moved scanner sources to package 'scan'

bind-expr-functions.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

@@ -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)

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 {

function.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 // ---- Function template
@@ -223,7 +224,7 @@ func (info *funcInfo) ParamSpec(paramName string) kern.ExprFuncParam {
 	return nil
 }
 
-func initActualParams(ctx kern.ExprContext, info kern.ExprFunc, callTerm *term) (actualParams map[string]any, err error) {
+func initActualParams(ctx kern.ExprContext, info kern.ExprFunc, callTerm *scan.Term) (actualParams map[string]any, err error) {
 	var varArgs []any
 	var varName string
 
@@ -235,7 +236,7 @@ func initActualParams(ctx kern.ExprContext, info kern.ExprFunc, callTerm *term)
 		return
 	}
 
-	for i, tree := range callTerm.children {
+	for i, tree := range callTerm.Children {
 		var paramValue any
 		paramCtx := ctx.Clone()
 		if paramValue, err = tree.Compute(paramCtx); err != nil {
@@ -254,14 +255,14 @@ func initActualParams(ctx kern.ExprContext, info kern.ExprFunc, callTerm *term)
 			} else if i < len(formalParams) {
 				spec := formalParams[i]
 				if spec.IsRepeat() {
-					varArgs = make([]any, 0, len(callTerm.children)-i)
+					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))
+				err = kern.ErrTooManyParams(info.Name(), len(formalParams), len(callTerm.Children))
 				break
 			}
 		} else {

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 {
@@ -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 {

kern/expr.go

@@ -2,15 +2,11 @@
 // All rights reserved.
 
 // expr.go
-package expr
-
-import (
-	kern "git.portale-stac.it/go-pkg/expr/kern"
-)
+package kern
 
 // ----Expression interface
 type Expr interface {
-	kern.Typer
-	Eval(ctx kern.ExprContext) (result any, err error)
+	Typer
+	Eval(ctx ExprContext) (result any, err error)
 	String() string
 }

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

@@ -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

@@ -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
@@ -44,35 +45,35 @@ 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 {
+			if len(param.Children) > 0 {
 				flags |= PfDefault
-				if defValue, err = param.children[0].Compute(ctx); err != nil {
+				if defValue, err = param.Children[0].Compute(ctx); err != nil {
 					return
 				}
 			}

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 +125,33 @@ 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 = evalSibling(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 = evalSibling(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 = evalSibling(ctx, opTerm.Children, intVal); err == nil {
 			v, err = NewIntIterator(args)
 		}
 	} else {
 		var list []any
-		if list, err = evalSibling(ctx, opTerm.children, firstChildValue); err == nil {
+		if list, err = evalSibling(ctx, opTerm.Children, firstChildValue); err == nil {
 			v = NewArrayIterator(list)
 		}
 	}
 	return
 }
 
-func evalSibling(ctx kern.ExprContext, terms []*term, firstChildValue any) (list []any, err error) {
+func evalSibling(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

@@ -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

@@ -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

@@ -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

@@ -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

@@ -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

@@ -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

@@ -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

@@ -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
 	}
 
@@ -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

@@ -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-context.go

@@ -6,29 +6,30 @@ package expr
 
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- context term
 
-func newContextTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 1),
-		position: posPrefix,
-		priority: priIncDec,
-		evalFunc: evalContextValue,
+func newContextTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 1),
+		Position: scan.PosPrefix,
+		Priority: scan.PriIncDec,
+		EvalFunc: evalContextValue,
 	}
 }
 
-func evalContextValue(ctx 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
 		}
@@ -53,12 +54,12 @@ func evalContextValue(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 			v = d
 		}
 	} else {
-		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
+		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleDollar, newContextTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleDollar, newContextTerm)
 }

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

@@ -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
@@ -106,7 +107,7 @@ 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{
@@ -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

@@ -9,30 +9,31 @@ 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
 	}
 
@@ -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

@@ -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

@@ -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

@@ -9,30 +9,31 @@ import (
 	"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) {
+func evalFilter(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var it kern.Iterator
 	var item 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
 	}
 
