewGolangFunctor(f FuncTemplate) *GolangFunctor {
+	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/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

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/dict-type.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-type.go

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

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

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

kern/formatter.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.
 
 // formatter.go

kern/fraction-type.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.
 
 // fraction-type.go
@@ -44,10 +44,11 @@ func MakeGeneratingFraction(s string) (f *FractionType, err error) {
 	if len(s) == 0 {
 		goto exit
 	}
-	if s[0] == '-' {
+	switch s[0] {
+	case '-':
 		sign = int64(-1)
 		s = s[1:]
-	} else if s[0] == '+' {
+	case '+':
 		s = s[1:]
 	}
 	//	if strings.HasSuffix(s, "()") {

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/linked-list.go

@@ -0,0 +1,273 @@
+// simple-list project slist.go
+package kern
+
+import (
+	"fmt"
+)
+
+type ListNode struct {
+	data any
+	next *ListNode
+}
+
+func (node *ListNode) Next() *ListNode {
+	return node.next
+}
+
+func (self *ListNode) Data() any {
+	return self.data
+}
+
+type LinkedList struct {
+	count uint32
+	first *ListNode
+	last  *ListNode
+}
+
+func NewLinkedList() (list *LinkedList) {
+	list = &LinkedList{0, nil, nil}
+	return
+}
+
+func (ls *LinkedList) Len() uint32 {
+	return ls.count
+}
+
+func (ls *LinkedList) Empty() bool {
+	return ls.count == 0
+}
+
+func (ls *LinkedList) PushFront(data any) *ListNode {
+	ls.first = &ListNode{data, ls.first}
+	if ls.last == nil {
+		ls.last = ls.first
+	}
+	ls.count++
+	return ls.first
+}
+
+func (ls *LinkedList) SeqPushFront(data any) (result *LinkedList) {
+	switch seq := data.(type) {
+	case Iterator:
+		result = ls.IterPushFront(seq)
+	default:
+		ls.PushFront(data)
+		result = ls
+	}
+	return
+}
+
+func (ls *LinkedList) IterPushFront(it Iterator) *LinkedList {
+	for item, err1 := it.Next(); err1 == nil; item, err1 = it.Next() {
+		ls.PushFront(item)
+	}
+	return ls
+}
+
+func (ls *LinkedList) PushBack(data any) (node *ListNode) {
+	node = &ListNode{data, nil}
+	if ls.last != nil {
+		ls.last.next = node
+	}
+	ls.last = node
+	if ls.first == nil {
+		ls.first = node
+	}
+	ls.count++
+	return
+}
+
+func (ls *LinkedList) SeqPushBack(data any) (result *LinkedList) {
+	switch seq := data.(type) {
+	case Iterator:
+		result = ls.IterPushBack(seq)
+	default:
+		ls.PushBack(data)
+		result = ls
+	}
+	return
+}
+
+func (ls *LinkedList) IterPushBack(it Iterator) *LinkedList {
+	for item, err1 := it.Next(); err1 == nil; item, err1 = it.Next() {
+		ls.PushBack(item)
+	}
+	return ls
+}
+
+func (ls *LinkedList) FirstNode() *ListNode {
+	return ls.first
+}
+
+func (ls *LinkedList) First() (data any, err error) {
+	if ls.first != nil {
+		data = ls.first.data
+	} else {
+		err = errorListEmpty()
+	}
+	return
+}
+
+func (ls *LinkedList) LastNode() *ListNode {
+	return ls.last
+}
+
+func (ls *LinkedList) Last() (data interface{}, err error) {
+	if ls.last != nil {
+		data = ls.last.data
+	} else {
+		err = errorListEmpty()
+	}
+	return
+}
+
+func (ls *LinkedList) NodeAt(index uint32) (node *ListNode, err error) {
+	if ls.count == 0 {
+		err = errorListEmpty()
+	} else if index > ls.count {
+		err = errorOutOfRange()
+	} else if index == ls.count-1 {
+		node = ls.last
+	} else {
+		current := ls.first
+		for pos := uint32(0); pos < index; pos++ {
+			current = current.next
+		}
+		node = current
+	}
+	return
+}
+
+func (ls *LinkedList) At(index uint32) (data interface{}, err error) {
+	node, err := ls.NodeAt(index)
+	if err == nil {
+		data = node.data
+	}
+	return
+}
+
+func (ls *LinkedList) Insert(index uint32, data interface{}) *ListNode {
+	var prev *ListNode
+
+	prev = nil
+	current := ls.first
+	for pos := uint32(0); current != nil && pos < index; pos++ {
+		prev = current
+		current = current.next
+	}
+
+	node := &ListNode{data, current}
+
+	if prev != nil {
+		prev.next = node
+	}
+
+	if ls.first == current {
+		ls.first = node
+	}
+	if node.next == nil {
+		ls.last = node
+	}
+	ls.count++
+	return node
+}
+
+func (ls *LinkedList) PushBackStringArray(items []string) {
+	for _, v := range items {
+		ls.PushBack(v)
+	}
+}
+
+// type TraverseOperator func(index uint32, elem interface{}, userData interface{}) (err error)
+
+// func (self *LinkedList) Traverse(op TraverseOperator, user_data interface{}) (err error) {
+// 	index := uint32(0)
+// 	for current := self.first; current != nil; current = current.next {
+// 		err = op(index, current.data, user_data)
+// 		if err != nil {
+// 			break
+// 		}
+// 		index++
+// 	}
+// 	return
+// }
+
+// func (self *LinkedList) Traverse2(observer Observer, abortOnError bool) (err error) {
+// 	index := uint32(0)
+// 	for current := self.first; current != nil; current = current.next {
+// 		err = observer.Observe(current, index)
+// 		if err != nil && abortOnError {
+// 			break
+// 		}
+// 		index++
+// 	}
+// 	return
+// }
+
+type EqualFunc func(current, target any) bool
+
+func (ls *LinkedList) FindFirst(eqFunc EqualFunc, targetData any) (targetNode *ListNode) {
+	for current := ls.first; current != nil && targetNode == nil; current = current.next {
+		if eqFunc(current.data, targetData) {
+			targetNode = current
+		}
+	}
+	return
+}
+
+func (ls *LinkedList) FindNext(eqFunc EqualFunc, startNode *ListNode) (targetNode *ListNode) {
+	if startNode != nil {
+		for current := startNode.next; current != nil && targetNode == nil; current = current.next {
+			if eqFunc(current.data, startNode.Data()) {
+				targetNode = current
+			}
+		}
+	}
+	return
+}
+
+// type DataFeeder func(user_data interface{}) interface{}
+// type NodeObserver func(node *ListNode, index uint32, userData interface{})
+
+// func (self *LinkedList) FeedTail(feeder DataFeeder, feederUserData interface{}, observer NodeObserver, observerUserData interface{}) (count uint32) {
+// 	count = 0
+// 	for item := feeder(feederUserData); item != nil; item = feeder(feederUserData) {
+// 		// fmt.Println("Item", count, item)
+// 		node := self.PushBack(item)
+// 		if observer != nil {
+// 			observer(node, count, observerUserData)
+// 		}
+// 		count++
+// 	}
+// 	return
+// }
+
+// func (self *LinkedList) FeedTail2(feeder Feeder, observer Observer, abortOnError bool) (count uint32, err error) {
+// 	count = 0
+// 	// item := feeder.Next()
+// 	for item, err1 := feeder.Next(); item != nil; item, err1 = feeder.Next() {
+// 		if err1 != nil {
+// 			if err == nil {
+// 				err = err1
+// 			}
+// 			if abortOnError {
+// 				break
+// 			}
+// 		}
+// 		// fmt.Println("Item", count, item)
+// 		node := self.PushBack(item)
+// 		if observer != nil {
+// 			observer.Observe(node, count)
+// 		}
+// 		count++
+// 	}
+// 	return
+// }
+
+func errorListEmpty() error {
+	return fmt.Errorf("List is empty")
+}
+
+func errorOutOfRange() error {
+	return fmt.Errorf("Out of range")
+}

kern/list-type.go

@@ -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-type.go
@@ -50,13 +50,13 @@ func ListFromStrings(stringList []string) (list *ListType) {
 	return
 }
 
-func (dict *ListType) ToString(opt FmtOpt) (s string) {
+func (ls *ListType) ToString(opt FmtOpt) (s string) {
 	indent := GetFormatIndent(opt)
 	flags := GetFormatFlags(opt)
 
 	var sb strings.Builder
 	sb.WriteByte('[')
-	if len(*dict) > 0 {
+	if len(*ls) > 0 {
 		innerOpt := MakeFormatOptions(flags, indent+1)
 		nest := strings.Repeat("  ", indent+1)
 
@@ -64,7 +64,7 @@ func (dict *ListType) ToString(opt FmtOpt) (s string) {
 			sb.WriteByte('\n')
 			sb.WriteString(nest)
 		}
-		for i, item := range []any(*dict) {
+		for i, item := range []any(*ls) {
 			if i > 0 {
 				if flags&MultiLine != 0 {
 					sb.WriteString(",\n")
@@ -96,11 +96,11 @@ func (dict *ListType) ToString(opt FmtOpt) (s string) {
 	return
 }
 
-func (dict *ListType) String() string {
-	return dict.ToString(0)
+func (ls *ListType) String() string {
+	return ls.ToString(0)
 }
 
-func (dict *ListType) TypeName() string {
+func (ls *ListType) TypeName() string {
 	return "list"
 }
 

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

lib-ext-darwin.go

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

lib-ext-linux.go

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

lib-ext-windows.go

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

list-iterator.go

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

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
@@ -6,23 +6,24 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- dict term
-func newDictTerm(args map[any]*term) *term {
-	return &term{
-		tk:       *NewValueToken(0, 0, SymDict, "{}", args),
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalDict,
+func newDictTerm(args map[any]*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(0, 0, scan.SymDict, "{}", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalDict,
 	}
 }
 
 // -------- dict func
-func evalDict(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	dict, _ := opTerm.value().(map[any]*term)
+func evalDict(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	dict, _ := opTerm.Value().(map[any]*scan.Term)
 	items := make(kern.DictType, len(dict))
 	for key, tree := range dict {
 		var param any

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
@@ -8,27 +8,28 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- expr term
-func newExprTerm(root *term) *term {
-	tk := NewValueToken(root.tk.row, root.tk.col, SymExpression, root.Source(), root)
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalExpr,
+func newExprTerm(root *scan.Term) *scan.Term {
+	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymExpression, root.Source(), root)
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalExpr,
 	}
 }
 
 // -------- eval expr
-func evalExpr(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	if ast, ok := opTerm.value().(*term); ok {
+func evalExpr(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	if ast, ok := opTerm.Value().(*scan.Term); ok {
 		v, err = ast.Compute(ctx)
 	} else {
-		err = fmt.Errorf("expression expected, got %T", opTerm.value())
+		err = fmt.Errorf("expression expected, got %T", opTerm.Value())
 	}
 	return
 }

operand-func.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-func.go
@@ -8,31 +8,32 @@ import (
 	"errors"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- function call term
-func newFuncCallTerm(tk *Token, args []*term) *term {
-	var pos termPosition = posLeaf
+func newFuncCallTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	var pos scan.TermPosition = scan.PosLeaf
 	if len(args) > 0 {
-		pos = posMultifix
+		pos = scan.PosMultifix
 	}
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: args,
-		position: pos,
-		priority: priValue,
-		evalFunc: evalFuncCall,
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: args,
+		Position: pos,
+		Priority: scan.PriValue,
+		EvalFunc: evalFuncCall,
 	}
 }
 
 // -------- eval func call
 // func _evalFuncCall(ctx ExprContext, opTerm *term) (v any, err error) {
-// 	name, _ := opTerm.tk.Value.(string)
-// 	params := make([]any, len(opTerm.children), len(opTerm.children)+5)
-// 	for i, tree := range opTerm.children {
+// 	name, _ := opTerm.Tk.Value.(string)
+// 	params := make([]any, len(opTerm.Children), len(opTerm.Children)+5)
+// 	for i, tree := range opTerm.Children {
 // 		var param any
-// 		if param, err = tree.compute(ctx); err != nil {
+// 		if param, err = tree.Compute(ctx); err != nil {
 // 			break
 // 		}
 // 		params[i] = param
@@ -44,39 +45,39 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 // 	return
 // }
 
-func evalFuncCall(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	name, _ := opTerm.tk.Value.(string)
+func evalFuncCall(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	name, _ := opTerm.Tk.Value.(string)
 	v, err = kern.CallFunctionByTerm(ctx, name, opTerm)
 	return
 }
 
 // -------- function definition term
-func newFuncDefTerm(tk *Token, args []*term) *term {
-	return &term{
-		tk:       *tk, // value is the expression body
-		parent:   nil,
-		children: args, // function params
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalFuncDef,
+func newFuncDefTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk, // value is the expression body
+		Parent:   nil,
+		Children: args, // function params
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalFuncDef,
 	}
 }
 
 // -------- eval func def
-func evalFuncDef(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	bodySpec := opTerm.value()
-	if ast, ok := bodySpec.(*ast); ok {
-		paramList := make([]kern.ExprFuncParam, 0, len(opTerm.children))
-		for _, param := range opTerm.children {
+func evalFuncDef(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	bodySpec := opTerm.Value()
+	if ast, ok := bodySpec.(*scan.Ast); ok {
+		paramList := make([]kern.ExprFuncParam, 0, len(opTerm.Children))
+		for _, param := range opTerm.Children {
 			var defValue any
-			flags := paramFlags(0)
-			if len(param.children) > 0 {
-				flags |= PfDefault
-				if defValue, err = param.children[0].Compute(ctx); err != nil {
+			flags := kern.FuncParamFlags(0)
+			if len(param.Children) > 0 {
+				flags |= kern.PfDefault
+				if defValue, err = param.Children[0].Compute(ctx); err != nil {
 					return
 				}
 			}
-			info := NewFuncParamFlagDef(param.Source(), flags, defValue)
+			info := kern.NewFuncParamFlagDef(param.Source(), flags, defValue)
 			paramList = append(paramList, info)
 		}
 		v = newExprFunctor(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
@@ -9,25 +9,26 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- iterator term
 
-func newIteratorTerm(tk *Token, args []*term) *term {
-	tk.Sym = SymIterator
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: args,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalIterator,
+func newIteratorTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
+	tk.Sym = scan.SymIterator
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: args,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalIterator,
 	}
 }
 
 // -------- eval iterator
 
-func evalTermArray(ctx kern.ExprContext, terms []*term) (values []any, err error) {
+func evalTermArray(ctx kern.ExprContext, terms []*scan.Term) (values []any, err error) {
 	values = make([]any, len(terms))
 	for i, t := range terms {
 		var value any
@@ -40,17 +41,17 @@ func evalTermArray(ctx kern.ExprContext, terms []*term) (values []any, err error
 	return
 }
 
-func evalFirstChild(ctx kern.ExprContext, iteratorTerm *term) (value any, err error) {
-	if len(iteratorTerm.children) < 1 || iteratorTerm.children[0] == nil {
+func evalFirstChild(ctx kern.ExprContext, iteratorTerm *scan.Term) (value any, err error) {
+	if len(iteratorTerm.Children) < 1 || iteratorTerm.Children[0] == nil {
 		err = iteratorTerm.Errorf("missing the data-source parameter")
 		return
 	}
 
-	value, err = iteratorTerm.children[0].Compute(ctx)
+	value, err = iteratorTerm.Children[0].Compute(ctx)
 	return
 }
 
-func getDataSourceDict(iteratorTerm *term, firstChildValue any) (ds map[string]kern.Functor, err error) {
+func getDataSourceDict(iteratorTerm *scan.Term, firstChildValue any) (ds map[string]kern.Functor, err error) {
 	if dictAny, ok := firstChildValue.(*kern.DictType); ok {
 		requiredFields := []string{kern.NextName}
 		fieldsMask := 0b1
@@ -74,13 +75,13 @@ func getDataSourceDict(iteratorTerm *term, firstChildValue any) (ds map[string]k
 					missingFields = append(missingFields, field)
 				}
 			}
-			err = iteratorTerm.children[0].Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
+			err = iteratorTerm.Children[0].Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
 		}
 	}
 	return
 }
 
-func evalIterator(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalIterator(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var firstChildValue any
 	var ds map[string]kern.Functor
 
@@ -100,8 +101,8 @@ func evalIterator(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 			if initFunc, exists := ds[kern.InitName]; exists && initFunc != nil {
 				var args []any
 				var resource any
-				if len(opTerm.children) > 1 {
-					if args, err = evalTermArray(ctx, opTerm.children[1:]); err != nil {
+				if len(opTerm.Children) > 1 {
+					if args, err = evalTermArray(ctx, opTerm.Children[1:]); err != nil {
 						return
 					}
 				} else {
@@ -124,33 +125,64 @@ func evalIterator(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		} else {
 			if dictIt, ok := firstChildValue.(*kern.DictType); ok {
 				var args []any
-				if args, err = evalSibling(ctx, opTerm.children, nil); err == nil {
+				if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
 					v, err = NewDictIterator(dictIt, args)
 				}
 			} else {
-				err = opTerm.children[0].Errorf("the data-source must be a dictionary")
+				err = opTerm.Children[0].Errorf("the data-source must be a dictionary")
 			}
 		}
 	} else if list, ok := firstChildValue.(*kern.ListType); ok {
 		var args []any
-		if args, err = evalSibling(ctx, opTerm.children, nil); err == nil {
+		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
 			v = NewListIterator(list, args)
 		}
 	} else if intVal, ok := firstChildValue.(int64); ok {
 		var args []any
-		if args, err = evalSibling(ctx, opTerm.children, intVal); err == nil {
+		if args, err = evalSiblings(ctx, opTerm.Children, intVal); err == nil {
 			v, err = NewIntIterator(args)
 		}
+	} else if it, ok := firstChildValue.(kern.Iterator); ok {
+		v, err = NewIterIter(it, ctx, opTerm.Children[1:])
 	} else {
-		var list []any
-		if list, err = evalSibling(ctx, opTerm.children, firstChildValue); err == nil {
-			v = NewArrayIterator(list)
+		var siblings []any
+		if siblings, err = evalSiblings(ctx, opTerm.Children, firstChildValue); err == nil {
+			v = NewArrayIterator(siblings)
 		}
 	}
 	return
 }
 
