Doc: many improvements

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

array-iterator.go

@@ -10,10 +10,12 @@ import (
 	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 type ListIterator struct {
-	a     *kern.ListType
+	a     *array.ArrayType
 	count int64
 	index int64
 	start int64
@@ -21,7 +23,7 @@ type ListIterator struct {
 	step  int64
 }
 
-func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
+func NewListIterator(list *array.ArrayType, args []any) (it *ListIterator) {
 	var argc int = 0
 	listLen := int64(len(([]any)(*list)))
 	if args != nil {
@@ -29,21 +31,21 @@ func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
 	}
 	it = &ListIterator{a: list, count: 0, index: -1, start: 0, stop: listLen - 1, step: 1}
 	if argc >= 1 {
-		if i, err := kern.ToGoInt64(args[0], "start index"); err == nil {
+		if i, err := types.ToGoInt64(args[0], "start index"); err == nil {
 			if i < 0 {
 				i = listLen + i
 			}
 			it.start = i
 		}
 		if argc >= 2 {
-			if i, err := kern.ToGoInt64(args[1], "stop index"); err == nil {
+			if i, err := types.ToGoInt64(args[1], "stop index"); err == nil {
 				if i < 0 {
 					i = listLen + i
 				}
 				it.stop = i
 			}
 			if argc >= 3 {
-				if i, err := kern.ToGoInt64(args[2], "step"); err == nil {
+				if i, err := types.ToGoInt64(args[2], "step"); err == nil {
 					if i < 0 {
 						i = -i
 					}
@@ -60,8 +62,8 @@ func NewListIterator(list *kern.ListType, args []any) (it *ListIterator) {
 	return
 }
 
-func NewArrayIterator(array []any) (it *ListIterator) {
+func NewArrayIterator(a []any) (it *ListIterator) {
-	it = &ListIterator{a: (*kern.ListType)(&array), count: 0, index: -1, start: 0, stop: int64(len(array)) - 1, step: 1}
+	it = &ListIterator{a: (*array.ArrayType)(&a), count: 0, index: -1, start: 0, stop: int64(len(a)) - 1, step: 1}
 	return
 }
 

builtin-base.go

@@ -12,6 +12,14 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/float"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 const (
@@ -24,42 +32,47 @@ func isNilFunc(ctx kern.ExprContext, name string, args map[string]any) (result a
 }
 
 func isIntFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsInteger(args[kern.ParamValue])
+	result = types.IsInteger(args[kern.ParamValue])
 	return
 }
 
 func isFloatFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsFloat(args[kern.ParamValue])
+	result = float.IsFloat(args[kern.ParamValue])
 	return
 }
 
 func isBoolFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsBool(args[kern.ParamValue])
+	result = boolean.IsBool(args[kern.ParamValue])
 	return
 }
 
 func isStringFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsString(args[kern.ParamValue])
+	result = str.IsString(args[kern.ParamValue])
 	return
 }
 
 func isFractionFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsFraction(args[kern.ParamValue])
+	result = fract.IsFraction(args[kern.ParamValue])
 	return
 }
 
 func isRationalFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsRational(args[kern.ParamValue])
+	result = fract.IsRational(args[kern.ParamValue])
 	return
 }
 
-func isListFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+func isArrayFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsList(args[kern.ParamValue])
+	result = array.IsArray(args[kern.ParamValue])
 	return
 }
 
 func isDictionaryFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	result = kern.IsDict(args[kern.ParamValue])
+	result = dict.IsDict(args[kern.ParamValue])
+	return
+}
+
+func isListFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	result = list.IsLinkedList(args[kern.ParamValue])
 	return
 }
 
@@ -67,7 +80,7 @@ func boolFunc(ctx kern.ExprContext, name string, args map[string]any) (result an
 	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = (v != 0)
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v.N() != 0
 	case float64:
 		result = v != 0.0
@@ -75,9 +88,9 @@ func boolFunc(ctx kern.ExprContext, name string, args map[string]any) (result an
 		result = v
 	case string:
 		result = len(v) > 0
-	case *kern.ListType:
+	case *array.ArrayType:
 		result = len(*v) > 0
-	case *kern.DictType:
+	case *dict.DictType:
 		result = len(*v) > 0
 	default:
 		err = kern.ErrCantConvert(name, v, "bool")
@@ -102,7 +115,7 @@ func intFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 		if i, err = strconv.Atoi(v); err == nil {
 			result = int64(i)
 		}
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = int64(v.N() / v.D())
 	default:
 		err = kern.ErrCantConvert(name, v, "int")
@@ -110,7 +123,7 @@ func intFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 	return
 }
 
-func decFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+func floatFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	switch v := args[kern.ParamValue].(type) {
 	case int64:
 		result = float64(v)
@@ -127,7 +140,7 @@ func decFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 		if f, err = strconv.ParseFloat(v, 64); err == nil {
 			result = f
 		}
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v.ToFloat()
 	default:
 		err = kern.ErrCantConvert(name, v, "float")
@@ -149,7 +162,7 @@ func stringFunc(ctx kern.ExprContext, name string, args map[string]any) (result
 		}
 	case string:
 		result = v
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v.ToString(0)
 	case kern.Formatter:
 		result = v.ToString(0)
@@ -174,19 +187,19 @@ func fractFunc(ctx kern.ExprContext, name string, args map[string]any) (result a
 		}
 
 		if err == nil {
-			result = kern.NewFraction(v, den)
+			result = fract.NewFraction(v, den)
 		}
 	case float64:
-		result, err = kern.Float64ToFraction(v)
+		result, err = fract.Float64ToFraction(v)
 	case bool:
 		if v {
-			result = kern.NewFraction(1, 1)
+			result = fract.NewFraction(1, 1)
 		} else {
-			result = kern.NewFraction(0, 1)
+			result = fract.NewFraction(0, 1)
 		}
 	case string:
-		result, err = kern.MakeGeneratingFraction(v)
+		result, err = fract.MakeGeneratingFraction(v)
-	case *kern.FractionType:
+	case *fract.FractionType:
 		result = v
 	default:
 		err = kern.ErrCantConvert(name, v, "float")
@@ -276,7 +289,7 @@ func charFunc(ctx kern.ExprContext, name string, args map[string]any) (result an
 }
 
 func seqFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
-	list := kern.NewLinkedList()
+	list := list.NewLinkedList()
 	items := args[kern.ParamValue].([]any)
 	for _, arg := range items {
 		list.PushBack(arg)
@@ -299,12 +312,13 @@ func ImportBuiltinsFuncs(ctx kern.ExprContext) {
 	ctx.RegisterFunc("isString", kern.NewGolangFunctor(isStringFunc), kern.TypeBoolean, anyParams)
 	ctx.RegisterFunc("isFract", kern.NewGolangFunctor(isFractionFunc), kern.TypeBoolean, anyParams)
 	ctx.RegisterFunc("isRational", kern.NewGolangFunctor(isRationalFunc), kern.TypeBoolean, anyParams)
-	ctx.RegisterFunc("isList", kern.NewGolangFunctor(isListFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isArray", kern.NewGolangFunctor(isArrayFunc), kern.TypeBoolean, anyParams)
 	ctx.RegisterFunc("isDict", kern.NewGolangFunctor(isDictionaryFunc), kern.TypeBoolean, anyParams)
+	ctx.RegisterFunc("isList", kern.NewGolangFunctor(isListFunc), kern.TypeBoolean, anyParams)
 
 	ctx.RegisterFunc("bool", kern.NewGolangFunctor(boolFunc), kern.TypeBoolean, anyParams)
 	ctx.RegisterFunc("int", kern.NewGolangFunctor(intFunc), kern.TypeInt, anyParams)
-	ctx.RegisterFunc("dec", kern.NewGolangFunctor(decFunc), kern.TypeFloat, anyParams)
+	ctx.RegisterFunc("float", kern.NewGolangFunctor(floatFunc), kern.TypeFloat, anyParams)
 	ctx.RegisterFunc("string", kern.NewGolangFunctor(stringFunc), kern.TypeString, anyParams)
 	ctx.RegisterFunc("fract", kern.NewGolangFunctor(fractFunc), kern.TypeFraction, []kern.ExprFuncParam{
 		kern.NewFuncParam(kern.ParamValue),

builtin-import.go

@@ -10,6 +10,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 func importFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
@@ -47,7 +48,7 @@ func doImport(ctx kern.ExprContext, name string, dirList []string, it kern.Itera
 			var expr *scan.Ast
 			scanner := scan.NewScanner(file, scan.DefaultTranslations())
 			parser := NewParser()
-			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymEos); err == nil {
+			if expr, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, sym.SymEos); err == nil {
 				result, err = expr.Eval(ctx)
 			}
 			if err != nil {

builtin-iterator.go

@@ -9,32 +9,39 @@ import (
 	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
 )
 
 const (
 	iterParamOperator = "operator"
 	iterParamVars     = "vars"
 	iterVarStatus     = "status"
+	iterParamStatus   = "status"
+	iterVarAbort      = "__abort"
 )
 
 func parseRunArgs(localCtx kern.ExprContext, args map[string]any) (it kern.Iterator, op kern.Functor, err error) {
 	var ok bool
 
 	if it, ok = args[kern.ParamIterator].(kern.Iterator); !ok {
-		err = fmt.Errorf("paramter %q must be an iterator, passed %v [%s]", kern.ParamIterator, args[kern.ParamIterator], kern.TypeName(args[kern.ParamIterator]))
+		// err = fmt.Errorf("parameter %q must be an iterator, passed %v [%s]", kern.ParamIterator, args[kern.ParamIterator], kern.TypeName(args[kern.ParamIterator]))
+		err = errBadParamType(kern.ParamIterator, kern.TypeIterator, args[kern.ParamIterator])
 		return
 	}
 
 	if args[iterParamOperator] != nil {
 		if op, ok = args[iterParamOperator].(kern.Functor); !ok || op == nil {
-			err = fmt.Errorf("paramter %q must be a function, passed %v [%s]", iterParamOperator, args[iterParamOperator], kern.TypeName(args[iterParamOperator]))
+			// err = fmt.Errorf("parameter %q must be a function, passed %v [%s]", iterParamOperator, args[iterParamOperator], kern.TypeName(args[iterParamOperator]))
+			err = errBadParamType(iterParamOperator, "function", args[iterParamOperator])
 			return
 		}
 	}
 
-	var vars *kern.DictType
+	var vars *dict.DictType
-	if vars, ok = args[iterParamVars].(*kern.DictType); !ok && args[iterParamVars] != nil {
+	if vars, ok = args[iterParamVars].(*dict.DictType); !ok && args[iterParamVars] != nil {
-		err = fmt.Errorf("paramter %q must be a dictionary, passed %v [%s]", iterParamVars, args[iterParamVars], kern.TypeName(args[iterParamVars]))
+		// err = fmt.Errorf("parameter %q must be a dictionary, passed %v [%s]", iterParamVars, args[iterParamVars], kern.TypeName(args[iterParamVars]))
+		err = errBadParamType(iterParamVars, kern.TypeDict, args[iterParamVars])
 		return
 	}
 
@@ -50,12 +57,21 @@ func parseRunArgs(localCtx kern.ExprContext, args map[string]any) (it kern.Itera
 	return
 }
 
+func errBadParamType(paramName, wantedType string, wantedValue any) error {
+	return fmt.Errorf("type of %q must be %s, passed %v [%s]", paramName, wantedType, wantedValue, kern.TypeName(wantedValue))
+}
+
+func abortFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
+	if status, provided := args[iterParamStatus]; provided {
+		ctx.UnsafeSetVar("@"+iterVarStatus, status)
+	}
+	ctx.UnsafeSetVar("@"+iterVarAbort, true)
+	return
+}
+
 func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
 	var it kern.Iterator
-	var ok bool
 	var op kern.Functor
-	var v any
-	// var usingDefaultOp = false
 	var params map[string]any
 	var item any
 
@@ -66,14 +82,20 @@ func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 		return
 	}
 
+	localCtx.RegisterFunc("abort", kern.NewGolangFunctor(abortFunc), kern.TypeAny, []kern.ExprFuncParam{
+		kern.NewFuncParamFlagDef(iterParamStatus, kern.PfOptional, "aborted"),
+	})
+
+	params = map[string]any{kern.ParamIndex: 0, kern.ParamItem: nil}
 	for item, err = it.Next(); err == nil; item, err = it.Next() {
 		if op != nil {
-			params = map[string]any{kern.ParamIndex: it.Index(), kern.ParamItem: item}
+			// params = map[string]any{kern.ParamIndex: it.Index(), kern.ParamItem: item}
-			if v, err = op.InvokeNamed(localCtx, iterParamOperator, params); err != nil {
+			params[kern.ParamIndex] = it.Index()
+			params[kern.ParamItem] = item
+			if _, err = op.InvokeNamed(localCtx, iterParamOperator, params); err != nil {
 				break
-			} else {
+			} else if abortAny, exists := localCtx.GetVar(iterVarAbort); exists {
-				var success bool
+				if abort, ok := boolean.ToBool(abortAny); ok && abort {
-				if success, ok = kern.ToBool(v); !success || !ok {
 					break
 				}
 			}
@@ -85,7 +107,7 @@ func runFunc(ctx kern.ExprContext, name string, args map[string]any) (result any
 	}
 	if err == nil {
 		if op == nil {
-			ctx.UnsafeSetVar(iterVarStatus, it.Count())
+			localCtx.UnsafeSetVar(iterVarStatus, it.Count())
 		}
 		result, _ = localCtx.GetVar(iterVarStatus)
 	}

builtin-math-arith.go

@@ -9,10 +9,14 @@ import (
 	"io"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/float"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
 )
 
 func checkNumberParamExpected(funcName string, paramValue any, paramPos, level, subPos int) (err error) {
-	if !(kern.IsNumber(paramValue) || kern.IsFraction(paramValue)) /*|| isList(paramValue)*/ {
+	if !(types.IsNumber(paramValue) || fract.IsFraction(paramValue)) /*|| isArray(paramValue)*/ {
 		err = fmt.Errorf("%s(): param nr %d (%d in %d) has wrong type %T, number expected",
 			funcName, paramPos+1, subPos+1, level, paramValue)
 	}
@@ -23,13 +27,13 @@ func doAdd(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 	var sumAsFloat, sumAsFract bool
 	var floatSum float64 = 0.0
 	var intSum int64 = 0
-	var fractSum *kern.FractionType
+	var fractSum *fract.FractionType
 	var v any
 
 	level++
 
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*kern.ListType); ok {
+		if list, ok := v.(*array.ArrayType); ok {
 			v = NewListIterator(list, nil)
 		}
 		if subIter, ok := v.(kern.Iterator); ok {
@@ -47,29 +51,29 @@ func doAdd(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 		count++
 
 		if !sumAsFloat {
-			if kern.IsFloat(v) {
+			if float.IsFloat(v) {
 				sumAsFloat = true
 				if sumAsFract {
 					floatSum = fractSum.ToFloat()
 				} else {
 					floatSum = float64(intSum)
 				}
-			} else if !sumAsFract && kern.IsFraction(v) {
+			} else if !sumAsFract && fract.IsFraction(v) {
-				fractSum = kern.NewFraction(intSum, 1)
+				fractSum = fract.NewFraction(intSum, 1)
 				sumAsFract = true
 			}
 		}
 
 		if sumAsFloat {
-			floatSum += kern.NumAsFloat(v)
+			floatSum += types.NumAsFloat(v)
 		} else if sumAsFract {
-			var item *kern.FractionType
+			var item *fract.FractionType
 			var ok bool
-			if item, ok = v.(*kern.FractionType); !ok {
+			if item, ok = v.(*fract.FractionType); !ok {
 				iv, _ := v.(int64)
-				item = kern.NewFraction(iv, 1)
+				item = fract.NewFraction(iv, 1)
 			}
-			fractSum = kern.SumFract(fractSum, item)
+			fractSum = fract.SumFract(fractSum, item)
 		} else {
 			iv, _ := v.(int64)
 			intSum += iv
@@ -98,12 +102,12 @@ func doMul(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 	var mulAsFloat, mulAsFract bool
 	var floatProd float64 = 1.0
 	var intProd int64 = 1
-	var fractProd *kern.FractionType
+	var fractProd *fract.FractionType
 	var v any
 
 	level++
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if list, ok := v.(*kern.ListType); ok {
+		if list, ok := v.(*array.ArrayType); ok {
 			v = NewListIterator(list, nil)
 		}
 		if subIter, ok := v.(kern.Iterator); ok {
@@ -123,29 +127,29 @@ func doMul(ctx kern.ExprContext, name string, it kern.Iterator, count, level int
 		count++
 
 		if !mulAsFloat {
-			if kern.IsFloat(v) {
+			if float.IsFloat(v) {
 				mulAsFloat = true
 				if mulAsFract {
 					floatProd = fractProd.ToFloat()
 				} else {
 					floatProd = float64(intProd)
 				}
-			} else if !mulAsFract && kern.IsFraction(v) {
+			} else if !mulAsFract && fract.IsFraction(v) {
-				fractProd = kern.NewFraction(intProd, 1)
+				fractProd = fract.NewFraction(intProd, 1)
 				mulAsFract = true
 			}
 		}
 
 		if mulAsFloat {
-			floatProd *= kern.NumAsFloat(v)
+			floatProd *= types.NumAsFloat(v)
 		} else if mulAsFract {
-			var item *kern.FractionType
+			var item *fract.FractionType
 			var ok bool
-			if item, ok = v.(*kern.FractionType); !ok {
+			if item, ok = v.(*fract.FractionType); !ok {
 				iv, _ := v.(int64)
-				item = kern.NewFraction(iv, 1)
+				item = fract.NewFraction(iv, 1)
 			}
-			fractProd = kern.MulFract(fractProd, item)
+			fractProd = fract.MulFract(fractProd, item)
 		} else {
 			iv, _ := v.(int64)
 			intProd *= iv

builtin-os-file-iter-byte.go

@@ -59,8 +59,8 @@ func (it *fileFileByteIterator) Clean() (err error) {
 			it.reader = nil
 		}
 	}
-	it.reset()
+	// it.reset()
-	it.b = 0
+	// it.b = 0
 	return
 }
 

builtin-os-file-iter-line.go

@@ -62,8 +62,8 @@ func (it *fileFileLineIterator) Clean() (err error) {
 			it.reader = nil
 		}
 	}
-	it.reset()
+	// it.reset()
-	it.line = ""
+	// it.line = ""
 	return
 }
 

builtin-string.go

@@ -10,6 +10,8 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 const (
@@ -43,8 +45,8 @@ func joinStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result
 		if v, exists := args[kern.ParamItem]; exists {
 			argv := v.([]any)
 			if len(argv) == 1 {
-				if ls, ok := argv[0].(*kern.ListType); ok {
+				if a, ok := argv[0].(*array.ArrayType); ok {
-					result, err = doJoinStr(name, sep, NewListIterator(ls, nil))
+					result, err = doJoinStr(name, sep, NewListIterator(a, nil))
 				} else if it, ok := argv[0].(kern.Iterator); ok {
 					result, err = doJoinStr(name, sep, it)
 				} else if s, ok := argv[0].(string); ok {
@@ -72,11 +74,11 @@ func subStrFunc(ctx kern.ExprContext, name string, args map[string]any) (result
 		return nil, kern.ErrWrongParamType(name, kern.ParamSource, kern.TypeString, args[kern.ParamSource])
 	}
 
-	if start, err = kern.ToGoInt(args[kern.ParamStart], name+"()"); err != nil {
+	if start, err = types.ToGoInt(args[kern.ParamStart], name+"()"); err != nil {
 		return
 	}
 
-	if count, err = kern.ToGoInt(args[kern.ParamCount], name+"()"); err != nil {
+	if count, err = types.ToGoInt(args[kern.ParamCount], name+"()"); err != nil {
 		return
 	}
 
@@ -194,11 +196,11 @@ func splitStrFunc(ctx kern.ExprContext, name string, args map[string]any) (resul
 	} else {
 		parts = []string{}
 	}
-	list := make(kern.ListType, len(parts))
+	a := make(array.ArrayType, len(parts))
 	for i, part := range parts {
-		list[i] = part
+		a[i] = part
 	}
-	result = &list
+	result = &a
 	return
 }
 

cmd/ecli/ecli.adoc

@@ -34,6 +34,7 @@ Expression Calculator Interactive Tool
 The tool combines the expression evaluation capabilities of the Expr package with an interactive shell environment, making it ideal for:
 
 - Interactive expression testing and prototyping
+- Command history survival across sessions
 - Batch expression evaluation from scripts
 - Data processing and transformation
 - Mathematical computations with fractions and complex operators
@@ -89,11 +90,14 @@ Within the REPL, you can use the following commands:
 |===
 | Command | Description
 
-| `help` | Display available commands and command-line options
+| `base [2\|8\|10\|16]` | Set the integer output base. Use without arguments to show current base
 | `exit` | Exit the REPL
-| `multiline` | Toggle multi-line input mode for complex expressions
+| `help` | Display available commands and command-line options
-| `tty` | Toggle TTY mode
+| `ml` | Enable/Disable multi-line input mode for complex expressions
-| `source <file>` | Execute expressions from a file
+| `mods` | List all builtin modules (with `*` marking imported ones)
+| `output [on\|off\|status]` | Enable/Disable printing of expression results
+| `source <file>` | Load and execute expressions from a file
+| `tty` | Enable/Disable ANSI terminal output
 |===
 
 == Features
@@ -160,8 +164,16 @@ hello world
 
 [source,bash]
 ----
->>> [1, 2, 3, 4, 5] | map(. * 2)
+>>> it = [1, 2, 3, 4, 5] map $_ * 2
-[2, 4, 6, 8, 10]
+$($([#5]))
+>>> $$(it)
+[<
+  2,
+  4,
+  6,
+  8,
+  10
+>]
 ----
 
 === Evaluating from Command Line
@@ -192,7 +204,7 @@ Or from command line:
 
 [source,bash]
 ----
-./ecli -e '@include "expressions.expr"'
+./ecli -e "@expressions.expr"
 ----
 
 == Configuration
@@ -233,16 +245,16 @@ The build process generates:
 
 === Multi-line Input
 
-For complex expressions, toggle multi-line mode:
+For complex expressions, split operations across multiple lines terminating with a backslash (`\`):
 
 [source]
 ----
->>> multiline
+>>> ml
->>> result = [1, 2, 3, 4, 5] 
+>>> result = [1, 2, 3, 4, 5] \
-...   | filter(. > 2)
+...   filter $_ > 2 \
-...   | map(. * 2)
+...   map $_ * 2
->>> result
+>>> $$(result)
-[6, 8, 10]
+[<6, 8, 10>
 ----
 
 === Script Execution
@@ -260,16 +272,29 @@ Execute it:
 
 [source,bash]
 ----
-./ecli -e '@source "calculations.expr"' -e 'result'
+./ecli -e '@calculations.expr' -e 'result'
+50
 ----
 
-=== Chaining Operations
+=== Other Iterator Examples
 
 [source]
 ----
 >>> data = [{"name": "alice", "age": 30}, {"name": "bob", "age": 25}]
->>> data | map(.name)
+
-[alice, bob]
+// Extract names using map iterator
+>>> $$(data map ($_).name)
+[<
+  "alice",
+  "bob"
+>]
+
+// Filter ages greater than 28
+>>> $$(data filter ($_).age > 28 map ($_).name)
+[<
+  "alice"
+>]
+
 ----
 
 == Troubleshooting

cmd/ecli/graph.go

@@ -3,6 +3,9 @@
 
 //go:build graph
 
+// NOTE: Enable this build tag to print the graph of the expression instead of evaluating it.
+//       go run -tags graph cmd/ecli/main.go
+
 // graph.go
 package main
 

cmd/ecli/main.go

@@ -14,6 +14,9 @@ import (
 	"git.portale-stac.it/go-pkg/expr"
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 	"git.portale-stac.it/go-pkg/utils"
 
 	// https://pkg.go.dev/github.com/ergochat/readline#section-readme
@@ -225,10 +228,10 @@ func compute(opt *Options, ctx kern.ExprContext, r io.Reader, outputEnabled bool
 func printResult(opt *Options, result any) {
 	if f, ok := result.(kern.Formatter); ok {
 		fmt.Println(f.ToString(opt.formOpt))
-	} else if kern.IsInteger(result) {
+	} else if types.IsInteger(result) {
 		fmt.Printf(opt.baseVerb, result)
 		fmt.Println()
-	} else if kern.IsString(result) {
+	} else if str.IsString(result) {
 		fmt.Printf("\"%s\"\n", result)
 	} else {
 		fmt.Println(result)
@@ -257,7 +260,7 @@ func registerLocalFunctions(ctx kern.ExprContext) {
 		vars := ctx.EnumVars(func(name string) bool {
 			return len(name) > 0 && name[0] == '_'
 		})
-		result = kern.ListFromStrings(vars)
+		result = array.ArrayFromStrings(vars)
 		return
 	}
 
@@ -309,7 +312,7 @@ func registerLocalFunctions(ctx kern.ExprContext) {
 			name, _, _ := strings.Cut(e, "=")
 			vars = append(vars, name)
 		}
-		result = kern.ListFromStrings(vars)
+		result = array.ArrayFromStrings(vars)
 		return
 	}
 

dict-iterator.go

@@ -11,6 +11,9 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 type dictIterMode int
@@ -22,7 +25,7 @@ const (
 )
 
 type DictIterator struct {
-	a        *kern.DictType
+	a        *dict.DictType
 	count    int64
 	index    int64
 	keys     []any
@@ -67,7 +70,7 @@ func (it *DictIterator) makeKeys(m map[any]any, sort sortType) {
 	}
 }
 
-func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err error) {
+func NewDictIterator(dict *dict.DictType, args []any) (it *DictIterator, err error) {
 	var sortType = sortTypeNone
 	var s string
 	var argAny any
@@ -78,7 +81,7 @@ func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err err
 	} else {
 		argAny = "default"
 	}
-	if s, err = kern.ToGoString(argAny, "sort type"); err == nil {
+	if s, err = str.ToGoString(argAny, "sort type"); err == nil {
 		switch strings.ToLower(s) {
 		case "a", "asc":
 			sortType = sortTypeAsc
@@ -99,7 +102,7 @@ func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err err
 				argAny = "default"
 			}
 
-			if s, err = kern.ToGoString(argAny, "iteration mode"); err == nil {
+			if s, err = str.ToGoString(argAny, "iteration mode"); err == nil {
 				switch strings.ToLower(s) {
 				case "k", "key", "keys":
 					dictIt.iterMode = dictIterModeKeys
@@ -124,7 +127,7 @@ func NewDictIterator(dict *kern.DictType, args []any) (it *DictIterator, err err
 }
 
 func NewMapIterator(m map[any]any) (it *DictIterator) {
-	it = &DictIterator{a: (*kern.DictType)(&m), count: 0, index: -1, keys: nil}
+	it = &DictIterator{a: (*dict.DictType)(&m), count: 0, index: -1, keys: nil}
 	it.makeKeys(m, sortTypeNone)
 	return
 }
@@ -190,7 +193,7 @@ func (it *DictIterator) Current() (item any, err error) {
 		case dictIterModeItems:
 			a := *(it.a)
 			pair := []any{it.keys[it.index], a[it.keys[it.index]]}
-			item = kern.NewList(pair)
+			item = array.NewArray(pair)
 		}
 	} else {
 		err = io.EOF

global-context.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
 )
 
 //var globalCtx *SimpleStore
@@ -68,7 +69,7 @@ func GlobalCtrlGet(ctx kern.ExprContext, name string) (currentValue any) {
 
 func CtrlEnable(ctx kern.ExprContext, name string) (currentStatus bool) {
 	name = fixCtrlVar(name)
-	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
+	if v, exists := ctx.GetVar(name); exists && boolean.IsBool(v) {
 		currentStatus, _ = v.(bool)
 	}
 
@@ -78,7 +79,7 @@ func CtrlEnable(ctx kern.ExprContext, name string) (currentStatus bool) {
 
 func CtrlDisable(ctx kern.ExprContext, name string) (currentStatus bool) {
 	name = fixCtrlVar(name)
-	if v, exists := ctx.GetVar(name); exists && kern.IsBool(v) {
+	if v, exists := ctx.GetVar(name); exists && boolean.IsBool(v) {
 		currentStatus, _ = v.(bool)
 	}
 

helpers.go

@@ -12,6 +12,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/float"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -50,9 +52,9 @@ func EvalStringV(source string, args []Arg) (result any, err error) {
 			} else {
 				err = fmt.Errorf("invalid function specification: %q", arg.Name)
 			}
-		} else if integer, ok := kern.AnyInteger(arg.Value); ok {
+		} else if integer, ok := types.AnyInteger(arg.Value); ok {
 			ctx.SetVar(arg.Name, integer)
-		} else if float, ok := kern.AnyFloat(arg.Value); ok {
+		} else if float, ok := float.AnyFloat(arg.Value); ok {
 			ctx.SetVar(arg.Name, float)
 		} else if _, ok := arg.Value.(string); ok {
 			ctx.SetVar(arg.Name, arg.Value)

import-utils.go

@@ -13,6 +13,7 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -22,7 +23,7 @@ const (
 )
 
 func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(kern.IsString(paramValue) /*|| isList(paramValue)*/) {
+	if !(str.IsString(paramValue) /*|| isArray(paramValue)*/) {
 		err = fmt.Errorf("%s(): param nr %d has wrong type %s, string expected", funcName, paramPos+1, kern.TypeName(paramValue))
 	}
 	return

int-iterator.go

@@ -10,6 +10,8 @@ import (
 	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
 )
 
 type IntIterator struct {
@@ -20,6 +22,16 @@ type IntIterator struct {
 	step  int64
 }
 