@@ -45,7 +46,7 @@ func evalFilter(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 success, valid := kern.ToBool(rightValue); valid {
 				if success {
 					values.AppendItem(item)
@@ -70,5 +71,5 @@ func evalFilter(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwFilter, newFilterTerm)
+	scan.RegisterTermConstructor(scan.SymKwFilter, newFilterTerm)
 }

operator-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

@@ -10,32 +10,33 @@ 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
 
-	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
 	}
 
@@ -43,10 +44,10 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		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 +102,5 @@ 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

@@ -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

@@ -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

@@ -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

@@ -6,34 +6,35 @@ 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) {
+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
 	}
 
@@ -41,19 +42,19 @@ func evalPrepend(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		list, _ := rightValue.(*kern.ListType)
 		newList := append(kern.ListType{leftValue}, *list...)
 		v = &newList
-		if opTerm.children[1].symbol() == SymVariable {
-			ctx.UnsafeSetVar(opTerm.children[1].Source(), v)
+		if opTerm.Children[1].Symbol() == scan.SymVariable {
+			ctx.UnsafeSetVar(opTerm.Children[1].Source(), v)
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
 
-func evalAppend(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalAppend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 
-	if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
 		return
 	}
 
@@ -61,11 +62,11 @@ func evalAppend(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 		list, _ := leftValue.(*kern.ListType)
 		newList := append(*list, rightValue)
 		v = &newList
-		if opTerm.children[0].symbol() == SymVariable {
-			ctx.UnsafeSetVar(opTerm.children[0].Source(), v)
+		if opTerm.Children[0].Symbol() == scan.SymVariable {
+			ctx.UnsafeSetVar(opTerm.Children[0].Source(), v)
 		}
 	} else {
-		err = opTerm.errIncompatibleTypes(leftValue, rightValue)
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
@@ -90,6 +91,6 @@ 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

@@ -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

@@ -9,34 +9,35 @@ import (
 	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 //-------- join term
 
-func newJoinTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priIterOp,
-		evalFunc: evalJoin,
+func newJoinTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriIterOp,
+		EvalFunc: evalJoin,
 	}
 }
 
-func evalJoin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
+func evalJoin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var itLeft, itRight kern.Iterator
 	var item 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 rightValue, err = opTerm.children[1].Compute(ctx); err != nil {
+	if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
 		return
 	}
 
@@ -63,5 +64,5 @@ func evalJoin(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwJoin, newJoinTerm)
+	scan.RegisterTermConstructor(scan.SymKwJoin, newJoinTerm)
 }

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

@@ -9,30 +9,31 @@ import (
 	"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) {
+func evalMap(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var it kern.Iterator
 	var item 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
 	}
 
@@ -45,7 +46,7 @@ func evalMap(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 {
 			values.AppendItem(rightValue)
 		}
 		ctx.DeleteVar("_#")
@@ -66,5 +67,5 @@ func evalMap(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymKwMap, newMapTerm)
+	scan.RegisterTermConstructor(scan.SymKwMap, newMapTerm)
 }

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

@@ -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

@@ -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

@@ -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

@@ -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

@@ -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

@@ -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

@@ -6,35 +6,36 @@ 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
 	}
 
@@ -42,31 +43,31 @@ func evalRightShift(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
-func newLeftShiftTerm(tk *Token) (inst *term) {
-	return &term{
-		tk:       *tk,
-		children: make([]*term, 0, 2),
-		position: posInfix,
-		priority: priBinShift,
-		evalFunc: evalLeftShift,
+func newLeftShiftTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriBinShift,
+		EvalFunc: evalLeftShift,
 	}
 }
 
-func bitLeftShift(opTerm *term, leftValue, rightValue any) (v any, err error) {
+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
 	}
 
@@ -76,6 +77,6 @@ func evalLeftShift(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymDoubleGreater, newRightShiftTerm)
-	registerTermConstructor(SymDoubleLess, newLeftShiftTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleGreater, newRightShiftTerm)
+	scan.RegisterTermConstructor(scan.SymDoubleLess, newLeftShiftTerm)
 }

operator-sign.go

@@ -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

@@ -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

@@ -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

@@ -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()
 		}

scan/ast.go

@@ -2,7 +2,7 @@
 // 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

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

scan/symbol.go

@@ -2,7 +2,7 @@
 // All rights reserved.
 