-func evalSibling(ctx kern.ExprContext, terms []*term, firstChildValue any) (list []any, err error) {
+// func evalIterIter(ctx kern.ExprContext, firstChildValue any, siblings []any) (v any, err error) {
+// 	var op kern.Functor
+// 	var args map[string]any
+
+// 	if it, ok := firstChildValue.(kern.Iterator); ok {
+// 		if len(siblings) > 1 {
+// 			if op, ok = siblings[1].(kern.Functor); ok {
+// 				args = make(map[string]any, len(siblings)-2)
+// 				for i, arg := range siblings[2:] {
+// 					switch a := arg.(type) {
+// 					case *kern.DictType:
+// 						for keyAny, item := range *a {
+// 							if key, ok := keyAny.(string); ok {
+// 								args[key] = item
+// 							}
+// 						}
+// 					default:
+// 						args["arg"+strconv.Itoa(i+1)] = arg
+// 					}
+// 				}
+// 			} else if op == nil {
+// 				return nil, fmt.Errorf("the first sibling parameter must be a functor to be used as operation for the iterator")
+// 			}
+// 		}
+// 		v, err = NewIterIter(it, ctx, op, args)
+// 	}
+// 	return
+// }
+
+func evalSiblings(ctx kern.ExprContext, terms []*scan.Term, firstChildValue any) (list []any, err error) {
 	items := make([]any, 0, len(terms))
 	for i, tree := range terms {
 		var param any

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
@@ -6,27 +6,28 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- list term
-func newListTermA(args ...*term) *term {
+func newListTermA(args ...*scan.Term) *scan.Term {
 	return newListTerm(0, 0, args)
 }
 
-func newListTerm(row, col int, args []*term) *term {
-	return &term{
-		tk:       *NewValueToken(row, col, SymList, "[]", args),
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalList,
+func newListTerm(row, col int, args []*scan.Term) *scan.Term {
+	return &scan.Term{
+		Tk:       *scan.NewValueToken(row, col, scan.SymList, "[]", args),
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalList,
 	}
 }
 
 // -------- list func
-func evalList(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	list, _ := opTerm.value().([]*term)
+func evalList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	list, _ := opTerm.Value().([]*scan.Term)
 	items := make(kern.ListType, len(list))
 	for i, tree := range list {
 		var param any

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
@@ -6,32 +6,33 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- literal term
-func newLiteralTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalLiteral,
+func newLiteralTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalLiteral,
 	}
 }
 
 // -------- eval func
-func evalLiteral(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	v = opTerm.tk.Value
+func evalLiteral(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	v = opTerm.Tk.Value
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymString, newLiteralTerm)
-	registerTermConstructor(SymInteger, newLiteralTerm)
-	registerTermConstructor(SymFloat, newLiteralTerm)
-	registerTermConstructor(SymFraction, newLiteralTerm)
-	registerTermConstructor(SymBool, newLiteralTerm)
-	registerTermConstructor(SymKwNil, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymString, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymInteger, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFloat, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymFraction, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymBool, newLiteralTerm)
+	scan.RegisterTermConstructor(scan.SymKwNil, newLiteralTerm)
 }

operand-selector-case.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-selector-case.go
@@ -9,19 +9,20 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- selector case term
 
 type selectorCase struct {
-	filterList *term
-	caseExpr   Expr
+	filterList *scan.Term
+	caseExpr   kern.Expr
 }
 
 func (sc *selectorCase) String() string {
 	var sb strings.Builder
 	if sc.filterList != nil {
-		sc.filterList.toString(&sb)
+		sc.filterList.ToString(&sb)
 		sb.WriteByte(' ')
 	}
 	sb.WriteByte('{')
@@ -30,23 +31,23 @@ func (sc *selectorCase) String() string {
 	return sb.String()
 }
 
-func newSelectorCaseTerm(row, col int, filterList *term, caseExpr Expr) *term {
-	tk := NewValueToken(row, col, SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalSelectorCase,
+func newSelectorCaseTerm(row, col int, filterList *scan.Term, caseExpr kern.Expr) *scan.Term {
+	tk := scan.NewValueToken(row, col, scan.SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalSelectorCase,
 	}
 }
 
 // -------- eval selector case
-func evalSelectorCase(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalSelectorCase(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var ok bool
-	if v, ok = opTerm.value().(*selectorCase); !ok {
-		err = fmt.Errorf("selector-case expected, got %T", opTerm.value())
+	if v, ok = opTerm.Value().(*selectorCase); !ok {
+		err = fmt.Errorf("selector-case expected, got %T", opTerm.Value())
 	}
 	return
 }

operand-var.go

@@ -1,4 +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
@@ -8,24 +8,25 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- variable term
-func newVarTerm(tk *Token) *term {
-	t := &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalVar,
+func newVarTerm(tk *scan.Token) *scan.Term {
+	t := &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalVar,
 	}
-	t.tk.Sym = SymVariable
+	t.Tk.Sym = scan.SymVariable
 	return t
 }
 
 // -------- eval func
-func evalVar(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalVar(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var exists bool
 	name := opTerm.Source()
 	if v, exists = ctx.GetVar(name); !exists {
@@ -40,5 +41,5 @@ func evalVar(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymIdentifier, newVarTerm)
+	scan.RegisterTermConstructor(scan.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
@@ -6,22 +6,23 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
 //-------- assign term
 
-func newAssignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priAssign,
-		evalFunc: evalAssign,
+func newAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAssign,
+		EvalFunc: evalAssign,
 	}
 }
 
-func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *term, value any) (err error) {
+func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term, value any) (err error) {
 	var collectionValue, keyListValue, keyValue any
 	var keyList *kern.ListType
 	var ok bool
@@ -56,32 +57,32 @@ func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *ter
 	return
 }
 
-func assignValue(ctx kern.ExprContext, leftTerm *term, v any) (err error) {
-	if leftTerm.symbol() == SymIndex {
-		err = assignCollectionItem(ctx, leftTerm.children[0], leftTerm.children[1], v)
+func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any) (err error) {
+	if leftTerm.Symbol() == scan.SymIndex {
+		err = assignCollectionItem(ctx, leftTerm.Children[0], leftTerm.Children[1], v)
 	} else {
 		ctx.UnsafeSetVar(leftTerm.Source(), v)
 	}
 	return
 }
 
-func evalAssign(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	if err = opTerm.checkOperands(); err != nil {
+func evalAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	leftSym := leftTerm.symbol()
-	if leftSym != SymVariable && leftSym != SymIndex {
-		err = leftTerm.tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.tk.source)
+	leftTerm := opTerm.Children[0]
+	leftSym := leftTerm.Symbol()
+	if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
 
-	rightChild := opTerm.children[1]
+	rightChild := opTerm.Children[1]
 
 	if v, err = rightChild.Compute(ctx); err == nil {
 		if functor, ok := v.(kern.Functor); ok {
-			if leftSym == SymVariable {
+			if leftSym == scan.SymVariable {
 				if info := functor.GetFunc(); info != nil {
 					ctx.RegisterFunc(leftTerm.Source(), info.Functor(), info.ReturnType(), info.Params())
 				} else if funcDef, ok := functor.(*exprFunctor); ok {
@@ -106,17 +107,17 @@ func evalAssign(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- assign term
 
-func newOpAssignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priAssign,
-		evalFunc: evalOpAssign,
+func newOpAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAssign,
+		EvalFunc: evalOpAssign,
 	}
 }
 
-func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *term) (value any, err error) {
+func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term) (value any, err error) {
 	var collectionValue, keyListValue, keyValue any
 	var keyList *kern.ListType
 	var ok bool
@@ -151,52 +152,52 @@ func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *t
 	return
 }
 
-func getAssignValue(ctx kern.ExprContext, leftTerm *term) (value any, err error) {
-	if leftTerm.symbol() == SymIndex {
-		value, err = getCollectionItemValue(ctx, leftTerm.children[0], leftTerm.children[1])
+func getAssignValue(ctx kern.ExprContext, leftTerm *scan.Term) (value any, err error) {
+	if leftTerm.Symbol() == scan.SymIndex {
+		value, err = getCollectionItemValue(ctx, leftTerm.Children[0], leftTerm.Children[1])
 	} else {
 		value, _ = ctx.GetVar(leftTerm.Source())
 	}
 	return
 }
 
-func evalOpAssign(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue, leftValue any
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	leftSym := leftTerm.symbol()
-	if leftSym != SymVariable && leftSym != SymIndex {
-		err = leftTerm.tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.tk.source)
+	leftTerm := opTerm.Children[0]
+	leftSym := leftTerm.Symbol()
+	if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
 
-	rightChild := opTerm.children[1]
+	rightChild := opTerm.Children[1]
 
 	if rightValue, err = rightChild.Compute(ctx); err == nil {
 		if leftValue, err = getAssignValue(ctx, leftTerm); err == nil {
-			switch opTerm.symbol() {
-			case SymPlusEqual:
+			switch opTerm.Symbol() {
+			case scan.SymPlusEqual:
 				v, err = sumValues(opTerm, leftValue, rightValue)
-			case SymMinusEqual:
+			case scan.SymMinusEqual:
 				v, err = diffValues(opTerm, leftValue, rightValue)
-			case SymStarEqual:
+			case scan.SymStarEqual:
 				v, err = mulValues(opTerm, leftValue, rightValue)
-			case SymSlashEqual:
+			case scan.SymSlashEqual:
 				v, err = divValues(opTerm, leftValue, rightValue)
-			case SymPercEqual:
+			case scan.SymPercEqual:
 				v, err = remainderValues(opTerm, leftValue, rightValue)
-			case SymAmpersandEqual:
+			case scan.SymAmpersandEqual:
 				v, err = bitwiseAnd(opTerm, leftValue, rightValue)
-			case SymVertBarEqual:
+			case scan.SymVertBarEqual:
 				v, err = bitwiseOr(opTerm, leftValue, rightValue)
-			case SymCaretEqual:
+			case scan.SymCaretEqual:
 				v, err = bitwiseXor(opTerm, leftValue, rightValue)
-			case SymDoubleLessEqual:
+			case scan.SymDoubleLessEqual:
 				v, err = bitLeftShift(opTerm, leftValue, rightValue)
-			case SymDoubleGreaterEqual:
+			case scan.SymDoubleGreaterEqual:
 				v, err = bitRightShift(opTerm, leftValue, rightValue)
 			default:
 				err = opTerm.Errorf("unsupported assign operator %q", opTerm.Source())
@@ -211,15 +212,15 @@ func evalOpAssign(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymEqual, newAssignTerm)
-	registerTermConstructor(SymPlusEqual, newOpAssignTerm)
-	registerTermConstructor(SymMinusEqual, newOpAssignTerm)
-	registerTermConstructor(SymStarEqual, newOpAssignTerm)
-	registerTermConstructor(SymSlashEqual, newOpAssignTerm)
-	registerTermConstructor(SymPercEqual, newOpAssignTerm)
-	registerTermConstructor(SymDoubleLessEqual, newOpAssignTerm)
-	registerTermConstructor(SymDoubleGreaterEqual, newOpAssignTerm)
-	registerTermConstructor(SymAmpersandEqual, newOpAssignTerm)
-	registerTermConstructor(SymVertBarEqual, newOpAssignTerm)
-	registerTermConstructor(SymCaretEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymEqual, newAssignTerm)
+	scan.RegisterTermConstructor(scan.SymPlusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymMinusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymStarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymSlashEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymPercEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleLessEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleGreaterEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymAmpersandEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymVertBarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(scan.SymCaretEqual, newOpAssignTerm)
 }

operator-bitwise.go

@@ -1,4 +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
@@ -6,24 +6,25 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- Bitwise NOT term
 
-func newBitwiseNotTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priBitwiseNot,
-		evalFunc: evalBitwiseNot,
+func newBitwiseNotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriBitwiseNot,
+		EvalFunc: evalBitwiseNot,
 	}
 }
 
-func evalBitwiseNot(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var value any
 
-	if value, err = opTerm.evalPrefix(ctx); err != nil {
+	if value, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
@@ -31,24 +32,24 @@ func evalBitwiseNot(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		i, _ := value.(int64)
 		v = ^i
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(value)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(value)
 	}
 	return
 }
 
 //-------- Bitwise AND term
 
-func newBitwiseAndTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBitwiseAnd,
-		evalFunc: evalBitwiseAnd,
+func newBitwiseAndTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBitwiseAnd,
+		EvalFunc: evalBitwiseAnd,
 	}
 }
 
-func bitwiseAnd(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitwiseAnd(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	var leftInt, rightInt int64
 	var lok, rok bool
 
@@ -58,15 +59,15 @@ func bitwiseAnd(opTerm *term, leftValue, rightValue any) (v any, err error) {
 	if lok && rok {
 		v = leftInt & rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalBitwiseAnd(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseAnd(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 	v, err = bitwiseAnd(opTerm, leftValue, rightValue)
@@ -75,17 +76,17 @@ func evalBitwiseAnd(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- Bitwise OR term
 
-func newBitwiseOrTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBitwiseOr,
-		evalFunc: evalBitwiseOr,
+func newBitwiseOrTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBitwiseOr,
+		EvalFunc: evalBitwiseOr,
 	}
 }
 
-func bitwiseOr(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitwiseOr(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	var leftInt, rightInt int64
 	var lok, rok bool
 
@@ -95,15 +96,15 @@ func bitwiseOr(opTerm *term, leftValue, rightValue any) (v any, err error) {
 	if lok && rok {
 		v = leftInt | rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalBitwiseOr(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseOr(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -113,17 +114,17 @@ func evalBitwiseOr(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- Bitwise XOR term
 
-func newBitwiseXorTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBitwiseOr,
-		evalFunc: evalBitwiseXor,
+func newBitwiseXorTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBitwiseXor,
+		EvalFunc: evalBitwiseXor,
 	}
 }
 
-func bitwiseXor(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitwiseXor(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	var leftInt, rightInt int64
 	var lok, rok bool
 
@@ -133,15 +134,15 @@ func bitwiseXor(opTerm *term, leftValue, rightValue any) (v any, err error) {
 	if lok && rok {
 		v = leftInt ^ rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalBitwiseXor(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalBitwiseXor(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -151,8 +152,8 @@ func evalBitwiseXor(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymTilde, newBitwiseNotTerm)
-	registerTermConstructor(SymAmpersand, newBitwiseAndTerm)
-	registerTermConstructor(SymVertBar, newBitwiseOrTerm)
-	registerTermConstructor(SymCaret, newBitwiseXorTerm)
+	scan.RegisterTermConstructor(scan.SymTilde, newBitwiseNotTerm)
+	scan.RegisterTermConstructor(scan.SymAmpersand, newBitwiseAndTerm)
+	scan.RegisterTermConstructor(scan.SymVertBar, newBitwiseOrTerm)
+	scan.RegisterTermConstructor(scan.SymCaret, newBitwiseXorTerm)
 }

operator-bool.go

@@ -1,4 +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
@@ -8,48 +8,49 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- NOT term
 
-func newNotTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priNot,
-		evalFunc: evalNot,
+func newNotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriNot,
+		EvalFunc: evalNot,
 	}
 }
 
-func evalNot(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if rightValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if rightValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	if b, ok := kern.ToBool(rightValue); ok {
 		v = !b
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(rightValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
 	}
 	return
 }
 
 //-------- AND term
 
-func newAndTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priAnd,
-		evalFunc: evalAnd,
+func newAndTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriAnd,
+		EvalFunc: evalAnd,
 	}
 }
 
-func evalAnd(ctx kern.ExprContext, self *term) (v any, err error) {
+func evalAnd(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
 		v, err = evalAndWithShortcut(ctx, self)
 	} else {
@@ -58,12 +59,12 @@ func evalAnd(ctx kern.ExprContext, self *term) (v any, err error) {
 	return
 }
 
-func evalAndWithoutShortcut(ctx kern.ExprContext, self *term) (v any, err error) {
+func evalAndWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var leftBool, rightBool bool
 	var lok, rok bool
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = self.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -73,33 +74,33 @@ func evalAndWithoutShortcut(ctx kern.ExprContext, self *term) (v any, err error)
 	if lok && rok {
 		v = leftBool && rightBool
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = self.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalAndWithShortcut(ctx kern.ExprContext, self *term) (v any, err error) {
+func evalAndWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if err = self.checkOperands(); err != nil {
+	if err = self.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = self.children[0].Compute(ctx); err != nil {
+	if leftValue, err = self.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
 	if leftBool, lok := kern.ToBool(leftValue); !lok {
 		// err = fmt.Errorf("got %s as left operand type of 'AND' operator, it must be bool", expr.TypeName(leftValue))
 		// return
-		err = self.errIncompatibleType(leftValue, "left")
+		err = self.ErrIncompatibleType(leftValue, "left")
 	} else if !leftBool {
 		v = false
-	} else if rightValue, err = self.children[1].Compute(ctx); err == nil {
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
 		if rightBool, rok := kern.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
-			err = self.errIncompatibleTypes(leftValue, rightValue)
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	}
 	return
@@ -107,17 +108,17 @@ func evalAndWithShortcut(ctx kern.ExprContext, self *term) (v any, err error) {
 
 //-------- OR term
 
-func newOrTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priOr,
-		evalFunc: evalOr,
+func newOrTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriOr,
+		EvalFunc: evalOr,
 	}
 }
 
-func evalOr(ctx kern.ExprContext, self *term) (v any, err error) {
+func evalOr(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	if kern.CtrlIsEnabled(ctx, kern.ControlBoolShortcut) {
 		v, err = evalOrWithShortcut(ctx, self)
 	} else {
@@ -126,12 +127,12 @@ func evalOr(ctx kern.ExprContext, self *term) (v any, err error) {
 	return
 }
 
-func evalOrWithoutShortcut(ctx kern.ExprContext, self *term) (v any, err error) {
+func evalOrWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var leftBool, rightBool bool
 	var lok, rok bool
 
-	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = self.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -141,19 +142,19 @@ func evalOrWithoutShortcut(ctx kern.ExprContext, self *term) (v any, err error)
 	if lok && rok {
 		v = leftBool || rightBool
 	} else {
-		err = self.errIncompatibleTypes(leftValue, rightValue)
+		err = self.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalOrWithShortcut(ctx kern.ExprContext, self *term) (v any, err error) {
+func evalOrWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if err = self.checkOperands(); err != nil {
+	if err = self.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = self.children[0].Compute(ctx); err != nil {
+	if leftValue, err = self.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
@@ -162,11 +163,11 @@ func evalOrWithShortcut(ctx kern.ExprContext, self *term) (v any, err error) {
 		return
 	} else if leftBool {
 		v = true
-	} else if rightValue, err = self.children[1].Compute(ctx); err == nil {
+	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
 		if rightBool, rok := kern.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
-			err = self.errIncompatibleTypes(leftValue, rightValue)
+			err = self.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	}
 	return
@@ -174,7 +175,7 @@ func evalOrWithShortcut(ctx kern.ExprContext, self *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymNot, newNotTerm)
-	registerTermConstructor(SymAnd, newAndTerm)
-	registerTermConstructor(SymOr, newOrTerm)
+	scan.RegisterTermConstructor(scan.SymNot, newNotTerm)
+	scan.RegisterTermConstructor(scan.SymAnd, newAndTerm)
+	scan.RegisterTermConstructor(scan.SymOr, newOrTerm)
 }

operator-builtin.go

@@ -1,4 +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
@@ -8,24 +8,25 @@ import (
 	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- builtin term
 
-func newBuiltinTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalBuiltin,
+func newBuiltinTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalBuiltin,
 	}
 }
 