+func NewIntIteratorFromInterval(p *interval.IntervalType) (it *IntIterator, err error) {
+	b := p.Begin()
+	e := p.End()
+	s := p.Step()
+	if b > e {
+		s = -s
+	}
+	return NewIntIteratorA(b, e, s)
+}
+
 func NewIntIteratorA(args ...any) (it *IntIterator, err error) {
 	return NewIntIterator(args)
 }
@@ -31,16 +43,16 @@ func NewIntIterator(args []any) (it *IntIterator, err error) {
 	}
 	it = &IntIterator{count: 0, index: -1, start: 0, stop: 0, step: 1}
 	if argc >= 1 {
-		if it.stop, err = kern.ToGoInt64(args[0], "start index"); err != nil {
+		if it.stop, err = types.ToGoInt64(args[0], "start index"); err != nil {
 			return
 		}
 		if argc >= 2 {
 			it.start = it.stop
-			if it.stop, err = kern.ToGoInt64(args[1], "stop index"); err != nil {
+			if it.stop, err = types.ToGoInt64(args[1], "stop index"); err != nil {
 				return
 			}
 			if argc >= 3 {
-				if it.step, err = kern.ToGoInt64(args[2], "step"); err != nil {
+				if it.step, err = types.ToGoInt64(args[2], "step"); err != nil {
 					return
 				}
 			} else if it.start > it.stop {

iter-factory.go

@@ -9,6 +9,9 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 func NewFormalIterator(value any) (it kern.Iterator) {
@@ -26,11 +29,11 @@ func NewIterator(ctx kern.ExprContext, value any, ops []*scan.Term) (it kern.Ite
 	}
 
 	switch v := value.(type) {
-	case *kern.ListType:
+	case *array.ArrayType:
 		it = NewListIterator(v, nil)
-	case *kern.LinkedList:
+	case *list.LinkedList:
 		it = NewLinkedListIterator(v, nil)
-	case *kern.DictType:
+	case *dict.DictType:
 		it, err = NewDictIterator(v, nil)
 	case []any:
 		it = NewArrayIterator(v)

kern/clone-value.go

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

kern/cloner.go

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

kern/common-type-names.go

@@ -6,6 +6,7 @@ package kern
 
 const (
 	TypeAny           = "any"
+	TypeArray         = "array"
 	TypeNil           = "nil"
 	TypeBoolean       = "boolean"
 	TypeFloat         = "float"
@@ -15,7 +16,7 @@ const (
 	TypeItem          = "item"
 	TypeIterator      = "iterator"
 	TypeNumber        = "number"
-	TypePair          = "pair"
+	TypeIntPair       = "int-pair"
 	TypeString        = "string"
 	TypeDict          = "dict"
 	TypeListOf        = "list-of-"

kern/compare.go

@@ -1,41 +0,0 @@
-// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-package kern
-
-import "reflect"
-
-func Equal(value1, value2 any) (equal bool) {
-	if value1 == nil && value2 == nil {
-		equal = true
-	} else if value1 == nil || value2 == nil {
-		equal = false
-	} else if IsBool(value1) && IsBool(value2) {
-		equal = value1.(bool) == value2.(bool)
-	} else if IsList(value1) && IsList(value2) {
-		ls1 := value1.(*ListType)
-		ls2 := value2.(*ListType)
-		equal = ls1.Equals(*ls2)
-	} else if IsDict(value1) && IsDict(value2) {
-		d1 := value1.(*DictType)
-		d2 := value2.(*DictType)
-		equal = d1.Equals(*d2)
-	} else if IsLinkedList(value1) && IsLinkedList(value2) {
-		ll1 := value1.(*LinkedList)
-		ll2 := value2.(*LinkedList)
-		equal = ll1.Equals(ll2)
-	} else if IsInteger(value1) && IsInteger(value2) {
-		equal = value1.(int64) == value2.(int64)
-	} else if IsString(value1) && IsString(value2) {
-		equal = value1.(string) == value2.(string)
-	} else if IsFloat(value1) && IsFloat(value2) {
-		equal = value1.(float64) == value2.(float64)
-	} else if IsNumOrFract(value1) && IsNumOrFract(value2) {
-		if eq, err := CmpAnyFract(value1, value2); err == nil {
-			equal = eq == 0
-		}
-	} else if !reflect.DeepEqual(value1, value2) {
-		equal = false
-	}
-	return
-}

kern/consts.go

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

kern/equaler.go

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

kern/expr-context.go

@@ -29,35 +29,6 @@ type ExprContext interface {
 	RegisterFuncInfo(info ExprFunc)
 	RegisterFunc(name string, f Functor, returnType string, param []ExprFuncParam) (funcInfo ExprFunc, err error)
 
-	ToDict() (dict *DictType)
+	ToDict() (dict any) // must be a *DictType
 	ToString(opt FmtOpt) string
 }
-
-func ContextToDict(ctx ExprContext) (dict *DictType) {
-	var keys []string
-	// Variables
-	keys = ctx.EnumVars(nil)
-	vars := MakeDict()
-	for _, key := range keys {
-		value, _ := ctx.GetVar(key)
-		vars.SetItem(key, value)
-	}
-
-	// Functions
-	keys = ctx.EnumFuncs(func(name string) bool { return true })
-	funcs := MakeDict()
-	for _, key := range keys {
-		funcInfo, _ := ctx.GetFuncInfo(key)
-		funcs.SetItem(key, funcInfo)
-	}
-
-	dict = MakeDict()
-	dict.SetItem("vars", vars)
-	dict.SetItem("funcs", funcs)
-	return
-}
-
-func ContextToString(ctx ExprContext, opt FmtOpt) string {
-	dict := ctx.ToDict()
-	return dict.ToString(opt)
-}

kern/formatter.go

@@ -21,6 +21,10 @@ const (
 	Base16
 )
 
+type Formatter interface {
+	ToString(options FmtOpt) string
+}
+
 const (
 	TruncateEllipsis = "(...)"
 	MinTruncateSize  = 10
@@ -45,10 +49,6 @@ func GetFormatIndent(opt FmtOpt) int {
 	return int(opt >> 16)
 }
 
-type Formatter interface {
-	ToString(options FmtOpt) string
-}
-
 func Format(sb *strings.Builder, item any, opt FmtOpt) {
 	if s, ok := item.(string); ok {
 		sb.WriteByte('"')
@@ -73,22 +73,3 @@ func GetFormatted(v any, opt FmtOpt) (text string) {
 	}
 	return
 }
-
-type Typer interface {
-	TypeName() string
-}
-
-func TypeName(v any) (name string) {
-	if v == nil {
-		name = "nil"
-	} else if typer, ok := v.(Typer); ok {
-		name = typer.TypeName()
-	} else if IsInteger(v) {
-		name = "integer"
-	} else if IsFloat(v) {
-		name = "float"
-	} else {
-		name = fmt.Sprintf("%T", v)
-	}
-	return
-}

kern/list-type.go

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

kern/term.go

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

kern/typer.go

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

kern/util.go

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

linked-list-iterator.go

@@ -10,16 +10,17 @@ import (
 	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 type LinkedListIterator struct {
-	a       *kern.LinkedList
+	a       *list.LinkedList
 	count   int64
 	index   int64
-	current *kern.ListNode
+	current *list.ListNode
 }
 
-func NewLinkedListIterator(list *kern.LinkedList, args []any) (it *LinkedListIterator) {
+func NewLinkedListIterator(list *list.LinkedList, args []any) (it *LinkedListIterator) {
 	it = &LinkedListIterator{a: list, count: 0, index: -1, current: list.FirstNode()}
 	return
 }

operand-dict.go

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

operand-expr.go

@@ -9,11 +9,12 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 // -------- expr term
 func newExprTerm(root *scan.Term) *scan.Term {
-	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), scan.SymExpression, root.Source(), root)
+	tk := scan.NewValueToken(root.Tk.Row(), root.Tk.Col(), sym.SymExpression, root.Source(), root)
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,

operand-iterator.go

@@ -10,12 +10,17 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 // -------- iterator term
 
 func newIteratorTerm(tk *scan.Token, args []*scan.Term) *scan.Term {
-	tk.Sym = scan.SymIterator
+	tk.Sym = sym.SymIterator
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,
@@ -52,7 +57,7 @@ func evalFirstChild(ctx kern.ExprContext, iteratorTerm *scan.Term) (value any, e
 }
 
 func getDataSourceDict(iteratorTerm *scan.Term, firstChildValue any) (ds map[string]kern.Functor, err error) {
-	if dictAny, ok := firstChildValue.(*kern.DictType); ok {
+	if dictAny, ok := firstChildValue.(*dict.DictType); ok {
 		requiredFields := []string{kern.NextName}
 		fieldsMask := 0b1
 		foundFields := 0
@@ -123,7 +128,7 @@ func evalIterator(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 			v = dc
 		} else {
-			if dictIt, ok := firstChildValue.(*kern.DictType); ok {
+			if dictIt, ok := firstChildValue.(*dict.DictType); ok {
 				var args []any
 				if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
 					v, err = NewDictIterator(dictIt, args)
@@ -132,21 +137,23 @@ func evalIterator(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 				err = opTerm.Children[0].Errorf("the data-source must be a dictionary")
 			}
 		}
-	} else if list, ok := firstChildValue.(*kern.ListType); ok {
+	} else if a, ok := firstChildValue.(*array.ArrayType); ok {
 		var args []any
 		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
-			v = NewListIterator(list, args)
+			v = NewListIterator(a, args)
 		}
-	} else if list, ok := firstChildValue.(*kern.LinkedList); ok {
+	} else if ll, ok := firstChildValue.(*list.LinkedList); ok {
 		var args []any
 		if args, err = evalSiblings(ctx, opTerm.Children, nil); err == nil {
-			v = NewLinkedListIterator(list, args)
+			v = NewLinkedListIterator(ll, args)
-		}
-	} else if intVal, ok := firstChildValue.(int64); ok {
-		var args []any
-		if args, err = evalSiblings(ctx, opTerm.Children, intVal); err == nil {
-			v, err = NewIntIterator(args)
 		}
+	} else if intervalVal, ok := firstChildValue.(*interval.IntervalType); ok {
+		v, err = NewIntIteratorFromInterval(intervalVal)
+		// } else if intVal, ok := firstChildValue.(int64); ok {
+		// 	var args []any
+		// 	if args, err = evalSiblings(ctx, opTerm.Children, intVal); err == nil {
+		// 		v, err = NewIntIterator(args)
+		// 	}
 	} else if it, ok := firstChildValue.(kern.Iterator); ok {
 		v, err = NewIterIter(it, ctx, opTerm.Children[1:])
 	} else {

operand-linked-list.go

@@ -7,6 +7,8 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 // -------- list term
@@ -16,7 +18,7 @@ import (
 
 func newLinkedListTerm(row, col int, args []*scan.Term) *scan.Term {
 	return &scan.Term{
-		Tk:       *scan.NewValueToken(row, col, scan.SymLinkedList, "[<>]", args),
+		Tk:       *scan.NewValueToken(row, col, sym.SymLinkedList, "[<>]", args),
 		Parent:   nil,
 		Children: nil,
 		Position: scan.PosLeaf,
@@ -27,9 +29,9 @@ func newLinkedListTerm(row, col int, args []*scan.Term) *scan.Term {
 
 // -------- list func
 func evalLinkedList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	list, _ := opTerm.Value().([]*scan.Term)
+	listTerm, _ := opTerm.Value().([]*scan.Term)
-	items := kern.NewLinkedList()
+	items := list.NewLinkedList()
-	for _, tree := range list {
+	for _, tree := range listTerm {
 		var param any
 		if param, err = tree.Compute(ctx); err != nil {
 			break

operand-list.go

@@ -7,6 +7,8 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 // -------- list term
@@ -16,7 +18,7 @@ func newListTermA(args ...*scan.Term) *scan.Term {
 
 func newListTerm(row, col int, args []*scan.Term) *scan.Term {
 	return &scan.Term{
-		Tk:       *scan.NewValueToken(row, col, scan.SymList, "[]", args),
+		Tk:       *scan.NewValueToken(row, col, sym.SymList, "[]", args),
 		Parent:   nil,
 		Children: nil,
 		Position: scan.PosLeaf,
@@ -28,7 +30,7 @@ func newListTerm(row, col int, args []*scan.Term) *scan.Term {
 // -------- list func
 func evalList(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	list, _ := opTerm.Value().([]*scan.Term)
-	items := make(kern.ListType, len(list))
+	items := make(array.ArrayType, len(list))
 	for i, tree := range list {
 		var param any
 		if param, err = tree.Compute(ctx); err != nil {

operand-literal.go

@@ -7,10 +7,22 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
 )
 
 // -------- literal term
 func newLiteralTerm(tk *scan.Token) *scan.Term {
+
+	if tk.Sym == sym.SymFraction {
+		if v, isString := tk.Value.(string); isString {
+			var err error
+			if tk.Value, err = fract.MakeGeneratingFraction(v); err != nil {
+				return nil
+			}
+		}
+	}
+
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,
@@ -29,10 +41,10 @@ func evalLiteral(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymString, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymString, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymInteger, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymInteger, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymFloat, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymFloat, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymFraction, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymFraction, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymBool, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymBool, newLiteralTerm)
-	scan.RegisterTermConstructor(scan.SymKwNil, newLiteralTerm)
+	scan.RegisterTermConstructor(sym.SymKwNil, newLiteralTerm)
 }

operand-selector-case.go

@@ -5,11 +5,9 @@
 package expr
 
 import (
-	"fmt"
-	"strings"
-
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 // -------- selector case term
@@ -19,20 +17,20 @@ type selectorCase struct {
 	caseExpr   kern.Expr
 }
 
-func (sc *selectorCase) String() string {
+// func (sc *selectorCase) String() string {
-	var sb strings.Builder
+// 	var sb strings.Builder
-	if sc.filterList != nil {
+// 	if sc.filterList != nil {
-		sc.filterList.ToString(&sb)
+// 		sc.filterList.ToString(&sb)
-		sb.WriteByte(' ')
+// 		sb.WriteByte(' ')
-	}
+// 	}
-	sb.WriteByte('{')
+// 	sb.WriteByte('{')
-	sb.WriteString(sc.caseExpr.String())
+// 	sb.WriteString(sc.caseExpr.String())
-	sb.WriteByte('}')
+// 	sb.WriteByte('}')
-	return sb.String()
+// 	return sb.String()
-}
+// }
 
 func newSelectorCaseTerm(row, col int, filterList *scan.Term, caseExpr kern.Expr) *scan.Term {
-	tk := scan.NewValueToken(row, col, scan.SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
+	tk := scan.NewValueToken(row, col, sym.SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
 	return &scan.Term{
 		Tk:       *tk,
 		Parent:   nil,
@@ -45,9 +43,14 @@ func newSelectorCaseTerm(row, col int, filterList *scan.Term, caseExpr kern.Expr
 
 // -------- eval selector case
 func evalSelectorCase(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
-	var ok bool
+	v, _ = opTerm.Value().(*selectorCase)
-	if v, ok = opTerm.Value().(*selectorCase); !ok {
-		err = fmt.Errorf("selector-case expected, got %T", opTerm.Value())
-	}
 	return
 }
+
+// func evalSelectorCase(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+// 	var ok bool
+// 	if v, ok = opTerm.Value().(*selectorCase); !ok {
+// 		err = fmt.Errorf("selector-case expected, got %T", opTerm.Value())
+// 	}
+// 	return
+// }

operand-var.go

@@ -9,6 +9,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 // -------- variable term
@@ -21,7 +22,7 @@ func newVarTerm(tk *scan.Token) *scan.Term {
 		Priority: scan.PriValue,
 		EvalFunc: evalVar,
 	}
-	t.Tk.Sym = scan.SymVariable
+	t.Tk.Sym = sym.SymVariable
 	return t
 }
 
@@ -41,5 +42,5 @@ func evalVar(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymIdentifier, newVarTerm)
+	scan.RegisterTermConstructor(sym.SymIdentifier, newVarTerm)
 }

operator-assign.go

@@ -7,6 +7,10 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -44,7 +48,7 @@ func evalDeepCopyAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err err
 
 func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term, value any) (err error) {
 	var collectionValue, keyListValue, keyValue any
-	var keyList *kern.ListType
+	var keyList *array.ArrayType
 	var ok bool
 
 	if collectionValue, err = collectionTerm.Compute(ctx); err != nil {
@@ -53,7 +57,7 @@ func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *sca
 
 	if keyListValue, err = keyListTerm.Compute(ctx); err != nil {
 		return
-	} else if keyList, ok = keyListValue.(*kern.ListType); !ok || len(*keyList) != 1 {
+	} else if keyList, ok = keyListValue.(*array.ArrayType); !ok || len(*keyList) != 1 {
 		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, kern.TypeName(keyListValue))
 		return
 	}
@@ -63,14 +67,20 @@ func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *sca
 	}
 
 	switch collection := collectionValue.(type) {
-	case *kern.ListType:
+	case *array.ArrayType:
 		if index, ok := keyValue.(int64); ok {
 			err = collection.SetItem(index, value)
 		} else {
 			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
 		}
-	case *kern.DictType:
+	case *dict.DictType:
 		collection.SetItem(keyValue, value)
+	case *list.LinkedList:
+		if index, ok := keyValue.(int64); ok {
+			err = collection.SetItem(index, value)
+		} else {
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
+		}
 	default:
 		err = collectionTerm.Errorf("collection expected")
 	}
@@ -78,7 +88,7 @@ func assignCollectionItem(ctx kern.ExprContext, collectionTerm, keyListTerm *sca
 }
 
 func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any, deepCopy bool) (err error) {
-	if leftTerm.Symbol() == scan.SymIndex {
+	if leftTerm.Symbol() == sym.SymIndex {
 		err = assignCollectionItem(ctx, leftTerm.Children[0], leftTerm.Children[1], v)
 	} else {
 		if deepCopy {
@@ -92,7 +102,7 @@ func assignValue(ctx kern.ExprContext, leftTerm *scan.Term, v any, deepCopy bool
 func evalAssignDictItem(ctx kern.ExprContext, dotTerm *scan.Term, valueTerm kern.Term) (v any, err error) {
 	var ok bool
 	var dictAny, dotKey any
-	var dict *kern.DictType
+	var dt *dict.DictType
 
 	if err = dotTerm.CheckOperands(); err != nil {
 		return
@@ -102,14 +112,14 @@ func evalAssignDictItem(ctx kern.ExprContext, dotTerm *scan.Term, valueTerm kern
 	if dictAny, err = dotLeftTerm.Compute(ctx); err != nil {
 		return
 	}
-	if dict, ok = dictAny.(*kern.DictType); !ok {
+	if dt, ok = dictAny.(*dict.DictType); !ok {
-		err = dotTerm.Tk.ErrorExpectedGot(kern.DictTypeName)
+		err = dotTerm.Tk.ErrorExpectedGot(dict.DictTypeName)
 		return
 	}
 
 	dotRightTerm := dotTerm.Children[1]
 	dotRightSym := dotRightTerm.Symbol()
-	if dotRightSym == scan.SymVariable || dotRightSym == scan.SymString {
+	if dotRightSym == sym.SymVariable || dotRightSym == sym.SymString {
 		dotKey = util.UnquoteString(dotRightTerm.Source())
 	} else if dotKey, err = dotRightTerm.Compute(ctx); err != nil {
 		return
@@ -119,7 +129,7 @@ func evalAssignDictItem(ctx kern.ExprContext, dotTerm *scan.Term, valueTerm kern
 		return
 	}
 
-	dict.SetItem(dotKey, v)
+	dt.SetItem(dotKey, v)
 	return
 }
 
@@ -130,9 +140,9 @@ func generalEvalAssign(ctx kern.ExprContext, opTerm *scan.Term, deepCopy bool) (
 
 	leftTerm := opTerm.Children[0]
 	leftSym := leftTerm.Symbol()
-	if leftSym == scan.SymDot {
+	if leftSym == sym.SymDot {
 		return evalAssignDictItem(ctx, opTerm.Children[0], opTerm.GetChild(1))
-	} else if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+	} else if leftSym != sym.SymVariable && leftSym != sym.SymIndex {
 		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
@@ -141,7 +151,7 @@ func generalEvalAssign(ctx kern.ExprContext, opTerm *scan.Term, deepCopy bool) (
 
 	if v, err = rightChild.Compute(ctx); err == nil {
 		if functor, ok := v.(kern.Functor); ok {
-			if leftSym == scan.SymVariable {
+			if leftSym == sym.SymVariable {
 				if info := functor.GetFunc(); info != nil {
 					ctx.RegisterFunc(leftTerm.Source(), info.Functor(), info.ReturnType(), info.Params())
 				} else if funcDef, ok := functor.(*exprFunctor); ok {
@@ -178,7 +188,7 @@ func newOpAssignTerm(tk *scan.Token) (inst *scan.Term) {
 
 func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *scan.Term) (value any, err error) {
 	var collectionValue, keyListValue, keyValue any
-	var keyList *kern.ListType
+	var keyList *array.ArrayType
 	var ok bool
 
 	if collectionValue, err = collectionTerm.Compute(ctx); err != nil {
@@ -187,7 +197,7 @@ func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *s
 
 	if keyListValue, err = keyListTerm.Compute(ctx); err != nil {
 		return
-	} else if keyList, ok = keyListValue.(*kern.ListType); !ok || len(*keyList) != 1 {
+	} else if keyList, ok = keyListValue.(*array.ArrayType); !ok || len(*keyList) != 1 {
 		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, kern.TypeName(keyListValue))
 		return
 	}
@@ -197,13 +207,13 @@ func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *s
 	}
 
 	switch collection := collectionValue.(type) {
-	case *kern.ListType:
+	case *array.ArrayType:
 		if index, ok := keyValue.(int64); ok {
 			value = (*collection)[index]
 		} else {
 			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, kern.TypeName(keyValue))
 		}
-	case *kern.DictType:
+	case *dict.DictType:
 		value = (*collection)[keyValue]
 	default:
 		err = collectionTerm.Errorf("collection expected")
@@ -212,7 +222,7 @@ func getCollectionItemValue(ctx kern.ExprContext, collectionTerm, keyListTerm *s
 }
 
 func getAssignValue(ctx kern.ExprContext, leftTerm *scan.Term) (value any, err error) {
-	if leftTerm.Symbol() == scan.SymIndex {
+	if leftTerm.Symbol() == sym.SymIndex {
 		value, err = getCollectionItemValue(ctx, leftTerm.Children[0], leftTerm.Children[1])
 	} else {
 		value, _ = ctx.GetVar(leftTerm.Source())
@@ -228,7 +238,7 @@ func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 	leftTerm := opTerm.Children[0]
 	leftSym := leftTerm.Symbol()
-	if leftSym != scan.SymVariable && leftSym != scan.SymIndex {
+	if leftSym != sym.SymVariable && leftSym != sym.SymIndex {
 		err = leftTerm.Tk.Errorf("left operand of %q must be a variable or a collection's item", opTerm.Tk.Source())
 		return
 	}
@@ -238,25 +248,25 @@ func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	if rightValue, err = rightChild.Compute(ctx); err == nil {
 		if leftValue, err = getAssignValue(ctx, leftTerm); err == nil {
 			switch opTerm.Symbol() {
-			case scan.SymPlusEqual:
+			case sym.SymPlusEqual:
 				v, err = sumValues(opTerm, leftValue, rightValue)
-			case scan.SymMinusEqual:
+			case sym.SymMinusEqual:
 				v, err = diffValues(opTerm, leftValue, rightValue)
-			case scan.SymStarEqual:
+			case sym.SymStarEqual:
 				v, err = mulValues(opTerm, leftValue, rightValue)
-			case scan.SymSlashEqual:
+			case sym.SymSlashEqual:
 				v, err = divValues(opTerm, leftValue, rightValue)
-			case scan.SymPercEqual:
+			case sym.SymPercEqual:
 				v, err = remainderValues(opTerm, leftValue, rightValue)
-			case scan.SymAmpersandEqual:
+			case sym.SymAmpersandEqual:
 				v, err = bitwiseAnd(opTerm, leftValue, rightValue)
-			case scan.SymVertBarEqual:
+			case sym.SymVertBarEqual:
 				v, err = bitwiseOr(opTerm, leftValue, rightValue)
-			case scan.SymCaretEqual:
+			case sym.SymCaretEqual:
 				v, err = bitwiseXor(opTerm, leftValue, rightValue)
-			case scan.SymDoubleLessEqual:
+			case sym.SymDoubleLessEqual:
 				v, err = bitLeftShift(opTerm, leftValue, rightValue)
-			case scan.SymDoubleGreaterEqual:
+			case sym.SymDoubleGreaterEqual:
 				v, err = bitRightShift(opTerm, leftValue, rightValue)
 			default:
 				err = opTerm.Errorf("unsupported assign operator %q", opTerm.Source())
@@ -271,16 +281,16 @@ func evalOpAssign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymEqual, newAssignTerm)
+	scan.RegisterTermConstructor(sym.SymEqual, newAssignTerm)
-	scan.RegisterTermConstructor(scan.SymColonEqual, newDeepCopyAssignTerm)
+	scan.RegisterTermConstructor(sym.SymColonEqual, newDeepCopyAssignTerm)
-	scan.RegisterTermConstructor(scan.SymPlusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymPlusEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymMinusEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymMinusEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymStarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymStarEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymSlashEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymSlashEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymPercEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymPercEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymDoubleLessEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleLessEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymDoubleGreaterEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleGreaterEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymAmpersandEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymAmpersandEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymVertBarEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymVertBarEqual, newOpAssignTerm)
-	scan.RegisterTermConstructor(scan.SymCaretEqual, newOpAssignTerm)
+	scan.RegisterTermConstructor(sym.SymCaretEqual, newOpAssignTerm)
 }

operator-at.go

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

operator-bitwise.go

@@ -7,6 +7,8 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
 )
 
 //-------- Bitwise NOT term
@@ -28,7 +30,7 @@ func evalBitwiseNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error)
 		return
 	}
 
-	if kern.IsInteger(value) {
+	if types.IsInteger(value) {
 		i, _ := value.(int64)
 		v = ^i
 	} else {
@@ -152,8 +154,8 @@ func evalBitwiseXor(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error)
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymTilde, newBitwiseNotTerm)
+	scan.RegisterTermConstructor(sym.SymTilde, newBitwiseNotTerm)
-	scan.RegisterTermConstructor(scan.SymAmpersand, newBitwiseAndTerm)
+	scan.RegisterTermConstructor(sym.SymAmpersand, newBitwiseAndTerm)
-	scan.RegisterTermConstructor(scan.SymVertBar, newBitwiseOrTerm)
+	scan.RegisterTermConstructor(sym.SymVertBar, newBitwiseOrTerm)
-	scan.RegisterTermConstructor(scan.SymCaret, newBitwiseXorTerm)
+	scan.RegisterTermConstructor(sym.SymCaret, newBitwiseXorTerm)
 }

operator-bool.go

@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
 )
 
 //-------- NOT term
@@ -30,7 +32,7 @@ func evalNot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if b, ok := kern.ToBool(rightValue); ok {
+	if b, ok := boolean.ToBool(rightValue); ok {
 		v = !b
 	} else {
 		err = opTerm.ErrIncompatiblePrefixPostfixType(rightValue)
@@ -68,8 +70,8 @@ func evalAndWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err e
 		return
 	}
 
-	leftBool, lok = kern.ToBool(leftValue)
+	leftBool, lok = boolean.ToBool(leftValue)
-	rightBool, rok = kern.ToBool(rightValue)
+	rightBool, rok = boolean.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool && rightBool
@@ -90,14 +92,14 @@ func evalAndWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err erro
 		return
 	}
 
-	if leftBool, lok := kern.ToBool(leftValue); !lok {
+	if leftBool, lok := boolean.ToBool(leftValue); !lok {
 		// err = fmt.Errorf("got %s as left operand type of 'AND' operator, it must be bool", expr.TypeName(leftValue))
 		// return
 		err = self.ErrIncompatibleType(leftValue, "left")
 	} else if !leftBool {
 		v = false
 	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
-		if rightBool, rok := kern.ToBool(rightValue); rok {
+		if rightBool, rok := boolean.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
 			err = self.ErrIncompatibleTypes(leftValue, rightValue)
@@ -136,8 +138,8 @@ func evalOrWithoutShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err er
 		return
 	}
 
-	leftBool, lok = kern.ToBool(leftValue)
+	leftBool, lok = boolean.ToBool(leftValue)
-	rightBool, rok = kern.ToBool(rightValue)
+	rightBool, rok = boolean.ToBool(rightValue)
 
 	if lok && rok {
 		v = leftBool || rightBool
@@ -158,13 +160,13 @@ func evalOrWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error
 		return
 	}
 
-	if leftBool, lok := kern.ToBool(leftValue); !lok {
+	if leftBool, lok := boolean.ToBool(leftValue); !lok {
 		err = fmt.Errorf("got %s as left operand type of 'OR' operator, it must be bool", kern.TypeName(leftValue))
 		return
 	} else if leftBool {
 		v = true
 	} else if rightValue, err = self.Children[1].Compute(ctx); err == nil {
-		if rightBool, rok := kern.ToBool(rightValue); rok {
+		if rightBool, rok := boolean.ToBool(rightValue); rok {
 			v = rightBool
 		} else {
 			err = self.ErrIncompatibleTypes(leftValue, rightValue)
@@ -175,7 +177,7 @@ func evalOrWithShortcut(ctx kern.ExprContext, self *scan.Term) (v any, err error
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymNot, newNotTerm)
+	scan.RegisterTermConstructor(sym.SymNot, newNotTerm)
-	scan.RegisterTermConstructor(scan.SymAnd, newAndTerm)
+	scan.RegisterTermConstructor(sym.SymAnd, newAndTerm)
-	scan.RegisterTermConstructor(scan.SymOr, newOrTerm)
+	scan.RegisterTermConstructor(sym.SymOr, newOrTerm)
 }

operator-builtin.go

@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- builtin term
@@ -31,7 +33,7 @@ func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	count := 0
-	if kern.IsString(childValue) {
+	if str.IsString(childValue) {
 		module, _ := childValue.(string)
 		count, err = ImportInContextByGlobPattern(ctx, module)
 	} else {
@@ -65,5 +67,5 @@ func evalBuiltin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwBuiltin, newBuiltinTerm)
+	scan.RegisterTermConstructor(sym.SymKwBuiltin, newBuiltinTerm)
 }

operator-but.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- but term
@@ -28,5 +29,5 @@ func evalBut(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwBut, newButTerm)
+	scan.RegisterTermConstructor(sym.SymKwBut, newButTerm)
 }

operator-cat.go

@@ -10,6 +10,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- cat term
@@ -147,5 +148,5 @@ func (it *catIterator) CallOperation(name string, args map[string]any) (v any, e
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwCat, newCatTerm)
+	scan.RegisterTermConstructor(sym.SymKwCat, newCatTerm)
 }

operator-context.go

@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 //-------- context term
@@ -29,7 +31,7 @@ func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error
 
 	if len(opTerm.Children) == 0 {
 		sourceCtx = ctx
-	} else if opTerm.Children[0].Symbol() == scan.SymVariable && opTerm.Children[0].Source() == "global" {
+	} else if opTerm.Children[0].Symbol() == sym.SymVariable && opTerm.Children[0].Source() == "global" {
 		sourceCtx = ctx.GetGlobal()
 	} else if childValue, err = opTerm.EvalPrefix(ctx); err == nil {
 		if dc, ok := childValue.(*dataCursor); ok {
@@ -48,7 +50,7 @@ func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error
 		}
 		if err == nil {
 			var item any
-			values := kern.NewLinkedListA()
+			values := list.NewLinkedListA()
 			for item, err = it.Next(); err == nil; item, err = it.Next() {
 				values.PushBack(item)
 			}
@@ -65,5 +67,5 @@ func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleDollar, newContextTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleDollar, newContextTerm)
 }

operator-ctrl.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- export all term
@@ -28,5 +29,5 @@ func evalExportAll(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleAt, newExportAllTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleAt, newExportAllTerm)
 }

operator-default.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- default term
@@ -29,7 +30,7 @@ func evalDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	leftTerm := opTerm.Children[0]
-	if leftTerm.Tk.Sym != scan.SymVariable {
+	if leftTerm.Tk.Sym != sym.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -63,7 +64,7 @@ func evalAlternate(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	leftTerm := opTerm.Children[0]
-	if leftTerm.Tk.Sym != scan.SymVariable {
+	if leftTerm.Tk.Sym != sym.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -99,7 +100,7 @@ func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err erro
 	}
 
 	leftTerm := opTerm.Children[0]
-	if leftTerm.Tk.Sym != scan.SymVariable {
+	if leftTerm.Tk.Sym != sym.SymVariable {
 		// err = leftTerm.Errorf("left operand of %q must be a variable", self.tk.source)
 		err = kern.ErrLeftOperandMustBeVariable(leftTerm, opTerm)
 		return
@@ -123,7 +124,7 @@ func evalAssignDefault(ctx kern.ExprContext, opTerm *scan.Term) (v any, err erro
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleQuestion, newDefaultTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleQuestion, newDefaultTerm)
-	scan.RegisterTermConstructor(scan.SymQuestionEqual, newDefaultAssignTerm)
+	scan.RegisterTermConstructor(sym.SymQuestionEqual, newDefaultAssignTerm)
-	scan.RegisterTermConstructor(scan.SymQuestionExclam, newAlternateTerm)
+	scan.RegisterTermConstructor(sym.SymQuestionExclam, newAlternateTerm)
 }

operator-digest.go

@@ -10,6 +10,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- digest term
@@ -48,9 +49,10 @@ func evalDigest(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		ctx.SetVar("#", it.Count())
 		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
 			if rightValue == nil {
-				break
+				err = io.EOF
 			} else {
 				lastValue = rightValue
+				ctx.SetVar(kern.ControlLastResult, lastValue)
 			}
 		}
 		ctx.DeleteVar("#")
@@ -69,5 +71,5 @@ func evalDigest(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwDigest, newDigestTerm)
+	scan.RegisterTermConstructor(sym.SymKwDigest, newDigestTerm)
 }

operator-dot.go

@@ -7,6 +7,8 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -35,7 +37,7 @@ func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 	switch unboxedValue := leftValue.(type) {
 	case kern.ExtIterator:
-		if indexTerm.Symbol() == scan.SymVariable /*|| indexTerm.Tk.Sym == scan.SymString */ {
+		if indexTerm.Symbol() == sym.SymVariable /*|| indexTerm.Tk.Sym == sym.SymString */ {
 			opName := indexTerm.Source()
 			if unboxedValue.HasOperation(opName) {
 				v, err = unboxedValue.CallOperation(opName, map[string]any{})
@@ -46,22 +48,7 @@ func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		} else {
 			err = indexTerm.Tk.ErrorExpectedGot("identifier")
 		}
-	case *kern.DictType:
+	case *dict.DictType:
-		// var ok bool
-		// s := opTerm.Children[1].Symbol()
-		// if s == scan.SymVariable || s == scan.SymString {
-		// 	src := opTerm.Children[1].Source()
-		// 	if len(src) > 1 && src[0] == '"' && src[len(src)-1] == '"' {
-		// 		src = src[1 : len(src)-1]
-		// 	}
-		// 	if v, ok = unboxedValue.GetItem(src); !ok {
-		// 		err = opTerm.Errorf("key %q not found", src)
-		// 	}
-		// } else if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
-		// 	if v, ok = unboxedValue.GetItem(rightValue); !ok {
-		// 		err = opTerm.Errorf("key %q not found", rightValue)
-		// 	}
-		// }
 		v, err = dotGetDictItemValue(ctx, unboxedValue, opTerm.Children[1])
 	default:
 		if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
@@ -71,11 +58,11 @@ func evalDot(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	return
 }
 