 // Symbol.go
-package expr
+package scan
 
 type Symbol int16
 

scan/t_scanner_test.go

@@ -2,7 +2,7 @@
 // All rights reserved.
 
 // t_scanner_test.go
-package expr
+package scan
 
 import (
 	"errors"

scan/term-constructor-registry.go

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

scan/term.go

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

scan/token.go

@@ -2,7 +2,7 @@
 // All rights reserved.
 
 // token.go
-package expr
+package scan
 
 import (
 	"fmt"
@@ -51,6 +51,18 @@ func NewErrorToken(row, col int, err error) *Token {
 	return NewValueToken(row, col, SymError, fmt.Sprintf("[%d:%d]", row, col), err)
 }
 
+func (tk *Token) Source() string {
+	return tk.source
+}
+
+func (tk *Token) Row() int {
+	return tk.row
+}
+
+func (tk *Token) Col() int {
+	return tk.col
+}
+
 func (tk *Token) Clone() (c *Token) {
 	return NewValueToken(tk.row, tk.col, tk.Sym, tk.source, tk.Value)
 }

symbol-map.go

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

t_ast_test.go

@@ -7,47 +7,49 @@ package expr
 import (
 	"errors"
 	"testing"
+
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 func TestAstString(t *testing.T) {
-	tree := NewAst()
+	tree := scan.NewAst()
 	if gotResult := tree.String(); gotResult != "(nil)" {
 		t.Errorf(`result: got %q, want "(nil)"`, gotResult)
 	}
 }
 
 func TestAddTokensGood(t *testing.T) {
-	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
-	tk2 := NewToken(0, 0, SymPlus, "+")
-	tk3 := NewValueToken(0, 0, SymInteger, "50", 500)
+	tk1 := scan.NewValueToken(0, 0, scan.SymInteger, "100", 100)
+	tk2 := scan.NewToken(0, 0, scan.SymPlus, "+")
+	tk3 := scan.NewValueToken(0, 0, scan.SymInteger, "50", 500)
 
-	tree := NewAst()
-	if gotErr := tree.addTokens(tk1, tk2, tk3); gotErr != nil {
+	tree := scan.NewAst()
+	if gotErr := tree.AddTokens(tk1, tk2, tk3); gotErr != nil {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}
 }
 
 func TestAddTokensBad(t *testing.T) {
-	tk0 := NewValueToken(0, 0, SymInteger, "200", 200)
-	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
-	tk2 := NewToken(0, 0, SymPlus, "+")
-	tk3 := NewValueToken(0, 0, SymInteger, "50", 500)
+	tk0 := scan.NewValueToken(0, 0, scan.SymInteger, "200", 200)
+	tk1 := scan.NewValueToken(0, 0, scan.SymInteger, "100", 100)
+	tk2 := scan.NewToken(0, 0, scan.SymPlus, "+")
+	tk3 := scan.NewValueToken(0, 0, scan.SymInteger, "50", 500)
 
 	wantErr := errors.New(`[0:0] two adjacent operators: "200" and "100"`)
 
-	tree := NewAst()
-	if gotErr := tree.addTokens(tk0, tk1, tk2, tk3); gotErr != nil && gotErr.Error() != wantErr.Error() {
+	tree := scan.NewAst()
+	if gotErr := tree.AddTokens(tk0, tk1, tk2, tk3); gotErr != nil && gotErr.Error() != wantErr.Error() {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}
 }
 
 func TestAddUnknownTokens(t *testing.T) {
-	tk0 := NewToken(0, 0, SymPercent, "%")
+	tk0 := scan.NewToken(0, 0, scan.SymPercent, "%")
 
 	wantErr := errors.New(`unexpected token "%"`)
 