-func evalBuiltin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
@@ -36,7 +37,7 @@ func evalBuiltin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 	} 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() {
@@ -64,5 +65,5 @@ func evalBuiltin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwBuiltin, newBuiltinTerm)
+	scan.RegisterTermConstructor(scan.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
@@ -6,26 +6,27 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- but term
 
-func newButTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBut,
-		evalFunc: evalBut,
+func newButTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBut,
+		EvalFunc: evalBut,
 	}
 }
 
-func evalBut(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	_, v, err = opTerm.evalInfix(ctx)
+func evalBut(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	_, v, err = opTerm.EvalInfix(ctx)
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymKwBut, newButTerm)
+	scan.RegisterTermConstructor(scan.SymKwBut, newButTerm)
 }

operator-cat.go

@@ -0,0 +1,151 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-cat.go
+package expr
+
+import (
+	"fmt"
+	"io"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+)
+
+//-------- cat term
+
+func newCatTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalCat,
+	}
+}
+
+func evalCat(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+	var itLeft, itRight kern.Iterator
+	// var item any
+	var ok bool
+
+	if err = opTerm.CheckOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
+		return
+	}
+
+	if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
+		return
+	}
+
+	if itLeft, ok = leftValue.(kern.Iterator); !ok {
+		if itLeft, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of JOIN must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
+	}
+
+	if itRight, ok = rightValue.(kern.Iterator); !ok {
+		if itRight, err = NewIterator(ctx, rightValue, nil); err != nil {
+			return nil, fmt.Errorf("right operand of JOIN must be an iterable data-source; got %s", kern.TypeName(rightValue))
+		}
+	}
+
+	// values := kern.NewListA()
+	// for _, it := range []kern.Iterator{itLeft, itRight} {
+	// 	for item, err = it.Next(); err == nil; item, err = it.Next() {
+	// 		values.AppendItem(item)
+	// 	}
+	// }
+	// if err == io.EOF {
+	// 	err = nil
+	// }
+	// v = values
+	v = newCatIterator(itLeft, itRight)
+	return
+}
+
+const catIteratorType = "cat"
+
+type catIterator struct {
+	kern.IteratorBase
+	itLeft    kern.Iterator
+	itRight   kern.Iterator
+	itCurrent kern.Iterator
+}
+
+func newCatIterator(itLeft, itRight kern.Iterator) (it *catIterator) {
+	it = &catIterator{
+		IteratorBase: kern.IteratorBase{},
+		itLeft:       itLeft,
+		itRight:      itRight,
+		itCurrent:    itLeft,
+	}
+	it.Reset()
+	return
+}
+
+func (it *catIterator) TypeName() string {
+	return catIteratorType
+}
+
+func (it *catIterator) String() string {
+	return fmt.Sprintf("$(%s %s %s)", it.itLeft, catIteratorType, it.itRight)
+}
+
+func (it *catIterator) Next() (item any, err error) {
+	if it.itCurrent == nil {
+		err = io.EOF
+	} else {
+		if item, err = it.itCurrent.Next(); err == nil {
+			it.Increment()
+		} else if err == io.EOF {
+			if it.itCurrent == it.itLeft {
+				it.itCurrent = it.itRight
+			} else {
+				return
+			}
+			if item, err = it.itCurrent.Next(); err == nil {
+				it.Increment()
+			} else {
+				it.itCurrent = nil
+			}
+		}
+	}
+	it.SetCurrent(item)
+	return
+}
+
+// func (it *catIterator) Reset() (err error) {
+// 	err = it.itLeft.Reset()
+// 	it.IteratorBase.Reset()
+// 	return
+// }
+
+func (it *catIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	// case kern.ResetName:
+	// 	err = it.Reset()
+	// case kern.CleanName:
+	// 	err = it.Clean()
+	case kern.IndexName:
+		v = it.Index()
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.Count()
+	default:
+		err = kern.ErrNoOperation(name)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwCat, newCatTerm)
+}

operator-context.go

@@ -1,37 +1,42 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-context-value.go
 package expr
 
 import (
+	"io"
+
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- context term
 
-func newContextTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priIncDec,
-		evalFunc: evalContextValue,
+func newContextTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalContextValue,
 	}
 }
 
-func evalContextValue(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-
 	var sourceCtx kern.ExprContext
-	if len(opTerm.children) == 0 {
+
+	if len(opTerm.Children) == 0 {
 		sourceCtx = ctx
-	} else if opTerm.children[0].symbol() == SymVariable && opTerm.children[0].Source() == "global" {
+	} else if opTerm.Children[0].Symbol() == scan.SymVariable && opTerm.Children[0].Source() == "global" {
 		sourceCtx = ctx.GetGlobal()
-	} else if childValue, err = opTerm.evalPrefix(ctx); err == nil {
+	} else if childValue, err = opTerm.EvalPrefix(ctx); err == nil {
 		if dc, ok := childValue.(*dataCursor); ok {
 			sourceCtx = dc.ctx
 		}
+	} else {
+		return
 	}
 
 	if sourceCtx != nil {
@@ -52,13 +57,27 @@ func evalContextValue(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 			}
 			v = d
 		}
+	} else if childValue != nil {
+		if it, ok := childValue.(kern.Iterator); ok {
+			var item any
+			values := kern.NewListA()
+			for item, err = it.Next(); err == nil; item, err = it.Next() {
+				values.AppendItem(item)
+			}
+			if err == io.EOF {
+				err = nil
+				v = values
+			}
+		} else {
+			err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
+		}
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleDollar, newContextTerm)
+	scan.RegisterTermConstructor(scan.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
@@ -6,26 +6,27 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- export all term
 
-func newExportAllTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalExportAll,
+func newExportAllTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: nil,
+		Position: scan.PosLeaf,
+		Priority: scan.PriValue,
+		EvalFunc: evalExportAll,
 	}
 }
 
-func evalExportAll(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalExportAll(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	CtrlEnable(ctx, kern.ControlExportAll)
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleAt, newExportAllTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleAt, newExportAllTerm)
 }

operator-default.go

@@ -1,4 +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
@@ -6,29 +6,30 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- default term
 
-func newDefaultTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDefault,
-		evalFunc: evalDefault,
+func newDefaultTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalDefault,
 	}
 }
 
-func evalDefault(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	if leftTerm.tk.Sym != SymVariable {
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -36,7 +37,7 @@ func evalDefault(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists {
 		v = leftValue
-	} else if rightValue, err = opTerm.children[1].Compute(ctx); err == nil {
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 		v = rightValue
 	}
 	return
@@ -44,32 +45,32 @@ func evalDefault(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- alternate term
 
-func newAlternateTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDefault,
-		evalFunc: evalAlternate,
+func newAlternateTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalAlternate,
 	}
 }
 
-func evalAlternate(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalAlternate(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	if leftTerm.tk.Sym != SymVariable {
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
 	}
 
 	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists && leftValue != nil {
-		if rightValue, err = opTerm.children[1].Compute(ctx); err == nil {
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 			v = rightValue
 		}
 	} else {
@@ -80,25 +81,25 @@ func evalAlternate(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- default assign term
 
-func newDefaultAssignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDefault,
-		evalFunc: evalAssignDefault,
+func newDefaultAssignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDefault,
+		EvalFunc: evalAssignDefault,
 	}
 }
 
-func evalAssignDefault(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	leftTerm := opTerm.children[0]
-	if leftTerm.tk.Sym != SymVariable {
+	leftTerm := opTerm.Children[0]
+	if leftTerm.Tk.Sym != scan.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -106,11 +107,11 @@ func evalAssignDefault(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 	if leftValue, exists := ctx.GetVar(leftTerm.Source()); exists {
 		v = leftValue
-	} else if rightValue, err = opTerm.children[1].Compute(ctx); err == nil {
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 		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
@@ -122,7 +123,7 @@ func evalAssignDefault(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleQuestion, newDefaultTerm)
-	registerTermConstructor(SymQuestionEqual, newDefaultAssignTerm)
-	registerTermConstructor(SymQuestionExclam, newAlternateTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleQuestion, newDefaultTerm)
+	scan.RegisterTermConstructor(scan.SymQuestionEqual, newDefaultAssignTerm)
+	scan.RegisterTermConstructor(scan.SymQuestionExclam, newAlternateTerm)
 }

operator-digest.go

@@ -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
@@ -9,34 +9,35 @@ import (
 	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- digest term
 
-func newDigestTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priIterOp,
-		evalFunc: evalDigest,
+func newDigestTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalDigest,
 	}
 }
 
-func evalDigest(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalDigest(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var it kern.Iterator
 	var item, lastValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = opTerm.children[0].Compute(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
+	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))
 	}
 
@@ -45,7 +46,7 @@ func evalDigest(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		ctx.SetVar("_", item)
 		ctx.SetVar("__", it.Index())
 		ctx.SetVar("_#", it.Count())
-		if rightValue, err = opTerm.children[1].Compute(ctx); err == nil {
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 			if rightValue == nil {
 				break
 			} else {
@@ -68,5 +69,5 @@ func evalDigest(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwDigest, newDigestTerm)
+	scan.RegisterTermConstructor(scan.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
@@ -6,34 +6,35 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- dot term
-func newDotTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDot,
-		evalFunc: evalDot,
+func newDotTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDot,
+		EvalFunc: evalDot,
 	}
 }
 
-func evalDot(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
-	if leftValue, err = opTerm.children[0].Compute(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	indexTerm := opTerm.children[1]
+	indexTerm := opTerm.Children[1]
 
 	switch unboxedValue := leftValue.(type) {
 	case kern.ExtIterator:
-		if indexTerm.symbol() == SymVariable /*|| indexTerm.symbol() == SymString */ {
+		if indexTerm.Tk.Sym == scan.SymVariable /*|| indexTerm.Tk.Sym == scan.SymString */ {
 			opName := indexTerm.Source()
 			if unboxedValue.HasOperation(opName) {
 				v, err = unboxedValue.CallOperation(opName, map[string]any{})
@@ -42,27 +43,27 @@ func evalDot(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 				v = false
 			}
 		} else {
-			err = indexTerm.tk.ErrorExpectedGot("identifier")
+			err = indexTerm.Tk.ErrorExpectedGot("identifier")
 		}
 	case *kern.DictType:
 		var ok bool
-		s := opTerm.children[1].symbol()
-		if s == SymVariable || s == SymString {
-			src := opTerm.children[1].Source()
+		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.errKeyNotFound(src)
+				err = opTerm.Errorf("key %q not found", src)
 			}
-		} else if rightValue, err = opTerm.children[1].Compute(ctx); err == nil {
+		} else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 			if v, ok = unboxedValue.GetItem(rightValue); !ok {
-				err = opTerm.errKeyNotFound(rightValue)
+				err = opTerm.Errorf("key %q not found", rightValue)
 			}
 		}
 	default:
-		if rightValue, err = opTerm.children[1].Compute(ctx); err == nil {
-			err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+			err = opTerm.Errorf("incompatible types: %s and %s", kern.TypeName(leftValue), kern.TypeName(rightValue))
 		}
 	}
 	return
@@ -70,5 +71,5 @@ func evalDot(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDot, newDotTerm)
+	scan.RegisterTermConstructor(scan.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
@@ -8,24 +8,25 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- fact term
 
-func newFactTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPostfix,
-		priority: priFact,
-		evalFunc: evalFact,
+func newFactTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPostfix,
+		Priority: scan.PriFact,
+		EvalFunc: evalFact,
 	}
 }
 
-func evalFact(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalFact(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue any
 
-	if leftValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
@@ -40,12 +41,12 @@ func evalFact(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 			err = fmt.Errorf("factorial of a negative integer (%d) is not allowed", i)
 		}
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(leftValue)
+		err = opTerm.Errorf("incompatible type for factorial: %s", kern.TypeName(leftValue))
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymExclamation, newFactTerm)
+	scan.RegisterTermConstructor(scan.SymExclamation, newFactTerm)
 }

operator-filter.go

@@ -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
@@ -6,69 +6,162 @@ package expr
 
 import (
 	"fmt"
-	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- map term
 
-func newFilterTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priIterOp,
-		evalFunc: evalFilter,
+func newFilterTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalFilter,
 	}
 }
 
-func evalFilter(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	var leftValue, rightValue any
+func evalFilter(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	// 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 {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = opTerm.children[0].Compute(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
-		return nil, fmt.Errorf("left operand of FILTER must be an iterable data-source; got %s", kern.TypeName(leftValue))
+	if it, ok = leftValue.(kern.Iterator); !ok {
+		if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of FILTER must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
 	}
 
-	values := kern.NewListA()
-	for item, err = it.Next(); err == nil; item, err = it.Next() {
-		ctx.SetVar("_", item)
+	// values := kern.NewListA()
+	// for item, err = it.Next(); err == nil; item, err = it.Next() {
+	// 	ctx.SetVar("_", item)
+	// 	ctx.SetVar("__", it.Index())
+	// 	ctx.SetVar("_#", it.Count())
+	// 	if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+	// 		if success, valid := kern.ToBool(rightValue); valid {
+	// 			if success {
+	// 				values.AppendItem(item)
+	// 			}
+	// 		} else {
+	// 			err = fmt.Errorf("filter expression must return a boolean or a castable to boolean, got %v [%T]", rightValue, rightValue)
+	// 		}
+	// 	}
+	// 	ctx.DeleteVar("_#")
+	// 	ctx.DeleteVar("__")
+	// 	ctx.DeleteVar("_")
+	// 	if err != nil {
+	// 		break
+	// 	}
+	// }
+	// if err == io.EOF {
+	// 	err = nil
+	// }
+	// v = values
+
+	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())
-		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)
-			}
-		}
+		result, err = it.expr.Compute(ctx)
 		ctx.DeleteVar("_#")
 		ctx.DeleteVar("__")
 		ctx.DeleteVar("_")
+
+		if err == nil {
+			if success, valid := kern.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() {
-	registerTermConstructor(SymKwFilter, newFilterTerm)
+	scan.RegisterTermConstructor(scan.SymKwFilter, newFilterTerm)
 }

operator-fraction.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operand-fraction.go
@@ -10,27 +10,27 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- fraction term
-func newFractionTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priFraction,
-		evalFunc: evalFraction,
+func newFractionTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriFraction,
+		EvalFunc: evalFraction,
 	}
 }
 
 // -------- eval func
-func evalFraction(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalFraction(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var numValue, denValue any
 	var num, den int64
 	var ok bool
 
-	if numValue, denValue, err = opTerm.evalInfix(ctx); err != nil {
+	if numValue, denValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 	if num, ok = numValue.(int64); !ok {
@@ -42,7 +42,7 @@ func evalFraction(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		return
 	}
 	if den == 0 {
-		err = opTerm.errDivisionByZero()
+		err = opTerm.Errorf("division by zero")
 		return
 	}
 
@@ -71,5 +71,5 @@ func evalFraction(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 // init
 func init() {
 	// registerTermConstructor(SymVertBar, newFractionTerm)
-	registerTermConstructor(SymColon, newFractionTerm)
+	scan.RegisterTermConstructor(scan.SymColon, newFractionTerm)
 }

operator-groupby.go

@@ -10,43 +10,47 @@ import (
 	"strconv"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- group by term
 
-func newGroupByTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priIterOp,
-		evalFunc: evalGroupBy,
+func newGroupByTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalGroupBy,
 	}
 }
 
-func evalGroupBy(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var it kern.Iterator
 	var item any
 	var sKey string
 	var keyByIndex bool
+	var ok bool
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = opTerm.children[0].Compute(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
-		return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+	if it, ok = leftValue.(kern.Iterator); !ok {
+		if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
 	}
 
-	rightTk := opTerm.children[1].tk
-	if rightTk.IsSymbol(SymVariable) && rightTk.source == "__" {
+	rightTk := opTerm.Children[1].Tk
+	if rightTk.IsSymbol(scan.SymVariable) && rightTk.Source() == "__" {
 		keyByIndex = true
-	} else if rightValue, err = opTerm.children[1].Compute(ctx); err != nil {
+	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
 		return
 	} else if kern.IsString(rightValue) {
 		sKey = rightValue.(string)
@@ -101,5 +105,5 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwGroupBy, newGroupByTerm)
+	scan.RegisterTermConstructor(scan.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
@@ -6,17 +6,18 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- in term
 
-func newInTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalIn,
+func newInTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalIn,
 	}
 }
 
@@ -25,10 +26,10 @@ func newInTerm(tk *Token) (inst *term) {
 // 	return
 // }
 
-func evalIn(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalIn(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -39,12 +40,12 @@ func evalIn(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		dict, _ := rightValue.(*kern.DictType)
 		v = dict.HasKey(leftValue)
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymKwIn, newInTerm)
+	scan.RegisterTermConstructor(scan.SymKwIn, newInTerm)
 }

operator-include.go

@@ -1,4 +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
@@ -6,24 +6,25 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- include term
 
-func newIncludeTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalInclude,
+func newIncludeTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalInclude,
 	}
 }
 
-func evalInclude(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalInclude(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
@@ -49,7 +50,7 @@ func evalInclude(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 			count++
 		}
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	if err != nil {
 		//v = count
@@ -60,5 +61,5 @@ func evalInclude(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwInclude, newIncludeTerm)
+	scan.RegisterTermConstructor(scan.SymKwInclude, newIncludeTerm)
 }

operator-index.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-index.go
@@ -6,16 +6,17 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- index term
-func newIndexTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priDot,
-		evalFunc: evalIndex,
+func newIndexTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriDot,
+		EvalFunc: evalIndex,
 	}
 }
 
@@ -24,7 +25,7 @@ func verifyKey(indexList *kern.ListType) (index any, err error) {
 	return
 }
 
-func verifyIndex(indexTerm *term, indexList *kern.ListType, maxValue int) (index int, err error) {
+func verifyIndex(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (index int, err error) {
 	var v int
 
 	if v, err = kern.ToGoInt((*indexList)[0], "index expression"); err == nil {
@@ -40,7 +41,7 @@ func verifyIndex(indexTerm *term, indexList *kern.ListType, maxValue int) (index
 	return
 }
 
-func verifyRange(indexTerm *term, indexList *kern.ListType, maxValue int) (startIndex, endIndex int, err error) {
+func verifyRange(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (startIndex, endIndex int, err error) {
 	v, _ := ((*indexList)[0]).(*intPair)
 	startIndex = v.a
 	endIndex = v.b
@@ -63,16 +64,16 @@ func verifyRange(indexTerm *term, indexList *kern.ListType, maxValue int) (start
 	return
 }
 