-func dotGetDictItemValue(ctx kern.ExprContext, d *kern.DictType, rightTerm *scan.Term) (v any, err error) {
+func dotGetDictItemValue(ctx kern.ExprContext, d *dict.DictType, rightTerm *scan.Term) (v any, err error) {
 	var ok bool
 	var rightValue any
 	s := rightTerm.Symbol()
-	if s == scan.SymVariable || s == scan.SymString {
+	if s == sym.SymVariable || s == sym.SymString {
 		// src := rightTerm.Source()
 		// if len(src) > 1 && src[0] == '"' && src[len(src)-1] == '"' {
 		// 	src = src[1 : len(src)-1]
@@ -101,5 +88,5 @@ func errDictKeyNotFound(term *scan.Term, key any) error {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDot, newDotTerm)
+	scan.RegisterTermConstructor(sym.SymDot, newDotTerm)
 }

operator-fact.go

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

operator-filter.go

@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
 )
 
 //-------- map term
@@ -117,7 +119,7 @@ func (it *filterIterator) Next() (item any, err error) {
 		ctx.DeleteVar("_")
 
 		if err == nil {
-			if success, valid := kern.ToBool(result); valid {
+			if success, valid := boolean.ToBool(result); valid {
 				if success {
 					item = attempt
 					break
@@ -163,5 +165,5 @@ func (it *filterIterator) CallOperation(name string, args map[string]any) (v any
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwFilter, newFilterTerm)
+	scan.RegisterTermConstructor(sym.SymKwFilter, newFilterTerm)
 }

operator-fraction.go

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

operator-groupby.go

@@ -11,6 +11,10 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- group by term
@@ -48,17 +52,17 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	rightTk := opTerm.Children[1].Tk
-	if rightTk.IsSymbol(scan.SymVariable) && rightTk.Source() == "__" {
+	if rightTk.IsSymbol(sym.SymVariable) && rightTk.Source() == "__" {
 		keyByIndex = true
 	} else if rightValue, err = opTerm.Children[1].Compute(ctx); err != nil {
 		return
-	} else if kern.IsString(rightValue) {
+	} else if str.IsString(rightValue) {
 		sKey = rightValue.(string)
 	} else {
 		return nil, fmt.Errorf("right operand of GROUPBY must be a string or identifier '__'; got %s", kern.TypeName(rightValue))
 	}
 
-	values := kern.MakeDict()
+	values := dict.MakeDict()
 	for item, err = it.Next(); err == nil; item, err = it.Next() {
 		ctx.SetVar("_", item)
 		ctx.SetVar("__", it.Index())
@@ -66,7 +70,7 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 		var sItemKey string
 
-		if d, ok := item.(*kern.DictType); ok {
+		if d, ok := item.(*dict.DictType); ok {
 			if keyByIndex || len(sKey) == 0 {
 				sItemKey = strconv.Itoa(int(it.Index()))
 			} else if d.HasKey(sKey) {
@@ -86,12 +90,12 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 			sItemKey = strconv.Itoa(int(it.Index()))
 		}
 
-		var ls *kern.ListType
+		var ls *array.ArrayType
 		if lsAny, exists := values.GetItem(sItemKey); exists && lsAny != nil {
-			ls = lsAny.(*kern.ListType)
+			ls = lsAny.(*array.ArrayType)
 		}
 		if ls == nil {
-			ls = kern.NewListA()
+			ls = array.NewArrayA()
 		}
 		ls.AppendItem(item)
 		values.SetItem(sItemKey, ls)
@@ -109,5 +113,5 @@ func evalGroupBy(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwGroupBy, newGroupByTerm)
+	scan.RegisterTermConstructor(sym.SymKwGroupBy, newGroupByTerm)
 }

operator-in.go

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

operator-include.go

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

operator-index.go

@@ -5,8 +5,16 @@
 package expr
 
 import (
+	"strings"
+
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 // -------- index term
@@ -20,15 +28,15 @@ func newIndexTerm(tk *scan.Token) (inst *scan.Term) {
 	}
 }
 
-func verifyKey(indexList *kern.ListType) (index any, err error) {
+func verifyKey(indexList *array.ArrayType) (index any, err error) {
 	index = (*indexList)[0]
 	return
 }
 
-func verifyIndex(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (index int, err error) {
+func verifyIndex(indexTerm kern.Term, indexList *array.ArrayType, maxValue int64) (index int64, err error) {
-	var v int
+	var v int64
 
-	if v, err = kern.ToGoInt((*indexList)[0], "index expression"); err == nil {
+	if v, err = types.ToGoInt64((*indexList)[0], "index expression"); err == nil {
 		if v < 0 && v >= -maxValue {
 			v = maxValue + v
 		}
@@ -41,32 +49,32 @@ func verifyIndex(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (
 	return
 }
 
-func verifyRange(indexTerm *scan.Term, indexList *kern.ListType, maxValue int) (startIndex, endIndex int, err error) {
+// func verifyInterval(indexTerm kern.Term, indexList *array.ArrayType, maxValue int64) (startIndex, endIndex int64, err error) {
-	v, _ := ((*indexList)[0]).(*intPair)
+// 	v, _ := ((*indexList)[0]).(*interval.IntervalType)
-	startIndex = v.a
+// 	startIndex = v.Begin()
-	endIndex = v.b
+// 	endIndex = v.End()
-	if endIndex == kern.ConstLastIndex {
+// 	if endIndex == kern.ConstLastIndex {
-		endIndex = maxValue
+// 		endIndex = int64(maxValue)
-	}
+// 	}
-	if startIndex < 0 && startIndex >= -maxValue {
+// 	if startIndex < 0 && startIndex >= -maxValue {
-		startIndex = maxValue + startIndex
+// 		startIndex = int64(maxValue) + startIndex
-	}
+// 	}
-	if endIndex < 0 && endIndex >= -maxValue {
+// 	if endIndex < 0 && endIndex >= -maxValue {
-		endIndex = maxValue + endIndex
+// 		endIndex = int64(maxValue) + endIndex
-	}
+// 	}
-	if startIndex < 0 || startIndex > maxValue {
+// 	if startIndex < 0 || startIndex > maxValue {
-		err = indexTerm.Errorf("range start-index %d is out of bounds", startIndex)
+// 		err = indexTerm.Errorf("%s start-index %d is out of bounds", interval.TypeName, startIndex)
-	} else if endIndex < 0 || endIndex > maxValue {
+// 	} else if endIndex < 0 || endIndex > maxValue {
-		err = indexTerm.Errorf("range end-index %d is out of bounds", endIndex)
+// 		err = indexTerm.Errorf("%s end-index %d is out of bounds", interval.TypeName, endIndex)
-	} else if startIndex > endIndex {
+// 	} else if startIndex > endIndex {
-		err = indexTerm.Errorf("range start-index %d must not be greater than end-index %d", startIndex, endIndex)
+// 		err = indexTerm.Errorf("%s start-index %d must not be greater than end-index %d", interval.TypeName, startIndex, endIndex)
-	}
+// 	}
-	return
+// 	return
-}
+// }
 
 func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
-	var indexList *kern.ListType
+	var indexList *array.ArrayType
 	var ok bool
 
 	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
@@ -74,7 +82,7 @@ func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	indexTerm := opTerm.Children[1]
-	if indexList, ok = rightValue.(*kern.ListType); !ok {
+	if indexList, ok = rightValue.(*array.ArrayType); !ok {
 		err = opTerm.Errorf("invalid index expression")
 		return
 	} else if len(*indexList) != 1 {
@@ -82,51 +90,12 @@ func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsInteger((*indexList)[0]) {
+	if types.IsInteger((*indexList)[0]) {
-		switch unboxedValue := leftValue.(type) {
+		v, err = collectionItemByIndex(opTerm, leftValue, rightValue, indexList)
-		case *kern.ListType:
+	} else if interval.IsInterval((*indexList)[0]) {
-			var index int
+		v, err = subCollectionByIndex(opTerm, leftValue, rightValue, indexList)
-			if index, err = verifyIndex(indexTerm, indexList, len(*unboxedValue)); err == nil {
+	} else if dict.IsDict(leftValue) {
-				v = (*unboxedValue)[index]
+		d := leftValue.(*dict.DictType)
-			}
-		case *kern.LinkedList:
-			var index int
-			if index, err = verifyIndex(indexTerm, indexList, unboxedValue.Len()); err == nil {
-				v, err = unboxedValue.At(index)
-			}
-		case string:
-			var index int
-			if index, err = verifyIndex(indexTerm, indexList, len(unboxedValue)); err == nil {
-				v = string(unboxedValue[index])
-			}
-		case *kern.DictType:
-			v, err = getDictItem(unboxedValue, indexTerm, indexList, rightValue)
-		default:
-			err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
-		}
-	} else if isIntPair((*indexList)[0]) {
-		switch unboxedValue := leftValue.(type) {
-		case *kern.ListType:
-			var start, end int
-			if start, end, err = verifyRange(indexTerm, indexList, len(*unboxedValue)); err == nil {
-				sublist := kern.ListType((*unboxedValue)[start:end])
-				v = &sublist
-			}
-		case *kern.LinkedList:
-			var start, end int
-			if start, end, err = verifyRange(indexTerm, indexList, unboxedValue.Len()); err == nil {
-				v = unboxedValue.Sub(start, end)
-			}
-		case string:
-			var start, end int
-			if start, end, err = verifyRange(indexTerm, indexList, len(unboxedValue)); err == nil {
-				v = unboxedValue[start:end]
-			}
-		default:
-			err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
-		}
-	} else if kern.IsDict(leftValue) {
-		d := leftValue.(*kern.DictType)
 		v, err = getDictItem(d, indexTerm, indexList, rightValue)
 	} else {
 		rightChild := opTerm.Children[1]
@@ -135,7 +104,126 @@ func evalIndex(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	return
 }
 
-func getDictItem(d *kern.DictType, indexTerm *scan.Term, indexList *kern.ListType, rightValue any) (v any, err error) {
+func collectionItemByIndex(opTerm kern.Term, leftValue, rightValue any, indexList *array.ArrayType) (v any, err error) {
+	indexTerm := opTerm.GetChild(1)
+	switch unboxedValue := leftValue.(type) {
+	case *array.ArrayType:
+		var index int64
+		if index, err = verifyIndex(indexTerm, indexList, int64(len(*unboxedValue))); err == nil {
+			v = (*unboxedValue)[index]
+		}
+	case *list.LinkedList:
+		var index int64
+		if index, err = verifyIndex(indexTerm, indexList, int64(unboxedValue.Len())); err == nil {
+			v, err = unboxedValue.At(index)
+		}
+	case string:
+		var index int64
+		if index, err = verifyIndex(indexTerm, indexList, int64(len(unboxedValue))); err == nil {
+			v = string(unboxedValue[index])
+		}
+	case *dict.DictType:
+		v, err = getDictItem(unboxedValue, indexTerm, indexList, rightValue)
+	default:
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func subCollectionByIndex(opTerm kern.Term, leftValue, rightValue any, indexList *array.ArrayType) (v any, err error) {
+	triple := (*indexList)[0].(*interval.IntervalType)
+	switch unboxedValue := leftValue.(type) {
+	case *array.ArrayType:
+		v = intervalSubArray(unboxedValue, triple)
+	case *list.LinkedList:
+		v = intervalSubLinkedList(unboxedValue, triple)
+	case string:
+		v = intervalSubString(unboxedValue, triple)
+	default:
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func fixInterval(p *interval.IntervalType, maxLength int) (b, e, s int) {
+	b, e, s = p.ToIntTriple()
+	if b < 0 {
+		b = maxLength + b
+	}
+	if e < 0 {
+		e = maxLength + e //+ 1
+	}
+	return
+}
+
+func intervalSubString(source string, p *interval.IntervalType) (result string) {
+	b, e, s := fixInterval(p, len(source))
+	if b <= e {
+		e = min(e, len(source))
+		if s == 1 {
+			result = source[b:e]
+		} else {
+			var sb strings.Builder
+			for i := b; i < e; i += s {
+				sb.WriteByte(source[i])
+			}
+			result = sb.String()
+		}
+	} else {
+		var sb strings.Builder
+		for i := b; i >= e; i -= s {
+			sb.WriteByte(source[i])
+		}
+		result = sb.String()
+	}
+	return
+}
+
+func intervalSubArray(source *array.ArrayType, p *interval.IntervalType) (result *array.ArrayType) {
+	var a array.ArrayType
+	b, e, s := fixInterval(p, len(*source))
+	if b <= e {
+		e = min(e, len(*source))
+		if s == 1 {
+			a = (*source)[b:e]
+		} else {
+			size := (e-b)/s + 1
+			a = make(array.ArrayType, 0, size)
+			for i := b; i < e; i += s {
+				a = append(a, (*source)[i])
+			}
+		}
+	} else {
+		size := (b-e)/s + 1
+		a = make(array.ArrayType, 0, size)
+		for i := b; i > e; i -= s {
+			a = append(a, (*source)[i])
+		}
+	}
+	result = &a
+	return
+}
+
+func intervalSubLinkedList(source *list.LinkedList, p *interval.IntervalType) (result *list.LinkedList) {
+	b, e, s := fixInterval(p, source.Len())
+	revert := b > e
+	if revert {
+		b, e = e, b
+		source = source.Revert()
+	}
+	e = min(e, source.Len())
+	if s == 1 {
+		result = source.Sub(int64(b), int64(e))
+	} else {
+		result = source.SubStep(int64(b), int64(e), int64(s))
+	}
+	if revert {
+		source = source.Revert()
+	}
+	return
+}
+
+func getDictItem(d *dict.DictType, indexTerm kern.Term, indexList *array.ArrayType, rightValue any) (v any, err error) {
 	var ok bool
 	var indexValue any
 
@@ -149,5 +237,5 @@ func getDictItem(d *kern.DictType, indexTerm *scan.Term, indexList *kern.ListTyp
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymIndex, newIndexTerm)
+	scan.RegisterTermConstructor(sym.SymIndex, newIndexTerm)
 }

operator-insert.go

@@ -7,6 +7,9 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 //-------- prepend term
@@ -31,34 +34,38 @@ func newAppendTerm(tk *scan.Token) (inst *scan.Term) {
 	}
 }
 
-func prependToList(opTerm *scan.Term, leftValue, rightValue any) (result any, err error) {
+func prependToList(opTerm kern.Term, leftValue, rightValue any) (result any, err error) {
-	if list, ok := rightValue.(*kern.ListType); ok {
+	if a, ok := rightValue.(*array.ArrayType); ok {
 		var it kern.Iterator
 		if it, ok = leftValue.(kern.Iterator); !ok {
 			it = NewFormalIterator(leftValue)
 		}
 
-		ls := kern.NewLinkedList()
+		ls := list.NewLinkedList()
 		ls.SeqPushBack(it)
 
-		newList := kern.ListType(nil)
+		newArray := array.ArrayType(nil)
-		if newSize := len(*list) + int(ls.Len()); newSize > cap(*list) {
+		if newSize := len(*a) + int(ls.Len()); newSize > cap(*a) {
-			newList = make([]any, 0, newSize)
+			newArray = make([]any, 0, newSize)
 			for node := ls.FirstNode(); node != nil; node = node.Next() {
-				newList = append(newList, node.Data())
+				newArray = append(newArray, node.Data())
 			}
 		}
-		for _, item := range *list {
+		for _, item := range *a {
-			newList = append(newList, item)
+			newArray = append(newArray, item)
 		}
-		result = &newList
+		if opTerm.GetRightChild().IsVar() {
-	} else if list, ok := rightValue.(*kern.LinkedList); ok {
+			// Update the original array if the right operand is a variable
+			*a = newArray
+		}
+		result = &newArray
+	} else if ll, ok := rightValue.(*list.LinkedList); ok {
 		var it kern.Iterator
 		if it, ok = leftValue.(kern.Iterator); !ok {
 			it = NewFormalIterator(leftValue)
 		}
 
-		result = list.SeqPushBack(it)
+		result = ll.SeqPushBack(it)
 	} else {
 		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
@@ -76,34 +83,38 @@ func evalPrepend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	return
 }
 
-func appendToList(opTerm *scan.Term, leftValue, rightValue any) (result any, err error) {
+func appendToList(opTerm kern.Term, leftValue, rightValue any) (result any, err error) {
-	if list, ok := leftValue.(*kern.ListType); ok {
+	if a, ok := leftValue.(*array.ArrayType); ok {
 		var it kern.Iterator
 		if it, ok = rightValue.(kern.Iterator); !ok {
 			it = NewFormalIterator(rightValue)
 		}
 
-		ls := kern.NewLinkedList()
+		ls := list.NewLinkedList()
 		ls.SeqPushBack(it)
 
-		newList := *list
+		newArray := *a
-		if newSize := len(*list) + int(ls.Len()); newSize > cap(*list) {
+		if newSize := len(*a) + int(ls.Len()); newSize > cap(*a) {
-			newList = make([]any, 0, newSize)
+			newArray = make([]any, 0, newSize)
-			for _, item := range *list {
+			for _, item := range *a {
-				newList = append(newList, item)
+				newArray = append(newArray, item)
 			}
 		}
 		for node := ls.FirstNode(); node != nil; node = node.Next() {
-			newList = append(newList, node.Data())
+			newArray = append(newArray, node.Data())
 		}
-		result = &newList
+		if opTerm.GetLeftChild().IsVar() {
-	} else if list, ok := leftValue.(*kern.LinkedList); ok {
+			// Update the original array if the left operand is a variable
+			*a = newArray
+		}
+		result = &newArray
+	} else if ll, ok := leftValue.(*list.LinkedList); ok {
 		var it kern.Iterator
 		if it, ok = rightValue.(kern.Iterator); !ok {
 			it = NewFormalIterator(rightValue)
 		}
 
-		result = list.SeqPushBack(it)
+		result = ll.SeqPushBack(it)
 	} else {
 		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
@@ -122,26 +133,8 @@ func evalAppend(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	return
 }
 
-// func evalAssignAppend(ctx ExprContext, self *term) (v any, err error) {
-// 	var leftValue, rightValue any
-
-// 	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
-// 		return
-// 	}
-
-// 	if IsList(leftValue) {
-// 		list, _ := leftValue.(*ListType)
-// 		newList := append(*list, rightValue)
-// 		v = &newList
-// 		if
-// 	} else {
-// 		err = self.errIncompatibleTypes(leftValue, rightValue)
-// 	}
-// 	return
-// }
-
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymPlusGreater, newPrependTerm)
+	scan.RegisterTermConstructor(sym.SymPlusGreater, newPrependTerm)
-	scan.RegisterTermConstructor(scan.SymLessPlus, newAppendTerm)
+	scan.RegisterTermConstructor(sym.SymLessPlus, newAppendTerm)
 }

operator-interval.go

@@ -0,0 +1,103 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-interval.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/interval"
+)
+
+// -------- interval term
+
+func newIntervalTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriInterval,
+		EvalFunc: evalInterval,
+	}
+}
+
+func changeColonToInterval(t *scan.Term) {
+	if t.IsSymbol(sym.SymDoubleDot) {
+		t.SetSymbol(sym.SymInterval)
+		t.EvalFunc = evalInterval
+		if child := t.GetLeftChild(); child != nil && child.IsSymbol(sym.SymDoubleDot) {
+			child.SetSymbol(sym.SymInterval)
+		}
+	}
+}
+
+func evalInterval(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var begin, end int64
+
+	step := int64(1)
+	switch opTerm.GetChildCount() {
+	case 0:
+		begin = 0
+		end = int64(kern.ConstLastIndex)
+	case 1:
+		var leftValue any
+		if leftValue, err = opTerm.GetChild(0).Compute(ctx); err != nil {
+			return
+		}
+		if begin, err = checkIntervalComponent(opTerm, leftValue); err != nil {
+			return
+		}
+		end = int64(kern.ConstLastIndex)
+	default:
+		var beginValue, endValue, stepValue any
+		subTerm := opTerm.GetLeftChild()
+		if subTerm.IsOneOf(sym.SymInterval, sym.SymDoubleDot) {
+			if beginValue, endValue, err = subTerm.EvalInfix(ctx); err != nil {
+				return
+			}
+			if stepValue, err = opTerm.GetRightChild().Compute(ctx); err != nil {
+				return
+			}
+			step, err = checkIntervalComponent(opTerm.GetRightChild(), stepValue)
+		} else if beginValue, endValue, err = opTerm.EvalInfix(ctx); err != nil {
+			return
+		}
+		if begin, err = checkIntervalComponent(opTerm, beginValue); err != nil {
+			return
+		}
+		if end, err = checkIntervalComponent(opTerm, endValue); err != nil {
+			return
+		}
+	}
+
+	if step <= 0 {
+		err = opTerm.Errorf("invalid %s specification: step must be positive", interval.TypeName)
+	} else {
+		v = interval.NewInterval(begin, end, step)
+	}
+	return
+}
+
+func checkIntervalComponent(t kern.Term, value any) (component int64, err error) {
+	if component, err = types.ToGoInt64(value, "%s expression"); err != nil {
+		err = t.Errorf(err.Error(), interval.TypeName)
+	}
+	return
+}
+
+// func errIntervalInvalidSpecification(t kern.Term) error {
+// 	return t.Errorf("invalid %s specification", interval.TypeName)
+// }
+
+func errIntervalUnexpectedExpression(t *scan.Term) error {
+	return t.Errorf("unexpected %s expression", interval.TypeName)
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(sym.SymInterval, newIntervalTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleDot, newIntervalTerm)
+}

operator-iter-value.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- iter value term
@@ -39,5 +40,5 @@ func evalIterValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 // init
 func init() {
 	//	registerTermConstructor(SymOpenClosedRound, newIterValueTerm)
-	scan.RegisterTermConstructor(scan.SymDereference, newIterValueTerm)
+	scan.RegisterTermConstructor(sym.SymDereference, newIterValueTerm)
 }

operator-length.go

@@ -7,6 +7,11 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- length term
@@ -28,25 +33,19 @@ func evalLength(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsList(childValue) {
+	if array.IsArray(childValue) {
-		ls, _ := childValue.(*kern.ListType)
+		ls, _ := childValue.(*array.ArrayType)
 		v = int64(len(*ls))
-	} else if kern.IsString(childValue) {
+	} else if str.IsString(childValue) {
 		s, _ := childValue.(string)
 		v = int64(len(s))
-	} else if kern.IsDict(childValue) {
+	} else if dict.IsDict(childValue) {
-		m, _ := childValue.(*kern.DictType)
+		m, _ := childValue.(*dict.DictType)
 		v = int64(len(*m))
-	} else if lls, ok := childValue.(*kern.LinkedList); ok {
+	} else if lls, ok := childValue.(*list.LinkedList); ok {
 		v = int64(lls.Len())
 	} else if it, ok := childValue.(kern.Iterator); ok {
 		v = int64(it.Count())
-		// if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(CountName) {
-		// 	count, _ := extIt.CallOperation(CountName, nil)
-		// 	v, _ = ToGoInt(count, "")
-		// } else {
-		// 	v = int64(it.Index() + 1)
-		// }
 	} else {
 		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}
@@ -55,5 +54,5 @@ func evalLength(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymHash, newLengthTerm)
+	scan.RegisterTermConstructor(sym.SymHash, newLengthTerm)
 }

operator-map.go

@@ -9,6 +9,7 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- map term
@@ -44,32 +45,11 @@ func evalMap(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		}
 	}
 
-	// values := kern.NewListA()
-	// for item, err = it.Next(); err == nil; item, err = it.Next() {
-	// 	ctx.SetVar("_", item)
-	// 	ctx.SetVar("__", it.Index())
-	// 	ctx.SetVar("_#", it.Count())
-	// 	if rightValue, err = opTerm.Children[1].Compute(ctx); err == nil {
-	// 		values.AppendItem(rightValue)
-	// 	}
-	// 	ctx.DeleteVar("_#")
-	// 	ctx.DeleteVar("__")
-	// 	ctx.DeleteVar("_")
-	// 	if err != nil {
-	// 		break
-	// 	}
-	// }
-	// if err == io.EOF {
-	// 	err = nil
-	// }
-	// if err == nil {
-	// 	v = values
-	// }
 	v, err = NewIterIter(it, ctx, opTerm.Children[1:])
 	return
 }
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwMap, newMapTerm)
+	scan.RegisterTermConstructor(sym.SymKwMap, newMapTerm)
 }

operator-plugin.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- plugin term
@@ -37,5 +38,5 @@ func evalPlugin(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwPlugin, newPluginTerm)
+	scan.RegisterTermConstructor(sym.SymKwPlugin, newPluginTerm)
 }

operator-post-inc-dec.go

@@ -7,6 +7,8 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
 )
 
 // -------- post increment term
@@ -31,7 +33,7 @@ func evalPostInc(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		var namePrefix string
 		v, err = it.Next()
 
-		if opTerm.Children[0].Symbol() == scan.SymVariable {
+		if opTerm.Children[0].Symbol() == sym.SymVariable {
 			namePrefix = opTerm.Children[0].Source()
 		}
 		ctx.UnsafeSetVar(namePrefix+"_index", it.Index())
@@ -49,7 +51,7 @@ func evalPostInc(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 				ctx.UnsafeSetVar(namePrefix+"_value", v1)
 			}
 		}
-	} else if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
+	} else if types.IsInteger(childValue) && opTerm.Children[0].Symbol() == sym.SymVariable {
 		v = childValue
 		i, _ := childValue.(int64)
 		ctx.SetVar(opTerm.Children[0].Source(), i+1)
@@ -79,7 +81,7 @@ func evalPostDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 	/* if it, ok := childValue.(Iterator); ok {
 		v, err = it.Next()
-	} else  */if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
+	} else  */if types.IsInteger(childValue) && opTerm.Children[0].Symbol() == sym.SymVariable {
 		v = childValue
 		i, _ := childValue.(int64)
 		ctx.SetVar(opTerm.Children[0].Source(), i-1)
@@ -91,6 +93,6 @@ func evalPostDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoublePlus, newPostIncTerm)
+	scan.RegisterTermConstructor(sym.SymDoublePlus, newPostIncTerm)
-	scan.RegisterTermConstructor(scan.SymDoubleMinus, newPostDecTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleMinus, newPostDecTerm)
 }

operator-pre-inc-dec.go

@@ -7,6 +7,8 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
 )
 
 // -------- pre increment term
@@ -27,7 +29,7 @@ func evalPreInc(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
+	if types.IsInteger(childValue) && opTerm.Children[0].Symbol() == sym.SymVariable {
 		i := childValue.(int64) + 1
 		ctx.SetVar(opTerm.Children[0].Source(), i)
 		v = i
@@ -56,7 +58,7 @@ func evalPreDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsInteger(childValue) && opTerm.Children[0].Symbol() == scan.SymVariable {
+	if types.IsInteger(childValue) && opTerm.Children[0].Symbol() == sym.SymVariable {
 		i := childValue.(int64) - 1
 		ctx.SetVar(opTerm.Children[0].Source(), i)
 		v = i
@@ -68,6 +70,6 @@ func evalPreDec(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymPreInc, newPreIncTerm)
+	scan.RegisterTermConstructor(sym.SymPreInc, newPreIncTerm)
-	scan.RegisterTermConstructor(scan.SymPreDec, newPreDecTerm)
+	scan.RegisterTermConstructor(sym.SymPreDec, newPreDecTerm)
 }

operator-prod.go

@@ -9,6 +9,12 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/float"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- multiply term
@@ -24,15 +30,15 @@ func newMultiplyTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 func mulValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
-	if kern.IsString(leftValue) && kern.IsInteger(rightValue) {
+	if str.IsString(leftValue) && types.IsInteger(rightValue) {
 		s, _ := leftValue.(string)
 		n, _ := rightValue.(int64)
 		v = strings.Repeat(s, int(n))
-	} else if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+	} else if types.IsNumOrFract(leftValue) && types.IsNumOrFract(rightValue) {
-		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+		if float.IsFloat(leftValue) || float.IsFloat(rightValue) {
-			v = kern.NumAsFloat(leftValue) * kern.NumAsFloat(rightValue)
+			v = types.NumAsFloat(leftValue) * types.NumAsFloat(rightValue)
-		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+		} else if fract.IsFraction(leftValue) || fract.IsFraction(rightValue) {
-			v, err = kern.MulAnyFract(leftValue, rightValue)
+			v, err = fract.MulAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
@@ -67,16 +73,16 @@ func newDivideTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 func divValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
-	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+	if types.IsNumOrFract(leftValue) && types.IsNumOrFract(rightValue) {
-		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+		if float.IsFloat(leftValue) || float.IsFloat(rightValue) {
-			d := kern.NumAsFloat(rightValue)
+			d := types.NumAsFloat(rightValue)
 			if d == 0.0 {
 				err = opTerm.ErrDivisionByZero()
 			} else {
-				v = kern.NumAsFloat(leftValue) / d
+				v = types.NumAsFloat(leftValue) / d
 			}
-		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+		} else if fract.IsFraction(leftValue) || fract.IsFraction(rightValue) {
-			v, err = kern.DivAnyFract(leftValue, rightValue)
+			v, err = fract.DivAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			if rightInt, _ := rightValue.(int64); rightInt == 0 {
@@ -85,11 +91,11 @@ func divValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error)
 				v = leftInt / rightInt
 			}
 		}
-	} else if kern.IsString(leftValue) && kern.IsString(rightValue) {
+	} else if str.IsString(leftValue) && str.IsString(rightValue) {
 		source := leftValue.(string)
 		sep := rightValue.(string)
-		v = kern.ListFromStrings(strings.Split(source, sep))
+		v = array.ArrayFromStrings(strings.Split(source, sep))
-	} else if kern.IsString(leftValue) && kern.IsInteger(rightValue) {
+	} else if str.IsString(leftValue) && types.IsInteger(rightValue) {
 		source := leftValue.(string)
 		partSize := int(rightValue.(int64))
 		if partSize == 0 {
@@ -108,7 +114,7 @@ func divValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error)
 			if remainder > 0 {
 				parts = append(parts, source[len(source)-remainder:])
 			}
-			v = kern.NewList(parts)
+			v = array.NewArray(parts)
 		}
 	} else {
 		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
@@ -145,12 +151,12 @@ func evalDivideAsFloat(ctx kern.ExprContext, floatDivTerm *scan.Term) (v any, er
 		return
 	}
 