-	tree := NewAst()
-	if _, gotErr := tree.addToken(tk0); gotErr != nil && gotErr.Error() != wantErr.Error() {
+	tree := scan.NewAst()
+	if _, gotErr := tree.AddToken(tk0); gotErr != nil && gotErr.Error() != wantErr.Error() {
 		t.Errorf("err: got <%v>, want <%v>", gotErr, wantErr)
 	}
 }

t_common_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 type inputType struct {
@@ -70,7 +71,7 @@ func getWantedError(input *inputType) error {
 }
 
 func doTest(t *testing.T, ctx kern.ExprContext, section string, input *inputType, count int) (good bool) {
-	var ast Expr
+	var ast kern.Expr
 	var gotResult any
 	var gotErr error
 
@@ -84,7 +85,7 @@ func doTest(t *testing.T, ctx kern.ExprContext, section string, input *inputType
 	logTest(t, count, section, input.source, input.wantResult, wantErr)
 
 	r := strings.NewReader(input.source)
-	scanner := NewScanner(r, DefaultTranslations())
+	scanner := scan.NewScanner(r, scan.DefaultTranslations())
 
 	good = true
 	if ast, gotErr = parser.Parse(scanner); gotErr == nil {

t_dict_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 func TestDictParser(t *testing.T) {
@@ -52,7 +53,7 @@ func TestDictParser(t *testing.T) {
 	// }
 
 	for i, input := range inputs {
-		var expr *ast
+		var expr *scan.Ast
 		var gotResult any
 		var gotErr error
 
@@ -65,7 +66,7 @@ func TestDictParser(t *testing.T) {
 		logTest(t, i+1, "Dict", input.source, input.wantResult, input.wantErr)
 
 		r := strings.NewReader(input.source)
-		scanner := NewScanner(r, DefaultTranslations())
+		scanner := scan.NewScanner(r, scan.DefaultTranslations())
 
 		good := true
 		if expr, gotErr = parser.Parse(scanner); gotErr == nil {
@@ -124,7 +125,7 @@ func TestDictToStringMultiLine(t *testing.T) {
   "first": 1
 }`
 	args := map[any]any{
-		"first": newLiteralTerm(NewValueToken(0, 0, SymInteger, "1", 1)),
+		"first": newLiteralTerm(scan.NewValueToken(0, 0, scan.SymInteger, "1", 1)),
 	}
 	dict := kern.NewDict(args)
 	got := dict.ToString(kern.MultiLine)
@@ -146,7 +147,7 @@ func TestDictToString(t *testing.T) {
 	section := "dict-ToString-SL"
 	want := `{"first": 1}`
 	args := map[any]any{
-		"first": newLiteralTerm(NewValueToken(0, 0, SymInteger, "1", 1)),
+		"first": newLiteralTerm(scan.NewValueToken(0, 0, scan.SymInteger, "1", 1)),
 	}
 	dict := kern.NewDict(args)
 	got := dict.ToString(0)

t_symbol_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 func TestOperatorEnding(t *testing.T) {
@@ -28,7 +29,7 @@ func TestOperatorEnding(t *testing.T) {
 }
 
 func testStringEndingWithOperator(source string) bool {
-	return StringEndsWithOperator(source)
+	return scan.StringEndsWithOperator(source)
 }
 
 func testStringArrayEndingWithOperatorSpec(t *testing.T, section string, inputs []inputType, spec ...int) {

t_term_test.go

@@ -6,15 +6,17 @@ package expr
 
 import (
 	"testing"
+
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 func TestString(t *testing.T) {
-	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
-	tk2 := NewToken(0, 0, SymPlus, "+")
-	tk3 := NewValueToken(0, 0, SymInteger, "50", 500)
+	tk1 := scan.NewValueToken(0, 0, scan.SymInteger, "100", 100)
+	tk2 := scan.NewToken(0, 0, scan.SymPlus, "+")
+	tk3 := scan.NewValueToken(0, 0, scan.SymInteger, "50", 500)
 