-func evalIndex(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var indexList *kern.ListType
 	var ok bool
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	indexTerm := opTerm.children[1]
+	indexTerm := opTerm.Children[1]
 	if indexList, ok = rightValue.(*kern.ListType); !ok {
 		err = opTerm.Errorf("invalid index expression")
 		return
@@ -96,7 +97,7 @@ func evalIndex(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		case *kern.DictType:
 			v, err = getDictItem(unboxedValue, indexTerm, indexList, rightValue)
 		default:
-			err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+			err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 		}
 	} else if isIntPair((*indexList)[0]) {
 		switch unboxedValue := leftValue.(type) {
@@ -112,19 +113,19 @@ func evalIndex(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 				v = unboxedValue[start:end]
 			}
 		default:
-			err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+			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]
+		rightChild := opTerm.Children[1]
 		err = rightChild.Errorf("invalid index type: %v", (*indexList)[0])
 	}
 	return
 }
 
-func getDictItem(d *kern.DictType, indexTerm *term, indexList *kern.ListType, rightValue any) (v any, err error) {
+func getDictItem(d *kern.DictType, indexTerm *scan.Term, indexList *kern.ListType, rightValue any) (v any, err error) {
 	var ok bool
 	var indexValue any
 
@@ -138,5 +139,5 @@ func getDictItem(d *kern.DictType, indexTerm *term, indexList *kern.ListType, ri
 
 // init
 func init() {
-	registerTermConstructor(SymIndex, newIndexTerm)
+	scan.RegisterTermConstructor(scan.SymIndex, newIndexTerm)
 }

operator-insert.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-insert.go
@@ -6,70 +6,124 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- prepend term
 
-func newPrependTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priInsert,
-		evalFunc: evalPrepend,
+func newPrependTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriInsert,
+		EvalFunc: evalPrepend,
 	}
 }
 
-func newAppendTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priInsert,
-		evalFunc: evalAppend,
+func newAppendTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriInsert,
+		EvalFunc: evalAppend,
 	}
 }
 
-func evalPrepend(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	var leftValue, rightValue any
-
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
-		return
-	}
-
-	if kern.IsList(rightValue) {
-		list, _ := rightValue.(*kern.ListType)
-		newList := append(kern.ListType{leftValue}, *list...)
-		v = &newList
-		if opTerm.children[1].symbol() == SymVariable {
-			ctx.UnsafeSetVar(opTerm.children[1].Source(), v)
+func prependToList(ctx kern.ExprContext, opTerm *scan.Term, leftValue, rightValue any) (result any, err error) {
+	if list, ok := rightValue.(*kern.ListType); ok {
+		var it kern.Iterator
+		if it, ok = leftValue.(kern.Iterator); !ok {
+			if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+				return
+			}
 		}
+
+		ls := kern.NewLinkedList()
+		ls.SeqPushBack(it)
+
+		newList := kern.ListType(nil)
+		if newSize := len(*list) + int(ls.Len()); newSize > cap(*list) {
+			newList = make([]any, 0, newSize)
+			for node := ls.FirstNode(); node != nil; node = node.Next() {
+				newList = append(newList, node.Data())
+			}
+		}
+		for _, item := range *list {
+			newList = append(newList, item)
+		}
+		result = &newList
+
+		// ***** EVENTUALMENTE ABILITARE LA MODIFICA DELLA VARIABILE
+		// ***** CON UN OPERATORE SPECIFICO
+		// if opTerm.Children[1].Symbol() == scan.SymVariable {
+		// 	ctx.UnsafeSetVar(opTerm.Children[1].Source(), result)
+		// }
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalAppend(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalPrepend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	if kern.IsList(leftValue) {
-		list, _ := leftValue.(*kern.ListType)
-		newList := append(*list, rightValue)
-		v = &newList
-		if opTerm.children[0].symbol() == SymVariable {
-			ctx.UnsafeSetVar(opTerm.children[0].Source(), v)
+	v, err = prependToList(ctx, opTerm, leftValue, rightValue)
+	return
+}
+
+func appendToList(ctx kern.ExprContext, opTerm *scan.Term, leftValue, rightValue any) (result any, err error) {
+	if list, ok := leftValue.(*kern.ListType); ok {
+		var it kern.Iterator
+		if it, ok = rightValue.(kern.Iterator); !ok {
+			if it, err = NewIterator(ctx, rightValue, nil); err != nil {
+				return
+			}
 		}
+
+		ls := kern.NewLinkedList()
+		ls.SeqPushBack(it)
+
+		newList := *list
+		if newSize := len(*list) + int(ls.Len()); newSize > cap(*list) {
+			newList = make([]any, 0, newSize)
+			for _, item := range *list {
+				newList = append(newList, item)
+			}
+		}
+		for node := ls.FirstNode(); node != nil; node = node.Next() {
+			newList = append(newList, node.Data())
+		}
+		result = &newList
+
+		// ***** EVENTUALMENTE ABILITARE LA MODIFICA DELLA VARIABILE
+		// ***** CON UN OPERATORE SPECIFICO
+		// if opTerm.Children[0].Symbol() == scan.SymVariable {
+		// 	ctx.UnsafeSetVar(opTerm.Children[0].Source(), result)
+		// }
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
+func evalAppend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	v, err = appendToList(ctx, opTerm, leftValue, rightValue)
+
+	return
+}
+
 // func evalAssignAppend(ctx ExprContext, self *term) (v any, err error) {
 // 	var leftValue, rightValue any
 
@@ -90,6 +144,6 @@ func evalAppend(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymPlusGreater, newPrependTerm)
-	registerTermConstructor(SymLessPlus, newAppendTerm)
+	scan.RegisterTermConstructor(scan.SymPlusGreater, newPrependTerm)
+	scan.RegisterTermConstructor(scan.SymLessPlus, newAppendTerm)
 }

operator-iter-value.go

@@ -1,4 +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-iter-value.go
@@ -6,31 +6,32 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- iter value term
 
-func newIterValueTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priDereference,
-		evalFunc: evalIterValue,
+func newIterValueTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriDereference,
+		EvalFunc: evalIterValue,
 	}
 }
 
-func evalIterValue(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalIterValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	if it, ok := childValue.(kern.Iterator); ok {
 		v, err = it.Current()
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
@@ -38,5 +39,5 @@ func evalIterValue(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 // init
 func init() {
 	//	registerTermConstructor(SymOpenClosedRound, newIterValueTerm)
-	registerTermConstructor(SymDereference, newIterValueTerm)
+	scan.RegisterTermConstructor(scan.SymDereference, newIterValueTerm)
 }

operator-join.go

@@ -1,67 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// operator-join.go
-package expr
-
-import (
-	"fmt"
-	"io"
-
-	"git.portale-stac.it/go-pkg/expr/kern"
-)
-
-//-------- join term
-
-func newJoinTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priIterOp,
-		evalFunc: evalJoin,
-	}
-}
-
-func evalJoin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	var leftValue, rightValue any
-	var itLeft, itRight kern.Iterator
-	var item any
-
-	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, err = NewIterator(leftValue); err != nil {
-		return nil, fmt.Errorf("left operand of JOIN must be an iterable data-source; got %s", kern.TypeName(leftValue))
-	}
-
-	if itRight, err = NewIterator(rightValue); err != nil {
-		return nil, fmt.Errorf("right operand of JOIN must be an iterable data-source; got %s", kern.TypeName(rightValue))
-	}
-
-	values := kern.NewListA()
-	for _, it := range []kern.Iterator{itLeft, itRight} {
-		for item, err = it.Next(); err == nil; item, err = it.Next() {
-			values.AppendItem(item)
-		}
-	}
-	if err == io.EOF {
-		err = nil
-	}
-	v = values
-	return
-}
-
-// init
-func init() {
-	registerTermConstructor(SymKwJoin, newJoinTerm)
-}

operator-length.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-length.go
@@ -6,24 +6,25 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- length term
 
-func newLengthTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalLength,
+func newLengthTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalLength,
 	}
 }
 
-func evalLength(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalLength(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
@@ -45,12 +46,12 @@ func evalLength(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		// 	v = int64(it.Index() + 1)
 		// }
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymHash, newLengthTerm)
+	scan.RegisterTermConstructor(scan.SymHash, newLengthTerm)
 }

operator-map.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-map.go
@@ -6,65 +6,70 @@ package expr
 
 import (
 	"fmt"
-	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- map term
 
-func newMapTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priIterOp,
-		evalFunc: evalMap,
+func newMapTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalMap,
 	}
 }
 
-func evalMap(ctx kern.ExprContext, opTerm *term) (v any, err error) {
-	var leftValue, rightValue any
+func evalMap(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	// 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 {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
 
-	if leftValue, err = opTerm.children[0].Compute(ctx); err != nil {
+	if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 		return
 	}
 
-	if it, err = NewIterator(leftValue); err != nil {
-		return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+	if it, ok = leftValue.(kern.Iterator); !ok {
+		if it, err = NewIterator(ctx, leftValue, nil); err != nil {
+			return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", kern.TypeName(leftValue))
+		}
 	}
 
-	values := kern.NewListA()
-	for item, err = it.Next(); err == nil; item, err = it.Next() {
-		ctx.SetVar("_", item)
-		ctx.SetVar("__", it.Index())
-		ctx.SetVar("_#", it.Count())
-		if rightValue, err = opTerm.children[1].Compute(ctx); err == nil {
-			values.AppendItem(rightValue)
-		}
-		ctx.DeleteVar("_#")
-		ctx.DeleteVar("__")
-		ctx.DeleteVar("_")
-		if err != nil {
-			break
-		}
-	}
-	if err == io.EOF {
-		err = nil
-	}
-	if err == nil {
-		v = values
-	}
+	// values := kern.NewListA()
+	// for item, err = it.Next(); err == nil; item, err = it.Next() {
+	// 	ctx.SetVar("_", item)
+	// 	ctx.SetVar("__", it.Index())
+	// 	ctx.SetVar("_#", it.Count())
+	// 	if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
+	// 		values.AppendItem(rightValue)
+	// 	}
+	// 	ctx.DeleteVar("_#")
+	// 	ctx.DeleteVar("__")
+	// 	ctx.DeleteVar("_")
+	// 	if err != nil {
+	// 		break
+	// 	}
+	// }
+	// if err == io.EOF {
+	// 	err = nil
+	// }
+	// if err == nil {
+	// 	v = values
+	// }
+	v, err = NewIterIter(it, ctx, opTerm.Children[1:])
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymKwMap, newMapTerm)
+	scan.RegisterTermConstructor(scan.SymKwMap, newMapTerm)
 }

operator-plugin.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-plugin.go
@@ -6,25 +6,26 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- plugin term
 
-func newPluginTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalPlugin,
+func newPluginTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalPlugin,
 	}
 }
 
-func evalPlugin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalPlugin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 	var count int
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
@@ -36,5 +37,5 @@ func evalPlugin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwPlugin, newPluginTerm)
+	scan.RegisterTermConstructor(scan.SymKwPlugin, newPluginTerm)
 }

operator-post-inc-dec.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-post-inc-dec.go
@@ -6,24 +6,24 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- post increment term
 
-func newPostIncTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPostfix,
-		priority: priIncDec,
-		evalFunc: evalPostInc,
+func newPostIncTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPostfix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPostInc,
 	}
 }
 
-func evalPostInc(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalPostInc(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
@@ -31,8 +31,8 @@ func evalPostInc(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		var namePrefix string
 		v, err = it.Next()
 
-		if opTerm.children[0].symbol() == SymVariable {
-			namePrefix = opTerm.children[0].Source()
+		if opTerm.Children[0].Symbol() == scan.SymVariable {
+			namePrefix = opTerm.Children[0].Source()
 		}
 		ctx.UnsafeSetVar(namePrefix+"_index", it.Index())
 		if c, err1 := it.Current(); err1 == nil {
@@ -49,49 +49,48 @@ func evalPostInc(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 				ctx.UnsafeSetVar(namePrefix+"_value", v1)
 			}
 		}
-	} else if kern.IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	} else if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		v = childValue
 		i, _ := childValue.(int64)
-		ctx.SetVar(opTerm.children[0].Source(), i+1)
+		ctx.SetVar(opTerm.Children[0].Source(), i+1)
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // -------- post decrement term
 
-func newPostDecTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPostfix,
-		priority: priIncDec,
-		evalFunc: evalPostDec,
+func newPostDecTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPostfix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPostDec,
 	}
 }
 
-func evalPostDec(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalPostDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	/* if it, ok := childValue.(Iterator); ok {
 		v, err = it.Next()
-	} else  */if kern.IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	} else  */if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		v = childValue
 		i, _ := childValue.(int64)
-		ctx.SetVar(opTerm.children[0].Source(), i-1)
+		ctx.SetVar(opTerm.Children[0].Source(), i-1)
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoublePlus, newPostIncTerm)
-	registerTermConstructor(SymDoubleMinus, newPostDecTerm)
+	scan.RegisterTermConstructor(scan.SymDoublePlus, newPostIncTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleMinus, newPostDecTerm)
 }

operator-pre-inc-dec.go

@@ -1,4 +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-pre-inc-dec.go
@@ -6,68 +6,68 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- pre increment term
 
-func newPreIncTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priIncDec,
-		evalFunc: evalPreInc,
+func newPreIncTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPreInc,
 	}
 }
 
-func evalPreInc(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalPreInc(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if kern.IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		i := childValue.(int64) + 1
-		ctx.SetVar(opTerm.children[0].Source(), i)
+		ctx.SetVar(opTerm.Children[0].Source(), i)
 		v = i
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // -------- pre decrement term
 
-func newPreDecTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priIncDec,
-		evalFunc: evalPreDec,
+func newPreDecTerm(tk *scan.Token) *scan.Term {
+	return &scan.Term{
+		Tk:       *tk,
+		Parent:   nil,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalPreDec,
 	}
 }
 
-func evalPreDec(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalPreDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
-	if kern.IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+	if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
 		i := childValue.(int64) - 1
-		ctx.SetVar(opTerm.children[0].Source(), i)
+		ctx.SetVar(opTerm.Children[0].Source(), i)
 		v = i
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymPreInc, newPreIncTerm)
-	registerTermConstructor(SymPreDec, newPreDecTerm)
+	scan.RegisterTermConstructor(scan.SymPreInc, newPreIncTerm)
+	scan.RegisterTermConstructor(scan.SymPreDec, newPreDecTerm)
 }

operator-prod.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-prod.go
@@ -8,21 +8,22 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- multiply term
 
-func newMultiplyTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalMultiply,
+func newMultiplyTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalMultiply,
 	}
 }
 
-func mulValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func mulValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	if kern.IsString(leftValue) && kern.IsInteger(rightValue) {
 		s, _ := leftValue.(string)
 		n, _ := rightValue.(int64)
@@ -38,15 +39,15 @@ func mulValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
 			v = leftInt * rightInt
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalMultiply(ctx kern.ExprContext, prodTerm *term) (v any, err error) {
+func evalMultiply(ctx kern.ExprContext, prodTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = prodTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = prodTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -55,22 +56,22 @@ func evalMultiply(ctx kern.ExprContext, prodTerm *term) (v any, err error) {
 
 //-------- divide term
 
-func newDivideTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalDivide,
+func newDivideTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalDivide,
 	}
 }
 
-func divValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func divValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
 		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
 			d := kern.NumAsFloat(rightValue)
 			if d == 0.0 {
-				err = opTerm.errDivisionByZero()
+				err = opTerm.ErrDivisionByZero()
 			} else {
 				v = kern.NumAsFloat(leftValue) / d
 			}
@@ -79,7 +80,7 @@ func divValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
 		} else {
 			leftInt, _ := leftValue.(int64)
 			if rightInt, _ := rightValue.(int64); rightInt == 0 {
-				err = opTerm.errDivisionByZero()
+				err = opTerm.ErrDivisionByZero()
 			} else {
 				v = leftInt / rightInt
 			}
@@ -92,7 +93,7 @@ func divValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
 		source := leftValue.(string)
 		partSize := int(rightValue.(int64))
 		if partSize == 0 {
-			err = opTerm.errDivisionByZero()
+			err = opTerm.ErrDivisionByZero()
 		} else {
 			partCount := len(source) / partSize
 			remainder := len(source) % partSize
@@ -110,15 +111,15 @@ func divValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
 			v = kern.NewList(parts)
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalDivide(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalDivide(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -127,66 +128,66 @@ func evalDivide(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- divide as float term
 
-func newDivideAsFloatTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalDivideAsFloat,
+func newDivideAsFloatTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalDivideAsFloat,
 	}
 }
 
-func evalDivideAsFloat(ctx kern.ExprContext, floatDivTerm *term) (v any, err error) {
+func evalDivideAsFloat(ctx kern.ExprContext, floatDivTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = floatDivTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = floatDivTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
 	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
 		d := kern.NumAsFloat(rightValue)
 		if d == 0.0 {
-			err = floatDivTerm.errDivisionByZero()
+			err = floatDivTerm.ErrDivisionByZero()
 		} else {
 			v = kern.NumAsFloat(leftValue) / d
 		}
 	} else {
-		err = floatDivTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = floatDivTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
 //-------- reminder term
 
-func newRemainderTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priProduct,
-		evalFunc: evalRemainder,
+func newRemainderTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriProduct,
+		EvalFunc: evalRemainder,
 	}
 }
-func remainderValues(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func remainderValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
 		rightInt, _ := rightValue.(int64)
 		if rightInt == 0 {
-			err = opTerm.errDivisionByZero()
+			err = opTerm.ErrDivisionByZero()
 		} else {
 			leftInt, _ := leftValue.(int64)
 			v = leftInt % rightInt
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalRemainder(ctx kern.ExprContext, remainderTerm *term) (v any, err error) {
+func evalRemainder(ctx kern.ExprContext, remainderTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = remainderTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = remainderTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -195,8 +196,8 @@ func evalRemainder(ctx kern.ExprContext, remainderTerm *term) (v any, err error)
 
 // init
 func init() {
-	registerTermConstructor(SymStar, newMultiplyTerm)
-	registerTermConstructor(SymSlash, newDivideTerm)
-	registerTermConstructor(SymDotSlash, newDivideAsFloatTerm)
-	registerTermConstructor(SymPercent, newRemainderTerm)
+	scan.RegisterTermConstructor(scan.SymStar, newMultiplyTerm)
+	scan.RegisterTermConstructor(scan.SymSlash, newDivideTerm)
+	scan.RegisterTermConstructor(scan.SymDotSlash, newDivideAsFloatTerm)
+	scan.RegisterTermConstructor(scan.SymPercent, newRemainderTerm)
 }

operator-range.go

@@ -1,4 +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-range.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // -------- range term
@@ -28,35 +29,35 @@ func isIntPair(v any) bool {
 	return ok
 }
 
-func newRangeTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRange,
-		evalFunc: evalRange,
+func newRangeTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRange,
+		EvalFunc: evalRange,
 	}
 }
 
-func changeColonToRange(t *term) {
-	if t.tk.IsSymbol(SymColon) {
-		t.tk.Sym = SymRange
-		t.evalFunc = evalRange
+func changeColonToRange(t *scan.Term) {
+	if t.Tk.IsSymbol(scan.SymColon) {
+		t.Tk.Sym = scan.SymRange
+		t.EvalFunc = evalRange
 	}
 }
 