-	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+	if types.IsNumOrFract(leftValue) && types.IsNumOrFract(rightValue) {
-		d := kern.NumAsFloat(rightValue)
+		d := types.NumAsFloat(rightValue)
 		if d == 0.0 {
 			err = floatDivTerm.ErrDivisionByZero()
 		} else {
-			v = kern.NumAsFloat(leftValue) / d
+			v = types.NumAsFloat(leftValue) / d
 		}
 	} else {
 		err = floatDivTerm.ErrIncompatibleTypes(leftValue, rightValue)
@@ -170,7 +176,7 @@ func newRemainderTerm(tk *scan.Token) (inst *scan.Term) {
 	}
 }
 func remainderValues(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
-	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
+	if types.IsInteger(leftValue) && types.IsInteger(rightValue) {
 		rightInt, _ := rightValue.(int64)
 		if rightInt == 0 {
 			err = opTerm.ErrDivisionByZero()
@@ -196,8 +202,8 @@ func evalRemainder(ctx kern.ExprContext, remainderTerm *scan.Term) (v any, err e
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymStar, newMultiplyTerm)
+	scan.RegisterTermConstructor(sym.SymStar, newMultiplyTerm)
-	scan.RegisterTermConstructor(scan.SymSlash, newDivideTerm)
+	scan.RegisterTermConstructor(sym.SymSlash, newDivideTerm)
-	scan.RegisterTermConstructor(scan.SymDotSlash, newDivideAsFloatTerm)
+	scan.RegisterTermConstructor(sym.SymDotSlash, newDivideAsFloatTerm)
-	scan.RegisterTermConstructor(scan.SymPercent, newRemainderTerm)
+	scan.RegisterTermConstructor(sym.SymPercent, newRemainderTerm)
 }

operator-range.go

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

operator-rel.go

@@ -9,6 +9,12 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/boolean"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- equal term
@@ -26,22 +32,22 @@ func newEqualTerm(tk *scan.Token) (inst *scan.Term) {
 // type deepFuncTemplate func(a, b any) (eq bool, err error)
 
 func equals(a, b any, deepCmp kern.DeepFuncTemplate) (eq bool, err error) {
-	if kern.IsNumOrFract(a) && kern.IsNumOrFract(b) {
+	if types.IsNumOrFract(a) && types.IsNumOrFract(b) {
-		if kern.IsNumber(a) && kern.IsNumber(b) {
+		if types.IsNumber(a) && types.IsNumber(b) {
-			if kern.IsInteger(a) && kern.IsInteger(b) {
+			if types.IsInteger(a) && types.IsInteger(b) {
 				li, _ := a.(int64)
 				ri, _ := b.(int64)
 				eq = li == ri
 			} else {
-				eq = kern.NumAsFloat(a) == kern.NumAsFloat(b)
+				eq = types.NumAsFloat(a) == types.NumAsFloat(b)
 			}
 		} else {
 			var cmp int
-			if cmp, err = kern.CmpAnyFract(a, b); err == nil {
+			if cmp, err = fract.CmpAnyFract(a, b); err == nil {
 				eq = cmp == 0
 			}
 		}
-	} else if deepCmp != nil && kern.IsList(a) && kern.IsList(b) {
+	} else if deepCmp != nil && array.IsArray(a) && array.IsArray(b) {
 		eq, err = deepCmp(a, b)
 	} else {
 		eq = reflect.DeepEqual(a, b)
@@ -75,7 +81,7 @@ func newNotEqualTerm(tk *scan.Token) (inst *scan.Term) {
 
 func evalNotEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	if v, err = evalEqual(ctx, opTerm); err == nil {
-		b, _ := kern.ToBool(v)
+		b, _ := boolean.ToBool(v)
 		v = !b
 	}
 	return
@@ -94,29 +100,29 @@ func newLessTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 func lessThan(self *scan.Term, a, b any) (isLess bool, err error) {
-	if kern.IsNumOrFract(a) && kern.IsNumOrFract(b) {
+	if types.IsNumOrFract(a) && types.IsNumOrFract(b) {
-		if kern.IsNumber(a) && kern.IsNumber(b) {
+		if types.IsNumber(a) && types.IsNumber(b) {
-			if kern.IsInteger(a) && kern.IsInteger(b) {
+			if types.IsInteger(a) && types.IsInteger(b) {
 				li, _ := a.(int64)
 				ri, _ := b.(int64)
 				isLess = li < ri
 			} else {
-				isLess = kern.NumAsFloat(a) < kern.NumAsFloat(b)
+				isLess = types.NumAsFloat(a) < types.NumAsFloat(b)
 			}
 		} else {
 			var cmp int
-			if cmp, err = kern.CmpAnyFract(a, b); err == nil {
+			if cmp, err = fract.CmpAnyFract(a, b); err == nil {
 				isLess = cmp < 0
 			}
 		}
-	} else if kern.IsString(a) && kern.IsString(b) {
+	} else if str.IsString(a) && str.IsString(b) {
 		ls, _ := a.(string)
 		rs, _ := b.(string)
 		isLess = ls < rs
 		// Inclusion test
-	} else if kern.IsList(a) && kern.IsList(b) {
+	} else if array.IsArray(a) && array.IsArray(b) {
-		aList, _ := a.(*kern.ListType)
+		aList, _ := a.(*array.ArrayType)
-		bList, _ := b.(*kern.ListType)
+		bList, _ := b.(*array.ArrayType)
 		isLess = len(*aList) < len(*bList) && bList.Contains(aList)
 	} else {
 		err = self.ErrIncompatibleTypes(a, b)
@@ -149,8 +155,8 @@ func newLessEqualTerm(tk *scan.Token) (inst *scan.Term) {
 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) {
+			if array.IsArray(a) && array.IsArray(b) {
-				isLessEq, err = kern.SameContent(a, b)
+				isLessEq, err = array.SameContent(a, b)
 			} else {
 				isLessEq, err = equals(a, b, nil)
 			}
@@ -219,10 +225,10 @@ func evalGreaterEqual(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleEqual, newEqualTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleEqual, newEqualTerm)
-	scan.RegisterTermConstructor(scan.SymNotEqual, newNotEqualTerm)
+	scan.RegisterTermConstructor(sym.SymNotEqual, newNotEqualTerm)
-	scan.RegisterTermConstructor(scan.SymLess, newLessTerm)
+	scan.RegisterTermConstructor(sym.SymLess, newLessTerm)
-	scan.RegisterTermConstructor(scan.SymLessOrEqual, newLessEqualTerm)
+	scan.RegisterTermConstructor(sym.SymLessOrEqual, newLessEqualTerm)
-	scan.RegisterTermConstructor(scan.SymGreater, newGreaterTerm)
+	scan.RegisterTermConstructor(sym.SymGreater, newGreaterTerm)
-	scan.RegisterTermConstructor(scan.SymGreaterOrEqual, newGreaterEqualTerm)
+	scan.RegisterTermConstructor(sym.SymGreaterOrEqual, newGreaterEqualTerm)
 }

operator-selector.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 //-------- selector term
@@ -82,5 +83,5 @@ func evalSelector(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymSelector, newSelectorTerm)
+	scan.RegisterTermConstructor(sym.SymSelector, newSelectorTerm)
 }

operator-shift.go

@@ -7,6 +7,8 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
 )
 
 //-------- bit right shift term
@@ -22,7 +24,7 @@ func newRightShiftTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 func bitRightShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
-	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
+	if types.IsInteger(leftValue) && types.IsInteger(rightValue) {
 		leftInt := leftValue.(int64)
 		rightInt := rightValue.(int64)
 		v = leftInt >> rightInt
@@ -56,7 +58,7 @@ func newLeftShiftTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 func bitLeftShift(opTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
-	if kern.IsInteger(leftValue) && kern.IsInteger(rightValue) {
+	if types.IsInteger(leftValue) && types.IsInteger(rightValue) {
 		leftInt := leftValue.(int64)
 		rightInt := rightValue.(int64)
 		v = leftInt << rightInt
@@ -81,6 +83,6 @@ func evalLeftShift(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymDoubleGreater, newRightShiftTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleGreater, newRightShiftTerm)
-	scan.RegisterTermConstructor(scan.SymDoubleLess, newLeftShiftTerm)
+	scan.RegisterTermConstructor(sym.SymDoubleLess, newLeftShiftTerm)
 }

operator-sign.go

@@ -7,6 +7,9 @@ package expr
 import (
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/float"
 )
 
 //-------- plus sign term
@@ -38,15 +41,15 @@ func evalSign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
-	if kern.IsFloat(rightValue) {
+	if float.IsFloat(rightValue) {
-		if opTerm.Tk.Sym == scan.SymChangeSign {
+		if opTerm.Tk.Sym == sym.SymChangeSign {
 			f, _ := rightValue.(float64)
 			v = -f
 		} else {
 			v = rightValue
 		}
-	} else if kern.IsInteger(rightValue) {
+	} else if types.IsInteger(rightValue) {
-		if opTerm.Tk.Sym == scan.SymChangeSign {
+		if opTerm.Tk.Sym == sym.SymChangeSign {
 			i, _ := rightValue.(int64)
 			v = -i
 		} else {
@@ -60,6 +63,6 @@ func evalSign(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymUnchangeSign, newPlusSignTerm)
+	scan.RegisterTermConstructor(sym.SymUnchangeSign, newPlusSignTerm)
-	scan.RegisterTermConstructor(scan.SymChangeSign, newMinusSignTerm)
+	scan.RegisterTermConstructor(sym.SymChangeSign, newMinusSignTerm)
 }

operator-sum.go

@@ -10,6 +10,14 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/float"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+	"git.portale-stac.it/go-pkg/expr/types/str"
 )
 
 //-------- plus term
@@ -25,39 +33,46 @@ func newPlusTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 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)) {
+	if (str.IsString(leftValue) && types.IsNumberString(rightValue)) || (str.IsString(rightValue) && types.IsNumberString(leftValue)) {
 		v = fmt.Sprintf("%v%v", leftValue, rightValue)
-	} else if kern.IsNumber(leftValue) && kern.IsNumber(rightValue) {
+	} else if types.IsNumber(leftValue) && types.IsNumber(rightValue) {
-		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+		if float.IsFloat(leftValue) || float.IsFloat(rightValue) {
-			v = kern.NumAsFloat(leftValue) + kern.NumAsFloat(rightValue)
+			v = types.NumAsFloat(leftValue) + types.NumAsFloat(rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt + rightInt
 		}
-	} else if kern.IsList(leftValue) && kern.IsList(rightValue) {
+	} else if array.IsArray(leftValue) && array.IsArray(rightValue) {
-		var leftList, rightList *kern.ListType
+		var leftList, rightList *array.ArrayType
-		leftList, _ = leftValue.(*kern.ListType)
+		leftList, _ = leftValue.(*array.ArrayType)
-		rightList, _ = rightValue.(*kern.ListType)
+		rightList, _ = rightValue.(*array.ArrayType)
 
-		sumList := make(kern.ListType, 0, len(*leftList)+len(*rightList))
+		sumList := make(array.ArrayType, 0, len(*leftList)+len(*rightList))
 		sumList = append(sumList, *leftList...)
 		sumList = append(sumList, *rightList...)
 		v = &sumList
-	} else if (kern.IsFraction(leftValue) && kern.IsNumber(rightValue)) || (kern.IsFraction(rightValue) && kern.IsNumber(leftValue)) {
+	} else if list.IsLinkedList(leftValue) && list.IsLinkedList(rightValue) {
-		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+		lsLeft := leftValue.(*list.LinkedList)
-			v = kern.NumAsFloat(leftValue) + kern.NumAsFloat(rightValue)
+		lsRight := rightValue.(*list.LinkedList)
+		ls := lsLeft.Clone()
+		ls.SeqClonePushBack(NewLinkedListIterator(lsRight, nil))
+		v = ls
+	} else if (fract.IsFraction(leftValue) && types.IsNumber(rightValue)) || (fract.IsFraction(rightValue) && types.IsNumber(leftValue)) {
+		if float.IsFloat(leftValue) || float.IsFloat(rightValue) {
+			v = types.NumAsFloat(leftValue) + types.NumAsFloat(rightValue)
 		} else {
-			v, err = kern.SumAnyFract(leftValue, rightValue)
+			v, err = fract.SumAnyFract(leftValue, rightValue)
 		}
-	} else if kern.IsDict(leftValue) && kern.IsDict(rightValue) {
+	} else if dict.IsDict(leftValue) && dict.IsDict(rightValue) {
-		leftDict, _ := leftValue.(*kern.DictType)
+		leftDict, _ := leftValue.(*dict.DictType)
-		rightDict, _ := rightValue.(*kern.DictType)
+		rightDict, _ := rightValue.(*dict.DictType)
-		c := leftDict.Clone()
+		clone := leftDict.Clone()
+		c := clone.(*dict.DictType)
 		c.Merge(rightDict)
 		v = c
-	} else if kern.IsFraction(leftValue) && kern.IsFraction(rightValue) {
+	} else if fract.IsFraction(leftValue) && fract.IsFraction(rightValue) {
-		v, err = kern.SumAnyFract(leftValue, rightValue)
+		v, err = fract.SumAnyFract(leftValue, rightValue)
 	} else {
 		err = plusTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
@@ -87,20 +102,20 @@ func newMinusTerm(tk *scan.Token) (inst *scan.Term) {
 }
 
 func diffValues(minusTerm *scan.Term, leftValue, rightValue any) (v any, err error) {
-	if kern.IsNumOrFract(leftValue) && kern.IsNumOrFract(rightValue) {
+	if types.IsNumOrFract(leftValue) && types.IsNumOrFract(rightValue) {
-		if kern.IsFloat(leftValue) || kern.IsFloat(rightValue) {
+		if float.IsFloat(leftValue) || float.IsFloat(rightValue) {
-			v = kern.NumAsFloat(leftValue) - kern.NumAsFloat(rightValue)
+			v = types.NumAsFloat(leftValue) - types.NumAsFloat(rightValue)
-		} else if kern.IsFraction(leftValue) || kern.IsFraction(rightValue) {
+		} else if fract.IsFraction(leftValue) || fract.IsFraction(rightValue) {
-			v, err = kern.SubAnyFract(leftValue, rightValue)
+			v, err = fract.SubAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt - rightInt
 		}
-	} else if kern.IsList(leftValue) && kern.IsList(rightValue) {
+	} else if array.IsArray(leftValue) && array.IsArray(rightValue) {
-		leftList, _ := leftValue.(*kern.ListType)
+		leftList, _ := leftValue.(*array.ArrayType)
-		rightList, _ := rightValue.(*kern.ListType)
+		rightList, _ := rightValue.(*array.ArrayType)
-		diffList := make(kern.ListType, 0, len(*leftList)-len(*rightList))
+		diffList := make(array.ArrayType, 0, len(*leftList)-len(*rightList))
 		for _, item := range *leftList {
 			if slices.Index(*rightList, item) < 0 {
 				diffList = append(diffList, item)
@@ -125,6 +140,6 @@ func evalMinus(ctx kern.ExprContext, minusTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymPlus, newPlusTerm)
+	scan.RegisterTermConstructor(sym.SymPlus, newPlusTerm)
-	scan.RegisterTermConstructor(scan.SymMinus, newMinusTerm)
+	scan.RegisterTermConstructor(sym.SymMinus, newMinusTerm)
 }

operator-unset.go

@@ -9,6 +9,8 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 //-------- unset term
@@ -50,8 +52,8 @@ func evalUnset(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	}
 
 	count := 0
-	if kern.IsList(childValue) {
+	if array.IsArray(childValue) {
-		list, _ := childValue.(*kern.ListType)
+		list, _ := childValue.(*array.ArrayType)
 		for _, item := range *list {
 			if deleted, err = deleteContextItem(ctx, opTerm, item); err != nil {
 				break
@@ -70,5 +72,5 @@ func evalUnset(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 
 // init
 func init() {
-	scan.RegisterTermConstructor(scan.SymKwUnset, newUnsetTerm)
+	scan.RegisterTermConstructor(sym.SymKwUnset, newUnsetTerm)
 }

parser.go

@@ -10,6 +10,7 @@ import (
 	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 	"golang.org/x/exp/constraints"
 )
 
@@ -58,7 +59,7 @@ func NewParser() (p *parser) {
 }
 
 func (parser *parser) Next(scanner *scan.Scanner) (tk *scan.Token) {
-	for tk = scanner.Next(); tk.IsSymbol(scan.SymComment); tk = scanner.Next() {
+	for tk = scanner.Next(); tk.IsSymbol(sym.SymComment); tk = scanner.Next() {
 	}
 	return
 }
@@ -66,10 +67,10 @@ func (parser *parser) Next(scanner *scan.Scanner) (tk *scan.Token) {
 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 := scan.SymUnknown
+	lastSym := sym.SymUnknown
-	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
+	for lastSym != sym.SymClosedRound && lastSym != sym.SymEos {
 		var subTree *scan.Ast
-		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedRound); err != nil {
+		if subTree, err = parser.parseItem(scanner, ctx, sym.SymComma, sym.SymClosedRound); err != nil {
 			break
 		}
 		prev := scanner.Previous()
@@ -80,11 +81,11 @@ func (parser *parser) parseFuncCall(scanner *scan.Scanner, ctx parserContext, tk
 			break
 		}
 
-		itemExpected = prev.Sym == scan.SymComma
+		itemExpected = prev.Sym == sym.SymComma
 		lastSym = scanner.Previous().Sym
 	}
 	if err == nil {
-		if lastSym != scan.SymClosedRound {
+		if lastSym != sym.SymClosedRound {
 			err = errors.New("unterminated arguments list")
 		} else {
 			tree = newFuncCallTerm(tk, args)
@@ -97,13 +98,13 @@ func (parser *parser) parseFuncDef(scanner *scan.Scanner) (tree *scan.Term, err
 	// Example: "add = func(x,y) {x+y}
 	var body *scan.Ast
 	args := make([]*scan.Term, 0)
-	lastSym := scan.SymUnknown
+	lastSym := sym.SymUnknown
 	defaultParamsStarted := false
 	itemExpected := false
 	tk := scanner.Previous()
-	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
+	for lastSym != sym.SymClosedRound && lastSym != sym.SymEos {
 		tk = parser.Next(scanner)
-		if tk.IsSymbol(scan.SymIdentifier) {
+		if tk.IsSymbol(sym.SymIdentifier) {
 			param := scan.NewTerm(tk)
 			if len(args) > 0 {
 				if pos := paramAlreadyDefined(args, param); pos > 0 {
@@ -113,10 +114,10 @@ func (parser *parser) parseFuncDef(scanner *scan.Scanner) (tree *scan.Term, err
 			}
 			args = append(args, param)
 			tk = parser.Next(scanner)
-			if tk.Sym == scan.SymEqual {
+			if tk.Sym == sym.SymEqual {
 				var paramExpr *scan.Ast
 				defaultParamsStarted = true
-				if paramExpr, err = parser.parseItem(scanner, parserNoFlags, scan.SymComma, scan.SymClosedRound); err != nil {
+				if paramExpr, err = parser.parseItem(scanner, parserNoFlags, sym.SymComma, sym.SymClosedRound); err != nil {
 					break
 				}
 				param.ForceChild(paramExpr.Root())
@@ -130,25 +131,25 @@ func (parser *parser) parseFuncDef(scanner *scan.Scanner) (tree *scan.Term, err
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == scan.SymComma
+		itemExpected = lastSym == sym.SymComma
 	}
 
-	if err == nil && lastSym != scan.SymClosedRound {
+	if err == nil && lastSym != sym.SymClosedRound {
 		err = tk.ErrorExpectedGot(")")
 	}
 	if err == nil {
 		tk = parser.Next(scanner)
-		if tk.IsSymbol(scan.SymOpenBrace) {
+		if tk.IsSymbol(sym.SymOpenBrace) {
-			body, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, scan.SymClosedBrace)
+			body, err = parser.parseGeneral(scanner, allowMultiExpr|allowVarRef, sym.SymClosedBrace)
 		} else {
 			err = tk.ErrorExpectedGot("{")
 		}
 	}
 	if err == nil {
-		if scanner.Previous().Sym != scan.SymClosedBrace {
+		if scanner.Previous().Sym != sym.SymClosedBrace {
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
-			tk = scanner.MakeValueToken(scan.SymExpression, "", body)
+			tk = scanner.MakeValueToken(sym.SymExpression, "", body)
 			tree = newFuncDefTerm(tk, args)
 		}
 	}
@@ -165,40 +166,35 @@ func paramAlreadyDefined(args []*scan.Term, param *scan.Term) (position int) {
 	return
 }
 
-func (parser *parser) parseList(scanner *scan.Scanner, ctx parserContext, termSym scan.Symbol) (listTerm *scan.Term, err error) {
+func (parser *parser) parseList(scanner *scan.Scanner, ctx parserContext, termSym sym.Symbol) (listTerm *scan.Term, err error) {
 	r, c := scanner.LastPos()
 	args := make([]*scan.Term, 0)
-	lastSym := scan.SymUnknown
+	lastSym := sym.SymUnknown
 	itemExpected := false
 	itemCtx := remFlags(ctx, allowIndex)
-	for lastSym != termSym && lastSym != scan.SymEos {
+	for lastSym != termSym && lastSym != sym.SymEos {
-		zeroRequired := scanner.Current().Sym == scan.SymColon
 		var itemTree *scan.Ast
-		if itemTree, err = parser.parseItem(scanner, itemCtx, scan.SymComma, termSym); err == nil {
+		if itemTree, err = parser.parseItem(scanner, itemCtx, sym.SymComma, termSym); err == nil {
 			root := itemTree.Root()
 			if root != nil {
-				if hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymColon {
+				if root.Symbol() == sym.SymDoubleDot {
-					changeColonToRange(root)
+					if hasFlag(ctx, allowIndex) {
-				}
+						changeColonToInterval(root)
-				if !hasFlag(ctx, allowIndex) && root.Symbol() == scan.SymRange {
+					} else {
 						// err = root.Errorf("unexpected range expression")
-					err = errRangeUnexpectedExpression(root)
+						err = errIntervalUnexpectedExpression(root)
 						break
 					}
+				}
+				// if hasFlag(ctx, allowIndex) && root.Symbol() == sym.SymDoubleDot {
+				// 	changeColonToInterval(root)
+				// }
+				// if !hasFlag(ctx, allowIndex) && root.Symbol() == sym.SymInterval {
+				// 	// err = root.Errorf("unexpected range expression")
+				// 	err = errIntervalUnexpectedExpression(root)
+				// 	break
+				// }
 				args = append(args, root)
-				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 := 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()
 				err = prev.ErrorExpectedGot("list-item")
@@ -208,16 +204,16 @@ func (parser *parser) parseList(scanner *scan.Scanner, ctx parserContext, termSy
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		if itemExpected = lastSym == scan.SymComma; itemExpected {
+		if itemExpected = lastSym == sym.SymComma; itemExpected {
 			remFlags(ctx, allowIndex)
 		}
 	}
 	if err == nil {
 		if lastSym != termSym {
 			err = scanner.Previous().ErrorExpectedGot("]")
-		} else if termSym == scan.SymClosedSquare {
+		} else if termSym == sym.SymClosedSquare {
 			listTerm = newListTerm(r, c, args)
-		} else if termSym == scan.SymGreaterClosedSquare {
+		} else if termSym == sym.SymGreaterClosedSquare {
 			listTerm = newLinkedListTerm(r, c, args)
 		} else {
 			err = fmt.Errorf("[%d:%d] unknown list type", r, c)
@@ -229,11 +225,11 @@ func (parser *parser) parseList(scanner *scan.Scanner, ctx parserContext, termSy
 func (parser *parser) parseIterDef(scanner *scan.Scanner, ctx parserContext) (subtree *scan.Term, err error) {
 	tk := scanner.Previous()
 	args := make([]*scan.Term, 0)
-	lastSym := scan.SymUnknown
+	lastSym := sym.SymUnknown
 	itemExpected := false
-	for lastSym != scan.SymClosedRound && lastSym != scan.SymEos {
+	for lastSym != sym.SymClosedRound && lastSym != sym.SymEos {
 		var subTree *scan.Ast
-		if subTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedRound); err == nil {
+		if subTree, err = parser.parseItem(scanner, ctx, sym.SymComma, sym.SymClosedRound); err == nil {
 			if subTree.Root() != nil {
 				args = append(args, subTree.Root())
 			} else if itemExpected {
@@ -245,10 +241,10 @@ func (parser *parser) parseIterDef(scanner *scan.Scanner, ctx parserContext) (su
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == scan.SymComma
+		itemExpected = lastSym == sym.SymComma
 	}
 	if err == nil {
-		if lastSym != scan.SymClosedRound {
+		if lastSym != sym.SymClosedRound {
 			err = scanner.Previous().ErrorExpectedGot(")")
 		} else {
 			subtree = newIteratorTerm(tk, args)
@@ -259,16 +255,16 @@ func (parser *parser) parseIterDef(scanner *scan.Scanner, ctx parserContext) (su
 
 // func (parser *parser) parseDictKey(scanner *scan.Scanner) (key any, err error) {
 // 	tk := parser.Next(scanner)
-// 	if tk.Sym == scan.SymError {
+// 	if tk.Sym == sym.SymError {
 // 		err = tk.Error()
 // 		return
 // 	}
-// 	if tk.Sym == scan.SymClosedBrace || tk.Sym == scan.SymEos {
+// 	if tk.Sym == sym.SymClosedBrace || tk.Sym == sym.SymEos {
 // 		return
 // 	}
-// 	if tk.Sym == scan.SymInteger || tk.Sym == scan.SymString || tk.Sym == scan.SymIdentifier {
+// 	if tk.Sym == sym.SymInteger || tk.Sym == sym.SymString || tk.Sym == sym.SymIdentifier {
 // 		tkSep := parser.Next(scanner)
-// 		if tkSep.Sym != scan.SymColon {
+// 		if tkSep.Sym != sym.SymColon {
 // 			err = tkSep.ErrorExpectedGot(":")
 // 		} else {
 // 			key = tk.Value
@@ -281,15 +277,15 @@ func (parser *parser) parseIterDef(scanner *scan.Scanner, ctx parserContext) (su
 
 func (parser *parser) parseDictKey(scanner *scan.Scanner) (key *scan.Term, err error) {
 	var keyTree *scan.Ast
-	if keyTree, err = parser.parseItem(scanner, parserNoFlags, scan.SymColon, scan.SymClosedBrace); err == nil {
+	if keyTree, err = parser.parseItem(scanner, parserNoFlags, sym.SymColon, sym.SymClosedBrace); err == nil {
 		key = keyTree.Root()
 		tkSep := scanner.Previous()
-		sym := tkSep.Sym
+		symbol := tkSep.Sym
-		if sym == scan.SymClosedBrace || sym == scan.SymEos {
+		if symbol == sym.SymClosedBrace || symbol == sym.SymEos {
 			if key != nil {
 				err = tkSep.ErrorExpectedGot(":")
 			}
-		} else if sym != scan.SymColon {
+		} else if symbol != sym.SymColon {
 			err = tkSep.ErrorExpectedGot(":")
 		}
 	}
@@ -298,9 +294,9 @@ func (parser *parser) parseDictKey(scanner *scan.Scanner) (key *scan.Term, err e
 
 func (parser *parser) parseDictionary(scanner *scan.Scanner, ctx parserContext) (subtree *scan.Term, err error) {
 	args := make(map[any]*scan.Term, 0)
-	lastSym := scan.SymUnknown
+	lastSym := sym.SymUnknown
 	itemExpected := false
-	for lastSym != scan.SymClosedBrace && lastSym != scan.SymEos {
+	for lastSym != sym.SymClosedBrace && lastSym != sym.SymEos {
 		var valueTree *scan.Ast
 		var key any
 		if key, err = parser.parseDictKey(scanner); err != nil {
@@ -313,7 +309,7 @@ func (parser *parser) parseDictionary(scanner *scan.Scanner, ctx parserContext)
 			}
 			break
 		}
-		if valueTree, err = parser.parseItem(scanner, ctx, scan.SymComma, scan.SymClosedBrace); err == nil {
+		if valueTree, err = parser.parseItem(scanner, ctx, sym.SymComma, sym.SymClosedBrace); err == nil {
 			if valueTree.Root() != nil {
 				args[key] = valueTree.Root()
 			} else /*if key != nil*/ {
@@ -325,10 +321,10 @@ func (parser *parser) parseDictionary(scanner *scan.Scanner, ctx parserContext)
 			break
 		}
 		lastSym = scanner.Previous().Sym
-		itemExpected = lastSym == scan.SymComma
+		itemExpected = lastSym == sym.SymComma
 	}
 	if err == nil {
-		if lastSym != scan.SymClosedBrace {
+		if lastSym != sym.SymClosedBrace {
 			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
 			subtree = newDictTerm(args)
@@ -344,12 +340,12 @@ func (parser *parser) parseSelectorCase(scanner *scan.Scanner, ctx parserContext
 	tk := parser.Next(scanner)
 	startRow := tk.Row()
 	startCol := tk.Col()
-	if tk.Sym == scan.SymOpenSquare {
+	if tk.Sym == sym.SymOpenSquare {
 		if defaultCase {
 			err = tk.Errorf("case list in default clause")
 			return
 		}
-		if filterList, err = parser.parseList(scanner, remFlags(ctx, allowIndex), scan.SymClosedSquare); err != nil {
+		if filterList, err = parser.parseList(scanner, remFlags(ctx, allowIndex), sym.SymClosedSquare); err != nil {
 			return
 		}
 		tk = parser.Next(scanner)
@@ -359,8 +355,8 @@ func (parser *parser) parseSelectorCase(scanner *scan.Scanner, ctx parserContext
 		filterList = newListTerm(startRow, startCol, make([]*scan.Term, 0))
 	}
 
-	if tk.Sym == scan.SymOpenBrace {
+	if tk.Sym == sym.SymOpenBrace {
-		if caseExpr, err = parser.parseGeneral(scanner, ctx|allowMultiExpr, scan.SymClosedBrace); err != nil {
+		if caseExpr, err = parser.parseGeneral(scanner, ctx|allowMultiExpr, sym.SymClosedBrace); err != nil {
 			return
 		}
 	} else {
@@ -390,7 +386,7 @@ func (parser *parser) parseSelector(scanner *scan.Scanner, tree *scan.Ast, ctx p
 	var caseTerm *scan.Term
 
 	ctx = remFlags(ctx, allowIndex)
-	tk := scanner.MakeToken(scan.SymSelector, '?')
+	tk := scanner.MakeToken(sym.SymSelector, '?')
 	if selectorTerm, err = tree.AddToken(tk); err != nil {
 		return
 	}
@@ -401,11 +397,11 @@ func (parser *parser) parseSelector(scanner *scan.Scanner, tree *scan.Ast, ctx p
 	return
 }
 
-func (parser *parser) parseItem(scanner *scan.Scanner, ctx parserContext, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
+func (parser *parser) parseItem(scanner *scan.Scanner, ctx parserContext, termSymbols ...sym.Symbol) (tree *scan.Ast, err error) {
 	return parser.parseGeneral(scanner, ctx|allowVarRef, termSymbols...)
 }
 