-	tree := NewAst()
-	if gotErr := tree.addTokens(tk1, tk2, tk3); gotErr == nil {
+	tree := scan.NewAst()
+	if gotErr := tree.AddTokens(tk1, tk2, tk3); gotErr == nil {
 		t.Log("Tree:", tree)
 	} else {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
@@ -22,22 +24,22 @@ func TestString(t *testing.T) {
 }
 
 func TestGetRoom(t *testing.T) {
-	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
+	tk1 := scan.NewValueToken(0, 0, scan.SymInteger, "100", 100)
 
-	tree := NewAst()
-	if gotErr := tree.addTokens(tk1); gotErr == nil {
-		t.Log("Tree-root room:", tree.root.getRoom())
+	tree := scan.NewAst()
+	if gotErr := tree.AddTokens(tk1); gotErr == nil {
+		t.Log("Tree-root room:", tree.Root().GetRoom())
 	} else {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}
 }
 
 func TestGetChildrenCount(t *testing.T) {
-	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
+	tk1 := scan.NewValueToken(0, 0, scan.SymInteger, "100", 100)
 
-	tree := NewAst()
-	if gotErr := tree.addTokens(tk1); gotErr == nil {
-		t.Log("Tree-root children count:", tree.root.GetChildCount())
+	tree := scan.NewAst()
+	if gotErr := tree.AddTokens(tk1); gotErr == nil {
+		t.Log("Tree-root children count:", tree.Root().GetChildCount())
 	} else {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}

t_token_test.go

@@ -7,27 +7,29 @@ package expr
 import (
 	"fmt"
 	"testing"
+
+	"git.portale-stac.it/go-pkg/expr/scan"
 )
 
 func TestDevString(t *testing.T) {
 	type inputType struct {
 		source     string
-		sym        Symbol
+		sym        scan.Symbol
 		value      any
 		wantResult string
 	}
 
 	inputs := []inputType{
-		/*   1 */ {"100", SymInteger, 100, fmt.Sprintf(`[%d]"100"{100}`, SymInteger)},
-		/*   2 */ {"+", SymPlus, nil, fmt.Sprintf(`[%d]"+"{}`, SymPlus)},
+		/*   1 */ {"100", scan.SymInteger, 100, fmt.Sprintf(`[%d]"100"{100}`, scan.SymInteger)},
+		/*   2 */ {"+", scan.SymPlus, nil, fmt.Sprintf(`[%d]"+"{}`, scan.SymPlus)},
 	}
 
 	for i, input := range inputs {
-		var tk *Token
+		var tk *scan.Token
 		if input.value == nil {
-			tk = NewToken(0, 0, input.sym, input.source)
+			tk = scan.NewToken(0, 0, input.sym, input.source)
 		} else {
-			tk = NewValueToken(0, 0, input.sym, input.source, input.value)
+			tk = scan.NewValueToken(0, 0, input.sym, input.source, input.value)
 		}
 
 		t.Logf("Test nr %2d: %q --> %q", i+1, input.source, input.wantResult)