-func evalRange(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalRange(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if len(opTerm.children) == 0 {
+	if len(opTerm.Children) == 0 {
 		leftValue = int64(0)
 		rightValue = int64(-1)
-	} else if len(opTerm.children) == 1 {
-		if leftValue, err = opTerm.children[0].Compute(ctx); err != nil {
+	} else if len(opTerm.Children) == 1 {
+		if leftValue, err = opTerm.Children[0].Compute(ctx); err != nil {
 			return
 		}
 		rightValue = int64(kern.ConstLastIndex)
-	} else if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	} else if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 	if !(kern.IsInteger(leftValue) && kern.IsInteger(rightValue)) {
@@ -72,15 +73,15 @@ func evalRange(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
-func errRangeInvalidSpecification(t *term) error {
+func errRangeInvalidSpecification(t *scan.Term) error {
 	return t.Errorf("invalid range specification")
 }
 
-func errRangeUnexpectedExpression(t *term) error {
+func errRangeUnexpectedExpression(t *scan.Term) error {
 	return t.Errorf("unexpected range expression")
 }
 
 // init
 func init() {
-	registerTermConstructor(SymRange, newRangeTerm)
+	scan.RegisterTermConstructor(scan.SymRange, newRangeTerm)
 }

operator-rel.go

@@ -1,4 +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-rel.go
@@ -8,17 +8,18 @@ import (
 	"reflect"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- equal term
 
-func newEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalEqual,
+func newEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalEqual,
 	}
 }
 
@@ -49,10 +50,10 @@ func equals(a, b any, deepCmp kern.DeepFuncTemplate) (eq bool, err error) {
 	return
 }
 
-func evalEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -62,17 +63,17 @@ func evalEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- not equal term
 
-func newNotEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalNotEqual,
+func newNotEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalNotEqual,
 	}
 }
 
-func evalNotEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalNotEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	if v, err = evalEqual(ctx, opTerm); err == nil {
 		b, _ := kern.ToBool(v)
 		v = !b
@@ -82,17 +83,17 @@ func evalNotEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- less term
 
-func newLessTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalLess,
+func newLessTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalLess,
 	}
 }
 
-func lessThan(self *term, a, b any) (isLess bool, err error) {
+func lessThan(self *scan.Term, a, b any) (isLess bool, err error) {
 	if kern.IsNumOrFract(a) && kern.IsNumOrFract(b) {
 		if kern.IsNumber(a) && kern.IsNumber(b) {
 			if kern.IsInteger(a) && kern.IsInteger(b) {
@@ -118,15 +119,15 @@ func lessThan(self *term, a, b any) (isLess bool, err error) {
 		bList, _ := b.(*kern.ListType)
 		isLess = len(*aList) < len(*bList) && bList.Contains(aList)
 	} else {
-		err = self.errIncompatibleTypes(a, b)
+		err = self.ErrIncompatibleTypes(a, b)
 	}
 	return
 }
 
-func evalLess(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalLess(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 	v, err = lessThan(opTerm, leftValue, rightValue)
@@ -135,17 +136,17 @@ func evalLess(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- less or equal term
 
-func newLessEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalLessEqual,
+func newLessEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalLessEqual,
 	}
 }
 
-func lessThanOrEqual(self *term, a, b any) (isLessEq bool, err error) {
+func lessThanOrEqual(self *scan.Term, a, b any) (isLessEq bool, err error) {
 	if isLessEq, err = lessThan(self, a, b); err == nil {
 		if !isLessEq {
 			if kern.IsList(a) && kern.IsList(b) {
@@ -158,10 +159,10 @@ func lessThanOrEqual(self *term, a, b any) (isLessEq bool, err error) {
 	return
 }
 
-func evalLessEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalLessEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -172,20 +173,20 @@ func evalLessEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- greater term
 
-func newGreaterTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalGreater,
+func newGreaterTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalGreater,
 	}
 }
 
-func evalGreater(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalGreater(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -195,20 +196,20 @@ func evalGreater(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 //-------- greater or equal term
 
-func newGreaterEqualTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priRelational,
-		evalFunc: evalGreaterEqual,
+func newGreaterEqualTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalGreaterEqual,
 	}
 }
 
-func evalGreaterEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalGreaterEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -218,10 +219,10 @@ func evalGreaterEqual(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleEqual, newEqualTerm)
-	registerTermConstructor(SymNotEqual, newNotEqualTerm)
-	registerTermConstructor(SymLess, newLessTerm)
-	registerTermConstructor(SymLessOrEqual, newLessEqualTerm)
-	registerTermConstructor(SymGreater, newGreaterTerm)
-	registerTermConstructor(SymGreaterOrEqual, newGreaterEqualTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleEqual, newEqualTerm)
+	scan.RegisterTermConstructor(scan.SymNotEqual, newNotEqualTerm)
+	scan.RegisterTermConstructor(scan.SymLess, newLessTerm)
+	scan.RegisterTermConstructor(scan.SymLessOrEqual, newLessEqualTerm)
+	scan.RegisterTermConstructor(scan.SymGreater, newGreaterTerm)
+	scan.RegisterTermConstructor(scan.SymGreaterOrEqual, newGreaterEqualTerm)
 }

operator-selector.go

@@ -1,4 +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-selector.go
@@ -6,17 +6,18 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- selector term
 
-func newSelectorTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 3),
-		position: posInfix,
-		priority: priSelector,
-		evalFunc: evalSelector,
+func newSelectorTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 3),
+		Position: scan.PosInfix,
+		Priority: scan.PriSelector,
+		EvalFunc: evalSelector,
 	}
 }
 
@@ -25,7 +26,7 @@ func trySelectorCase(ctx kern.ExprContext, exprValue, caseSel any, caseIndex int
 	if caseData.filterList == nil {
 		selectedValue, err = caseData.caseExpr.Eval(ctx)
 		match = true
-	} else if filterList, ok := caseData.filterList.value().([]*term); ok {
+	} else if filterList, ok := caseData.filterList.Value().([]*scan.Term); ok {
 		if len(filterList) == 0 {
 			var valueAsInt = int64(0)
 			if b, ok := exprValue.(bool); ok {
@@ -53,33 +54,33 @@ func trySelectorCase(ctx kern.ExprContext, exprValue, caseSel any, caseIndex int
 	return
 }
 
-func evalSelector(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalSelector(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var exprValue any
 	var match bool
 
-	if err = opTerm.checkOperands(); err != nil {
+	if err = opTerm.CheckOperands(); err != nil {
 		return
 	}
-	exprTerm := opTerm.children[0]
+	exprTerm := opTerm.Children[0]
 	if exprValue, err = exprTerm.Compute(ctx); err != nil {
 		return
 	}
 
-	caseListTerm := opTerm.children[1]
-	caseList, _ := caseListTerm.value().([]*term)
+	caseListTerm := opTerm.Children[1]
+	caseList, _ := caseListTerm.Value().([]*scan.Term)
 	for i, caseTerm := range caseList {
-		caseSel := caseTerm.value()
+		caseSel := caseTerm.Value()
 		if match, v, err = trySelectorCase(ctx, exprValue, caseSel, i); err != nil || match {
 			break
 		}
 	}
 	if err == nil && !match {
-		err = exprTerm.tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
+		err = exprTerm.Tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymSelector, newSelectorTerm)
+	scan.RegisterTermConstructor(scan.SymSelector, newSelectorTerm)
 }

operator-shift.go

@@ -1,4 +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-shift.go
@@ -6,76 +6,81 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- bit right shift term
 
-func newRightShiftTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBinShift,
-		evalFunc: evalRightShift,
+func newRightShiftTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBinShift,
+		EvalFunc: evalRightShift,
 	}
 }
 
-func bitRightShift(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitRightShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
 		leftInt := leftValue.(int64)
 		rightInt := rightValue.(int64)
 		v = leftInt >> rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalRightShift(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalRightShift(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	v, err = bitRightShift(opTerm, leftValue, rightValue)
+	if v, err = bitRightShift(opTerm, leftValue, rightValue); err != nil {
+		v, err = prependToList(ctx, opTerm, leftValue, rightValue)
+	}
 	return
 }
 
-func newLeftShiftTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBinShift,
-		evalFunc: evalLeftShift,
+func newLeftShiftTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBinShift,
+		EvalFunc: evalLeftShift,
 	}
 }
 
-func bitLeftShift(opTerm *term, leftValue, rightValue any) (v any, err error) {
+func bitLeftShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
 		leftInt := leftValue.(int64)
 		rightInt := rightValue.(int64)
 		v = leftInt << rightInt
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalLeftShift(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalLeftShift(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
-	v, err = bitLeftShift(opTerm, leftValue, rightValue)
+	if v, err = bitLeftShift(opTerm, leftValue, rightValue); err != nil {
+		v, err = appendToList(ctx, opTerm, leftValue, rightValue)
+	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleGreater, newRightShiftTerm)
-	registerTermConstructor(SymDoubleLess, newLeftShiftTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleGreater, newRightShiftTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleLess, newLeftShiftTerm)
 }

operator-sign.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-sign.go
@@ -6,61 +6,60 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- plus sign term
 
-func newPlusSignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk: *tk,
-		// class:    classOperator,
-		// kind:     kindUnknown,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalSign,
+func newPlusSignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalSign,
 	}
 }
 
-func newMinusSignTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalSign,
+func newMinusSignTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalSign,
 	}
 }
 
-func evalSign(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalSign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var rightValue any
 
-	if rightValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if rightValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
 	if kern.IsFloat(rightValue) {
-		if opTerm.tk.Sym == SymChangeSign {
+		if opTerm.Tk.Sym == scan.SymChangeSign {
 			f, _ := rightValue.(float64)
 			v = -f
 		} else {
 			v = rightValue
 		}
 	} else if kern.IsInteger(rightValue) {
-		if opTerm.tk.Sym == SymChangeSign {
+		if opTerm.Tk.Sym == scan.SymChangeSign {
 			i, _ := rightValue.(int64)
 			v = -i
 		} else {
 			v = rightValue
 		}
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(rightValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymUnchangeSign, newPlusSignTerm)
-	registerTermConstructor(SymChangeSign, newMinusSignTerm)
+	scan.RegisterTermConstructor(scan.SymUnchangeSign, newPlusSignTerm)
+	scan.RegisterTermConstructor(scan.SymChangeSign, newMinusSignTerm)
 }

operator-sum.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // operator-sum.go
@@ -9,21 +9,22 @@ import (
 	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- plus term
 
-func newPlusTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priSum,
-		evalFunc: evalPlus,
+func newPlusTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriSum,
+		EvalFunc: evalPlus,
 	}
 }
 
-func sumValues(plusTerm *term, leftValue, rightValue any) (v any, err error) {
+func sumValues(plusTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	if (kern.IsString(leftValue) && kern.IsNumberString(rightValue)) || (kern.IsString(rightValue) && kern.IsNumberString(leftValue)) {
 		v = fmt.Sprintf("%v%v", leftValue, rightValue)
 	} else if kern.IsNumber(leftValue) && kern.IsNumber(rightValue) {
@@ -58,15 +59,15 @@ func sumValues(plusTerm *term, leftValue, rightValue any) (v any, err error) {
 	} else if kern.IsFraction(leftValue) && kern.IsFraction(rightValue) {
 		v, err = kern.SumAnyFract(leftValue, rightValue)
 	} else {
-		err = plusTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = plusTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return v, err
 }
 
-func evalPlus(ctx kern.ExprContext, plusTerm *term) (v any, err error) {
+func evalPlus(ctx kern.ExprContext, plusTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = plusTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = plusTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -75,17 +76,17 @@ func evalPlus(ctx kern.ExprContext, plusTerm *term) (v any, err error) {
 
 //-------- minus term
 
-func newMinusTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priSum,
-		evalFunc: evalMinus,
+func newMinusTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriSum,
+		EvalFunc: evalMinus,
 	}
 }
 
-func diffValues(minusTerm *term, leftValue, rightValue any) (v any, err error) {
+func diffValues(minusTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
 	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
 		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
 			v = kern.NumAsFloat(leftValue) - kern.NumAsFloat(rightValue)
@@ -107,15 +108,15 @@ func diffValues(minusTerm *term, leftValue, rightValue any) (v any, err error) {
 		}
 		v = &diffList
 	} else {
-		err = minusTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = minusTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalMinus(ctx kern.ExprContext, minusTerm *term) (v any, err error) {
+func evalMinus(ctx kern.ExprContext, minusTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = minusTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = minusTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -124,6 +125,6 @@ func evalMinus(ctx kern.ExprContext, minusTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymPlus, newPlusTerm)
-	registerTermConstructor(SymMinus, newMinusTerm)
+	scan.RegisterTermConstructor(scan.SymPlus, newPlusTerm)
+	scan.RegisterTermConstructor(scan.SymMinus, newMinusTerm)
 }

operator-unset.go

@@ -1,4 +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-unset.go
@@ -8,21 +8,22 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- unset term
 
-func newUnsetTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priSign,
-		evalFunc: evalUnset,
+func newUnsetTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriSign,
+		EvalFunc: evalUnset,
 	}
 }
 
-func deleteContextItem(ctx kern.ExprContext, opTerm *term, item any) (deleted bool, err error) {
+func deleteContextItem(ctx kern.ExprContext, opTerm *scan.Term, item any) (deleted bool, err error) {
 	if name, ok := item.(string); ok {
 		var size int
 		if strings.HasSuffix(name, "()") {
@@ -35,16 +36,16 @@ func deleteContextItem(ctx kern.ExprContext, opTerm *term, item any) (deleted bo
 			deleted = ctx.VarCount() < size
 		}
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(item)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(item)
 	}
 	return
 }
 
-func evalUnset(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalUnset(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
 	var deleted bool
 
-	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+	if childValue, err = opTerm.EvalPrefix(ctx); err != nil {
 		return
 	}
 
@@ -69,5 +70,5 @@ func evalUnset(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwUnset, newUnsetTerm)
+	scan.RegisterTermConstructor(scan.SymKwUnset, newUnsetTerm)
 }

parser.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // parser.go
@@ -7,6 +7,7 @@ package expr
 import (
 	"errors"
 
+	"git.portale-stac.it/go-pkg/expr/scan"
 	"golang.org/x/exp/constraints"
 )
 
@@ -54,34 +55,34 @@ func NewParser() (p *parser) {
 	return p
 }
 
-func (parser *parser) Next(scanner *scanner) (tk *Token) {
-	for tk = scanner.Next(); tk.IsSymbol(SymComment); tk = scanner.Next() {
+func (parser *parser) Next(scanner *scan.Scanner) (tk *scan.Token) {
+	for tk = scanner.Next(); tk.IsSymbol(scan.SymComment); tk = scanner.Next() {
 	}
 	return
 }
 
-func (parser *parser) parseFuncCall(scanner *scanner, ctx parserContext, tk *Token) (tree *term, err error) {
-	args := make([]*term, 0, 10)
+func (parser *parser) parseFuncCall(scanner *scan.Scanner, ctx parserContext, tk *scan.Token) (tree *scan.Term, err error) {
+	args := make([]*scan.Term, 0, 10)
 	itemExpected := false
-	lastSym := SymUnknown
-	for lastSym != SymClosedRound && lastSym != SymEos {
-		var subTree *ast
-		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedRound); err != nil {
+	lastSym := scan.SymUnknown
+	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
+		var subTree *scan.Ast
+		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedRound); err != nil {
 			break
 		}
 		prev := scanner.Previous()
-		if subTree.root != nil {
-			args = append(args, subTree.root)
+		if subTree.Root() != nil {
+			args = append(args, subTree.Root())
 		} else if itemExpected {
 			err = prev.ErrorExpectedGot("function-param-value")
 			break
 		}
 
-		itemExpected = prev.Sym == SymComma
+		itemExpected = prev.Sym == scan.SymComma
 		lastSym = scanner.Previous().Sym
 	}
 	if err == nil {
-		if lastSym != SymClosedRound {
+		if lastSym != scan.SymClosedRound {
 			err = errors.New("unterminated arguments list")
 		} else {
 			tree = newFuncCallTerm(tk, args)
@@ -90,18 +91,18 @@ func (parser *parser) parseFuncCall(scanner *scanner, ctx parserContext, tk *Tok
 	return
 }
 
-func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
+func (parser *parser) parseFuncDef(scanner *scan.Scanner) (tree *scan.Term, err error) {
 	// Example: "add = func(x,y) {x+y}
-	var body *ast
-	args := make([]*term, 0)
-	lastSym := SymUnknown
+	var body *scan.Ast
+	args := make([]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	defaultParamsStarted := false
 	itemExpected := false
 	tk := scanner.Previous()
-	for lastSym != SymClosedRound && lastSym != SymEos {
+	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
 		tk = parser.Next(scanner)
-		if tk.IsSymbol(SymIdentifier) {
-			param := newTerm(tk)
+		if tk.IsSymbol(scan.SymIdentifier) {
+			param := scan.NewTerm(tk)
 			if len(args) > 0 {
 				if pos := paramAlreadyDefined(args, param); pos > 0 {
 					err = tk.Errorf("parameter %q at position %d already defined at position %d", param.Source(), len(args)+1, pos)
@@ -110,13 +111,13 @@ func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 			}
 			args = append(args, param)
 			tk = parser.Next(scanner)
-			if tk.Sym == SymEqual {
-				var paramExpr *ast
+			if tk.Sym == scan.SymEqual {
+				var paramExpr *scan.Ast
 				defaultParamsStarted = true
-				if paramExpr, err = parser.parseItem(scanner, parserNoFlags, SymComma, SymClosedRound); err != nil {
+				if paramExpr, err = parser.parseItem(scanner, parserNoFlags, scan.SymComma, scan.SymClosedRound); err != nil {
 					break
 				}
-				param.forceChild(paramExpr.root)
+				param.ForceChild(paramExpr.Root())
 			} else if defaultParamsStarted {
 				err = tk.Errorf("can't mix default and non-default parameters")
 				break
@@ -127,32 +128,32 @@ func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == SymComma
+		itemExpected = lastSym == scan.SymComma
 	}
 
-	if err == nil && lastSym != SymClosedRound {
+	if err == nil && lastSym != scan.SymClosedRound {
 		err = tk.ErrorExpectedGot(")")
 	}
 	if err == nil {
 		tk = parser.Next(scanner)
-		if tk.IsSymbol(SymOpenBrace) {
-			body, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, SymClosedBrace)
+		if tk.IsSymbol(scan.SymOpenBrace) {
+			body, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymClosedBrace)
 		} else {
 			err = tk.ErrorExpectedGot("{")
 		}
 	}
 	if err == nil {
-		if scanner.Previous().Sym != SymClosedBrace {
+		if scanner.Previous().Sym != scan.SymClosedBrace {
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
-			tk = scanner.makeValueToken(SymExpression, "", body)
+			tk = scanner.MakeValueToken(scan.SymExpression, "", body)
 			tree = newFuncDefTerm(tk, args)
 		}
 	}
 	return
 }
 