-func (parser *parser) Parse(scanner *scan.Scanner, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
+func (parser *parser) Parse(scanner *scan.Scanner, termSymbols ...sym.Symbol) (tree *scan.Ast, err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			if errVal, ok := r.(error); ok {
@@ -415,23 +411,23 @@ func (parser *parser) Parse(scanner *scan.Scanner, termSymbols ...scan.Symbol) (
 			}
 		}
 	}()
-	termSymbols = append(termSymbols, scan.SymEos)
+	termSymbols = append(termSymbols, sym.SymEos)
 	return parser.parseGeneral(scanner, allowMultiExpr, termSymbols...)
 }
 
 func couldBeACollection(t *scan.Term) bool {
-	var sym = scan.SymUnknown
+	var symbol = sym.SymUnknown
 	if t != nil {
-		sym = t.Symbol()
+		symbol = t.Symbol()
 	}
-	// return sym == scan.SymList || sym == scan.SymString || sym == scan.SymDict || sym == scan.SymExpression || sym == scan.SymVariable
+	// return sym == sym.SymList || sym == sym.SymString || sym == sym.SymDict || sym == sym.SymExpression || sym == sym.SymVariable
-	return slices.Contains([]scan.Symbol{scan.SymList, scan.SymLinkedList, scan.SymString, scan.SymDict, scan.SymExpression, scan.SymVariable, scan.SymIndex}, sym)
+	return slices.Contains([]sym.Symbol{sym.SymList, sym.SymLinkedList, sym.SymString, sym.SymDict, sym.SymExpression, sym.SymVariable, sym.SymIndex}, symbol)
 }
 
 func listSubTree(tree *scan.Ast, listTerm *scan.Term, allowIndeces bool) (root *scan.Term, err error) {
 	var tk *scan.Token
 	if allowIndeces {
-		tk = scan.NewToken(listTerm.Tk.Row(), listTerm.Tk.Col(), scan.SymIndex, listTerm.Source())
+		tk = scan.NewToken(listTerm.Tk.Row(), listTerm.Tk.Col(), sym.SymIndex, listTerm.Source())
 		root = scan.NewTerm(tk)
 		if err = tree.AddTerm(root); err == nil {
 			err = tree.AddTerm(listTerm)
@@ -445,22 +441,22 @@ func listSubTree(tree *scan.Ast, listTerm *scan.Term, allowIndeces bool) (root *
 
 func changePrefix(tk *scan.Token) {
 	switch tk.Sym {
-	case scan.SymMinus:
+	case sym.SymMinus:
-		tk.SetSymbol(scan.SymChangeSign)
+		tk.SetSymbol(sym.SymChangeSign)
-	case scan.SymPlus:
+	case sym.SymPlus:
-		tk.SetSymbol(scan.SymUnchangeSign)
+		tk.SetSymbol(sym.SymUnchangeSign)
-	case scan.SymStar:
+	case sym.SymStar:
-		tk.SetSymbol(scan.SymDereference)
+		tk.SetSymbol(sym.SymDereference)
-	case scan.SymExclamation:
+	case sym.SymExclamation:
-		tk.SetSymbol(scan.SymNot)
+		tk.SetSymbol(sym.SymNot)
-	case scan.SymDoublePlus:
+	case sym.SymDoublePlus:
-		tk.SetSymbol(scan.SymPreInc)
+		tk.SetSymbol(sym.SymPreInc)
-	case scan.SymDoubleMinus:
+	case sym.SymDoubleMinus:
-		tk.SetSymbol(scan.SymPreDec)
+		tk.SetSymbol(sym.SymPreDec)
 	}
 }
 
-func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, termSymbols ...scan.Symbol) (tree *scan.Ast, err error) {
+func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, termSymbols ...sym.Symbol) (tree *scan.Ast, err error) {
 	var selectorTerm *scan.Term = nil
 	var currentTerm *scan.Term = nil
 	var tk *scan.Token
@@ -473,7 +469,7 @@ func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, ter
 		// 	continue
 		// }
 
-		if tk.Sym == scan.SymSemiColon {
+		if tk.Sym == sym.SymSemiColon {
 			if hasFlag(ctx, allowMultiExpr) {
 				tree.ToForest()
 				firstToken = true
@@ -493,9 +489,9 @@ func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, ter
 		}
 
 		switch tk.Sym {
-		case scan.SymOpenRound:
+		case sym.SymOpenRound:
 			var subTree *scan.Ast
-			if subTree, err = parser.parseGeneral(scanner, ctx, scan.SymClosedRound); err == nil {
+			if subTree, err = parser.parseGeneral(scanner, ctx, sym.SymClosedRound); err == nil {
 				if subTree.Root() == nil {
 					err = tk.ErrorExpectedGotString("expression", "()")
 				} else {
@@ -504,26 +500,26 @@ func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, ter
 					currentTerm = exprTerm
 				}
 			}
-		case scan.SymFuncCall:
+		case sym.SymFuncCall:
 			var funcCallTerm *scan.Term
 			if funcCallTerm, err = parser.parseFuncCall(scanner, ctx, tk); err == nil {
 				err = tree.AddTerm(funcCallTerm)
 				currentTerm = funcCallTerm
 			}
-		case scan.SymOpenSquare:
+		case sym.SymOpenSquare:
 			var listTerm *scan.Term
 			newCtx := addFlagsCond(addFlags(ctx, squareContext), allowIndex, couldBeACollection(currentTerm))
-			if listTerm, err = parser.parseList(scanner, newCtx, scan.SymClosedSquare); err == nil {
+			if listTerm, err = parser.parseList(scanner, newCtx, sym.SymClosedSquare); err == nil {
 				currentTerm, err = listSubTree(tree, listTerm, hasFlag(newCtx, allowIndex))
 			}
-		case scan.SymOpenSquareLess:
+		case sym.SymOpenSquareLess:
 			var listTerm *scan.Term
 			newCtx := addFlagsCond(addFlags(ctx, listContext), allowIndex, false)
-			if listTerm, err = parser.parseList(scanner, newCtx, scan.SymGreaterClosedSquare); err == nil {
+			if listTerm, err = parser.parseList(scanner, newCtx, sym.SymGreaterClosedSquare); err == nil {
 				currentTerm, err = listSubTree(tree, listTerm, hasFlag(newCtx, allowIndex))
 			}
-		case scan.SymOpenBrace:
+		case sym.SymOpenBrace:
-			if currentTerm != nil && currentTerm.Symbol() == scan.SymColon {
+			if currentTerm != nil && currentTerm.Symbol() == sym.SymColon {
 				err = currentTerm.Errorf(`selector-case outside of a selector context`)
 			} else {
 				var mapTerm *scan.Term
@@ -532,54 +528,61 @@ func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, ter
 					currentTerm = mapTerm
 				}
 			}
-		case scan.SymEqual, scan.SymPlusEqual, scan.SymMinusEqual, scan.SymStarEqual, scan.SymSlashEqual, scan.SymPercEqual, scan.SymAmpersandEqual, scan.SymVertBarEqual, scan.SymDoubleLessEqual, scan.SymDoubleGreaterEqual, scan.SymCaretEqual:
+		case sym.SymEqual, sym.SymPlusEqual, sym.SymMinusEqual, sym.SymStarEqual, sym.SymSlashEqual, sym.SymPercEqual, sym.SymAmpersandEqual, sym.SymVertBarEqual, sym.SymDoubleLessEqual, sym.SymDoubleGreaterEqual, sym.SymCaretEqual:
 			currentTerm, err = tree.AddToken(tk)
 			firstToken = true
-		case scan.SymFuncDef:
+		case sym.SymFuncDef:
 			var funcDefTerm *scan.Term
 			if funcDefTerm, err = parser.parseFuncDef(scanner); err == nil {
 				err = tree.AddTerm(funcDefTerm)
 				currentTerm = funcDefTerm
 			}
-		case scan.SymDollarRound:
+		case sym.SymDollarRound:
 			var iterDefTerm *scan.Term
 			if iterDefTerm, err = parser.parseIterDef(scanner, ctx); err == nil {
 				err = tree.AddTerm(iterDefTerm)
 				currentTerm = iterDefTerm
 			}
-		case scan.SymIdentifier:
+		case sym.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)
 			}
-		case scan.SymQuestion:
+		case sym.SymQuestion:
 			if selectorTerm, err = parser.parseSelector(scanner, tree, ctx); err == nil {
 				currentTerm = selectorTerm
 				addFlags(ctx, selectorContext)
 			}
-		case scan.SymColon, scan.SymDoubleColon:
+		case sym.SymColon, sym.SymDoubleColon:
 			var caseTerm *scan.Term
 			if selectorTerm != nil {
-				if caseTerm, err = parser.parseSelectorCase(scanner, ctx, tk.Sym == scan.SymDoubleColon); err == nil {
+				if caseTerm, err = parser.parseSelectorCase(scanner, ctx, tk.Sym == sym.SymDoubleColon); err == nil {
 					addSelectorCase(selectorTerm, caseTerm)
 					currentTerm = caseTerm
-					if tk.Sym == scan.SymDoubleColon {
+					if tk.Sym == sym.SymDoubleColon {
 						selectorTerm = nil
 					}
 				}
 			} else {
+				// err = tk.Errorf("colon outside a selector context")
 				currentTerm, err = tree.AddToken(tk)
-				if tk.IsOneOfA(scan.SymColon, scan.SymRange) {
 				// Colon outside a selector term acts like a separator
-					firstToken = true
+				firstToken = tk.IsOneOfA(sym.SymColon, sym.SymInterval)
 			}
+		case sym.SymDoubleDot:
+			currentTerm, err = tree.AddToken(tk)
+			if currentTerm.GetLeftChild() == nil {
+				zeroTk := scan.NewValueToken(tk.Row(), tk.Col(), sym.SymInteger, "0", int64(0))
+				tree.AddToken(zeroTk)
 			}
+			// Double dot acts like a separator
+			firstToken = tk.IsOneOfA(sym.SymDoubleDot, sym.SymInterval)
 		default:
 			currentTerm, err = tree.AddToken(tk)
 		}
 
-		if currentTerm != nil && currentTerm.Tk.Sym != scan.SymSelector && currentTerm.Parent != nil && currentTerm.Parent.Tk.Sym != scan.SymSelector {
+		if currentTerm != nil && currentTerm.Tk.Sym != sym.SymSelector && currentTerm.Parent != nil && currentTerm.Parent.Tk.Sym != sym.SymSelector {
 			selectorTerm = nil
 			remFlags(ctx, selectorContext)
 		}
@@ -589,7 +592,7 @@ func (parser *parser) parseGeneral(scanner *scan.Scanner, ctx parserContext, ter
 	if err == nil {
 		if !tk.IsOneOf(termSymbols) {
 			var symDesc string
-			if tk.IsSymbol(scan.SymError) {
+			if tk.IsSymbol(sym.SymError) {
 				symDesc = tk.ErrorText()
 			} else {
 				symDesc = scan.SymToString(tk.Sym)

scan/scanner.go

@@ -12,7 +12,7 @@ import (
 	"strconv"
 	"strings"
 
-	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/sym"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
@@ -23,10 +23,12 @@ type Scanner struct {
 	stream        *bufio.Reader
 	row           int
 	column        int
-	translations map[Symbol]Symbol
+	translations  map[sym.Symbol]sym.Symbol
+	unreadByte    byte
+	prevRowLength int
 }
 
-func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *Scanner) {
+func NewScanner(s io.Reader, translations map[sym.Symbol]sym.Symbol) (inst *Scanner) {
 	inst = &Scanner{
 		stream:       bufio.NewReader(s),
 		row:          1,
@@ -37,15 +39,15 @@ func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *Scanner) {
 	return inst
 }
 
-func DefaultTranslations() map[Symbol]Symbol {
+func DefaultTranslations() map[sym.Symbol]sym.Symbol {
-	return map[Symbol]Symbol{
+	return map[sym.Symbol]sym.Symbol{
-		SymDoubleAmpersand: SymAnd,
+		sym.SymDoubleAmpersand: sym.SymAnd,
-		SymKwAnd:           SymAnd,
+		sym.SymKwAnd:           sym.SymAnd,
-		SymDoubleVertBar:   SymOr,
+		sym.SymDoubleVertBar:   sym.SymOr,
-		SymKwOr:            SymOr,
+		sym.SymKwOr:            sym.SymOr,
-		// SymTilde:           SymNot,
+		sym.SymKwNot:           sym.SymNot,
-		SymKwNot:       SymNot,
+		sym.SymLessGreater:     sym.SymNotEqual,
-		SymLessGreater: SymNotEqual,
+		// SymTilde:           sym.SymNot,
 	}
 }
 
@@ -57,9 +59,25 @@ func (scanner *Scanner) Current() *Token {
 	return scanner.current
 }
 
+func (scanner *Scanner) setUnreadChar(ch byte) {
+	scanner.column--
+	if scanner.column == 0 {
+		scanner.column = scanner.prevRowLength
+		scanner.row--
+	}
+	scanner.unreadByte = ch
+}
+
 func (scanner *Scanner) readChar() (ch byte, err error) {
-	if ch, err = scanner.stream.ReadByte(); err == nil {
+	if scanner.unreadByte != 0 {
+		ch = scanner.unreadByte
+		scanner.unreadByte = 0
+	} else {
+		ch, err = scanner.stream.ReadByte()
+	}
+	if err == nil {
 		if ch == '\n' {
+			scanner.prevRowLength = scanner.column
 			scanner.row++
 			scanner.column = 0
 		} else {
@@ -128,237 +146,237 @@ func (scanner *Scanner) fetchNextToken() (tk *Token) {
 		switch ch {
 		case '+':
 			if next, _ := scanner.peek(); next == '+' {
-				tk = scanner.moveOn(SymDoublePlus, ch, next)
+				tk = scanner.moveOn(sym.SymDoublePlus, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymPlusEqual, ch, next)
+				tk = scanner.moveOn(sym.SymPlusEqual, ch, next)
 			} else if next == '>' {
-				tk = scanner.moveOn(SymPlusGreater, ch, next)
+				tk = scanner.moveOn(sym.SymPlusGreater, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymPlus, ch)
+				tk = scanner.MakeToken(sym.SymPlus, ch)
 			}
 		case '-':
 			if next, _ := scanner.peek(); next == '-' {
-				tk = scanner.moveOn(SymDoubleMinus, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleMinus, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymMinusEqual, ch, next)
+				tk = scanner.moveOn(sym.SymMinusEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymMinus, ch)
+				tk = scanner.MakeToken(sym.SymMinus, ch)
 			}
 		case '*':
 			if next, _ := scanner.peek(); next == '*' {
-				tk = scanner.moveOn(SymDoubleStar, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleStar, ch, next)
 				// } else if next == '/' {
 				// 	tk = self.moveOn(SymClosedComment, ch, next)
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymStarEqual, ch, next)
+				tk = scanner.moveOn(sym.SymStarEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymStar, ch)
+				tk = scanner.MakeToken(sym.SymStar, ch)
 			}
 		case '/':
 			if next, _ := scanner.peek(); next == '*' {
 				scanner.readChar()
 				tk = scanner.fetchBlockComment()
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymSlashEqual, ch, next)
+				tk = scanner.moveOn(sym.SymSlashEqual, ch, next)
 			} else if next == '/' {
 				scanner.readChar()
 				tk = scanner.fetchOnLineComment()
 			} else {
-				tk = scanner.MakeToken(SymSlash, ch)
+				tk = scanner.MakeToken(sym.SymSlash, ch)
 			}
 		case '\\':
 			if escape {
-				tk = scanner.MakeToken(SymBackSlash, ch)
+				tk = scanner.MakeToken(sym.SymBackSlash, ch)
 				escape = false
 			} else {
 				escape = true
 			}
 		case '|':
 			if next, _ := scanner.peek(); next == '|' {
-				tk = scanner.moveOn(SymDoubleVertBar, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleVertBar, ch, next)
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymVertBarEqual, ch, next)
+				tk = scanner.moveOn(sym.SymVertBarEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymVertBar, ch)
+				tk = scanner.MakeToken(sym.SymVertBar, ch)
 			}
 		case ',':
-			tk = scanner.MakeToken(SymComma, ch)
+			tk = scanner.MakeToken(sym.SymComma, ch)
 		case '^':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymCaretEqual, ch, next)
+				tk = scanner.moveOn(sym.SymCaretEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymCaret, ch)
+				tk = scanner.MakeToken(sym.SymCaret, ch)
 			}
 		case ':':
 			if next, _ := scanner.peek(); next == ':' {
-				tk = scanner.moveOn(SymDoubleColon, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleColon, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymColonEqual, ch, next)
+				tk = scanner.moveOn(sym.SymColonEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymColon, ch)
+				tk = scanner.MakeToken(sym.SymColon, ch)
 			}
 		case ';':
-			tk = scanner.MakeToken(SymSemiColon, ch)
+			tk = scanner.MakeToken(sym.SymSemiColon, ch)
 		case '.':
 			//if next, _ := self.peek(); next >= '0' && next <= '9' {
 			//	tk = self.parseNumber(ch)
 			//} else if next == '/' {
 			if next, _ := scanner.peek(); next == '/' {
-				tk = scanner.moveOn(SymDotSlash, ch, next)
+				tk = scanner.moveOn(sym.SymDotSlash, ch, next)
 			} else if next == '.' {
+				tk = scanner.moveOn(sym.SymDoubleDot, ch, next)
+				// TODO: this section needs verification
 				if next1, _ := scanner.peek(); next1 == '.' {
-					tk = scanner.moveOn(SymTripleDot, ch, next, next1)
+					tk = scanner.moveOn(sym.SymTripleDot, next, next1)
-				} else {
-					tk = scanner.moveOn(SymDoubleDot, ch, next)
 				}
 			} else {
-				tk = scanner.MakeToken(SymDot, ch)
+				tk = scanner.MakeToken(sym.SymDot, ch)
 			}
 		case '\'':
 			if escape {
-				tk = scanner.MakeToken(SymQuote, ch)
+				tk = scanner.MakeToken(sym.SymQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '"':
 			if escape {
-				tk = scanner.MakeToken(SymDoubleQuote, ch)
+				tk = scanner.MakeToken(sym.SymDoubleQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '`':
-			tk = scanner.MakeToken(SymBackTick, ch)
+			tk = scanner.MakeToken(sym.SymBackTick, ch)
 		case '!':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymNotEqual, ch, next)
+				tk = scanner.moveOn(sym.SymNotEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymExclamation, ch)
+				tk = scanner.MakeToken(sym.SymExclamation, ch)
 			}
 		case '?':
 			if next, _ := scanner.peek(); next == '?' {
-				tk = scanner.moveOn(SymDoubleQuestion, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleQuestion, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymQuestionEqual, ch, next)
+				tk = scanner.moveOn(sym.SymQuestionEqual, ch, next)
 			} else if next == '!' {
-				tk = scanner.moveOn(SymQuestionExclam, ch, next)
+				tk = scanner.moveOn(sym.SymQuestionExclam, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymQuestion, ch)
+				tk = scanner.MakeToken(sym.SymQuestion, ch)
 			}
 		case '&':
 			if next, _ := scanner.peek(); next == '&' {
-				tk = scanner.moveOn(SymDoubleAmpersand, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleAmpersand, ch, next)
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymAmpersandEqual, ch, next)
+				tk = scanner.moveOn(sym.SymAmpersandEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymAmpersand, ch)
+				tk = scanner.MakeToken(sym.SymAmpersand, ch)
 			}
 		case '%':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymPercEqual, ch, next)
+				tk = scanner.moveOn(sym.SymPercEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymPercent, ch)
+				tk = scanner.MakeToken(sym.SymPercent, ch)
 			}
 		case '#':
-			tk = scanner.MakeToken(SymHash, ch)
+			tk = scanner.MakeToken(sym.SymHash, ch)
 		case '@':
 			if next, _ := scanner.peek(); (next >= 'a' && next <= 'z') || (next >= 'A' && next <= 'Z') {
 				scanner.readChar()
-				if tk = scanner.fetchIdentifier(next); tk.Sym == SymIdentifier {
+				if tk = scanner.fetchIdentifier(next); tk.Sym == sym.SymIdentifier {
 					//tk.Sym = SymIdRef
 					tk.source = "@" + tk.source
 				} else {
 					tk = scanner.makeErrorToken(fmt.Errorf("invalid variable reference %q", tk.source))
 				}
 			} else if next == '@' {
-				tk = scanner.moveOn(SymDoubleAt, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleAt, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymAt, ch)
+				tk = scanner.MakeToken(sym.SymAt, ch)
 			}
 		case '_':
-			tk = scanner.MakeToken(SymUndescore, ch)
+			tk = scanner.MakeToken(sym.SymUndescore, ch)
 		case '=':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymDoubleEqual, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymEqual, ch)
+				tk = scanner.MakeToken(sym.SymEqual, ch)
 			}
 		case '<':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymLessOrEqual, ch, next)
+				tk = scanner.moveOn(sym.SymLessOrEqual, ch, next)
 			} else if next == '<' {
 				scanner.readChar()
 				next2, _ := scanner.readChar()
 				scanner.unreadChar()
 				if next2 == '=' {
-					tk = scanner.moveOn(SymDoubleLessEqual, ch, next, next2)
+					tk = scanner.moveOn(sym.SymDoubleLessEqual, ch, next, next2)
 				} else {
-					tk = scanner.accept(SymDoubleLess, ch, next)
+					tk = scanner.accept(sym.SymDoubleLess, ch, next)
 				}
 			} else if next == '>' {
-				tk = scanner.moveOn(SymLessGreater, ch, next)
+				tk = scanner.moveOn(sym.SymLessGreater, ch, next)
 			} else if next == '+' {
-				tk = scanner.moveOn(SymLessPlus, ch, next)
+				tk = scanner.moveOn(sym.SymLessPlus, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymLess, ch)
+				tk = scanner.MakeToken(sym.SymLess, ch)
 			}
 		case '>':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymGreaterOrEqual, ch, next)
+				tk = scanner.moveOn(sym.SymGreaterOrEqual, ch, next)
 			} else if next == '>' {
 				scanner.readChar()
 				next2, _ := scanner.readChar()
 				scanner.unreadChar()
 				if next2 == '=' {
-					tk = scanner.moveOn(SymDoubleGreaterEqual, ch, next, next2)
+					tk = scanner.moveOn(sym.SymDoubleGreaterEqual, ch, next, next2)
 				} else {
-					tk = scanner.accept(SymDoubleGreater, ch, next)
+					tk = scanner.accept(sym.SymDoubleGreater, ch, next)
 				}
 			} else if next == ']' {
-				tk = scanner.moveOn(SymGreaterClosedSquare, ch, next)
+				tk = scanner.moveOn(sym.SymGreaterClosedSquare, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymGreater, ch)
+				tk = scanner.MakeToken(sym.SymGreater, ch)
 			}
 		case '$':
 			if next, _ := scanner.peek(); next == '(' {
-				tk = scanner.moveOn(SymDollarRound, ch, next)
+				tk = scanner.moveOn(sym.SymDollarRound, ch, next)
 				tk.source += ")"
 			} else if next == '$' {
-				tk = scanner.moveOn(SymDoubleDollar, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleDollar, ch, next)
 			} else if next == '{' {
 				scanner.readChar()
 				if tk = scanner.fetchString('}', false); tk != nil {
-					tk.Sym = SymIdentifier
+					tk.Sym = sym.SymIdentifier
 				}
 			} else if next == '_' || (next >= 'a' && next <= 'z') || (next >= 'A' && next <= 'Z') {
 				scanner.readChar()
 				tk = scanner.fetchIdentifier(next)
 			} else {
-				tk = scanner.MakeToken(SymDollar, ch)
+				tk = scanner.MakeToken(sym.SymDollar, ch)
 			}
 		case '(':
 			//			if next, _ := scanner.peek(); next == ')' {
 			//				tk = scanner.moveOn(SymOpenClosedRound, ch, next)
 			//			} else {
-			tk = scanner.MakeToken(SymOpenRound, ch)
+			tk = scanner.MakeToken(sym.SymOpenRound, ch)
 			//			}
 		case ')':
-			tk = scanner.MakeToken(SymClosedRound, ch)
+			tk = scanner.MakeToken(sym.SymClosedRound, ch)
 		case '[':
 			if next, _ := scanner.peek(); next == '<' {
-				tk = scanner.moveOn(SymOpenSquareLess, ch, next)
+				tk = scanner.moveOn(sym.SymOpenSquareLess, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymOpenSquare, ch)
+				tk = scanner.MakeToken(sym.SymOpenSquare, ch)
 			}
 		case ']':
-			tk = scanner.MakeToken(SymClosedSquare, ch)
+			tk = scanner.MakeToken(sym.SymClosedSquare, ch)
 		case '{':
-			tk = scanner.MakeToken(SymOpenBrace, ch)
+			tk = scanner.MakeToken(sym.SymOpenBrace, ch)
 		case '}':
-			tk = scanner.MakeToken(SymClosedBrace, ch)
+			tk = scanner.MakeToken(sym.SymClosedBrace, ch)
 		case '~':
-			tk = scanner.MakeToken(SymTilde, ch)
+			tk = scanner.MakeToken(sym.SymTilde, ch)
 		case 0:
 			if escape {
 				tk = scanner.makeErrorToken(errors.New("incomplete escape sequence"))
@@ -366,9 +384,9 @@ func (scanner *Scanner) fetchNextToken() (tk *Token) {
 			escape = false
 		default:
 			if /*ch == '_' ||*/ (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') {
-				if tk = scanner.fetchIdentifier(ch); tk.Sym == SymKwFunc {
+				if tk = scanner.fetchIdentifier(ch); tk.Sym == sym.SymKwFunc {
 					if next, _ := scanner.peek(); next == '(' {
-						tk = scanner.moveOn(SymFuncDef, ch, next)
+						tk = scanner.moveOn(sym.SymFuncDef, ch, next)
 					}
 				}
 			} else if ch >= '0' && ch <= '9' {
@@ -416,19 +434,20 @@ func (scanner *Scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int
 	numBase = 10
 
 	if ch, err = scanner.peek(); err == nil {
-		if ch == 'b' || ch == 'B' {
+		switch ch {
+		case 'b', 'B':
 			numBase = 2
 			digitType = "binary"
 			scanner.readChar()
 			digitFunc = isBinaryDigit
 			firstCh, err = scanner.readChar()
-		} else if ch == 'o' || ch == 'O' {
+		case 'o', 'O':
 			numBase = 8
 			digitType = "octal"
 			scanner.readChar()
 			digitFunc = isOctalDigit
 			firstCh, err = scanner.readChar()
-		} else if ch == 'x' || ch == 'X' {
+		case 'x', 'X':
 			numBase = 16
 			digitType = "hex"
 			scanner.readChar()
@@ -450,7 +469,7 @@ func (scanner *Scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int
 func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 	var err error
 	var ch byte
-	var sym Symbol = SymInteger
+	var symbol sym.Symbol = sym.SymInteger
 	var sb strings.Builder
 	var isDigit func(byte) bool = isDecimalDigit
 	var numBase = 10
@@ -464,7 +483,11 @@ func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 
 	if numBase == 10 {
 		if err == nil && ch == '.' {
-			sym = SymFloat
+			if next, _ := scanner.peek(); next == '.' {
+				// do nothing, this is an interval operator
+				scanner.setUnreadChar('.')
+			} else {
+				symbol = sym.SymFloat
 				sb.WriteByte(ch)
 				ch, err = scanner.readChar()
 				if ch >= '0' && ch <= '9' {
@@ -473,9 +496,11 @@ func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 					}
 				}
 			}
+		}
 		if err == nil {
-			if ch == 'e' || ch == 'E' {
+			switch ch {
-				sym = SymFloat
+			case 'e', 'E':
+				symbol = sym.SymFloat
 				sb.WriteByte(ch)
 				if ch, err = scanner.readChar(); err == nil {
 					if ch == '+' || ch == '-' {
@@ -490,8 +515,8 @@ func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 						err = fmt.Errorf("[%d:%d] expected integer exponent, got %c", scanner.row, scanner.column, ch)
 					}
 				}
-			} else if ch == '(' {
+			case '(':
-				sym = SymFraction
+				symbol = sym.SymFraction
 				sb.WriteByte(ch)
 				ch, err = scanner.readChar()
 				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = scanner.readChar() {
@@ -515,18 +540,21 @@ func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 		var value any
 		_ = scanner.sync(err) // TODO: Check this function
 		txt := sb.String()
-		if sym == SymFloat {
+		switch symbol {
+		case sym.SymFloat:
 			value, err = strconv.ParseFloat(txt, 64)
-		} else if sym == SymFraction {
+		case sym.SymFraction:
-			value, err = kern.MakeGeneratingFraction(txt)
+			// value, err = kern.MakeGeneratingFraction(txt)
-		} else {
+			value = txt
+		default:
 			value, err = strconv.ParseInt(txt, numBase, 64)
 		}
-		if err == nil {
+		tk = scanner.MakeValueToken(symbol, txt, value)
-			tk = scanner.MakeValueToken(sym, txt, value)
+		// if err == nil {
-		} else {
+		// 	tk = scanner.MakeValueToken(sym, txt, value)
-			tk = scanner.makeErrorToken(err)
+		// } else {
-		}
+		// 	tk = scanner.makeErrorToken(err)
+		// }
 	}
 	return
 }
@@ -545,17 +573,17 @@ func (scanner *Scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 	} else {
 		txt := sb.String()
 		uptxt := strings.ToUpper(txt)
-		if sym, ok := keywords[uptxt]; ok {
+		if symbol, ok := sym.Keywords[uptxt]; ok {
-			tk = scanner.makeKeywordToken(sym, uptxt)
+			tk = scanner.makeKeywordToken(symbol, uptxt)
 		} else if uptxt == `TRUE` {
-			tk = scanner.MakeValueToken(SymBool, txt, true)
+			tk = scanner.MakeValueToken(sym.SymBool, txt, true)
 		} else if uptxt == `FALSE` {
-			tk = scanner.MakeValueToken(SymBool, txt, false)
+			tk = scanner.MakeValueToken(sym.SymBool, txt, false)
 		} else if ch, _ := scanner.peek(); ch == '(' {
 			scanner.readChar()
-			tk = scanner.MakeValueToken(SymFuncCall, txt+"(", txt)
+			tk = scanner.MakeValueToken(sym.SymFuncCall, txt+"(", txt)
 		} else {
-			tk = scanner.MakeValueToken(SymIdentifier, txt, txt)
+			tk = scanner.MakeValueToken(sym.SymIdentifier, txt, txt)
 		}
 	}
 
@@ -576,14 +604,14 @@ func (scanner *Scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 }
 
 func (scanner *Scanner) fetchBlockComment() *Token {
-	return scanner.fetchUntil(SymComment, false, '*', '/')
+	return scanner.fetchUntil(sym.SymComment, false, '*', '/')
 }
 
 func (scanner *Scanner) fetchOnLineComment() *Token {
-	return scanner.fetchUntil(SymComment, true, '\n')
+	return scanner.fetchUntil(sym.SymComment, true, '\n')
 }
 
-func (scanner *Scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (tk *Token) {
+func (scanner *Scanner) fetchUntil(sym sym.Symbol, allowEos bool, endings ...byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sb strings.Builder
@@ -652,9 +680,9 @@ 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(sym.SymString, `"`+txt+`"`, txt)
 		} else {
-			tk = scanner.MakeValueToken(SymString, txt, txt)
+			tk = scanner.MakeValueToken(sym.SymString, txt, txt)
 		}
 	}
 	return
@@ -676,7 +704,7 @@ func (scanner *Scanner) skipBlanks() (err error) {
 	return
 }
 
-func (scanner *Scanner) translate(sym Symbol) Symbol {
+func (scanner *Scanner) translate(sym sym.Symbol) sym.Symbol {
 	if scanner.translations != nil {
 		if translatedSym, ok := scanner.translations[sym]; ok {
 			return translatedSym
@@ -685,7 +713,7 @@ func (scanner *Scanner) translate(sym Symbol) Symbol {
 	return sym
 }
 