term.go

@@ -1,300 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// term.go
-package expr
-
-import (
-	"strings"
-
-	"git.portale-stac.it/go-pkg/expr/kern"
-)
-
-type termPriority uint32
-
-const (
-	priNone termPriority = iota
-	priRange
-	priIterOp // map, filter, digest, etc
-	priBut
-	priAssign
-	priInsert
-	priOr
-	priAnd
-	priNot
-	priRelational
-	priBitwiseOr
-	priBitwiseAnd
-	priBitwiseNot
-	priSum
-	priProduct
-	priFraction
-	priSelector
-	priBinShift
-	priSign
-	priFact
-	priIterValue
-	priDefault
-	priIncDec
-	priDot
-	priDereference
-	priValue
-)
-
-type termPosition uint8
-
-const (
-	posLeaf termPosition = iota
-	posInfix
-	posPrefix
-	posPostfix
-	posMultifix
-)
-
-type evalFuncType func(ctx kern.ExprContext, self *term) (v any, err error)
-
-type term struct {
-	tk       Token
-	parent   *term
-	children []*term
-	position termPosition // operator position: leaf, infix, prefix, postfix, multifix
-	priority termPriority // operator priority: higher value means higher priority
-	evalFunc evalFuncType
-}
-
-func (t *term) Clone() (d *term) {
-	var children []*term
-	if t.children != nil {
-		children = make([]*term, len(t.children))
-		for i, c := range t.children {
-			children[i] = c.Clone()
-		}
-	}
-	d = &term{
-		tk:       *t.tk.Clone(),
-		parent:   t.parent,
-		children: children,
-		position: t.position,
-		priority: t.priority,
-		evalFunc: t.evalFunc,
-	}
-	return
-}
-
-func (t *term) String() string {
-	var sb strings.Builder
-	t.toString(&sb)
-	return sb.String()
-}
-
-func (t *term) toString(sb *strings.Builder) {
-	if t.position == posLeaf {
-		sb.WriteString(t.tk.String())
-	} else {
-		sb.WriteByte('[')
-		sb.WriteString(t.tk.String())
-		if t.children != nil {
-			sb.WriteByte('(')
-			for i, c := range t.children {
-				if i > 0 {
-					sb.WriteByte(' ')
-				}
-				c.toString(sb)
-			}
-			sb.WriteByte(')')
-		}
-		sb.WriteByte(']')
-	}
-}
-
-func (t *term) GetChildCount() (count int) {
-	if t.position == posLeaf || t.children == nil {
-		count = 0
-	} else {
-		count = len(t.children)
-	}
-	return
-}
-
-func (t *term) getRoom() (room int) {
-	switch t.position {
-	case posLeaf:
-		room = 0
-	case posInfix:
-		room = 2
-	case posPostfix, posPrefix:
-		room = 1
-	default:
-		panic("Invalid node position")
-	}
-	return
-}
-
-func (t *term) isComplete() bool {
-	return t.GetChildCount() == t.getRoom()
-}
-
-func (t *term) removeLastChild() (child *term) {
-	if t.children != nil {
-		child = t.children[len(t.children)-1]
-		t.children = t.children[0 : len(t.children)-1]
-	} else {
-		panic("Can't get last child")
-	}
-	return
-}
-
-func (t *term) isLeaf() bool {
-	return t.position == posLeaf
-}
-
-func (t *term) getPriority() termPriority {
-	return t.priority
-}
-
-func (t *term) setParent(parent *term) {
-	t.parent = parent
-	if parent != nil && len(parent.children) < cap(parent.children) {
-		parent.children = append(parent.children, t)
-	}
-}
-
-func (t *term) symbol() Symbol {
-	return t.tk.Sym
-}
-
-func (t *term) Source() string {
-	return t.tk.source
-}
-
-func (t *term) value() any {
-	return t.tk.Value
-}
-
-func (t *term) GetChild(index int) (c kern.Term) {
-	if index >= 0 && index < len(t.children) {
-		c = t.children[index]
-	}
-	return
-}
-
-func (t *term) GetChildSource(index int) (s string) {
-	if index >= 0 && index < len(t.children) {
-		s = t.children[index].tk.source
-	}
-	return
-}
-
-func (t *term) IsAssign() bool {
-	return t.symbol() == SymEqual
-}
-
-func (t *term) Compute(ctx kern.ExprContext) (v any, err error) {
-	if t.evalFunc == nil {