-func paramAlreadyDefined(args []*term, param *term) (position int) {
+func paramAlreadyDefined(args []*scan.Term, param *scan.Term) (position int) {
 	position = 0
 	for i, arg := range args {
 		if arg.Source() == param.Source() {
@@ -162,39 +163,39 @@ func paramAlreadyDefined(args []*term, param *term) (position int) {
 	return
 }
 
-func (parser *parser) parseList(scanner *scanner, ctx parserContext) (listTerm *term, err error) {
-	r, c := scanner.lastPos()
-	args := make([]*term, 0)
-	lastSym := SymUnknown
+func (parser *parser) parseList(scanner *scan.Scanner, ctx parserContext) (listTerm *scan.Term, err error) {
+	r, c := scanner.LastPos()
+	args := make([]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	itemExpected := false
 	itemCtx := remFlags(ctx, allowIndex)
-	for lastSym != SymClosedSquare && lastSym != SymEos {
-		zeroRequired := scanner.current.Sym == SymColon
-		var itemTree *ast
-		if itemTree, err = parser.parseItem(scanner, itemCtx, SymComma, SymClosedSquare); err == nil {
-			root := itemTree.root
+	for lastSym != scan.SymClosedSquare && lastSym != scan.SymEos {
+		zeroRequired := scanner.Current().Sym == scan.SymColon
+		var itemTree *scan.Ast
+		if itemTree, err = parser.parseItem(scanner, itemCtx, scan.SymComma, scan.SymClosedSquare); err == nil {
+			root := itemTree.Root()
 			if root != nil {
-				if hasFlag(ctx, allowIndex) && root.symbol() == SymColon {
+				if hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymColon {
 					changeColonToRange(root)
 				}
-				if !hasFlag(ctx, allowIndex) && root.symbol() == SymRange {
+				if !hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymRange {
 					// err = root.Errorf("unexpected range expression")
 					err = errRangeUnexpectedExpression(root)
 					break
 				}
 				args = append(args, root)
-				if hasFlag(ctx, allowIndex) && root.symbol() == SymRange && zeroRequired { //len(root.children) == 0 {
-					if len(root.children) == 1 {
-						root.children = append(root.children, root.children[0])
-					} else if len(root.children) > 1 {
+				if hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymRange && zeroRequired { //len(root.children) == 0 {
+					if len(root.Children) == 1 {
+						root.Children = append(root.Children, root.Children[0])
+					} else if len(root.Children) > 1 {
 						// err = root.Errorf("invalid range specification")
 						err = errRangeInvalidSpecification(root)
 						break
 					}
-					zeroTk := NewValueToken(root.tk.row, root.tk.col, SymInteger, "0", int64(0))
-					zeroTerm := newTerm(zeroTk)
-					zeroTerm.setParent(root)
-					root.children[0] = zeroTerm
+					zeroTk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymInteger, "0", int64(0))
+					zeroTerm := scan.NewTerm(zeroTk)
+					zeroTerm.SetParent(root)
+					root.Children[0] = zeroTerm
 				}
 			} else if itemExpected {
 				prev := scanner.Previous()
@@ -205,12 +206,12 @@ func (parser *parser) parseList(scanner *scanner, ctx parserContext) (listTerm *
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		if itemExpected = lastSym == SymComma; itemExpected {
+		if itemExpected = lastSym == scan.SymComma; itemExpected {
 			remFlags(ctx, allowIndex)
 		}
 	}
 	if err == nil {
-		if lastSym != SymClosedSquare {
+		if lastSym != scan.SymClosedSquare {
 			err = scanner.Previous().ErrorExpectedGot("]")
 		} else {
 			listTerm = newListTerm(r, c, args)
@@ -219,16 +220,16 @@ func (parser *parser) parseList(scanner *scanner, ctx parserContext) (listTerm *
 	return
 }
 
-func (parser *parser) parseIterDef(scanner *scanner, ctx parserContext) (subtree *term, err error) {
+func (parser *parser) parseIterDef(scanner *scan.Scanner, ctx parserContext) (subtree *scan.Term, err error) {
 	tk := scanner.Previous()
-	args := make([]*term, 0)
-	lastSym := SymUnknown
+	args := make([]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	itemExpected := false
-	for lastSym != SymClosedRound && lastSym != SymEos {
-		var subTree *ast
-		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedRound); err == nil {
-			if subTree.root != nil {
-				args = append(args, subTree.root)
+	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
+		var subTree *scan.Ast
+		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedRound); err == nil {
+			if subTree.Root() != nil {
+				args = append(args, subTree.Root())
 			} else if itemExpected {
 				prev := scanner.Previous()
 				err = prev.ErrorExpectedGot("iterator-param")
@@ -238,10 +239,10 @@ func (parser *parser) parseIterDef(scanner *scanner, ctx parserContext) (subtree
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == SymComma
+		itemExpected = lastSym == scan.SymComma
 	}
 	if err == nil {
-		if lastSym != SymClosedRound {
+		if lastSym != scan.SymClosedRound {
 			err = scanner.Previous().ErrorExpectedGot(")")
 		} else {
 			subtree = newIteratorTerm(tk, args)
@@ -250,18 +251,18 @@ func (parser *parser) parseIterDef(scanner *scanner, ctx parserContext) (subtree
 	return
 }
 
-func (parser *parser) parseDictKey(scanner *scanner) (key any, err error) {
+func (parser *parser) parseDictKey(scanner *scan.Scanner) (key any, err error) {
 	tk := parser.Next(scanner)
-	if tk.Sym == SymError {
+	if tk.Sym == scan.SymError {
 		err = tk.Error()
 		return
 	}
-	if tk.Sym == SymClosedBrace || tk.Sym == SymEos {
+	if tk.Sym == scan.SymClosedBrace || tk.Sym == scan.SymEos {
 		return
 	}
-	if tk.Sym == SymInteger || tk.Sym == SymString {
+	if tk.Sym == scan.SymInteger || tk.Sym == scan.SymString {
 		tkSep := parser.Next(scanner)
-		if tkSep.Sym != SymColon {
+		if tkSep.Sym != scan.SymColon {
 			err = tkSep.ErrorExpectedGot(":")
 		} else {
 			key = tk.Value
@@ -272,12 +273,12 @@ func (parser *parser) parseDictKey(scanner *scanner) (key any, err error) {
 	return
 }
 
-func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subtree *term, err error) {
-	args := make(map[any]*term, 0)
-	lastSym := SymUnknown
+func (parser *parser) parseDictionary(scanner *scan.Scanner, ctx parserContext) (subtree *scan.Term, err error) {
+	args := make(map[any]*scan.Term, 0)
+	lastSym := scan.SymUnknown
 	itemExpected := false
-	for lastSym != SymClosedBrace && lastSym != SymEos {
-		var subTree *ast
+	for lastSym != scan.SymClosedBrace && lastSym != scan.SymEos {
+		var subTree *scan.Ast
 		var key any
 		if key, err = parser.parseDictKey(scanner); err != nil {
 			break
@@ -289,9 +290,9 @@ func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subt
 			}
 			break
 		}
-		if subTree, err = parser.parseItem(scanner, ctx, SymComma, SymClosedBrace); err == nil {
-			if subTree.root != nil {
-				args[key] = subTree.root
+		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedBrace); err == nil {
+			if subTree.Root() != nil {
+				args[key] = subTree.Root()
 			} else /*if key != nil*/ {
 				prev := scanner.Previous()
 				err = prev.ErrorExpectedGot("dictionary-value")
@@ -301,10 +302,10 @@ func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subt
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == SymComma
+		itemExpected = lastSym == scan.SymComma
 	}
 	if err == nil {
-		if lastSym != SymClosedBrace {
+		if lastSym != scan.SymClosedBrace {
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
 			subtree = newDictTerm(args)
@@ -313,14 +314,14 @@ func (parser *parser) parseDictionary(scanner *scanner, ctx parserContext) (subt
 	return
 }
 
-func (parser *parser) parseSelectorCase(scanner *scanner, ctx parserContext, defaultCase bool) (caseTerm *term, err error) {
-	var filterList *term
-	var caseExpr *ast
+func (parser *parser) parseSelectorCase(scanner *scan.Scanner, ctx parserContext, defaultCase bool) (caseTerm *scan.Term, err error) {
+	var filterList *scan.Term
+	var caseExpr *scan.Ast
 	ctx = remFlags(ctx, allowIndex)
 	tk := parser.Next(scanner)
-	startRow := tk.row
-	startCol := tk.col
-	if tk.Sym == SymOpenSquare {
+	startRow := tk.Row()
+	startCol := tk.Col()
+	if tk.Sym == scan.SymOpenSquare {
 		if defaultCase {
 			err = tk.Errorf("case list in default clause")
 			return
@@ -329,14 +330,14 @@ func (parser *parser) parseSelectorCase(scanner *scanner, ctx parserContext, def
 			return
 		}
 		tk = parser.Next(scanner)
-		startRow = tk.row
-		startCol = tk.col
+		startRow = tk.Row()
+		startCol = tk.Col()
 	} else if !defaultCase {
-		filterList = newListTerm(startRow, startCol, make([]*term, 0))
+		filterList = newListTerm(startRow, startCol, make([]*scan.Term, 0))
 	}
 
-	if tk.Sym == SymOpenBrace {
-		if caseExpr, err = parser.parseGeneral(scanner, ctx|allowMultiExpr, SymClosedBrace); err != nil {
+	if tk.Sym == scan.SymOpenBrace {
+		if caseExpr, err = parser.parseGeneral(scanner, ctx|allowMultiExpr, scan.SymClosedBrace); err != nil {
 			return
 		}
 	} else {
@@ -349,25 +350,25 @@ func (parser *parser) parseSelectorCase(scanner *scanner, ctx parserContext, def
 	return
 }
 
-func addSelectorCase(selectorTerm, caseTerm *term) {
-	if len(selectorTerm.children) < 2 {
+func addSelectorCase(selectorTerm, caseTerm *scan.Term) {
+	if len(selectorTerm.Children) < 2 {
 		caseListTerm := newListTermA(caseTerm)
-		selectorTerm.children = append(selectorTerm.children, caseListTerm)
+		selectorTerm.Children = append(selectorTerm.Children, caseListTerm)
 	} else {
-		caseListTerm := selectorTerm.children[1]
-		caseList, _ := caseListTerm.value().([]*term)
+		caseListTerm := selectorTerm.Children[1]
+		caseList, _ := caseListTerm.Value().([]*scan.Term)
 		caseList = append(caseList, caseTerm)
-		caseListTerm.tk.Value = caseList
+		caseListTerm.Tk.Value = caseList
 	}
-	caseTerm.parent = selectorTerm
+	caseTerm.Parent = selectorTerm
 }
 
-func (parser *parser) parseSelector(scanner *scanner, tree *ast, ctx parserContext) (selectorTerm *term, err error) {
-	var caseTerm *term
+func (parser *parser) parseSelector(scanner *scan.Scanner, tree *scan.Ast, ctx parserContext) (selectorTerm *scan.Term, err error) {
+	var caseTerm *scan.Term
 
 	ctx = remFlags(ctx, allowIndex)
-	tk := scanner.makeToken(SymSelector, '?')
-	if selectorTerm, err = tree.addToken(tk); err != nil {
+	tk := scanner.MakeToken(scan.SymSelector, '?')
+	if selectorTerm, err = tree.AddToken(tk); err != nil {
 		return
 	}
 
@@ -377,11 +378,11 @@ func (parser *parser) parseSelector(scanner *scanner, tree *ast, ctx parserConte
 	return
 }
 
-func (parser *parser) parseItem(scanner *scanner, ctx parserContext, termSymbols ...Symbol) (tree *ast, err error) {
+func (parser *parser) parseItem(scanner *scan.Scanner, ctx parserContext, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
 	return parser.parseGeneral(scanner, ctx|allowVarRef, termSymbols...)
 }
 
-func (parser *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, err error) {
+func (parser *parser) Parse(scanner *scan.Scanner, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			if errVal, ok := r.(error); ok {
@@ -391,56 +392,56 @@ func (parser *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast,
 			}
 		}
 	}()
-	termSymbols = append(termSymbols, SymEos)
+	termSymbols = append(termSymbols, scan.SymEos)
 	return parser.parseGeneral(scanner, allowMultiExpr, termSymbols...)
 }
 
-func couldBeACollection(t *term) bool {
-	var sym = SymUnknown
+func couldBeACollection(t *scan.Term) bool {
+	var sym = scan.SymUnknown
 	if t != nil {
-		sym = t.symbol()
+		sym = t.Symbol()
 	}
-	return sym == SymList || sym == SymString || sym == SymDict || sym == SymExpression || sym == SymVariable
+	return sym == scan.SymList || sym == scan.SymString || sym == scan.SymDict || sym == scan.SymExpression || sym == scan.SymVariable
 }
 
-func listSubTree(tree *ast, listTerm *term, allowIndeces bool) (root *term, err error) {
-	var tk *Token
+func listSubTree(tree *scan.Ast, listTerm *scan.Term, allowIndeces bool) (root *scan.Term, err error) {
+	var tk *scan.Token
 	if allowIndeces {
-		tk = NewToken(listTerm.tk.row, listTerm.tk.col, SymIndex, listTerm.Source())
-		root = newTerm(tk)
-		if err = tree.addTerm(root); err == nil {
-			err = tree.addTerm(listTerm)
+		tk = scan.NewToken(listTerm.Tk.Row(), listTerm.Tk.Col(), scan.SymIndex, listTerm.Source())
+		root = scan.NewTerm(tk)
+		if err = tree.AddTerm(root); err == nil {
+			err = tree.AddTerm(listTerm)
 		}
 	} else {
 		root = listTerm
-		err = tree.addTerm(listTerm)
+		err = tree.AddTerm(listTerm)
 	}
 	return
 }
 
-func changePrefix(tk *Token) {
+func changePrefix(tk *scan.Token) {
 	switch tk.Sym {
-	case SymMinus:
-		tk.SetSymbol(SymChangeSign)
-	case SymPlus:
-		tk.SetSymbol(SymUnchangeSign)
-	case SymStar:
-		tk.SetSymbol(SymDereference)
-	case SymExclamation:
-		tk.SetSymbol(SymNot)
-	case SymDoublePlus:
-		tk.SetSymbol(SymPreInc)
-	case SymDoubleMinus:
-		tk.SetSymbol(SymPreDec)
+	case scan.SymMinus:
+		tk.SetSymbol(scan.SymChangeSign)
+	case scan.SymPlus:
+		tk.SetSymbol(scan.SymUnchangeSign)
+	case scan.SymStar:
+		tk.SetSymbol(scan.SymDereference)
+	case scan.SymExclamation:
+		tk.SetSymbol(scan.SymNot)
+	case scan.SymDoublePlus:
+		tk.SetSymbol(scan.SymPreInc)
+	case scan.SymDoubleMinus:
+		tk.SetSymbol(scan.SymPreDec)
 	}
 }
 
-func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymbols ...Symbol) (tree *ast, err error) {
-	var selectorTerm *term = nil
-	var currentTerm *term = nil
-	var tk *Token
+func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
+	var selectorTerm *scan.Term = nil
+	var currentTerm *scan.Term = nil
+	var tk *scan.Token
 
-	tree = NewAst()
+	tree = scan.NewAst()
 	firstToken := true
 	// lastSym := SymUnknown
 	for tk = parser.Next(scanner); err == nil && tk != nil && !tk.IsTerm(termSymbols); /*&& !areSymbolsOutOfCtx(tk, selectorTerm, SymColon, SymDoubleColon)*/ tk = parser.Next(scanner) {
@@ -448,7 +449,7 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 		// 	continue
 		// }
 
-		if tk.Sym == SymSemiColon {
+		if tk.Sym == scan.SymSemiColon {
 			if hasFlag(ctx, allowMultiExpr) {
 				tree.ToForest()
 				firstToken = true
@@ -456,7 +457,7 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 				selectorTerm = nil
 				continue
 			} else {
-				err = tk.Errorf(`unexpected token %q, expected ",", "]", or ")"`, tk.source)
+				err = tk.Errorf(`unexpected token %q, expected ",", "]", or ")"`, tk.Source())
 				break
 			}
 		}
@@ -468,87 +469,87 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 		}
 
 		switch tk.Sym {
-		case SymOpenRound:
-			var subTree *ast
-			if subTree, err = parser.parseGeneral(scanner, ctx, SymClosedRound); err == nil {
-				if subTree.root == nil {
+		case scan.SymOpenRound:
+			var subTree *scan.Ast
+			if subTree, err = parser.parseGeneral(scanner, ctx, scan.SymClosedRound); err == nil {
+				if subTree.Root() == nil {
 					err = tk.ErrorExpectedGotString("expression", "()")
 				} else {
-					exprTerm := newExprTerm(subTree.root)
-					err = tree.addTerm(exprTerm)
+					exprTerm := newExprTerm(subTree.Root())
+					err = tree.AddTerm(exprTerm)
 					currentTerm = exprTerm
 				}
 			}
-		case SymFuncCall:
-			var funcCallTerm *term
+		case scan.SymFuncCall:
+			var funcCallTerm *scan.Term
 			if funcCallTerm, err = parser.parseFuncCall(scanner, ctx, tk); err == nil {
-				err = tree.addTerm(funcCallTerm)
+				err = tree.AddTerm(funcCallTerm)
 				currentTerm = funcCallTerm
 			}
-		case SymOpenSquare:
-			var listTerm *term
+		case scan.SymOpenSquare:
+			var listTerm *scan.Term
 			newCtx := addFlagsCond(addFlags(ctx, squareContext), allowIndex, couldBeACollection(currentTerm))
 			if listTerm, err = parser.parseList(scanner, newCtx); err == nil {
 				currentTerm, err = listSubTree(tree, listTerm, hasFlag(newCtx, allowIndex))
 			}
-		case SymOpenBrace:
-			if currentTerm != nil && currentTerm.symbol() == SymColon {
+		case scan.SymOpenBrace:
+			if currentTerm != nil && currentTerm.Symbol() == scan.SymColon {
 				err = currentTerm.Errorf(`selector-case outside of a selector context`)
 			} else {
-				var mapTerm *term
+				var mapTerm *scan.Term
 				if mapTerm, err = parser.parseDictionary(scanner, ctx); err == nil {
-					err = tree.addTerm(mapTerm)
+					err = tree.AddTerm(mapTerm)
 					currentTerm = mapTerm
 				}
 			}
-		case SymEqual, SymPlusEqual, SymMinusEqual, SymStarEqual, SymSlashEqual, SymPercEqual, SymAmpersandEqual, SymVertBarEqual, SymDoubleLessEqual, SymDoubleGreaterEqual, SymCaretEqual:
-			currentTerm, err = tree.addToken(tk)
+		case scan.SymEqual, scan.SymPlusEqual, scan.SymMinusEqual, scan.SymStarEqual, scan.SymSlashEqual, scan.SymPercEqual, scan.SymAmpersandEqual, scan.SymVertBarEqual, scan.SymDoubleLessEqual, scan.SymDoubleGreaterEqual, scan.SymCaretEqual:
+			currentTerm, err = tree.AddToken(tk)
 			firstToken = true
-		case SymFuncDef:
-			var funcDefTerm *term
+		case scan.SymFuncDef:
+			var funcDefTerm *scan.Term
 			if funcDefTerm, err = parser.parseFuncDef(scanner); err == nil {
-				err = tree.addTerm(funcDefTerm)
+				err = tree.AddTerm(funcDefTerm)
 				currentTerm = funcDefTerm
 			}
-		case SymDollarRound:
-			var iterDefTerm *term
+		case scan.SymDollarRound:
+			var iterDefTerm *scan.Term
 			if iterDefTerm, err = parser.parseIterDef(scanner, ctx); err == nil {
-				err = tree.addTerm(iterDefTerm)
+				err = tree.AddTerm(iterDefTerm)
 				currentTerm = iterDefTerm
 			}
-		case SymIdentifier:
-			if tk.source[0] == '@' && !hasFlag(ctx, allowVarRef) {
-				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.source)
+		case scan.SymIdentifier:
+			if tk.Source()[0] == '@' && !hasFlag(ctx, allowVarRef) {
+				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.Source())
 			} else {
-				currentTerm, err = tree.addToken(tk)
+				currentTerm, err = tree.AddToken(tk)
 			}
-		case SymQuestion:
+		case scan.SymQuestion:
 			if selectorTerm, err = parser.parseSelector(scanner, tree, ctx); err == nil {
 				currentTerm = selectorTerm
 				addFlags(ctx, selectorContext)
 			}
-		case SymColon, SymDoubleColon:
-			var caseTerm *term
+		case scan.SymColon, scan.SymDoubleColon:
+			var caseTerm *scan.Term
 			if selectorTerm != nil {
-				if caseTerm, err = parser.parseSelectorCase(scanner, ctx, tk.Sym == SymDoubleColon); err == nil {
+				if caseTerm, err = parser.parseSelectorCase(scanner, ctx, tk.Sym == scan.SymDoubleColon); err == nil {
 					addSelectorCase(selectorTerm, caseTerm)
 					currentTerm = caseTerm
-					if tk.Sym == SymDoubleColon {
+					if tk.Sym == scan.SymDoubleColon {
 						selectorTerm = nil
 					}
 				}
 			} else {
-				currentTerm, err = tree.addToken(tk)
-				if tk.IsOneOfA(SymColon, SymRange) {
+				currentTerm, err = tree.AddToken(tk)
+				if tk.IsOneOfA(scan.SymColon, scan.SymRange) {
 					// Colon outside a selector term acts like a separator
 					firstToken = true
 				}
 			}
 		default:
-			currentTerm, err = tree.addToken(tk)
+			currentTerm, err = tree.AddToken(tk)
 		}
 