-func (scanner *Scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) moveOn(sym 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 {
@@ -695,22 +723,22 @@ 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 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 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 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 sym.Symbol, source string, value any) (tk *Token) {
 	tk = NewValueToken(scanner.row, scanner.column, scanner.translate(sym), source, value)
 	return
 }

scan/symbol-map.go

@@ -1,14 +1,16 @@
 // Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// Symbol.go
+// symbol-map.go
 package scan
 
 import (
 	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
-var symbolMap map[Symbol]symbolSpec
+var symbolMap map[sym.Symbol]symbolSpec
 
 type SymbolClass int16
 
@@ -31,138 +33,139 @@ type symbolSpec struct {
 
 func init() {
 
-	symbolMap = map[Symbol]symbolSpec{
+	symbolMap = map[sym.Symbol]symbolSpec{
-		SymUnknown:             {"<unknown>", SymClassOther, PosLeaf},  //  -1: Unknown symbol
+		sym.SymUnknown:             {"<unknown>", SymClassOther, PosLeaf},  //  -1: Unknown symbol
-		SymNone:                {"<null>", SymClassOther, PosLeaf},     //   0: Null value for variable of type symbol
+		sym.SymNone:                {"<null>", SymClassOther, PosLeaf},     //   0: Null value for variable of type symbol
-		SymError:               {"<error>", SymClassOther, PosLeaf},    //   1: Error reading from stream
+		sym.SymError:               {"<error>", SymClassOther, PosLeaf},    //   1: Error reading from stream
-		SymEos:                 {"<eos>", SymClassOther, PosLeaf},      //   2: End of stream
+		sym.SymEos:                 {"<eos>", SymClassOther, PosLeaf},      //   2: End of stream
-		SymMinus:               {"-", SymClassOperator, PosInfix},      //   3: '-'
+		sym.SymMinus:               {"-", SymClassOperator, PosInfix},      //   3: '-'
-		SymMinusEqual:          {"-=", SymClassOperator, PosInfix},     //   4: '-='
+		sym.SymMinusEqual:          {"-=", SymClassOperator, PosInfix},     //   4: '-='
-		SymDoubleMinus:         {"--", SymClassOperator, PosPostfix},   //   5: '--'
+		sym.SymDoubleMinus:         {"--", SymClassOperator, PosPostfix},   //   5: '--'
-		SymPlus:                {"+", SymClassOperator, PosInfix},      //   6: '+'
+		sym.SymPlus:                {"+", SymClassOperator, PosInfix},      //   6: '+'
-		SymPlusEqual:           {"+=", SymClassOperator, PosInfix},     //   7: '+='
+		sym.SymPlusEqual:           {"+=", SymClassOperator, PosInfix},     //   7: '+='
-		SymDoublePlus:          {"++", SymClassOperator, PosPostfix},   //   8: '++'
+		sym.SymDoublePlus:          {"++", SymClassOperator, PosPostfix},   //   8: '++'
-		SymStar:                {"*", SymClassOperator, PosInfix},      //   9: '*'
+		sym.SymStar:                {"*", SymClassOperator, PosInfix},      //   9: '*'
-		SymDoubleStar:          {"**", SymClassOperator, PosInfix},     //  10: '**'
+		sym.SymDoubleStar:          {"**", SymClassOperator, PosInfix},     //  10: '**'
-		SymSlash:               {"/", SymClassOperator, PosInfix},      //  11: '/'
+		sym.SymSlash:               {"/", SymClassOperator, PosInfix},      //  11: '/'
-		SymBackSlash:           {"\\", SymClassOperator, PosLeaf},      //  12: '\'
+		sym.SymBackSlash:           {"\\", SymClassOperator, PosLeaf},      //  12: '\'
-		SymVertBar:             {"|", SymClassOperator, PosInfix},      //  13: '|'
+		sym.SymVertBar:             {"|", SymClassOperator, PosInfix},      //  13: '|'
-		SymDoubleVertBar:       {"||", SymClassOperator, PosInfix},     //  14: '||'
+		sym.SymDoubleVertBar:       {"||", SymClassOperator, PosInfix},     //  14: '||'
-		SymComma:               {",", SymClassOperator, PosInfix},      //  15: ','
+		sym.SymComma:               {",", SymClassOperator, PosInfix},      //  15: ','
-		SymColon:               {":", SymClassOperator, PosInfix},      //  16: ':'
+		sym.SymColon:               {":", SymClassOperator, PosInfix},      //  16: ':'
-		SymSemiColon:           {";", SymClassOperator, PosInfix},      //  17: ';'
+		sym.SymSemiColon:           {";", SymClassOperator, PosInfix},      //  17: ';'
-		SymDot:                 {".", SymClassOperator, PosInfix},      //  18: '.'
+		sym.SymDot:                 {".", SymClassOperator, PosInfix},      //  18: '.'
-		SymDotSlash:            {"./", SymClassOperator, PosInfix},     //  19: './'
+		sym.SymDotSlash:            {"./", SymClassOperator, PosInfix},     //  19: './'
-		SymQuote:               {"'", SymClassDelimiter, PosLeaf},      //  20: '\''
+		sym.SymQuote:               {"'", SymClassDelimiter, PosLeaf},      //  20: '\''
-		SymDoubleQuote:         {"\"", SymClassDelimiter, PosLeaf},     //  21: '"'
+		sym.SymDoubleQuote:         {"\"", SymClassDelimiter, PosLeaf},     //  21: '"'
-		SymBackTick:            {"`", SymClassDelimiter, PosLeaf},      //  22: '`'
+		sym.SymBackTick:            {"`", SymClassDelimiter, PosLeaf},      //  22: '`'
-		SymExclamation:         {"!", SymClassOperator, PosPostfix},    //  23: '!'
+		sym.SymExclamation:         {"!", SymClassOperator, PosPostfix},    //  23: '!'
-		SymQuestion:            {"?", SymClassOperator, PosInfix},      //  24: '?'
+		sym.SymQuestion:            {"?", SymClassOperator, PosInfix},      //  24: '?'
-		SymAmpersand:           {"&", SymClassOperator, PosInfix},      //  25: '&'
+		sym.SymAmpersand:           {"&", SymClassOperator, PosInfix},      //  25: '&'
-		SymDoubleAmpersand:     {"&&", SymClassOperator, PosInfix},     //  26: '&&'
+		sym.SymDoubleAmpersand:     {"&&", SymClassOperator, PosInfix},     //  26: '&&'
-		SymPercent:             {"%", SymClassOperator, PosInfix},      //  27: '%'
+		sym.SymPercent:             {"%", SymClassOperator, PosInfix},      //  27: '%'
-		SymAt:                  {"@", SymClassOperator, PosPrefix},     //  28: '@'
+		sym.SymAt:                  {"@", SymClassOperator, PosPrefix},     //  28: '@'
-		SymUndescore:           {"_", SymClassIdentifier, PosLeaf},     //  29: '_'
+		sym.SymUndescore:           {"_", SymClassIdentifier, PosLeaf},     //  29: '_'
-		SymEqual:               {"=", SymClassOperator, PosInfix},      //  30: '='
+		sym.SymEqual:               {"=", SymClassOperator, PosInfix},      //  30: '='
-		SymColonEqual:          {":=", SymClassOperator, PosInfix},     //  31: ':='
+		sym.SymColonEqual:          {":=", SymClassOperator, PosInfix},     //  31: ':='
-		SymDoubleEqual:         {"==", SymClassOperator, PosInfix},     //  32: '=='
+		sym.SymDoubleEqual:         {"==", SymClassOperator, PosInfix},     //  32: '=='
-		SymLess:                {"<", SymClassOperator, PosInfix},      //  33: '<'
+		sym.SymLess:                {"<", SymClassOperator, PosInfix},      //  33: '<'
-		SymLessOrEqual:         {"<=", SymClassOperator, PosInfix},     //  34: '<='
+		sym.SymLessOrEqual:         {"<=", SymClassOperator, PosInfix},     //  34: '<='
-		SymGreater:             {">", SymClassOperator, PosInfix},      //  35: '>'
+		sym.SymGreater:             {">", SymClassOperator, PosInfix},      //  35: '>'
-		SymGreaterOrEqual:      {">=", SymClassOperator, PosInfix},     //  36: '>='
+		sym.SymGreaterOrEqual:      {">=", SymClassOperator, PosInfix},     //  36: '>='
-		SymLessGreater:         {"<>", SymClassOperator, PosInfix},     //  37: '<>'
+		sym.SymLessGreater:         {"<>", SymClassOperator, PosInfix},     //  37: '<>'
-		SymNotEqual:            {"!=", SymClassOperator, PosInfix},     //  38: '!='
+		sym.SymNotEqual:            {"!=", SymClassOperator, PosInfix},     //  38: '!='
-		SymDollar:              {"$", SymClassOperator, PosPrefix},     //  39: '$'
+		sym.SymDollar:              {"$", SymClassOperator, PosPrefix},     //  39: '$'
-		SymHash:                {"#", SymClassOperator, PosPrefix},     //  40: '#'
+		sym.SymHash:                {"#", SymClassOperator, PosPrefix},     //  40: '#'
-		SymOpenRound:           {"(", SymClassParenthesis, PosPrefix},  //  41: '('
+		sym.SymOpenRound:           {"(", SymClassParenthesis, PosPrefix},  //  41: '('
-		SymClosedRound:         {")", SymClassParenthesis, PosPostfix}, //  42: ')'
+		sym.SymClosedRound:         {")", SymClassParenthesis, PosPostfix}, //  42: ')'
-		SymOpenSquare:          {"[", SymClassParenthesis, PosPrefix},  //  43: '['
+		sym.SymOpenSquare:          {"[", SymClassParenthesis, PosPrefix},  //  43: '['
-		SymClosedSquare:        {"]", SymClassParenthesis, PosPostfix}, //  44: ']'
+		sym.SymClosedSquare:        {"]", SymClassParenthesis, PosPostfix}, //  44: ']'
-		SymOpenBrace:           {"{", SymClassParenthesis, PosPrefix},  //  45: '{'
+		sym.SymOpenBrace:           {"{", SymClassParenthesis, PosPrefix},  //  45: '{'
-		SymClosedBrace:         {"}", SymClassParenthesis, PosPostfix}, //  46: '}'
+		sym.SymClosedBrace:         {"}", SymClassParenthesis, PosPostfix}, //  46: '}'
-		SymTilde:               {"~", SymClassOperator, PosPrefix},     //  47: '~'
+		sym.SymTilde:               {"~", SymClassOperator, PosPrefix},     //  47: '~'
-		SymDoubleQuestion:      {"??", SymClassOperator, PosInfix},     //  48: '??'
+		sym.SymDoubleQuestion:      {"??", SymClassOperator, PosInfix},     //  48: '??'
-		SymQuestionEqual:       {"?=", SymClassOperator, PosInfix},     //  49: '?='
+		sym.SymQuestionEqual:       {"?=", SymClassOperator, PosInfix},     //  49: '?='
-		SymQuestionExclam:      {"?!", SymClassOperator, PosInfix},     //  50: '?!'
+		sym.SymQuestionExclam:      {"?!", SymClassOperator, PosInfix},     //  50: '?!'
-		SymDoubleAt:            {"@@", SymClassCommand, PosLeaf},       //  51: '@@'
+		sym.SymDoubleAt:            {"@@", SymClassCommand, PosLeaf},       //  51: '@@'
-		SymDoubleColon:         {"::", SymClassOperator, PosInfix},     //  52: '::'
+		sym.SymDoubleColon:         {"::", SymClassOperator, PosInfix},     //  52: '::'
-		SymDoubleGreater:       {">>", SymClassOperator, PosInfix},     //  53: '>>'
+		sym.SymDoubleGreater:       {">>", SymClassOperator, PosInfix},     //  53: '>>'
-		SymDoubleLess:          {"<<", SymClassOperator, PosInfix},     //  54: '<<'
+		sym.SymDoubleLess:          {"<<", SymClassOperator, PosInfix},     //  54: '<<'
-		SymCaret:               {"^", SymClassOperator, PosInfix},      //  55: '^'
+		sym.SymCaret:               {"^", SymClassOperator, PosInfix},      //  55: '^'
-		SymDollarRound:         {"$(", SymClassOperator, PosPrefix},    //  56: '$('
+		sym.SymDollarRound:         {"$(", SymClassOperator, PosPrefix},    //  56: '$('
-		SymOpenClosedRound:     {"()", SymClassOperator, PosPostfix},   //  57: '()'
+		sym.SymOpenClosedRound:     {"()", SymClassOperator, PosPostfix},   //  57: '()'
-		SymDoubleDollar:        {"$$", SymClassCommand, PosLeaf},       //  58: '$$'
+		sym.SymDoubleDollar:        {"$$", SymClassCommand, PosLeaf},       //  58: '$$'
-		SymDoubleDot:           {"..", SymClassOperator, PosInfix},     //  59: '..'
+		sym.SymDoubleDot:           {"..", SymClassOperator, PosInfix},     //  59: '..'
-		SymTripleDot:           {"...", SymClassOperator, PosPostfix},  //  60: '...'
+		sym.SymTripleDot:           {"...", SymClassOperator, PosPostfix},  //  60: '...'
-		SymStarEqual:           {"*=", SymClassOperator, PosInfix},     //  61: '*='
+		sym.SymStarEqual:           {"*=", SymClassOperator, PosInfix},     //  61: '*='
-		SymSlashEqual:          {"/=", SymClassOperator, PosInfix},     //  62: '/='
+		sym.SymSlashEqual:          {"/=", SymClassOperator, PosInfix},     //  62: '/='
-		SymPercEqual:           {"%=", SymClassOperator, PosInfix},     //  63: '%='
+		sym.SymPercEqual:           {"%=", SymClassOperator, PosInfix},     //  63: '%='
-		SymDoubleLessEqual:     {"<<=", SymClassOperator, PosInfix},    //  64: '<<='
+		sym.SymDoubleLessEqual:     {"<<=", SymClassOperator, PosInfix},    //  64: '<<='
-		SymDoubleGreaterEqual:  {">>=", SymClassOperator, PosInfix},    //  65: '>>='
+		sym.SymDoubleGreaterEqual:  {">>=", SymClassOperator, PosInfix},    //  65: '>>='
-		SymAmpersandEqual:      {"&=", SymClassOperator, PosInfix},     //  66: '&='
+		sym.SymAmpersandEqual:      {"&=", SymClassOperator, PosInfix},     //  66: '&='
-		SymVertBarEqual:        {"|=", SymClassOperator, PosInfix},     //  67: '|='
+		sym.SymVertBarEqual:        {"|=", SymClassOperator, PosInfix},     //  67: '|='
-		SymCaretEqual:          {"^=", SymClassOperator, PosInfix},     //  68: '^='
+		sym.SymCaretEqual:          {"^=", SymClassOperator, PosInfix},     //  68: '^='
-		SymPlusGreater:         {"+>", SymClassOperator, PosInfix},     //  69: '+>'
+		sym.SymPlusGreater:         {"+>", SymClassOperator, PosInfix},     //  69: '+>'
-		SymLessPlus:            {"<+", SymClassOperator, PosInfix},     //  70: '<+'
+		sym.SymLessPlus:            {"<+", SymClassOperator, PosInfix},     //  70: '<+'
-		SymPreInc:              {"++", SymClassOperator, PosPrefix},    //  71: '++'
+		sym.SymPreInc:              {"++", SymClassOperator, PosPrefix},    //  71: '++'
-		SymPreDec:              {"--", SymClassOperator, PosPrefix},    //  72: '--'
+		sym.SymPreDec:              {"--", SymClassOperator, PosPrefix},    //  72: '--'
-		SymOpenSquareLess:      {"[<", SymClassOperator, PosPrefix},    //  97: '[<'
+		sym.SymOpenSquareLess:      {"[<", SymClassOperator, PosPrefix},    //  97: '[<'
-		SymGreaterClosedSquare: {">]", SymClassOperator, PosPostfix},   //  98: '>]'
+		sym.SymGreaterClosedSquare: {">]", SymClassOperator, PosPostfix},   //  98: '>]'
-		// SymChangeSign
+		// sym.SymChangeSign
-		// SymUnchangeSign
+		// sym.SymUnchangeSign
-		// SymIdentifier
+		// sym.SymIdentifier
-		// SymBool
+		// sym.SymBool
-		// SymInteger
+		// sym.SymInteger
-		// SymVariable
+		// sym.SymVariable
-		// SymFloat
+		// sym.SymFloat
-		// SymFraction
+		// sym.SymFraction
-		// SymString
+		// sym.SymString
-		// SymIterator
+		// sym.SymIterator
-		// SymOr:  "or",
+		// sym.SymOr:  "or",
-		// SymAnd: "and",
+		// sym.SymAnd: "and",
-		// SymNot: "not",
+		// sym.SymNot: "not",
-		// SymComment
+		// sym.SymComment
-		// SymFuncCall
+		// sym.SymFuncCall
-		// SymFuncDef
+		// sym.SymFuncDef
-		// SymList
+		// sym.SymList
-		// SymLinkedList
+		// sym.SymLinkedList
-		// SymDict
+		// sym.SymDict
-		// SymIndex
+		// sym.SymIndex
-		// SymExpression
+		// sym.SymExpression
-		// SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
+		// sym.SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
-		// SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
+		// sym.SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
-		// // SymOpenComment                       //   0: '/*'
+		// // sym.SymOpenComment                       //   0: '/*'
-		// // SymClosedComment                     //   0: '*/'
+		// // sym.SymClosedComment                     //   0: '*/'
-		// // SymOneLineComment                    //   0: '//'
+		// // sym.SymOneLineComment                    //   0: '//'
 		// keywordBase
-		SymKwAnd:     {"and", SymClassOperator, PosInfix},
+		sym.SymKwAnd:     {"and", SymClassOperator, PosInfix},
-		SymKwNot:     {"not", SymClassOperator, PosInfix},
+		sym.SymKwNot:     {"not", SymClassOperator, PosInfix},
-		SymKwOr:      {"or", SymClassOperator, PosInfix},
+		sym.SymKwOr:      {"or", SymClassOperator, PosInfix},
-		SymKwBut:     {"but", SymClassOperator, PosInfix},
+		sym.SymKwBut:     {"but", SymClassOperator, PosInfix},
-		SymKwMap:     {"map", SymClassOperator, PosInfix},
+		sym.SymKwMap:     {"map", SymClassOperator, PosInfix},
-		SymKwFilter:  {"filter", SymClassOperator, PosInfix},
+		sym.SymKwFilter:  {"filter", SymClassOperator, PosInfix},
-		SymKwDigest:  {"digest", SymClassOperator, PosInfix},
+		sym.SymKwDigest:  {"digest", SymClassOperator, PosInfix},
-		SymKwCat:     {"cat", SymClassOperator, PosInfix},
+		sym.SymKwCat:     {"cat", SymClassOperator, PosInfix},
-		SymKwJoin:    {"join", SymClassOperator, PosInfix},
+		sym.SymKwJoin:    {"join", SymClassOperator, PosInfix},
-		SymKwGroupBy: {"groupby", SymClassOperator, PosInfix},
+		sym.SymKwGroupBy: {"groupby", SymClassOperator, PosInfix},
-		SymKwFunc:    {"func(", SymClassDeclaration, PosPrefix},
+		sym.SymKwFunc:    {"func(", SymClassDeclaration, PosPrefix},
-		SymKwBuiltin: {"builtin", SymClassOperator, PosPrefix},
+		sym.SymKwBuiltin: {"builtin", SymClassOperator, PosPrefix},
-		SymKwPlugin:  {"plugin", SymClassOperator, PosPrefix},
+		sym.SymKwPlugin:  {"plugin", SymClassOperator, PosPrefix},
-		SymKwIn:      {"in", SymClassOperator, PosInfix},
+		sym.SymKwIn:      {"in", SymClassOperator, PosInfix},
-		SymKwInclude: {"include", SymClassOperator, PosPrefix},
+		sym.SymKwAt:      {"at", SymClassOperator, PosInfix},
-		SymKwNil:     {"nil", SymClassValue, PosLeaf},
+		sym.SymKwInclude: {"include", SymClassOperator, PosPrefix},
-		SymKwUnset:   {"unset", SymClassOperator, PosPrefix},
+		sym.SymKwNil:     {"nil", SymClassValue, PosLeaf},
+		sym.SymKwUnset:   {"unset", SymClassOperator, PosPrefix},
 	}
 }
 
-func SymToString(sym Symbol) string {
+func SymToString(sym sym.Symbol) string {
 	if s, ok := symbolMap[sym]; ok {
 		return s.repr
 	}
 	return ""
 }
 
-func SymListToString(symList []Symbol, quote bool) string {
+func SymListToString(symList []sym.Symbol, quote bool) string {
 	var sb strings.Builder
 	if len(symList) == 0 {
 		sb.WriteString("<nothing>")
@@ -185,13 +188,13 @@ func SymListToString(symList []Symbol, quote bool) string {
 }
 
 func StringEndsWithOperator(s string) bool {
-	return endingOperator(s) != SymNone
+	return endingOperator(s) != sym.SymNone
 }
 
-func endingOperator(s string) (sym Symbol) {
+func endingOperator(s string) (resultSym sym.Symbol) {
 	var matchLength = 0
 	var repr string
-	sym = SymNone
+	resultSym = sym.SymNone
 	lower := strings.TrimRight(strings.ToLower(s), " \t")
 	for symbol, spec := range symbolMap {
 		if len(spec.repr) > matchLength || repr == spec.repr {
@@ -199,9 +202,9 @@ func endingOperator(s string) (sym Symbol) {
 				if isNotEndingSymbol(spec) && repr != spec.repr {
 					repr = spec.repr
 					matchLength = len(spec.repr)
-					sym = symbol
+					resultSym = symbol
 				} else {
-					sym = SymNone
+					resultSym = sym.SymNone
 					break
 					// matchLength = 0
 				}

scan/t_scanner_test.go

@@ -10,59 +10,58 @@ import (
 	"strings"
 	"testing"
 
-	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 func TestScanner(t *testing.T) {
 	type inputType struct {
 		source    string
-		wantSym   Symbol
+		wantSym   sym.Symbol
 		wantValue any
 		wantErr   error
 	}
 
 	inputs := []inputType{
-		/*  1 */ {`123`, SymInteger, int64(123), nil},
+		/*  1 */ {`123`, sym.SymInteger, int64(123), nil},
-		/*  2 */ {"=", SymEqual, nil, nil},
+		/*  2 */ {"=", sym.SymEqual, nil, nil},
-		/*  3 */ {`--`, SymDoubleMinus, nil, nil},
+		/*  3 */ {`--`, sym.SymDoubleMinus, nil, nil},
-		/*  4 */ {`++`, SymDoublePlus, nil, nil},
+		/*  4 */ {`++`, sym.SymDoublePlus, nil, nil},
-		/*  5 */ {`**`, SymDoubleStar, nil, nil},
+		/*  5 */ {`**`, sym.SymDoubleStar, nil, nil},
-		/*  6 */ {`&&`, SymDoubleAmpersand, nil, nil},
+		/*  6 */ {`&&`, sym.SymDoubleAmpersand, nil, nil},
-		/*  7 */ {`||`, SymDoubleVertBar, nil, nil},
+		/*  7 */ {`||`, sym.SymDoubleVertBar, nil, nil},
-		/*  8 */ {`NOT`, SymKwNot, nil, nil},
+		/*  8 */ {`NOT`, sym.SymKwNot, nil, nil},
-		/*  9 */ {`AND`, SymKwAnd, nil, nil},
+		/*  9 */ {`AND`, sym.SymKwAnd, nil, nil},
-		/* 10 */ {`or`, SymKwOr, nil, nil},
+		/* 10 */ {`or`, sym.SymKwOr, nil, nil},
-		/* 11 */ {`+=`, SymPlusEqual, nil, nil},
+		/* 11 */ {`+=`, sym.SymPlusEqual, nil, nil},
-		/* 12 */ {`-=`, SymMinusEqual, nil, nil},
+		/* 12 */ {`-=`, sym.SymMinusEqual, nil, nil},
-		/* 13 */ {`|`, SymVertBar, nil, nil},
+		/* 13 */ {`|`, sym.SymVertBar, nil, nil},
-		/* 14 */ {`:`, SymColon, nil, nil},
+		/* 14 */ {`:`, sym.SymColon, nil, nil},
-		/* 15 */ {`;`, SymSemiColon, nil, nil},
+		/* 15 */ {`;`, sym.SymSemiColon, nil, nil},
-		/* 16 */ {`.`, SymDot, nil, nil},
+		/* 16 */ {`.`, sym.SymDot, nil, nil},
-		/* 17 */ {`0.5`, SymFloat, float64(0.5), nil},
+		/* 17 */ {`0.5`, sym.SymFloat, float64(0.5), nil},
-		/* 18 */ {`\\`, SymBackSlash, nil, nil},
+		/* 18 */ {`\\`, sym.SymBackSlash, nil, nil},
-		/* 19 */ {"`", SymBackTick, nil, nil},
+		/* 19 */ {"`", sym.SymBackTick, nil, nil},
-		/* 20 */ {"?", SymQuestion, nil, nil},
+		/* 20 */ {"?", sym.SymQuestion, nil, nil},
-		/* 21 */ {"&", SymAmpersand, nil, nil},
+		/* 21 */ {"&", sym.SymAmpersand, nil, nil},
-		/* 22 */ {"@", SymAt, nil, nil},
+		/* 22 */ {"@", sym.SymAt, nil, nil},
-		/* 23 */ {`#`, SymHash, nil, nil},
+		/* 23 */ {`#`, sym.SymHash, nil, nil},
-		/* 24 */ {`%`, SymPercent, nil, nil},
+		/* 24 */ {`%`, sym.SymPercent, nil, nil},
-		/* 25 */ {`\'`, SymQuote, nil, nil},
+		/* 25 */ {`\'`, sym.SymQuote, nil, nil},
-		/* 26 */ {`\"`, SymDoubleQuote, nil, nil},
+		/* 26 */ {`\"`, sym.SymDoubleQuote, nil, nil},
-		/* 27 */ {`_`, SymUndescore, nil, nil},
+		/* 27 */ {`_`, sym.SymUndescore, nil, nil},
-		/* 28 */ {`<>`, SymLessGreater, nil, nil},
+		/* 28 */ {`<>`, sym.SymLessGreater, nil, nil},
-		/* 29 */ {`[`, SymOpenSquare, nil, nil},
+		/* 29 */ {`[`, sym.SymOpenSquare, nil, nil},
-		/* 30 */ {`]`, SymClosedSquare, nil, nil},
+		/* 30 */ {`]`, sym.SymClosedSquare, nil, nil},
-		/* 31 */ {`{`, SymOpenBrace, nil, nil},
+		/* 31 */ {`{`, sym.SymOpenBrace, nil, nil},
-		/* 32 */ {`}`, SymClosedBrace, nil, nil},
+		/* 32 */ {`}`, sym.SymClosedBrace, nil, nil},
-		/* 33 */ {`(`, SymOpenRound, nil, nil},
+		/* 33 */ {`(`, sym.SymOpenRound, nil, nil},
-		/* 34 */ {`)`, SymClosedRound, nil, nil},
+		/* 34 */ {`)`, sym.SymClosedRound, nil, nil},
-		/* 35 */ {`1E+2`, SymFloat, float64(100), nil},
+		/* 35 */ {`1E+2`, sym.SymFloat, float64(100), nil},
-		/* 36 */ {`1E+x`, SymError, errors.New("[1:5] expected integer exponent, got x"), nil},
+		/* 36 */ {`1E+x`, sym.SymError, errors.New("[1:5] expected integer exponent, got x"), nil},
-		/* 37 */ {`$`, SymDollar, nil, nil},
+		/* 37 */ {`$`, sym.SymDollar, nil, nil},
-		/* 38 */ {`\`, SymError, errors.New("incomplete escape sequence"), nil},
+		/* 38 */ {`\`, sym.SymError, errors.New("incomplete escape sequence"), nil},
-		/* 39 */ {`"string"`, SymString, "string", nil},
+		/* 39 */ {`"string"`, sym.SymString, "string", nil},
-		/* 40 */ {`identifier`, SymIdentifier, "identifier", nil},
+		/* 40 */ {`identifier`, sym.SymIdentifier, "identifier", nil},
-		/* 41 */ {`1.2(3)`, SymFraction, kern.NewFraction(37, 30), nil},
 	}
 
 	for i, input := range inputs {
@@ -82,7 +81,7 @@ func TestScanner(t *testing.T) {
 			t.Errorf("%d: %q -> got = (nil), want %v (value %v [%T])", i+1, input.source, input.wantSym, input.wantValue, input.wantValue)
 			// } else if tk.Sym != input.wantSym || tk.Value != input.wantValue {
 		} else if tk.Sym != input.wantSym || !reflect.DeepEqual(tk.Value, input.wantValue) {
-			if tk.Sym == SymError && input.wantSym == tk.Sym {
+			if tk.Sym == sym.SymError && input.wantSym == tk.Sym {
 				if tkErr, tkOk := tk.Value.(error); tkOk {
 					if inputErr, inputOk := input.wantValue.(error); inputOk {
 						if tkErr.Error() != inputErr.Error() {

scan/term-constructor-registry.go

@@ -4,17 +4,19 @@
 // term-constructor-registry.go
 package scan
 
+import "git.portale-stac.it/go-pkg/expr/sym"
+
 const initialRegistryCapacity = 10
 
 type termContructor func(tk *Token) *Term
 
-var constructorRegistry map[Symbol]termContructor = nil
+var constructorRegistry map[sym.Symbol]termContructor = nil
 
-func RegisterTermConstructor(sym Symbol, constructor termContructor) {
+func RegisterTermConstructor(symmbol sym.Symbol, constructor termContructor) {
 	if constructorRegistry == nil {
-		constructorRegistry = make(map[Symbol]termContructor, initialRegistryCapacity)
+		constructorRegistry = make(map[sym.Symbol]termContructor, initialRegistryCapacity)
 	}
-	constructorRegistry[sym] = constructor
+	constructorRegistry[symmbol] = constructor
 }
 
 func NewTerm(tk *Token) (inst *Term) {

scan/term.go

@@ -8,13 +8,14 @@ import (
 	"strings"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 type TermPriority uint32
 
 const (
 	PriNone TermPriority = iota
-	PriRange
+	PriInterval
 	PriBut
 	PriAssign
 	PriIterOp // map, filter, digest, etc
@@ -160,7 +161,7 @@ func (t *Term) SetParent(parent *Term) {
 	}
 }
 
-func (t *Term) Symbol() Symbol {
+func (t *Term) Symbol() sym.Symbol {
 	return t.Tk.Sym
 }
 
@@ -186,9 +187,43 @@ func (t *Term) GetChildSource(index int) (s string) {
 	return
 }
 