-		err = t.Errorf("undefined eval-func for %q term", t.Source())
-	} else {
-		v, err = t.evalFunc(ctx, t)
-	}
-	return
-}
-
-// func (term *term) toInt(computedValue any, valueDescription string) (i int, err error) {
-// 	if index64, ok := computedValue.(int64); ok {
-// 		i = int(index64)
-// 	} else {
-// 		err = term.Errorf("%s, got %s (%v)", valueDescription, TypeName(computedValue), computedValue)
-// 	}
-// 	return
-// }
-
-func (t *term) errIncompatibleTypes(leftValue, rightValue any) error {
-	leftType := kern.TypeName(leftValue)
-	leftText := kern.GetFormatted(leftValue, kern.Truncate)
-	rightType := kern.TypeName(rightValue)
-	rightText := kern.GetFormatted(rightValue, kern.Truncate)
-	return t.tk.Errorf(
-		"left operand '%s' [%s] and right operand '%s' [%s] are not compatible with operator %q",
-		leftText, leftType,
-		rightText, rightType,
-		t.Source())
-}
-
-func (t *term) errIncompatibleType(value any, side string) error {
-	return t.tk.Errorf(
-		"operator %q does not support operand '%v' [%s] on its %s side",
-		t.Source(), value, kern.TypeName(value), side)
-}
-
-func (t *term) errIncompatiblePrefixPostfixType(value any) error {
-	return t.tk.Errorf(
-		"prefix/postfix operator %q does not support operand '%v' [%s]",
-		t.Source(), value, kern.TypeName(value))
-}
-
-func (t *term) errDivisionByZero() error {
-	return t.tk.Errorf("division by zero")
-}
-
-func (t *term) errKeyNotFound(key any) error {
-	return t.tk.Errorf("key '%v' not found", key)
-}
-
-func (t *term) Errorf(template string, args ...any) (err error) {
-	err = t.tk.Errorf(template, args...)
-	return
-}
-
-func (t *term) checkOperands() (err error) {
-	switch t.position {
-	case posInfix:
-		if t.children == nil || len(t.children) != 2 || t.anyChildrenNil() {
-			err = t.tk.Errorf("infix operator %q requires two non-nil operands, got %d", t.Source(), t.GetChildCount())
-		}
-	case posPrefix:
-		if t.children == nil || len(t.children) != 1 || t.children[0] == nil {
-			err = t.tk.Errorf("prefix operator %q requires one non-nil operand", t.tk.String())
-		}
-	case posPostfix:
-		if t.children == nil || len(t.children) != 1 || t.anyChildrenNil() {
-			err = t.tk.Errorf("postfix operator %q requires one non-nil operand", t.tk.String())
-		}
-	case posMultifix:
-		if t.children == nil || len(t.children) < 3 || t.anyChildrenNil() {
-			err = t.tk.Errorf("infix operator %q requires at least three not operands, got %d", t.Source(), t.GetChildCount())
-		}
-	}
-	return
-}
-
-func (t *term) anyChildrenNil() bool {
-	for _, child := range t.children {
-		if child == nil {
-			return true
-		}
-	}
-	return false
-}
-func (t *term) evalInfix(ctx kern.ExprContext) (leftValue, rightValue any, err error) {
-	if err = t.checkOperands(); err == nil {
-		if leftValue, err = t.children[0].Compute(ctx); err == nil {
-			rightValue, err = t.children[1].Compute(ctx)
-		}
-	}
-	return
-}
-
-func (t *term) evalPrefix(ctx kern.ExprContext) (childValue any, err error) {
-	if err = t.checkOperands(); err == nil {
-		childValue, err = t.children[0].Compute(ctx)
-	}
-	return
-}
-
-// NOTE Temporary solution to support function parameters with default value
-
-func (t *term) forceChild(c *term) {
-	if t.children == nil {
-		t.children = make([]*term, 0, 1)
-	}
-	t.children = append(t.children, c)
-}

util/byte-slider.go

@@ -2,7 +2,7 @@
 // All rights reserved.
 
 // byte-slider.go
-package expr
+package util
 
 import "bytes"
 

util/utils-unix.go

@@ -1,8 +1,8 @@
-//go:build unix
-
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
+//go:build unix
+
 // utils-unix.go
 package util