-		if currentTerm != nil && currentTerm.tk.Sym != SymSelector && currentTerm.parent != nil && currentTerm.parent.tk.Sym != SymSelector {
+		if currentTerm != nil && currentTerm.Tk.Sym != scan.SymSelector && currentTerm.Parent != nil && currentTerm.Parent.Tk.Sym != scan.SymSelector {
 			selectorTerm = nil
 			remFlags(ctx, selectorContext)
 		}
@@ -558,12 +559,12 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 	if err == nil {
 		if !tk.IsOneOf(termSymbols) {
 			var symDesc string
-			if tk.IsSymbol(SymError) {
+			if tk.IsSymbol(scan.SymError) {
 				symDesc = tk.ErrorText()
 			} else {
-				symDesc = SymToString(tk.Sym)
+				symDesc = scan.SymToString(tk.Sym)
 			}
-			err = tk.ErrorExpectedGotStringWithPrefix("expected one of", SymListToString(termSymbols, true), symDesc)
+			err = tk.ErrorExpectedGotStringWithPrefix("expected one of", scan.SymListToString(termSymbols, true), symDesc)
 		} else {
 			err = tk.Error()
 		}

plugins.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // plugin.go
@@ -100,7 +100,7 @@ func importPluginFromSearchPath(ctx kern.ExprContext, name any) (count int, err
 	var it kern.Iterator
 	dirList := buildSearchDirList(ctx, "plugin", ENV_EXPR_PLUGIN_PATH)
 	count = 0
-	if it, err = NewIterator(name); err != nil {
+	if it, err = NewIterator(ctx, name, nil); err != nil {
 		return
 	}
 	for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {

scan/ast.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // ast.go
-package expr
+package scan
 
 import (
 	"errors"
@@ -13,42 +13,46 @@ import (
 
 //-------- ast
 
-type ast struct {
-	forest []*term
-	root   *term
+type Ast struct {
+	forest []*Term
+	root   *Term
 }
 
-func NewAst() *ast {
-	return &ast{}
+func NewAst() *Ast {
+	return &Ast{}
 }
 
-func (ast *ast) TypeName() string {
+func (ast *Ast) TypeName() string {
 	return "Expression"
 }
 
-func (ast *ast) ToForest() {
+func (ast *Ast) Root() *Term {
+	return ast.root
+}
+
+func (ast *Ast) ToForest() {
 	if ast.root != nil {
 		if ast.forest == nil {
-			ast.forest = make([]*term, 0)
+			ast.forest = make([]*Term, 0)
 		}
 		ast.forest = append(ast.forest, ast.root)
 		ast.root = nil
 	}
 }
 
-func (ast *ast) String() string {
+func (ast *Ast) String() string {
 	var sb strings.Builder
 	if ast.root == nil {
 		sb.WriteString("(nil)")
 	} else {
-		ast.root.toString(&sb)
+		ast.root.ToString(&sb)
 	}
 	return sb.String()
 }
 
-func (ast *ast) addTokens(tokens ...*Token) (err error) {
+func (ast *Ast) AddTokens(tokens ...*Token) (err error) {
 	for _, tk := range tokens {
-		if _, err = ast.addToken(tk); err != nil {
+		if _, err = ast.AddToken(tk); err != nil {
 			break
 		}
 	}
@@ -60,16 +64,16 @@ func (ast *ast) addTokens(tokens ...*Token) (err error) {
 // 	return
 // }
 
-func (ast *ast) addToken(tk *Token) (t *term, err error) {
-	if t = newTerm(tk); t != nil {
-		err = ast.addTerm(t)
+func (ast *Ast) AddToken(tk *Token) (t *Term, err error) {
+	if t = NewTerm(tk); t != nil {
+		err = ast.AddTerm(t)
 	} else {
 		err = tk.Errorf("unexpected token %q", tk.String())
 	}
 	return
 }
 
-func (ast *ast) addTerm(node *term) (err error) {
+func (ast *Ast) AddTerm(node *Term) (err error) {
 	if ast.root == nil {
 		ast.root = node
 	} else {
@@ -78,35 +82,35 @@ func (ast *ast) addTerm(node *term) (err error) {
 	return
 }
 
-func (ast *ast) insert(tree, node *term) (root *term, err error) {
+func (ast *Ast) insert(tree, node *Term) (root *Term, err error) {
 	if tree.getPriority() < node.getPriority() {
 		root = tree
 		if tree.isComplete() {
-			var subRoot *term
+			var subRoot *Term
 			last := tree.removeLastChild()
 			if subRoot, err = ast.insert(last, node); err == nil {
-				subRoot.setParent(tree)
+				subRoot.SetParent(tree)
 			}
 		} else {
-			node.setParent(tree)
+			node.SetParent(tree)
 		}
 	} else if !node.isLeaf() {
 		root = node
-		tree.setParent(node)
+		tree.SetParent(node)
 	} else {
 		err = node.Errorf("two adjacent operators: %q and %q", tree, node)
 	}
 	return
 }
 
-func (ast *ast) Finish() {
+func (ast *Ast) Finish() {
 	if ast.root == nil && ast.forest != nil && len(ast.forest) >= 1 {
 		ast.root = ast.forest[len(ast.forest)-1]
 		ast.forest = ast.forest[0 : len(ast.forest)-1]
 	}
 }
 
-func (ast *ast) Eval(ctx kern.ExprContext) (result any, err error) {
+func (ast *Ast) Eval(ctx kern.ExprContext) (result any, err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			if errVal, ok := r.(error); ok {

scan/scanner.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // expr project scanner.go
-package expr
+package scan
 
 import (
 	"bufio"
@@ -13,9 +13,10 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/util"
 )
 
-type scanner struct {
+type Scanner struct {
 	current      *Token
 	prev         *Token
 	stage        *Token
@@ -25,8 +26,8 @@ type scanner struct {
 	translations map[Symbol]Symbol
 }
 
-func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *scanner) {
-	inst = &scanner{
+func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *Scanner) {
+	inst = &Scanner{
 		stream:       bufio.NewReader(s),
 		row:          1,
 		column:       1,
@@ -52,7 +53,11 @@ func DefaultTranslations() map[Symbol]Symbol {
 // 	return self.current
 // }
 
-func (scanner *scanner) readChar() (ch byte, err error) {
+func (scanner *Scanner) Current() *Token {
+	return scanner.current
+}
+
+func (scanner *Scanner) readChar() (ch byte, err error) {
 	if ch, err = scanner.stream.ReadByte(); err == nil {
 		if ch == '\n' {
 			scanner.row++
@@ -64,7 +69,7 @@ func (scanner *scanner) readChar() (ch byte, err error) {
 	return
 }
 
-func (scanner *scanner) unreadChar() (err error) {
+func (scanner *Scanner) unreadChar() (err error) {
 	if err = scanner.stream.UnreadByte(); err == nil {
 		if scanner.column--; scanner.column == 0 {
 			if scanner.row--; scanner.row == 0 {
@@ -77,7 +82,7 @@ func (scanner *scanner) unreadChar() (err error) {
 	return
 }
 
-func (scanner *scanner) UnreadToken() (err error) {
+func (scanner *Scanner) UnreadToken() (err error) {
 	if scanner.stage == nil {
 		scanner.stage = scanner.current
 		scanner.current = scanner.prev
@@ -87,7 +92,7 @@ func (scanner *scanner) UnreadToken() (err error) {
 	return
 }
 
-func (scanner *scanner) lastPos() (r, c int) {
+func (scanner *Scanner) LastPos() (r, c int) {
 	if scanner.prev != nil {
 		r = scanner.prev.row
 		c = scanner.prev.col
@@ -95,11 +100,11 @@ func (scanner *scanner) lastPos() (r, c int) {
 	return
 }
 
-func (scanner *scanner) Previous() *Token {
+func (scanner *Scanner) Previous() *Token {
 	return scanner.prev
 }
 
-func (scanner *scanner) Next() (tk *Token) {
+func (scanner *Scanner) Next() (tk *Token) {
 	scanner.prev = scanner.current
 	tk = scanner.current
 	if scanner.stage != nil {
@@ -111,7 +116,7 @@ func (scanner *scanner) Next() (tk *Token) {
 	return tk
 }
 
-func (scanner *scanner) fetchNextToken() (tk *Token) {
+func (scanner *Scanner) fetchNextToken() (tk *Token) {
 	var ch byte
 	if err := scanner.skipBlanks(); err != nil {
 		return scanner.makeErrorToken(err)
@@ -129,7 +134,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '>' {
 				tk = scanner.moveOn(SymPlusGreater, ch, next)
 			} else {
-				tk = scanner.makeToken(SymPlus, ch)
+				tk = scanner.MakeToken(SymPlus, ch)
 			}
 		case '-':
 			if next, _ := scanner.peek(); next == '-' {
@@ -137,7 +142,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '=' {
 				tk = scanner.moveOn(SymMinusEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymMinus, ch)
+				tk = scanner.MakeToken(SymMinus, ch)
 			}
 		case '*':
 			if next, _ := scanner.peek(); next == '*' {
@@ -147,7 +152,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next, _ = scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymStarEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymStar, ch)
+				tk = scanner.MakeToken(SymStar, ch)
 			}
 		case '/':
 			if next, _ := scanner.peek(); next == '*' {
@@ -159,11 +164,11 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 				scanner.readChar()
 				tk = scanner.fetchOnLineComment()
 			} else {
-				tk = scanner.makeToken(SymSlash, ch)
+				tk = scanner.MakeToken(SymSlash, ch)
 			}
 		case '\\':
 			if escape {
-				tk = scanner.makeToken(SymBackSlash, ch)
+				tk = scanner.MakeToken(SymBackSlash, ch)
 				escape = false
 			} else {
 				escape = true
@@ -174,24 +179,24 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next, _ = scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymVertBarEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymVertBar, ch)
+				tk = scanner.MakeToken(SymVertBar, ch)
 			}
 		case ',':
-			tk = scanner.makeToken(SymComma, ch)
+			tk = scanner.MakeToken(SymComma, ch)
 		case '^':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymCaretEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymCaret, ch)
+				tk = scanner.MakeToken(SymCaret, ch)
 			}
 		case ':':
 			if next, _ := scanner.peek(); next == ':' {
 				tk = scanner.moveOn(SymDoubleColon, ch, next)
 			} else {
-				tk = scanner.makeToken(SymColon, ch)
+				tk = scanner.MakeToken(SymColon, ch)
 			}
 		case ';':
-			tk = scanner.makeToken(SymSemiColon, ch)
+			tk = scanner.MakeToken(SymSemiColon, ch)
 		case '.':
 			//if next, _ := self.peek(); next >= '0' && next <= '9' {
 			//	tk = self.parseNumber(ch)
@@ -205,29 +210,29 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 					tk = scanner.moveOn(SymDoubleDot, ch, next)
 				}
 			} else {
-				tk = scanner.makeToken(SymDot, ch)
+				tk = scanner.MakeToken(SymDot, ch)
 			}
 		case '\'':
 			if escape {
-				tk = scanner.makeToken(SymQuote, ch)
+				tk = scanner.MakeToken(SymQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '"':
 			if escape {
-				tk = scanner.makeToken(SymDoubleQuote, ch)
+				tk = scanner.MakeToken(SymDoubleQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '`':
-			tk = scanner.makeToken(SymBackTick, ch)
+			tk = scanner.MakeToken(SymBackTick, ch)
 		case '!':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymNotEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymExclamation, ch)
+				tk = scanner.MakeToken(SymExclamation, ch)
 			}
 		case '?':
 			if next, _ := scanner.peek(); next == '?' {
@@ -237,7 +242,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '!' {
 				tk = scanner.moveOn(SymQuestionExclam, ch, next)
 			} else {
-				tk = scanner.makeToken(SymQuestion, ch)
+				tk = scanner.MakeToken(SymQuestion, ch)
 			}
 		case '&':
 			if next, _ := scanner.peek(); next == '&' {
@@ -245,16 +250,16 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next, _ = scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymAmpersandEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymAmpersand, ch)
+				tk = scanner.MakeToken(SymAmpersand, ch)
 			}
 		case '%':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymPercEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymPercent, ch)
+				tk = scanner.MakeToken(SymPercent, ch)
 			}
 		case '#':
-			tk = scanner.makeToken(SymHash, ch)
+			tk = scanner.MakeToken(SymHash, ch)
 		case '@':
 			if next, _ := scanner.peek(); (next >= 'a' && next <= 'z') || (next >= 'A' && next <= 'Z') {
 				scanner.readChar()
@@ -267,15 +272,15 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '@' {
 				tk = scanner.moveOn(SymDoubleAt, ch, next)
 			} else {
-				tk = scanner.makeToken(SymAt, ch)
+				tk = scanner.MakeToken(SymAt, ch)
 			}
 		case '_':
-			tk = scanner.makeToken(SymUndescore, ch)
+			tk = scanner.MakeToken(SymUndescore, ch)
 		case '=':
 			if next, _ := scanner.peek(); next == '=' {
 				tk = scanner.moveOn(SymDoubleEqual, ch, next)
 			} else {
-				tk = scanner.makeToken(SymEqual, ch)
+				tk = scanner.MakeToken(SymEqual, ch)
 			}
 		case '<':
 			if next, _ := scanner.peek(); next == '=' {
@@ -294,7 +299,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 			} else if next == '+' {
 				tk = scanner.moveOn(SymLessPlus, ch, next)
 			} else {
-				tk = scanner.makeToken(SymLess, ch)
+				tk = scanner.MakeToken(SymLess, ch)
 			}
 		case '>':
 			if next, _ := scanner.peek(); next == '=' {
@@ -309,7 +314,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 					tk = scanner.accept(SymDoubleGreater, ch, next)
 				}
 			} else {
-				tk = scanner.makeToken(SymGreater, ch)
+				tk = scanner.MakeToken(SymGreater, ch)
 			}
 		case '$':
 			if next, _ := scanner.peek(); next == '(' {
@@ -326,26 +331,26 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 				scanner.readChar()
 				tk = scanner.fetchIdentifier(next)
 			} else {
-				tk = scanner.makeToken(SymDollar, ch)
+				tk = scanner.MakeToken(SymDollar, ch)
 			}
 		case '(':
 			//			if next, _ := scanner.peek(); next == ')' {
 			//				tk = scanner.moveOn(SymOpenClosedRound, ch, next)
 			//			} else {
-			tk = scanner.makeToken(SymOpenRound, ch)
+			tk = scanner.MakeToken(SymOpenRound, ch)
 			//			}
 		case ')':
-			tk = scanner.makeToken(SymClosedRound, ch)
+			tk = scanner.MakeToken(SymClosedRound, ch)
 		case '[':
-			tk = scanner.makeToken(SymOpenSquare, ch)
+			tk = scanner.MakeToken(SymOpenSquare, ch)
 		case ']':
-			tk = scanner.makeToken(SymClosedSquare, ch)
+			tk = scanner.MakeToken(SymClosedSquare, ch)
 		case '{':
-			tk = scanner.makeToken(SymOpenBrace, ch)
+			tk = scanner.MakeToken(SymOpenBrace, ch)
 		case '}':
-			tk = scanner.makeToken(SymClosedBrace, ch)
+			tk = scanner.MakeToken(SymClosedBrace, ch)
 		case '~':
-			tk = scanner.makeToken(SymTilde, ch)
+			tk = scanner.MakeToken(SymTilde, ch)
 		case 0:
 			if escape {
 				tk = scanner.makeErrorToken(errors.New("incomplete escape sequence"))
@@ -372,7 +377,7 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 	return
 }
 
-func (scanner *scanner) sync(err error) error {
+func (scanner *Scanner) sync(err error) error {
 	if err == nil {
 		err = scanner.unreadChar()
 	}
@@ -395,7 +400,7 @@ func isHexDigit(ch byte) bool {
 	return (ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'f') || (ch >= 'A' && ch <= 'F')
 }
 
-func (scanner *scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int, digitFunc func(byte) bool, err error) {
+func (scanner *Scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int, digitFunc func(byte) bool, err error) {
 	var ch byte
 	var digitType string
 	firstCh = currentFirstCh
@@ -434,7 +439,7 @@ func (scanner *scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int
 	return
 }
 