-func (t *Term) IsAssign() bool {
+func (t *Term) GetLeftChild() (c kern.Term) {
-	return t.Symbol() == SymEqual
+	if t.Position == PosInfix && len(t.Children) > 0 {
+		c = t.Children[0]
 	}
+	return
+}
+
+func (t *Term) GetRightChild() (c kern.Term) {
+	if t.Position == PosInfix && len(t.Children) > 1 {
+		c = t.Children[1]
+	}
+	return
+}
+
+func (t *Term) IsSymbol(symbol sym.Symbol) bool {
+	return t.Symbol() == symbol
+}
+
+func (t *Term) IsOneOf(symbols ...sym.Symbol) bool {
+	return t.Tk.IsOneOf(symbols)
+}
+
+func (t *Term) IsAssign() bool {
+	return t.Symbol() == sym.SymEqual
+}
+
+func (t *Term) IsVar() bool {
+	return t.Symbol() == sym.SymVariable
+}
+
+func (t *Term) SetSymbol(symbol sym.Symbol) {
+	t.Tk.SetSymbol(symbol)
+}
+
+// func (t *Term) IsFunc() bool {
+// 	return t.Symbol() == SymFunction
+// }
 
 func (t *Term) Compute(ctx kern.ExprContext) (v any, err error) {
 	if t.EvalFunc == nil {
@@ -199,15 +234,6 @@ func (t *Term) Compute(ctx kern.ExprContext) (v any, err error) {
 	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)

scan/token.go

@@ -8,12 +8,14 @@ import (
 	"fmt"
 	"io"
 	"slices"
+
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 type Token struct {
 	row    int
 	col    int
-	Sym    Symbol
+	Sym    sym.Symbol
 	source string
 	Value  any
 }
@@ -36,19 +38,19 @@ func (tk *Token) String() string {
 	return tk.source
 }
 
-func NewToken(row, col int, sym Symbol, source string) *Token {
+func NewToken(row, col int, symbol sym.Symbol, source string) *Token {
-	return &Token{row: row, col: col, Sym: sym, source: source}
+	return &Token{row: row, col: col, Sym: symbol, source: source}
 }
 
-func NewValueToken(row, col int, sym Symbol, source string, value any) *Token {
+func NewValueToken(row, col int, symbol sym.Symbol, source string, value any) *Token {
-	return &Token{row: row, col: col, Sym: sym, source: source, Value: value}
+	return &Token{row: row, col: col, Sym: symbol, source: source, Value: value}
 }
 
 func NewErrorToken(row, col int, err error) *Token {
 	if err == io.EOF {
-		return NewToken(row, col, SymEos, "<EOF>")
+		return NewToken(row, col, sym.SymEos, "<EOF>")
 	}
-	return NewValueToken(row, col, SymError, fmt.Sprintf("[%d:%d]", row, col), err)
+	return NewValueToken(row, col, sym.SymError, fmt.Sprintf("[%d:%d]", row, col), err)
 }
 
 func (tk *Token) Source() string {
@@ -68,31 +70,31 @@ func (tk *Token) Clone() (c *Token) {
 }
 
 func (tk *Token) IsEos() bool {
-	return tk.Sym == SymEos
+	return tk.Sym == sym.SymEos
 }
 
 func (tk *Token) IsError() bool {
-	return tk.Sym == SymError
+	return tk.Sym == sym.SymError
 }
 
-func (tk *Token) IsTerm(termSymbols []Symbol) bool {
+func (tk *Token) IsTerm(symbols []sym.Symbol) bool {
-	return tk.IsEos() || tk.IsError() || tk.IsOneOf(termSymbols)
+	return tk.IsEos() || tk.IsError() || tk.IsOneOf(symbols)
 }
 
-func (tk *Token) IsOneOf(termSymbols []Symbol) bool {
+func (tk *Token) IsOneOf(symbols []sym.Symbol) bool {
-	return termSymbols != nil && slices.Index(termSymbols, tk.Sym) >= 0
+	return symbols != nil && slices.Index(symbols, tk.Sym) >= 0
 }
 
-func (tk *Token) IsOneOfA(termSymbols ...Symbol) bool {
+func (tk *Token) IsOneOfA(symbols ...sym.Symbol) bool {
-	return slices.Index(termSymbols, tk.Sym) >= 0
+	return slices.Index(symbols, tk.Sym) >= 0
 }
 
-func (tk *Token) IsSymbol(sym Symbol) bool {
+func (tk *Token) IsSymbol(symbol sym.Symbol) bool {
-	return tk.Sym == sym
+	return tk.Sym == symbol
 }
 
-func (tk *Token) SetSymbol(sym Symbol) {
+func (tk *Token) SetSymbol(symbol sym.Symbol) {
-	tk.Sym = sym
+	tk.Sym = symbol
 }
 
 func (tk *Token) Errorf(template string, args ...any) (err error) {
@@ -101,7 +103,7 @@ func (tk *Token) Errorf(template string, args ...any) (err error) {
 }
 
 func (tk *Token) Error() (err error) {
-	if tk.Sym == SymError {
+	if tk.Sym == sym.SymError {
 		if msg, ok := tk.Value.(error); ok {
 			err = fmt.Errorf("[%d:%d] %v", tk.row, tk.col, msg)
 		}
@@ -110,7 +112,7 @@ func (tk *Token) Error() (err error) {
 }
 
 func (tk *Token) ErrorText() (err string) {
-	if tk.Sym == SymError {
+	if tk.Sym == sym.SymError {
 		if msg, ok := tk.Value.(error); ok {
 			err = msg.Error()
 		}
@@ -137,6 +139,6 @@ func (tk *Token) ErrorExpectedGotStringWithPrefix(prefix, symbol, got string) (e
 	return
 }
 
-func (tk *Token) ErrorExpectedOneOfGot(expected ...Symbol) (err error) {
+func (tk *Token) ErrorExpectedOneOfGot(expected ...sym.Symbol) (err error) {
 	return tk.ErrorExpectedGotStringWithPrefix("expected one of ", SymListToString(expected, true), SymToString(tk.Sym))
 }

simple-store.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types"
 	"git.portale-stac.it/go-pkg/expr/util"
 	// "strings"
 )
@@ -76,12 +77,12 @@ func (ctx *SimpleStore) Clone() kern.ExprContext {
 // 	}
 // }
 
-func (ctx *SimpleStore) ToDict() (dict *kern.DictType) {
+func (ctx *SimpleStore) ToDict() any {
-	return kern.ContextToDict(ctx)
+	return types.ContextToDict(ctx)
 }
 
 func (ctx *SimpleStore) ToString(opt kern.FmtOpt) string {
-	return kern.ContextToString(ctx, opt)
+	return types.ContextToString(ctx, opt)
 }
 
 // func (ctx *SimpleStore) ToString(opt kern.FmtOpt) string {

sym/symbol.go

@@ -2,7 +2,7 @@
 // All rights reserved.
 
 // symbol.go
-package scan
+package sym
 
 type Symbol int16
 
@@ -101,7 +101,7 @@ const (
 	SymList                                  //  90: list
 	SymDict                                  //  91: dict
 	SymIndex                                 //  92: index
-	SymRange                                 //  93: range [index : index]
+	SymInterval                              //  93: range [index : index]
 	SymExpression                            //  94: expression
 	SymSelector                              //  95: selector <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
 	SymSelectorCase                          //  96: <selector-case> ::= [<list>] "{" <multi-expr> "}"
@@ -122,6 +122,7 @@ const (
 	SymKwBuiltin
 	SymKwPlugin
 	SymKwIn
+	SymKwAt
 	SymKwInclude
 	SymKwMap
 	SymKwFilter
@@ -133,17 +134,18 @@ const (
 	SymKwUnset
 )
 
-var keywords map[string]Symbol
+var Keywords map[string]Symbol
 
 func init() {
 	//keywords = make(map[string]Symbol)
-	keywords = map[string]Symbol{
+	Keywords = map[string]Symbol{
 		"AND":     SymKwAnd,
 		"BUILTIN": SymKwBuiltin,
 		"PLUGIN":  SymKwPlugin,
 		"BUT":     SymKwBut,
 		"FUNC":    SymKwFunc,
 		"IN":      SymKwIn,
+		"AT":      SymKwAt,
 		"INCLUDE": SymKwInclude,
 		"MAP":     SymKwMap,
 		"CAT":     SymKwCat,

t_array_test.go

@@ -0,0 +1,94 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_array_test.go
+package expr
+
+import (
+	"testing"
+
+	"git.portale-stac.it/go-pkg/expr/types/array"
+)
+
+func TestArray(t *testing.T) {
+	section := "Array"
+
+	inputs := []inputType{
+		/*   1 */ {`[]`, array.NewArrayA(), nil},
+		/*   2 */ {`[1,2,3]`, array.NewArrayA(int64(1), int64(2), int64(3)), nil},
+		/*   3 */ {`[1,2,"hello"]`, array.NewArrayA(int64(1), int64(2), "hello"), nil},
+		/*   4 */ {`[1+2, not true, "hello"]`, array.NewArrayA(int64(3), false, "hello"), nil},
+		/*   5 */ {`[1,2]+[3]`, array.NewArrayA(int64(1), int64(2), int64(3)), nil},
+		/*   6 */ {`[1,4,3,2]-[3]`, array.NewArrayA(int64(1), int64(4), int64(2)), nil},
+		/*   7 */ {`builtin "math.arith"; add([1,4,3,2])`, int64(10), nil},
+		/*   8 */ {`builtin "math.arith"; add([1,[2,2],3,2])`, int64(10), nil},
+		/*   9 */ {`builtin "math.arith"; mul([1,4,3.0,2])`, float64(24.0), nil},
+		/*  10 */ {`builtin "math.arith"; add([1,"hello"])`, nil, `add(): param nr 2 (2 in 1) has wrong type string, number expected`},
+		/*  11 */ {`[a=1,b=2,c=3] but a+b+c`, int64(6), nil},
+		/*  12 */ {`[1,2,3] <+ 2+2`, array.ArrayFromIntsA(1, 2, 3, 4), nil},
+		/*  13 */ {`2-1 +> [2,3]`, array.ArrayFromIntsA(1, 2, 3), nil},
+		/*  14 */ {`[1,2,3][1]`, int64(2), nil},
+		/*  15 */ {`ls=[1,2,3] but ls[1]`, int64(2), nil},
+		/*  16 */ {`ls=[1,2,3] but ls[-1]`, int64(3), nil},
+		/*  17 */ {`list=["one","two","three"]; list[10]`, nil, `[1:34] index 10 out of bounds`},
+		/*  18 */ {`["a", "b", "c"]`, array.NewArrayA("a", "b", "c"), nil},
+		/*  19 */ {`["a", "b", "c"]`, array.NewArray([]any{"a", "b", "c"}), nil},
+		/*  20 */ {`#["a", "b", "c"]`, int64(3), nil},
+		/*  21 */ {`"b" in ["a", "b", "c"]`, true, nil},
+		/*  22 */ {`a=[1,2]; (a)<+3`, array.NewArrayA(int64(1), int64(2), int64(3)), nil},
+		/*  23 */ {`a=[1,2]; (a)<+3; a`, array.NewArrayA(int64(1), int64(2)), nil},
+		/*  24 */ {`["a","b","c","d"][1]`, "b", nil},
+		/*  25 */ {`["a","b","c","d"][1,1]`, nil, `[1:19] one index only is allowed`},
+		/*  26 */ {`["a", "b", "c"] <+ ;`, nil, `[1:18] infix operator "<+" requires two non-nil operands, got 1`},
+		/*  27 */ {`but +> ["a", "b", "c"]`, nil, `[1:6] infix operator "+>" requires two non-nil operands, got 0`},
+		/*  28 */ {`a=[1,2]; a<+3`, array.NewArrayA(int64(1), int64(2), int64(3)), nil},
+		/*  29 */ {`a=[1,2]; 5+>a`, array.NewArrayA(int64(5), int64(1), int64(2)), nil},
+		/*  30 */ {`L=[1,2]; L[0]=9; L`, array.NewArrayA(int64(9), int64(2)), nil},
+		/*  31 */ {`L=[1,2]; L[5]=9; L`, nil, `index 5 out of bounds (0, 1)`},
+		/*  32 */ {`L=[1,2]; L[]=9; L`, nil, `[1:12] index/key specification expected, got [] [array]`},
+		/*  33 */ {`L=[1,2]; L[nil]=9;`, nil, `[1:12] index/key is nil`},
+		/*  34 */ {`2 IN [1,2,3]`, true, nil},
+		/*  35 */ {`2 AT [1,2,3]`, int64(1), nil},
+		/*  36 */ {`4 AT [1,2,3]`, int64(-1), nil},
+	}
+
+	// t.Setenv("EXPR_PATH", ".")
+
+	// RunTestSuiteSpec(t, section, inputs, 43)
+	RunTestSuite(t, section, inputs)
+}
+
+func TestArrayInsert(t *testing.T) {
+	section := "Array-Insert"
+	inputs := []inputType{
+		/*   1 */ {`["a", "b"] << nil`, array.NewArrayA("a", "b"), nil},
+		/*   2 */ {`["a", "b"] << []`, array.NewArrayA("a", "b", array.NewArrayA()), nil},
+		/*   3 */ {`["a", "b"] << $([])`, array.NewArrayA("a", "b"), nil},
+		/*   4 */ {`["a", "b"] << 3`, array.NewArrayA("a", "b", int64(3)), nil},
+		/*   5 */ {`3 << ["a", "b"]`, nil, `[1:5] left operand '3' [integer] and right operand '["a", "b"]' [array] are not compatible with operator "<<"`},
+		/*   6 */ {`nil >> ["a", "b"]`, array.NewArrayA("a", "b"), nil},
+		/*   7 */ {`[] >> ["a", "b"]`, array.NewArrayA(array.NewArrayA(), "a", "b"), nil},
+		/*   8 */ {`$([]) >> ["a", "b"]`, array.NewArrayA("a", "b"), nil},
+		/*   9 */ {`["a", "b"] << $([1,2,3])`, array.NewArrayA("a", "b", int64(1), int64(2), int64(3)), nil},
+		/*  10 */ {`L=["a", "b"]; L << $([1,2,3])`, array.NewArrayA("a", "b", int64(1), int64(2), int64(3)), nil},
+		/*  11 */ {`L=["a", "b"]; L << $([1,2,3]); L`, array.NewArrayA("a", "b", int64(1), int64(2), int64(3)), nil},
+		/*  12 */ {`L << $([1,2,3])`, nil, `undefined variable or function "L"`},
+		/*  13 */ {`[0] << $([1,2,3,4])`, array.NewArrayA(int64(0), int64(1), int64(2), int64(3), int64(4)), nil},
+		/*  14 */ {`L=[]; [1] >> L; L`, array.NewArrayA(array.ArrayFromIntsA(1)), nil},
+		/*  15 */ {`L=[]; L << [1]; L`, array.NewArrayA(array.ArrayFromIntsA(1)), nil},
+	}
+
+	// RunTestSuiteSpec(t, section, inputs, 14)
+	RunTestSuite(t, section, inputs)
+}
+
+func TestArrayDeepAssign(t *testing.T) {
+	section := "Array-DeepAssign"
+	inputs := []inputType{
+		/*   1 */ {`LL=["a", "b"]; L=LL; L[0]="x"; LL`, array.NewArrayA("x", "b"), nil},
+		/*   2 */ {`LL=["a", "b"]; L:=LL; L[0]="x"; LL`, array.NewArrayA("a", "b"), nil},
+	}
+
+	// runTestSuiteSpec(t, section, inputs, 4)
+	RunTestSuite(t, section, inputs)
+}

t_ast_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
 )
 
 func TestAstString(t *testing.T) {
@@ -19,9 +20,9 @@ func TestAstString(t *testing.T) {
 }
 
 func TestAddTokensGood(t *testing.T) {
-	tk1 := scan.NewValueToken(0, 0, scan.SymInteger, "100", 100)
+	tk1 := scan.NewValueToken(0, 0, sym.SymInteger, "100", 100)
-	tk2 := scan.NewToken(0, 0, scan.SymPlus, "+")
+	tk2 := scan.NewToken(0, 0, sym.SymPlus, "+")
-	tk3 := scan.NewValueToken(0, 0, scan.SymInteger, "50", 500)
+	tk3 := scan.NewValueToken(0, 0, sym.SymInteger, "50", 500)
 
 	tree := scan.NewAst()
 	if gotErr := tree.AddTokens(tk1, tk2, tk3); gotErr != nil {
@@ -30,10 +31,10 @@ func TestAddTokensGood(t *testing.T) {
 }
 
 func TestAddTokensBad(t *testing.T) {
-	tk0 := scan.NewValueToken(0, 0, scan.SymInteger, "200", 200)
+	tk0 := scan.NewValueToken(0, 0, sym.SymInteger, "200", 200)
-	tk1 := scan.NewValueToken(0, 0, scan.SymInteger, "100", 100)
+	tk1 := scan.NewValueToken(0, 0, sym.SymInteger, "100", 100)
-	tk2 := scan.NewToken(0, 0, scan.SymPlus, "+")
+	tk2 := scan.NewToken(0, 0, sym.SymPlus, "+")
-	tk3 := scan.NewValueToken(0, 0, scan.SymInteger, "50", 500)
+	tk3 := scan.NewValueToken(0, 0, sym.SymInteger, "50", 500)
 
 	wantErr := errors.New(`[0:0] two adjacent operators: "200" and "100"`)
 
@@ -44,7 +45,7 @@ func TestAddTokensBad(t *testing.T) {
 }
 
 func TestAddUnknownTokens(t *testing.T) {
-	tk0 := scan.NewToken(0, 0, scan.SymPercent, "%")
+	tk0 := scan.NewToken(0, 0, sym.SymPercent, "%")
 
 	wantErr := errors.New(`unexpected token "%"`)
 

t_bool_test.go

@@ -21,21 +21,21 @@ func TestBool(t *testing.T) {
 		/*   5 */ {`not "true"`, false, nil},
 		/*   6 */ {`not "false"`, false, nil},
 		/*   7 */ {`not ""`, true, nil},
-		/*   8 */ {`not []`, nil, errors.New(`[1:4] prefix/postfix operator "NOT" does not support operand '[]' [list]`)},
+		/*   8 */ {`not []`, nil, errors.New(`[1:4] prefix/postfix operator "NOT" does not support operand '[]' [array]`)},
 		/*   9 */ {`true and false`, false, nil},
-		/*  10 */ {`true and []`, nil, errors.New(`[1:9] left operand 'true' [bool] and right operand '[]' [list] are not compatible with operator "AND"`)},
+		/*  10 */ {`true and []`, nil, errors.New(`[1:9] left operand 'true' [bool] and right operand '[]' [array] are not compatible with operator "AND"`)},
-		/*  11 */ {`[] and false`, nil, errors.New(`[1:7] operator "AND" does not support operand '[]' [list] on its left side`)},
+		/*  11 */ {`[] and false`, nil, errors.New(`[1:7] operator "AND" does not support operand '[]' [array] on its left side`)},
 		/*  12 */ {`true or false`, true, nil},
 		/*  13 */ {`true or []`, true, nil},
-		/*  14 */ {`[] or false`, nil, errors.New(`got list as left operand type of 'OR' operator, it must be bool`)},
+		/*  14 */ {`[] or false`, nil, errors.New(`got array as left operand type of 'OR' operator, it must be bool`)},
 		/*  15 */ {`!true`, false, nil},
-		/*  13 */ //{`true or []`, nil, errors.New(`[1:8] left operand 'true' [bool] and right operand '[]' [list] are not compatible with operator "OR"`)},
+		/*  13 */ //{`true or []`, nil, errors.New(`[1:8] left operand 'true' [bool] and right operand '[]' [array] are not compatible with operator "OR"`)},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
 
 	// runTestSuiteSpec(t, section, inputs, 13)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestBoolNoShortcut(t *testing.T) {
@@ -48,13 +48,13 @@ func TestBoolNoShortcut(t *testing.T) {
 		/*   5 */ {`not "true"`, false, nil},
 		/*   6 */ {`not "false"`, false, nil},
 		/*   7 */ {`not ""`, true, nil},
-		/*   8 */ {`not []`, nil, `[1:4] prefix/postfix operator "NOT" does not support operand '[]' [list]`},
+		/*   8 */ {`not []`, nil, `[1:4] prefix/postfix operator "NOT" does not support operand '[]' [array]`},
 		/*   9 */ {`true and false`, false, nil},
-		/*  10 */ {`true and []`, nil, `[1:9] left operand 'true' [bool] and right operand '[]' [list] are not compatible with operator "AND"`},
+		/*  10 */ {`true and []`, nil, `[1:9] left operand 'true' [bool] and right operand '[]' [array] are not compatible with operator "AND"`},
-		/*  11 */ {`[] and false`, nil, `[1:7] left operand '[]' [list] and right operand 'false' [bool] are not compatible with operator "AND"`},
+		/*  11 */ {`[] and false`, nil, `[1:7] left operand '[]' [array] and right operand 'false' [bool] are not compatible with operator "AND"`},
 		/*  12 */ {`true or false`, true, nil},
-		/*  13 */ {`true or []`, nil, `[1:8] left operand 'true' [bool] and right operand '[]' [list] are not compatible with operator "OR"`},
+		/*  13 */ {`true or []`, nil, `[1:8] left operand 'true' [bool] and right operand '[]' [array] are not compatible with operator "OR"`},
-		/*  14 */ {`[] or false`, nil, `[1:6] left operand '[]' [list] and right operand 'false' [bool] are not compatible with operator "OR"`},
+		/*  14 */ {`[] or false`, nil, `[1:6] left operand '[]' [array] and right operand 'false' [bool] are not compatible with operator "OR"`},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
@@ -63,7 +63,7 @@ func TestBoolNoShortcut(t *testing.T) {
 	current := kern.SetCtrl(ctx, kern.ControlBoolShortcut, false)
 
 	// runCtxTestSuiteSpec(t, ctx, section, inputs, 1)
-	runCtxTestSuite(t, ctx, section, inputs)
+	RunCtxTestSuite(t, ctx, section, inputs)
 
 	kern.SetCtrl(ctx, kern.ControlBoolShortcut, current)
 }

t_builtin-base_test.go

@@ -7,7 +7,8 @@ package expr
 import (
 	"testing"
 
-	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 func TestFuncBase(t *testing.T) {
@@ -30,25 +31,25 @@ func TestFuncBase(t *testing.T) {
 		/*  14 */ {`isFloat(3.1)`, true, nil},
 		/*  15 */ {`isString("3.1")`, true, nil},
 		/*  16 */ {`isString("3" + 1)`, true, nil},
-		/*  17 */ {`isList(["3",  1])`, true, nil},
+		/*  17 */ {`isArray(["3",  1])`, true, nil},
 		/*  18 */ {`isDict({"a":"3",  "b":1})`, true, nil},
 		/*  19 */ {`isFract(1:3)`, true, nil},
 		/*  20 */ {`isFract(3:1)`, false, nil},
 		/*  21 */ {`isRational(3:1)`, true, nil},
-		/*  22 */ {`fract("2.2(3)")`, kern.NewFraction(67, 30), nil},
+		/*  22 */ {`fract("2.2(3)")`, fract.NewFraction(67, 30), nil},
-		/*  23 */ {`fract("1.21(3)")`, kern.NewFraction(91, 75), nil},
+		/*  23 */ {`fract("1.21(3)")`, fract.NewFraction(91, 75), nil},
-		/*  24 */ {`fract(1.21(3))`, kern.NewFraction(91, 75), nil},
+		/*  24 */ {`fract(1.21(3))`, fract.NewFraction(91, 75), nil},
-		/*  25 */ {`fract(1.21)`, kern.NewFraction(121, 100), nil},
+		/*  25 */ {`fract(1.21)`, fract.NewFraction(121, 100), nil},
-		/*  26 */ {`dec(2)`, float64(2), nil},
+		/*  26 */ {`float(2)`, float64(2), nil},
-		/*  27 */ {`dec(2.0)`, float64(2), nil},
+		/*  27 */ {`float(2.0)`, float64(2), nil},
-		/*  28 */ {`dec("2.0")`, float64(2), nil},
+		/*  28 */ {`float("2.0")`, float64(2), nil},
-		/*  29 */ {`dec(true)`, float64(1), nil},
+		/*  29 */ {`float(true)`, float64(1), nil},
-		/*  30 */ {`dec(true")`, nil, "[1:11] expected one of `,`, `)`, got `\"`"},
+		/*  30 */ {`float(true")`, nil, "[1:13] expected one of `,`, `)`, got `\"`"},
-		/*  31 */ {`dec()`, nil, `dec(): too few params -- expected 1, got 0`},
+		/*  31 */ {`float()`, nil, `float(): too few params -- expected 1, got 0`},
-		/*  32 */ {`dec(1,2,3)`, nil, `dec(): too many params -- expected 1, got 3`},
+		/*  32 */ {`float(1,2,3)`, nil, `float(): too many params -- expected 1, got 3`},
 		/*  33 */ {`isBool(false)`, true, nil},
-		/*  34 */ {`fract(1:2)`, kern.NewFraction(1, 2), nil},
+		/*  34 */ {`fract(1:2)`, fract.NewFraction(1, 2), nil},
-		/*  35 */ {`fract(12,2)`, kern.NewFraction(6, 1), nil},
+		/*  35 */ {`fract(12,2)`, fract.NewFraction(6, 1), nil},
 		/*  36 */ {`bool(2)`, true, nil},
 		/*  37 */ {`bool(1:2)`, true, nil},
 		/*  38 */ {`bool(1.0)`, true, nil},
@@ -58,9 +59,9 @@ func TestFuncBase(t *testing.T) {
 		/*  42 */ {`bool([])`, false, nil},
 		/*  43 */ {`bool({})`, false, nil},
 		/*  44 */ {`bool({1:"one"})`, true, nil},
-		/*  45 */ {`dec(false)`, float64(0), nil},
+		/*  45 */ {`float(false)`, float64(0), nil},
-		/*  46 */ {`dec(1:2)`, float64(0.5), nil},
+		/*  46 */ {`float(1:2)`, float64(0.5), nil},
-		/*  47 */ {`dec([1])`, nil, `dec(): can't convert list to float`},
+		/*  47 */ {`float([1])`, nil, `float(): can't convert array to float`},
 		/*  48 */ {`eval("a=3"); a`, int64(3), nil},
 		/*  49 */ {`int(5:2)`, int64(2), nil},
 
@@ -70,7 +71,7 @@ func TestFuncBase(t *testing.T) {
 	t.Setenv("EXPR_PATH", ".")
 
 	// runTestSuiteSpec(t, section, inputs, 49)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestFuncBaseString(t *testing.T) {
@@ -88,28 +89,29 @@ func TestFuncBaseString(t *testing.T) {
 	// t.Setenv("EXPR_PATH", ".")
 
 	// runTestSuiteSpec(t, section, inputs, 49)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestFuncBaseFraction(t *testing.T) {
 	section := "Builtin-Base-Fraction"
 
 	inputs := []inputType{
-		/*   1 */ {`fract(-0.5)`, kern.NewFraction(-1, 2), nil},
+		/*   1 */ {`fract(-0.5)`, fract.NewFraction(-1, 2), nil},
-		/*   2 */ {`fract("")`, (*kern.FractionType)(nil), `bad syntax`},
+		/*   2 */ {`fract("")`, (*fract.FractionType)(nil), `bad syntax`},
-		/*   3 */ {`fract("-1")`, kern.NewFraction(-1, 1), nil},
+		/*   3 */ {`fract("-1")`, fract.NewFraction(-1, 1), nil},
-		/*   4 */ {`fract("+1")`, kern.NewFraction(1, 1), nil},
+		/*   4 */ {`fract("+1")`, fract.NewFraction(1, 1), nil},
-		/*   5 */ {`fract("1a")`, (*kern.FractionType)(nil), `strconv.ParseInt: parsing "1a": invalid syntax`},
+		/*   5 */ {`fract("1a")`, (*fract.FractionType)(nil), `strconv.ParseInt: parsing "1a": invalid syntax`},
 		/*   6 */ {`fract(1,0)`, nil, `fract(): division by zero`},
 		/*   7 */ {`fract(5, "1")`, nil, `fract(): expected integer, got string ("1")`},
-		/*   8 */ {`fract(true)`, kern.NewFraction(1, 1), nil},
+		/*   8 */ {`fract(true)`, fract.NewFraction(1, 1), nil},
-		/*   9 */ {`fract(false)`, kern.NewFraction(0, 1), nil},
+		/*   9 */ {`fract(false)`, fract.NewFraction(0, 1), nil},
+		/*  10 */ {`1.2(3)`, fract.NewFraction(37, 30), nil},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
 
-	// runTestSuiteSpec(t, section, inputs, 8)
+	// RunTestSuiteSpec(t, section, inputs, 10)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestFuncBaseOthers(t *testing.T) {
@@ -118,10 +120,10 @@ func TestFuncBaseOthers(t *testing.T) {
 	inputs := []inputType{
 		/*   1 */ {`set("a", 3); a`, int64(3), nil},
 		/*   2 */ {`set(true, 3)`, nil, `set(): the "name" parameter must be a string, got a bool (true)`},
-		/*   3 */ {`seq(1,2,3)`, kern.NewLinkedListA(int64(1), int64(2), int64(3)), nil},
+		/*   3 */ {`seq(1,2,3)`, list.NewLinkedListA(int64(1), int64(2), int64(3)), nil},
 		// /*   4 */ {`seq(1,2,4)`, kern.NewLinkedListA(int64(1), int64(2), int64(3)), nil},
 	}
 
-	// runTestSuiteSpec(t, section, inputs, 4)
+	// RunTestSuiteSpec(t, section, inputs, 3)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }

t_builtin-fmt_test.go

@@ -24,7 +24,7 @@ func TestFuncFmt(t *testing.T) {
 	//t.Setenv("EXPR_PATH", ".")
 