-func (scanner *scanner) parseNumber(firstCh byte) (tk *Token) {
+func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sym Symbol = SymInteger
@@ -510,7 +515,7 @@ func (scanner *scanner) parseNumber(firstCh byte) (tk *Token) {
 			value, err = strconv.ParseInt(txt, numBase, 64)
 		}
 		if err == nil {
-			tk = scanner.makeValueToken(sym, txt, value)
+			tk = scanner.MakeValueToken(sym, txt, value)
 		} else {
 			tk = scanner.makeErrorToken(err)
 		}
@@ -518,7 +523,7 @@ func (scanner *scanner) parseNumber(firstCh byte) (tk *Token) {
 	return
 }
 
-func (scanner *scanner) fetchIdentifier(firstCh byte) (tk *Token) {
+func (scanner *Scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 	var err error
 	var sb strings.Builder
 	for ch := firstCh; err == nil && (ch == '_' || (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9')); ch, err = scanner.readChar() {
@@ -535,14 +540,14 @@ func (scanner *scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 		if sym, ok := keywords[uptxt]; ok {
 			tk = scanner.makeKeywordToken(sym, uptxt)
 		} else if uptxt == `TRUE` {
-			tk = scanner.makeValueToken(SymBool, txt, true)
+			tk = scanner.MakeValueToken(SymBool, txt, true)
 		} else if uptxt == `FALSE` {
-			tk = scanner.makeValueToken(SymBool, txt, false)
+			tk = scanner.MakeValueToken(SymBool, txt, false)
 		} else if ch, _ := scanner.peek(); ch == '(' {
 			scanner.readChar()
-			tk = scanner.makeValueToken(SymFuncCall, txt+"(", txt)
+			tk = scanner.MakeValueToken(SymFuncCall, txt+"(", txt)
 		} else {
-			tk = scanner.makeValueToken(SymIdentifier, txt, txt)
+			tk = scanner.MakeValueToken(SymIdentifier, txt, txt)
 		}
 	}
 
@@ -562,20 +567,20 @@ func (scanner *scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 	return
 }
 
-func (scanner *scanner) fetchBlockComment() *Token {
+func (scanner *Scanner) fetchBlockComment() *Token {
 	return scanner.fetchUntil(SymComment, false, '*', '/')
 }
 
-func (scanner *scanner) fetchOnLineComment() *Token {
+func (scanner *Scanner) fetchOnLineComment() *Token {
 	return scanner.fetchUntil(SymComment, true, '\n')
 }
 
-func (scanner *scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (tk *Token) {
+func (scanner *Scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sb strings.Builder
 	var value string
-	ring := NewByteSlider(len(endings))
+	ring := util.NewByteSlider(len(endings))
 	endReached := false
 	for ch, err = scanner.readChar(); err == nil && !endReached; {
 		sb.WriteByte(ch)
@@ -593,14 +598,14 @@ func (scanner *scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (
 	}
 
 	if endReached {
-		tk = scanner.makeValueToken(sym, "", value)
+		tk = scanner.MakeValueToken(sym, "", value)
 	} else {
 		tk = scanner.makeErrorToken(err)
 	}
 	return
 }
 
-func (scanner *scanner) fetchString(termCh byte, addQuote bool) (tk *Token) {
+func (scanner *Scanner) fetchString(termCh byte, addQuote bool) (tk *Token) {
 	var err error
 	var ch, prev byte
 	var sb strings.Builder
@@ -639,15 +644,15 @@ func (scanner *scanner) fetchString(termCh byte, addQuote bool) (tk *Token) {
 	} else {
 		txt := sb.String()
 		if addQuote {
-			tk = scanner.makeValueToken(SymString, `"`+txt+`"`, txt)
+			tk = scanner.MakeValueToken(SymString, `"`+txt+`"`, txt)
 		} else {
-			tk = scanner.makeValueToken(SymString, txt, txt)
+			tk = scanner.MakeValueToken(SymString, txt, txt)
 		}
 	}
 	return
 }
 
-func (scanner *scanner) peek() (next byte, err error) {
+func (scanner *Scanner) peek() (next byte, err error) {
 	var one []byte
 	if one, err = scanner.stream.Peek(1); err == nil {
 		next = one[0]
@@ -655,7 +660,7 @@ func (scanner *scanner) peek() (next byte, err error) {
 	return
 }
 
-func (scanner *scanner) skipBlanks() (err error) {
+func (scanner *Scanner) skipBlanks() (err error) {
 	var one []byte
 	for one, err = scanner.stream.Peek(1); err == nil && one[0] <= 32; one, err = scanner.stream.Peek(1) {
 		scanner.readChar()
@@ -663,7 +668,7 @@ func (scanner *scanner) skipBlanks() (err error) {
 	return
 }
 
-func (scanner *scanner) translate(sym Symbol) Symbol {
+func (scanner *Scanner) translate(sym Symbol) Symbol {
 	if scanner.translations != nil {
 		if translatedSym, ok := scanner.translations[sym]; ok {
 			return translatedSym
@@ -672,7 +677,7 @@ func (scanner *scanner) translate(sym Symbol) Symbol {
 	return sym
 }
 
-func (scanner *scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	// for i := 1; i < len(chars); i++ {
 	if len(chars) > 1 {
@@ -682,26 +687,26 @@ func (scanner *scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
 	return
 }
 
-func (scanner *scanner) accept(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) accept(sym Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	return
 }
 
-func (scanner *scanner) makeToken(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) MakeToken(sym Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	return
 }
 
-func (scanner *scanner) makeKeywordToken(sym Symbol, upperCaseKeyword string) (tk *Token) {
+func (scanner *Scanner) makeKeywordToken(sym Symbol, upperCaseKeyword string) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), upperCaseKeyword)
 	return
 }
 
-func (scanner *scanner) makeValueToken(sym Symbol, source string, value any) (tk *Token) {
+func (scanner *Scanner) MakeValueToken(sym Symbol, source string, value any) (tk *Token) {
 	tk = NewValueToken(scanner.row, scanner.column, scanner.translate(sym), source, value)
 	return
 }
 
-func (scanner *scanner) makeErrorToken(err error) *Token {
+func (scanner *Scanner) makeErrorToken(err error) *Token {
 	return NewErrorToken(scanner.row, scanner.column, err)
 }

scan/symbol-map.go

@@ -0,0 +1,232 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// Symbol.go
+package scan
+
+import (
+	"strings"
+)
+
+var symbolMap map[Symbol]symbolSpec
+
+type SymbolClass int16
+
+const (
+	SymClassOperator SymbolClass = iota
+	SymClassCommand
+	SymClassIdentifier
+	SymClassDelimiter
+	SymClassParenthesis
+	SymClassDeclaration
+	SymClassValue
+	SymClassOther
+)
+
+type symbolSpec struct {
+	repr   string
+	kind   SymbolClass
+	opType TermPosition
+}
+
+func init() {
+
+	symbolMap = map[Symbol]symbolSpec{
+		SymUnknown:            {"<unknown>", SymClassOther, PosLeaf},  //  -1: Unknown symbol
+		SymNone:               {"<null>", SymClassOther, PosLeaf},     //   0: Null value for variable of type symbol
+		SymError:              {"<error>", SymClassOther, PosLeaf},    //   1: Error reading from stream
+		SymEos:                {"<eos>", SymClassOther, PosLeaf},      //   2: End of stream
+		SymMinus:              {"-", SymClassOperator, PosInfix},      //   3: '-'
+		SymMinusEqual:         {"-=", SymClassOperator, PosInfix},     //   4: '-='
+		SymDoubleMinus:        {"--", SymClassOperator, PosPostfix},   //   5: '--'
+		SymPlus:               {"+", SymClassOperator, PosInfix},      //   6: '+'
+		SymPlusEqual:          {"+=", SymClassOperator, PosInfix},     //   7: '+='
+		SymDoublePlus:         {"++", SymClassOperator, PosPostfix},   //   8: '++'
+		SymStar:               {"*", SymClassOperator, PosInfix},      //   9: '*'
+		SymDoubleStar:         {"**", SymClassOperator, PosInfix},     //  10: '**'
+		SymSlash:              {"/", SymClassOperator, PosInfix},      //  11: '/'
+		SymBackSlash:          {"\\", SymClassOperator, PosLeaf},      //  12: '\'
+		SymVertBar:            {"|", SymClassOperator, PosInfix},      //  13: '|'
+		SymDoubleVertBar:      {"||", SymClassOperator, PosInfix},     //  14: '||'
+		SymComma:              {",", SymClassOperator, PosInfix},      //  15: ','
+		SymColon:              {":", SymClassOperator, PosInfix},      //  16: ':'
+		SymSemiColon:          {";", SymClassOperator, PosInfix},      //  17: ';'
+		SymDot:                {".", SymClassOperator, PosInfix},      //  18: '.'
+		SymDotSlash:           {"./", SymClassOperator, PosInfix},     //  19: './'
+		SymQuote:              {"'", SymClassDelimiter, PosLeaf},      //  20: '\''
+		SymDoubleQuote:        {"\"", SymClassDelimiter, PosLeaf},     //  21: '"'
+		SymBackTick:           {"`", SymClassDelimiter, PosLeaf},      //  22: '`'
+		SymExclamation:        {"!", SymClassOperator, PosPostfix},    //  23: '!'
+		SymQuestion:           {"?", SymClassOperator, PosInfix},      //  24: '?'
+		SymAmpersand:          {"&", SymClassOperator, PosInfix},      //  25: '&'
+		SymDoubleAmpersand:    {"&&", SymClassOperator, PosInfix},     //  26: '&&'
+		SymPercent:            {"%", SymClassOperator, PosInfix},      //  27: '%'
+		SymAt:                 {"@", SymClassOperator, PosPrefix},     //  28: '@'
+		SymUndescore:          {"_", SymClassIdentifier, PosLeaf},     //  29: '_'
+		SymEqual:              {"=", SymClassOperator, PosInfix},      //  30: '='
+		SymDoubleEqual:        {"==", SymClassOperator, PosInfix},     //  31: '=='
+		SymLess:               {"<", SymClassOperator, PosInfix},      //  32: '<'
+		SymLessOrEqual:        {"<=", SymClassOperator, PosInfix},     //  33: '<='
+		SymGreater:            {">", SymClassOperator, PosInfix},      //  34: '>'
+		SymGreaterOrEqual:     {">=", SymClassOperator, PosInfix},     //  35: '>='
+		SymLessGreater:        {"<>", SymClassOperator, PosInfix},     //  36: '<>'
+		SymNotEqual:           {"!=", SymClassOperator, PosInfix},     //  37: '!='
+		SymDollar:             {"$", SymClassOperator, PosPrefix},     //  38: '$'
+		SymHash:               {"#", SymClassOperator, PosPrefix},     //  39: '#'
+		SymOpenRound:          {"(", SymClassParenthesis, PosPrefix},  //  40: '('
+		SymClosedRound:        {")", SymClassParenthesis, PosPostfix}, //  41: ')'
+		SymOpenSquare:         {"[", SymClassParenthesis, PosPrefix},  //  42: '['
+		SymClosedSquare:       {"]", SymClassParenthesis, PosPostfix}, //  43: ']'
+		SymOpenBrace:          {"{", SymClassParenthesis, PosPrefix},  //  44: '{'
+		SymClosedBrace:        {"}", SymClassParenthesis, PosPostfix}, //  45: '}'
+		SymTilde:              {"~", SymClassOperator, PosPrefix},     //  46: '~'
+		SymDoubleQuestion:     {"??", SymClassOperator, PosInfix},     //  47: '??'
+		SymQuestionEqual:      {"?=", SymClassOperator, PosInfix},     //  48: '?='
+		SymQuestionExclam:     {"?!", SymClassOperator, PosInfix},     //  49: '?!'
+		SymDoubleAt:           {"@@", SymClassCommand, PosLeaf},       //  50: '@@'
+		SymDoubleColon:        {"::", SymClassOperator, PosInfix},     //  51: '::'
+		SymDoubleGreater:      {">>", SymClassOperator, PosInfix},     //  52: '>>'
+		SymDoubleLess:         {"<<", SymClassOperator, PosInfix},     //  53: '<<'
+		SymCaret:              {"^", SymClassOperator, PosInfix},      //  54: '^'
+		SymDollarRound:        {"$(", SymClassOperator, PosPrefix},    //  55: '$('
+		SymOpenClosedRound:    {"()", SymClassOperator, PosPostfix},   //  56: '()'
+		SymDoubleDollar:       {"$$", SymClassCommand, PosLeaf},       //  57: '$$'
+		SymDoubleDot:          {"..", SymClassOperator, PosInfix},     //  58: '..'
+		SymTripleDot:          {"...", SymClassOperator, PosPostfix},  //  59: '...'
+		SymStarEqual:          {"*=", SymClassOperator, PosInfix},     //  60: '*='
+		SymSlashEqual:         {"/=", SymClassOperator, PosInfix},     //  61: '/='
+		SymPercEqual:          {"%=", SymClassOperator, PosInfix},     //  62: '%='
+		SymDoubleLessEqual:    {"<<=", SymClassOperator, PosInfix},    //  63: '<<='
+		SymDoubleGreaterEqual: {">>=", SymClassOperator, PosInfix},    //  64: '>>='
+		SymAmpersandEqual:     {"&=", SymClassOperator, PosInfix},     //  65: '&='
+		SymVertBarEqual:       {"|=", SymClassOperator, PosInfix},     //  65: '|='
+		SymCaretEqual:         {"^=", SymClassOperator, PosInfix},     //  66: '^='
+		SymPlusGreater:        {"+>", SymClassOperator, PosInfix},     //  67: '+>'
+		SymLessPlus:           {"<+", SymClassOperator, PosInfix},     //  68: '<+'
+		SymPreInc:             {"++", SymClassOperator, PosPrefix},    //    : '++'
+		SymPreDec:             {"--", SymClassOperator, PosPrefix},    //    : '--'
+		// SymChangeSign
+		// SymUnchangeSign
+		// SymIdentifier
+		// SymBool
+		// SymInteger
+		// SymVariable
+		// SymFloat
+		// SymFraction
+		// SymString
+		// SymIterator
+		// SymOr:  "or",
+		// SymAnd: "and",
+		// SymNot: "not",
+		// SymComment
+		// SymFuncCall
+		// SymFuncDef
+		// SymList
+		// SymDict
+		// SymIndex
+		// SymExpression
+		// SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
+		// SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
+		// // SymOpenComment                       //   0: '/*'
+		// // SymClosedComment                     //   0: '*/'
+		// // SymOneLineComment                    //   0: '//'
+		// keywordBase
+		SymKwAnd:     {"and", SymClassOperator, PosInfix},
+		SymKwNot:     {"not", SymClassOperator, PosInfix},
+		SymKwOr:      {"or", SymClassOperator, PosInfix},
+		SymKwBut:     {"but", SymClassOperator, PosInfix},
+		SymKwMap:     {"map", SymClassOperator, PosInfix},
+		SymKwFilter:  {"filter", SymClassOperator, PosInfix},
+		SymKwDigest:  {"digest", SymClassOperator, PosInfix},
+		SymKwCat:     {"cat", SymClassOperator, PosInfix},
+		SymKwJoin:    {"join", SymClassOperator, PosInfix},
+		SymKwGroupBy: {"groupby", SymClassOperator, PosInfix},
+		SymKwFunc:    {"func(", SymClassDeclaration, PosPrefix},
+		SymKwBuiltin: {"builtin", SymClassOperator, PosPrefix},
+		SymKwPlugin:  {"plugin", SymClassOperator, PosPrefix},
+		SymKwIn:      {"in", SymClassOperator, PosInfix},
+		SymKwInclude: {"include", SymClassOperator, PosPrefix},
+		SymKwNil:     {"nil", SymClassValue, PosLeaf},
+		SymKwUnset:   {"unset", SymClassOperator, PosPrefix},
+	}
+}
+
+func SymToString(sym Symbol) string {
+	if s, ok := symbolMap[sym]; ok {
+		return s.repr
+	}
+	return ""
+}
+
+func SymListToString(symList []Symbol, quote bool) string {
+	var sb strings.Builder
+	if len(symList) == 0 {
+		sb.WriteString("<nothing>")
+	} else {
+		for _, sym := range symList {
+			if sb.Len() > 0 {
+				sb.WriteByte(',')
+				sb.WriteByte(' ')
+			}
+			if quote {
+				sb.WriteByte('`')
+			}
+			sb.WriteString(SymToString(sym))
+			if quote {
+				sb.WriteByte('`')
+			}
+		}
+	}
+	return sb.String()
+}
+
+func StringEndsWithOperator(s string) bool {
+	return endingOperator(s) != SymNone
+}
+
+// func endingOperator(s string) (sym Symbol) {
+// 	var matchLength = 0
+// 	sym = SymNone
+// 	lower := strings.TrimRight(strings.ToLower(s), " \t")
+// 	for symbol, spec := range symbolMap {
+// 		if strings.HasSuffix(lower, spec.repr) {
+// 			if len(spec.repr) > matchLength {
+// 				matchLength = len(spec.repr)
+// 				if spec.kind == symClassOperator && (spec.opType == PosInfix || spec.opType == PosPrefix) {
+// 					sym = symbol
+// 				} else {
+// 					sym = SymNone
+// 				}
+// 			}
+// 		}
+// 	}
+// 	return
+// }
+
+func endingOperator(s string) (sym Symbol) {
+	var matchLength = 0
+	var repr string
+	sym = SymNone
+	lower := strings.TrimRight(strings.ToLower(s), " \t")
+	for symbol, spec := range symbolMap {
+		if len(spec.repr) > matchLength || repr == spec.repr {
+			if strings.HasSuffix(lower, spec.repr) {
+				if isNotEndingSymbol(spec) && repr != spec.repr {
+					repr = spec.repr
+					matchLength = len(spec.repr)
+					sym = symbol
+				} else {
+					sym = SymNone
+					break
+					// matchLength = 0
+				}
+			}
+		}
+	}
+	return
+}
+
+func isNotEndingSymbol(spec symbolSpec) bool {
+	return (spec.kind == SymClassOperator && (spec.opType == PosInfix || spec.opType == PosPrefix)) ||
+		(spec.kind == SymClassParenthesis && spec.opType == PosPrefix)
+}

scan/symbol.go

@@ -1,8 +1,8 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
 // Symbol.go
-package expr
+package scan
 
 type Symbol int16
 
@@ -122,6 +122,7 @@ const (
 	SymKwMap
 	SymKwFilter
 	SymKwDigest
+	SymKwCat
 	SymKwGroupBy
 	SymKwJoin
 	SymKwNil
@@ -141,6 +142,7 @@ func init() {
 		"IN":      SymKwIn,
 		"INCLUDE": SymKwInclude,
 		"MAP":     SymKwMap,
+		"CAT":     SymKwCat,
 		"FILTER":  SymKwFilter,
 		"NOT":     SymKwNot,
 		"OR":      SymKwOr,