 	// runTestSuiteSpec(t, section, inputs, 1)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestFmt(t *testing.T) {
@@ -41,7 +41,7 @@ func TestFmt(t *testing.T) {
 	ctx := NewSimpleStore()
 	currentStdout := kern.SetCtrl(ctx, kern.ControlStdout, &b)
 
-	runCtxTestSuite(t, ctx, section, inputs)
+	RunCtxTestSuite(t, ctx, section, inputs)
 
 	kern.SetCtrl(ctx, kern.ControlStdout, currentStdout)
 	if b.String() != text+"\n" {

t_builtin-import_test.go

@@ -20,5 +20,5 @@ func TestFuncImport(t *testing.T) {
 	t.Setenv("EXPR_PATH", "test-resources")
 
 	//runTestSuiteSpec(t, section, inputs, 1)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }

t_builtin-iterator_test.go

@@ -5,27 +5,102 @@
 package expr
 
 import (
+	"fmt"
+	"io"
+	"os"
 	"testing"
+
+	"git.portale-stac.it/go-pkg/expr/types/list"
+)
+
+const (
+	testFilePath = "/tmp/.go-test.txt"
 )
 
 func TestFuncRun(t *testing.T) {
 	section := "Builtin-Iterator"
 
 	inputs := []inputType{
-		/*   1 */ {`builtin "iterator"; it=$(1,2,3); run(it)`, nil, nil},
+		/*   1 */ {`builtin "iterator"; it=$(1,2,3); run(it)`, int64(3), nil},
 		/*   2 */ {`builtin "iterator"; run($(1,2,3), func(index,item){item+10})`, nil, nil},
-		/*   3 */ {`builtin "iterator"; run($(4), func(index,item){status=status+item; true}, {"status":0})`, int64(6), nil},
+		/*   3 */ {`builtin "iterator"; run($(..4), func(index,item){status=status+item; true}, {"status":0})`, int64(6), nil},
 		/*   4 */ {`builtin ["iterator", "fmt"]; run($(1,2,3), func(index,item){println(item+10)})`, nil, nil},
-		/*   5 */ {`builtin "iterator"; run(nil)`, nil, `paramter "iterator" must be an iterator, passed <nil> [nil]`},
+		/*   5 */ {`builtin "iterator"; run(nil)`, nil, `type of "iterator" must be iterator, passed <nil> [nil]`},
-		/*   6 */ {`builtin "iterator"; run($(1,2,3), nil)`, nil, nil},
+		/*   6 */ {`builtin "iterator"; run($(1,2,3), nil)`, int64(3), nil},
-		/*   7 */ {`builtin "iterator"; run($(1,2,3), func(){1}, "prrr")`, nil, `paramter "vars" must be a dictionary, passed prrr [string]`},
+		/*   7 */ {`builtin "iterator"; run($(1,2,3), func(){1}, "prrr")`, nil, `type of "vars" must be dict, passed prrr [string]`},
-		/*   8 */ {`builtin "iterator"; run($(1,2,3), operator=nil)`, nil, nil},
+		/*   8 */ {`builtin "iterator"; run($(1,2,3), operator=nil)`, int64(3), nil},
 		/*   9 */ {`builtin "iterator"; run($(1,2,3), operatorx=nil)`, nil, `run(): unknown param "operatorx"`},
-		/*   10 */ {`builtin ["os.file", "iterator"]; it = fileLineIterator("test-file.txt"); run(it)`, nil, nil},
+		/*  10 */ {`builtin "iterator"; op = func(index, item){ (index > 2) ? {abort("aborted")} :: {status="ok"} }; run($(..5), op)`, "aborted", nil},
+		/*  11 */ {`builtin "iterator"; op = func(index, item){ (index > 2) ? {abort("aborted")} :: {status="ok"} }; run($(..1), op)`, "ok", nil},
+	}
+	//t.Setenv("EXPR_PATH", ".")
+
+	// RunTestSuiteSpec(t, section, inputs, 10)
+	RunTestSuite(t, section, inputs)
+
+	cleanupBuiltinIterator()
+}
+
+func TestFuncOsLineIter(t *testing.T) {
+	section := "Builtin-OS-File-Line-Iter"
+	inputs := []inputType{
+		/*  1 */ {fmt.Sprintf(`builtin ["os.file", "iterator"]; it = fileLineIterator(%q); run(it)`, testFilePath), int64(2), nil},
+		/*  2 */ {fmt.Sprintf(`builtin "os.file"; it=fileLineIterator(%q); it++`, testFilePath), "uno", nil},
+		/*  3 */ {fmt.Sprintf(`builtin "os.file"; it=fileLineIterator(%q); it++;it++;it++`, testFilePath), nil, io.EOF.Error()},
+		/*  4 */ {fmt.Sprintf(`builtin "os.file"; it=fileLineIterator(%q); it.clean`, testFilePath), nil, nil},
+		/*  5 */ {fmt.Sprintf(`builtin "os.file"; it=fileLineIterator(%q); string(it)`, testFilePath),
+			fmt.Sprintf(`$(fileLineIterator@%q)`, testFilePath), nil},
+		/*  6 */ {fmt.Sprintf(`builtin "os.file"; #$$(fileLineIterator(%q) filter (#${_} == 2))`, testFilePath), int64(0), nil},
+		/*  7 */ {fmt.Sprintf(`builtin "os.file"; #$$(fileLineIterator(%q) filter (#${_} == 3))`, testFilePath), int64(2), nil},
+		/*  8 */ {fmt.Sprintf(`builtin "os.file"; $$(fileLineIterator(%q) map ${__})`, testFilePath), list.NewLinkedListA(0, 1), nil},
+	}
+
+	if err := setupBuiltinIterator(); err != nil {
+		t.Error(err)
+		return
+	}
+
+	// RunTestSuiteSpec(t, section, inputs, 1)
+	RunTestSuite(t, section, inputs)
+
+	cleanupBuiltinIterator()
+}
+
+func TestFuncOsByteIter(t *testing.T) {
+	section := "Builtin-OS-File-Byte-Iter"
+	inputs := []inputType{
+		/*   1 */ {fmt.Sprintf(`builtin "os.file"; it=fileByteIterator(%q); string(it)`, testFilePath),
+			fmt.Sprintf(`$(fileByteIterator@%q)`, testFilePath), nil},
+		/*   2 */ {fmt.Sprintf(`builtin ["os.file", "string"]; it=fileByteIterator(%q); char(it++)`, testFilePath), `u`, nil},
+		/*   3 */ {fmt.Sprintf(`builtin ["os.file", "string"]; it=fileByteIterator(%q); it++; it.reset; char(it++)`, testFilePath), `u`, nil},
+	}
+
+	if err := setupBuiltinIterator(); err != nil {
+		t.Error(err)
+		return
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
 
-	// runTestSuiteSpec(t, section, inputs, 3)
+	// RunTestSuiteSpec(t, section, inputs, 24)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
+
+	cleanupBuiltinIterator()
+}
+
+func setupBuiltinIterator() (err error) {
+	var fh *os.File
+	// Create test file
+	if fh, err = os.Create(testFilePath); err == nil {
+		defer fh.Close()
+		fmt.Fprintln(fh, "uno")
+		fmt.Fprintln(fh, "due")
+	}
+	return
+}
+
+func cleanupBuiltinIterator() {
+	if fileExists(testFilePath) {
+		os.Remove(testFilePath)
+	}
 }

t_builtin-math-arith_test.go

@@ -29,5 +29,5 @@ func TestFuncMathArith(t *testing.T) {
 	// t.Setenv("EXPR_PATH", ".")
 
 	//runTestSuiteSpec(t, section, inputs, 10)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }

t_builtin-os-file_test.go

@@ -5,10 +5,13 @@
 package expr
 
 import (
-	"io"
 	"testing"
 )
 
+// const (
+// 	builtinOsFile_dummyFile = "/tmp/.go-test_dummy.txt"
+// )
+
 func TestFuncOs(t *testing.T) {
 	section := "Builtin-OS-File"
 	inputs := []inputType{
@@ -27,30 +30,29 @@ func TestFuncOs(t *testing.T) {
 		/*  13 */ {`builtin "os.file"; handle=fileClose(123)`, nil, `fileClose(): invalid file handle`},
 		/*  14 */ {`builtin "os.file"; handle=fileOpen("/tmp/dummy"); c=fileReadTextAll(handle); fileClose(handle); c`, "bye-bye", nil},
 		/*  15 */ {`builtin "os.file"; c=fileReadTextAll(123)`, nil, `fileReadTextAll(): invalid file handle 123 [int64]`},
-		/*  16 */ {`builtin "os.file"; it=fileLineIterator("test-file.txt"); it++`, "uno", nil},
+		/*  16 */ {`builtin "os.file"; handle=fileOpen("/etc/hosts"); fileClose(handle); string(handle)`, `reader`, nil},
-		/*  17 */ {`builtin "os.file"; it=fileLineIterator("test-file.txt"); it++;it++;it++`, nil, io.EOF.Error()},
+		/*  17 */ {`builtin "os.file"; handle=fileCreate("/tmp/dummy"); fileClose(handle); string(handle)`, `writer`, nil},
-		/*  18 */ {`builtin "os.file"; it=fileLineIterator("test-file.txt"); it.clean`, nil, nil},
-		/*  19 */ {`builtin "os.file"; it=fileLineIterator("test-file.txt"); string(it)`, `$(fileLineIterator@"test-file.txt")`, nil},
-		/*  20 */ {`builtin "os.file"; handle=fileOpen("/etc/hosts"); fileClose(handle); string(handle)`, `reader`, nil},
-		/*  21 */ {`builtin "os.file"; handle=fileCreate("/tmp/dummy"); fileClose(handle); string(handle)`, `writer`, nil},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
 
-	// runTestSuiteSpec(t, section, inputs, 24)
+	// RunTestSuiteSpec(t, section, inputs, 17)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
-func TestFuncOsByteIter(t *testing.T) {
+// func setupBuiltinOsFile() (err error) {
-	section := "Builtin-OS-File-Byte-Iter"
+// 	var fh *os.File
-	inputs := []inputType{
+// 	// Create test file
-		/*   1 */ {`builtin "os.file"; it=fileByteIterator("test-file.txt"); string(it)`, `$(fileByteIterator@"test-file.txt")`, nil},
+// 	if fh, err = os.Create(builtinOsFile_dummyFile); err == nil {
-		/*   2 */ {`builtin ["os.file", "string"]; it=fileByteIterator("test-file.txt"); char(it++)`, `u`, nil},
+// 		defer fh.Close()
-		/*   3 */ {`builtin ["os.file", "string"]; it=fileByteIterator("test-file.txt"); it++; it.reset; char(it++)`, `u`, nil},
+// 		fmt.Fprintln(fh, "uno")
-	}
+// 		fmt.Fprintln(fh, "due")
+// 	}
+// 	return
+// }
 
-	// t.Setenv("EXPR_PATH", ".")
+// func cleanupBuiltinOsFile() {
-
+// 	if fileExists(builtinOsFile_dummyFile) {
-	// runTestSuiteSpec(t, section, inputs, 24)
+// 		os.Remove(builtinOsFile_dummyFile)
-	runTestSuite(t, section, inputs)
+// 	}
-}
+// }

t_builtin-string_test.go

@@ -7,7 +7,7 @@ package expr
 import (
 	"testing"
 
-	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/array"
 )
 
 func TestFuncString(t *testing.T) {
@@ -30,7 +30,7 @@ func TestFuncString(t *testing.T) {
 		/*  14 */ {`builtin "string"; strEndsWith("0123456789", "xyz", "789")`, true, nil},
 		/*  15 */ {`builtin "string"; strEndsWith("0123456789", "xyz", "0125")`, false, nil},
 		/*  16 */ {`builtin "string"; strEndsWith("0123456789")`, nil, `strEndsWith(): too few params -- expected 2 or more, got 1`},
-		/*  17 */ {`builtin "string"; strSplit("one-two-three", "-")`, kern.NewListA("one", "two", "three"), nil},
+		/*  17 */ {`builtin "string"; strSplit("one-two-three", "-")`, array.NewArrayA("one", "two", "three"), nil},
 		/*  18 */ {`builtin "string"; strJoin("-", [1, "two", "three"])`, nil, `strJoin(): expected string, got integer (1)`},
 		/*  19 */ {`builtin "string"; strJoin()`, nil, `strJoin(): too few params -- expected 1 or more, got 0`},
 		/*  20 */ {`builtin "string"; strUpper("StOp")`, "STOP", nil},
@@ -52,7 +52,7 @@ func TestFuncString(t *testing.T) {
 		    	isFloat(any) -> boolean,
 		    	isFract(any) -> boolean,
 		    	isInt(any) -> boolean,
-		    	isList(any) -> boolean,
+		    	isArray(any) -> boolean,
 		    	isNil(any) -> boolean,
 		    	isString(any) -> boolean,
 		    	joinStr(separator, item="" ...) -> string,
@@ -68,5 +68,5 @@ func TestFuncString(t *testing.T) {
 	//t.Setenv("EXPR_PATH", ".")
 
 	// runTestSuiteSpec(t, section, inputs, 19)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }

t_common_test.go

@@ -6,6 +6,9 @@ package expr
 
 import (
 	"errors"
+	"os"
+	"path"
+	"runtime"
 	"strings"
 	"testing"
 
@@ -19,9 +22,27 @@ type inputType struct {
 	wantErr    any
 }
 
-func runCtxTestSuiteSpec(t *testing.T, ctx kern.ExprContext, section string, inputs []inputType, spec ...int) {
+func getSourceName(startFrame int) (sourcename string) {
+	for i := startFrame; i < 10; i++ {
+		_, sourcepath, _, ok := runtime.Caller(i)
+		if !ok {
+			break
+		}
+		sourcename = path.Base(sourcepath)
+		if sourcename != "t_common_test.go" {
+			break
+		}
+	}
+	return
+}
+
+func RunCtxTestSuiteSpec(t *testing.T, ctx kern.ExprContext, section string, inputs []inputType, spec ...int) {
 	succeeded := 0
 	failed := 0
+
+	sourcename := getSourceName(2)
+	t.Logf("Test suite %s from file %s", section, sourcename)
+
 	for _, count := range spec {
 		index := count - 1
 		if index >= 0 && index < len(inputs) {
@@ -40,15 +61,19 @@ func runCtxTestSuiteSpec(t *testing.T, ctx kern.ExprContext, section string, inp
 	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(spec), succeeded, failed)
 }
 
-func runTestSuiteSpec(t *testing.T, section string, inputs []inputType, spec ...int) {
+func RunTestSuiteSpec(t *testing.T, section string, inputs []inputType, spec ...int) {
-	runCtxTestSuiteSpec(t, nil, section, inputs, spec...)
+	RunCtxTestSuiteSpec(t, nil, section, inputs, spec...)
 }
 
-func runCtxTestSuite(t *testing.T, ctx kern.ExprContext, section string, inputs []inputType) {
+func RunCtxTestSuite(t *testing.T, ctx kern.ExprContext, section string, inputs []inputType) {
 
 	succeeded := 0
 	failed := 0
 
+	sourcename := getSourceName(2)
+
+	t.Logf("Test suite %s from file %s", section, sourcename)
+
 	for i, input := range inputs {
 		// fmt.Printf("%3d: %s\n", i+1, input.source)
 
@@ -61,8 +86,8 @@ func runCtxTestSuite(t *testing.T, ctx kern.ExprContext, section string, inputs
 	}
 	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(inputs), succeeded, failed)
 }
-func runTestSuite(t *testing.T, section string, inputs []inputType) {
+func RunTestSuite(t *testing.T, section string, inputs []inputType) {
-	runCtxTestSuite(t, nil, section, inputs)
+	RunCtxTestSuite(t, nil, section, inputs)
 }
 
 func getWantedError(input *inputType) error {
@@ -98,14 +123,21 @@ func doTest(t *testing.T, ctx kern.ExprContext, section string, input *inputType
 		gotResult, gotErr = ast.Eval(ctx)
 	}
 
+	if gotErr == nil {
+		if wantErr == nil {
 			eq := kern.Equal(gotResult, input.wantResult)
 
 			if !eq /*gotResult != input.wantResult*/ {
 				t.Errorf(">>>%s/%d: `%s` -> result = %v [%s], want = %v [%s]", section, count, input.source, gotResult, kern.TypeName(gotResult), input.wantResult, kern.TypeName(input.wantResult))
 				good = false
 			}
+		} else {
+			t.Errorf(">>>%s/%d: `%s` -> result = %v [%s], got-err = <nil>, expected-err = %v", section, count, input.source, gotResult, kern.TypeName(gotResult), wantErr)
+			good = false
+		}
+	}
 
-	if gotErr != wantErr {
+	if good && gotErr != wantErr {
 		if wantErr == nil || gotErr == nil || (gotErr.Error() != wantErr.Error()) {
 			t.Errorf(">>>%s/%d: %s -> got-err = <%v>, expected-err = <%v>", section, count, input.source, gotErr, wantErr)
 			good = false
@@ -145,3 +177,10 @@ func testIteratorCallOp(t *testing.T, section string, it kern.Iterator) {
 		t.Errorf(`%s -- CallOperation("fake") should return error`, section)
 	}
 }
+
+// Test utilities
+
+func fileExists(filePath string) bool {
+	_, err := os.Stat(filePath)
+	return !errors.Is(err, os.ErrNotExist)
+}

t_context_test.go

@@ -7,7 +7,7 @@ package expr
 import (
 	"testing"
 
-	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 func TestCtrlSet(t *testing.T) {
@@ -82,12 +82,12 @@ func TestList(t *testing.T) {
 	section := "Context"
 
 	inputs := []inputType{
-		/*  1 */ {`$$(5)`, kern.NewLinkedListA(5), nil},
+		/*  1 */ {`$$(5)`, list.NewLinkedListA(5), nil},
-		/*  2 */ {`$$($(2))`, kern.NewLinkedListA(0, 1), nil},
+		/*  2 */ {`$$($(..2))`, list.NewLinkedListA(0, 1), nil},
 		/*  3 */ {`string(($$global).funcs.bool)`, `bool(value):boolean{}`, nil},
 	}
 
 	// runTestSuiteSpec(t, section, inputs, 3)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 
 }

t_dict_test.go

@@ -11,44 +11,63 @@ import (
 
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/sym"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 func TestDictParser(t *testing.T) {
 	section := "Dict"
 
 	inputs := []inputType{
-		/*  1 */ {`{}`, kern.NewDict(nil), nil},
+		/*  1 */ {`{}`, dict.NewDict(nil), nil},
 		/*  2 */ {`{123}`, nil, errors.New("[1:6] expected `:`, got `}`")},
-		/*  3 */ {`{1:"one",2:"two",3:"three"}`, kern.NewDict(map[any]any{int64(1): "one", int64(2): "two", int64(3): "three"}), nil},
+		/*  3 */ {`{1:"one",2:"two",3:"three"}`, dict.NewDict(map[any]any{int64(1): "one", int64(2): "two", int64(3): "three"}), nil},
 		/*  4 */ {`{1:"one",2:"two",3:"three"}[3]`, "three", nil},
 		/*  5 */ {`#{1:"one",2:"two",3:"three"}`, int64(3), nil},
-		/*  6 */ {`{1:"one"} + {2:"two"}`, kern.NewDict(map[any]any{int64(1): "one", int64(2): "two"}), nil},
+		/*  6 */ {`{1:"one"} + {2:"two"}`, dict.NewDict(map[any]any{int64(1): "one", int64(2): "two"}), nil},
 		/*  7 */ {`2 in {1:"one", 2:"two"}`, true, nil},
-		/*  8 */ {`D={"a":1, "b":2}; D["a"]=9; D`, kern.NewDict(map[any]any{"a": int64(9), "b": int64(2)}), nil},
+		/*  8 */ {`D={"a":1, "b":2}; D["a"]=9; D`, dict.NewDict(map[any]any{"a": int64(9), "b": int64(2)}), nil},
-		/*  9 */ {`D={"a":1, "b":2}; D["z"]=9; D`, kern.NewDict(map[any]any{"z": int64(9), "a": int64(1), "b": int64(2)}), nil},
+		/*  9 */ {`D={"a":1, "b":2}; D["z"]=9; D`, dict.NewDict(map[any]any{"z": int64(9), "a": int64(1), "b": int64(2)}), nil},
 		/* 10 */ {`D={"a":1, "b":2}; D[nil]=9`, nil, errors.New(`[1:21] index/key is nil`)},
 		/* 11 */ {`D={"a":1, "b":2}; D["a"]`, int64(1), nil},
 		/* 12 */ {`m={
 			"a":1,
 			//"b":2,
 			"c":3
-			}`, kern.NewDict(map[any]any{"a": int64(1), "c": int64(3)}), nil},
+			}`, dict.NewDict(map[any]any{"a": int64(1), "c": int64(3)}), nil},
 		/* 13 */ {`D={"a":1, "b":2}; D."a"`, int64(1), nil},
 		/* 14 */ {`D={"a":1, "b":2}; D.a`, int64(1), nil},
 		/* 15 */ {`D={1:"a", 2:"b", 3:"c"}; D.(1+2)`, "c", nil},
 		/* 16 */ {`D={1:"a"}; D.2`, nil, `[1:15] key 2 not found`},
 		/* 17 */ {`D={1:"a"}; D."2"`, nil, `[1:17] key "2" not found`},
 		/* 18 */ {`D={"a":1, "b":2}; D.a = 10; D.a`, int64(10), nil},
-		/* 19 */ {`k="a"; D={k: 10}`, kern.NewDict(map[any]any{"a": int64(10)}), nil},
+		/* 19 */ {`k="a"; D={k: 10}`, dict.NewDict(map[any]any{"a": int64(10)}), nil},
 		/* 20 */ {`k=[<1,2>]; D={k: 10}`, nil, `[1:16] dict key can be integer or string, got lisked-list`},
 		/* 21 */ {`f=func(n){"x"+n}; d{f(5):10}`, nil, `[0:0] two adjacent operators: "d" and "{}"`},
-		/* 22 */ {`f=func(n){"x"+n}; d={f(5):10}`, kern.NewDict(map[any]any{"x5": int64(10)}), nil},
+		/* 22 */ {`f=func(n){"x"+n}; d={f(5):10}`, dict.NewDict(map[any]any{"x5": int64(10)}), nil},
 		/* 23 */ {`f=func(n){"x"+n}; d={f(5); "z":10}`, nil, "[1:27] expected one of  `:`, `}`, got `;`"},
-		/* 24 */ {`f=func(n){"x"+n}; d={f(5) but "z":10}`, kern.NewDict(map[any]any{"z": int64(10)}), nil},
+		/* 24 */ {`f=func(n){"x"+n}; d={f(5) but "z":10}`, dict.NewDict(map[any]any{"z": int64(10)}), nil},
+		/* 25 */ {`3 in {1:"one", 2:"two"}`, false, nil},
+		/* 26 */ {`1 at {"a":2, "b":3, "c":1}`, "c", nil},
+		/* 27 */ {`10 at {"a":2, "b":3, "c":1}`, nil, nil},
 	}
 
-	// runTestSuiteSpec(t, section, inputs, 23, 24)
+	// RunTestSuiteSpec(t, section, inputs, 1)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
+}
+
+func TestOperations(t *testing.T) {
+	section := "Dict-Operations"
+	inputs := []inputType{
+		/*   1 */ {`{"a":1} + {"b":2}`, dict.NewDict(map[any]any{"a": int64(1), "b": int64(2)}), nil},
+		/*   2 */ {`D={"a":1}; C={"b":2}; X=D+C; C."b" = 3; X`, dict.NewDict(map[any]any{"a": int64(1), "b": int64(2)}), nil},
+		/*   3 */ {`D={"a":1}; C={"b":2}; X=D+C; D."a" = 3; X`, dict.NewDict(map[any]any{"a": int64(1), "b": int64(2)}), nil},
+		/*   4 */ {`L=[8,9]; D={"a":L}; L[0]=11; D."a"[0]`, int64(11), nil},
+		/*   5 */ {`L=[8,9]; D:={"a":L}; L[0]=11; D."a"[0]`, int64(8), nil},
+	}
+	// runTestSuiteSpec(t, section, inputs, 1)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestAccessSubFields(t *testing.T) {
@@ -56,9 +75,9 @@ func TestAccessSubFields(t *testing.T) {
 	ctx := NewSimpleStore()
 	ctx.UnsafeSetVar(
 		"D",
-		kern.NewDict(map[any]any{
+		dict.NewDict(map[any]any{
-			"a": kern.NewDict(map[any]any{"uno": int64(10)}),
+			"a": dict.NewDict(map[any]any{"uno": int64(10)}),
-			"b": kern.NewListA(1, 2, 3),
+			"b": list.NewLinkedListA(1, 2, 3),
 		}),
 	) // D={"a": {"uno":1}}
 
@@ -67,9 +86,21 @@ func TestAccessSubFields(t *testing.T) {
 		/* 2 */ {`D.a.uno = 111; D.a."uno"`, int64(111), nil},
 		/* 3 */ {`D.a.uno = 111; D["a"]["uno"]`, int64(111), nil},
 		/* 4 */ {`D.b[1] = 22; D["b"][1]`, int64(22), nil},
+		// /* 4 */ {`D.b[1] = 22; D["b"][1]`, nil, `[1:3] collection expected`},
 	}
-	// runCtxTestSuiteSpec(t, ctx, section, inputs, 4)
+	RunCtxTestSuiteSpec(t, ctx, section, inputs, 4)
-	runCtxTestSuite(t, ctx, section, inputs)
+	// runCtxTestSuite(t, ctx, section, inputs)
+}
+
+func TestDictDeepAssign(t *testing.T) {
+	section := "Dict-DeepAssign"
+	inputs := []inputType{
+		/*   1 */ {`DD={"uno": 1, "due": 2}; D=DD; D["uno"]=11; DD`, dict.NewDict(map[any]any{"uno": int64(11), "due": int64(2)}), nil},
+		/*   2 */ {`DD={"uno": 1, "due": 2}; D:=DD; D["uno"]=11; DD`, dict.NewDict(map[any]any{"uno": int64(1), "due": int64(2)}), nil},
+	}
+
+	// runTestSuiteSpec(t, section, inputs, 4)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestDictToStringMultiLine(t *testing.T) {
@@ -79,9 +110,9 @@ func TestDictToStringMultiLine(t *testing.T) {
   "first": 1
 }`
 	args := map[any]any{
-		"first": newLiteralTerm(scan.NewValueToken(0, 0, scan.SymInteger, "1", 1)),
+		"first": newLiteralTerm(scan.NewValueToken(0, 0, sym.SymInteger, "1", 1)),
 	}
-	dict := kern.NewDict(args)
+	dict := dict.NewDict(args)
 	got := dict.ToString(kern.MultiLine)
 	// fmt.Printf("got=%q\n", got)
 
@@ -101,9 +132,9 @@ func TestDictToString(t *testing.T) {
 	section := "dict-ToString-SL"
 	want := `{"first": 1}`
 	args := map[any]any{
-		"first": newLiteralTerm(scan.NewValueToken(0, 0, scan.SymInteger, "1", 1)),
+		"first": newLiteralTerm(scan.NewValueToken(0, 0, sym.SymInteger, "1", 1)),
 	}
-	dict := kern.NewDict(args)
+	dict := dict.NewDict(args)
 	got := dict.ToString(0)
 	// fmt.Printf("got=%q\n", got)
 

t_expr_test.go

@@ -7,7 +7,7 @@ package expr
 import (
 	"testing"
 
-	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/dict"
 )
 
 func TestExpr(t *testing.T) {
@@ -16,23 +16,26 @@ func TestExpr(t *testing.T) {
 	inputs := []inputType{
 		/*   1 */ {`0?{}`, nil, nil},
 		/*   2 */ {`fact=func(n){(n)?{1}::{n*fact(n-1)}}; fact(5)`, int64(120), nil},
-		/*   3 */ {`builtin "os.file"; f=fileOpen("test-file.txt"); line=fileReadText(f); fileClose(f); line`, "uno", nil},
+		/*   3 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
-		/*   4 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
+		/*   4 */ {`1 ? {1} : [1+0] {3*(1+1)}`, int64(6), nil},
-		/*   5 */ {`1 ? {1} : [1+0] {3*(1+1)}`, int64(6), nil},
+		/*   5 */ {`a=3; a+=1; a`, int64(4), nil},
-		/*   6 */ {`a=3; a+=1; a`, int64(4), nil},
+		/*   6 */ {`a=3; a-=1; a`, int64(2), nil},
-		/*   7 */ {`a=3; a-=1; a`, int64(2), nil},
+		/*   7 */ {`a=3; a*=2; a`, int64(6), nil},
-		/*   8 */ {`a=3; a*=2; a`, int64(6), nil},
+		/*   8 */ {`v=[10,20,30]; v[0]+=1; v[0]`, int64(11), nil},
-		/*   9 */ {`v=[10,20,30]; v[0]+=1; v[0]`, int64(11), nil},
+		/*   9 */ {`r={"a":10}; r["a"]+=1; r["a"]`, int64(11), nil},
-		/*  10 */ {`r={"a":10}; r["a"]+=1; r["a"]`, int64(11), nil},
+		/*  10 */ {`a=3; a/=2`, int64(1), nil},
-		/*  11 */ {`a=3; a/=2`, int64(1), nil},
+		/*  11 */ {`*=2`, nil, `[1:2] infix operator "*=" requires two non-nil operands, got 1`},
-		/*  12 */ {`*=2`, nil, `[1:2] infix operator "*=" requires two non-nil operands, got 1`},
+		/*  12 */ {`a=3; a*=2+1; a`, int64(9), nil},
-		/*  13 */ {`a=3; a*=2+1; a`, int64(9), nil},
+		/*  13 */ {`a=3; (a*=2)+1; a`, int64(6), nil},
-		/*  14 */ {`a=3; (a*=2)+1; a`, int64(6), nil},
+		/*  14 */ {`a=3; a*=2)+1; a`, nil, `[1:11] unexpected token ")"`},
-		/*  15 */ {`a=3; a*=2)+1; a`, nil, `[1:11] unexpected token ")"`},
+		/*  15 */ {`v=[2]; a=1; v[a-=1]=5; v[0]`, int64(5), nil},
-		/*  16 */ {`v=[2]; a=1; v[a-=1]=5; v[0]`, int64(5), nil},
+		/*  16 */ {`true ? {"a"} :: {"b"}`, "a", nil},
-		/*  17 */ {`true ? {"a"} :: {"b"}`, "a", nil},
+		/*  17 */ {`2 ? {"a"}`, nil, `[1:2] no case catches the value (2) of the selection expression`},
-		/*  18 */ {`$$`, kern.NewDict(map[any]any{"vars": kern.NewDict(nil), "funcs": kern.NewDict(nil)}), nil},
+		/*  18 */ {`2 ? 5`, nil, "[1:6] expected `{`, got `5`"},
-		/*  19 */ {`
+		/*  19 */ {`a=2; ${a}`, int64(2), nil},
+		/*  20 */ {`$_=2; $_`, int64(2), nil},
+		/*  21 */ {`$$`, dict.NewDict(map[any]any{"vars": dict.NewDict(nil), "funcs": dict.NewDict(nil)}), nil},
+		/*  22 */ {`
 		ds={
 			"init":func(@end){@current=0 but true},
 			//"current":func(){current},
@@ -44,11 +47,9 @@ func TestExpr(t *testing.T) {
 		it++;
 		it++
 `, int64(1), nil},
-		/*  20 */ {`a=2; ${a}`, int64(2), nil},
-		/*  21 */ {`$_=2; $_`, int64(2), nil},
 	}
 	// t.Setenv("EXPR_PATH", ".")
 
-	// runTestSuiteSpec(t, section, inputs, 21)
+	// RunTestSuiteSpec(t, section, inputs, 19)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }

t_fractions_test.go

@@ -8,37 +8,38 @@ import (
 	"testing"
 
 	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/fract"
 )
 
 func TestFractionsParser(t *testing.T) {
 	section := "Fraction"
 	inputs := []inputType{
-		/*   1 */ {`1:2`, kern.NewFraction(1, 2), nil},
+		/*   1 */ {`1:2`, fract.NewFraction(1, 2), nil},
-		/*   2 */ {`1:2 + 1`, kern.NewFraction(3, 2), nil},
+		/*   2 */ {`1:2 + 1`, fract.NewFraction(3, 2), nil},
-		/*   3 */ {`1:2 - 1`, kern.NewFraction(-1, 2), nil},
+		/*   3 */ {`1:2 - 1`, fract.NewFraction(-1, 2), nil},
-		/*   4 */ {`1:2 * 1`, kern.NewFraction(1, 2), nil},
+		/*   4 */ {`1:2 * 1`, fract.NewFraction(1, 2), nil},
-		/*   5 */ {`1:2 * 2:3`, kern.NewFraction(2, 6), nil},
+		/*   5 */ {`1:2 * 2:3`, fract.NewFraction(2, 6), nil},
-		/*   6 */ {`1:2 / 2:3`, kern.NewFraction(3, 4), nil},
+		/*   6 */ {`1:2 / 2:3`, fract.NewFraction(3, 4), nil},
 		/*   7 */ {`1:"5"`, nil, `denominator must be integer, got string (5)`},
 		/*   8 */ {`"1":5`, nil, `numerator must be integer, got string (1)`},
-		/*   9 */ {`1:+5`, kern.NewFraction(1, 5), nil},
+		/*   9 */ {`1:+5`, fract.NewFraction(1, 5), nil},
-		/*  10 */ {`1:(-2)`, kern.NewFraction(-1, 2), nil},
+		/*  10 */ {`1:(-2)`, fract.NewFraction(-1, 2), nil},
-		/*  11 */ {`builtin "math.arith"; add(1:2, 2:3)`, kern.NewFraction(7, 6), nil},
+		/*  11 */ {`builtin "math.arith"; add(1:2, 2:3)`, fract.NewFraction(7, 6), nil},
 		/*  12 */ {`builtin "math.arith"; add(1:2, 1.0, 2)`, float64(3.5), nil},
-		/*  13 */ {`builtin "math.arith"; mul(1:2, 2:3)`, kern.NewFraction(2, 6), nil},
+		/*  13 */ {`builtin "math.arith"; mul(1:2, 2:3)`, fract.NewFraction(2, 6), nil},
 		/*  14 */ {`builtin "math.arith"; mul(1:2, 1.0, 2)`, float64(1.0), nil},
 		/*  15 */ {`1:0`, nil, `[1:3] division by zero`},
 		/*  16 */ {`1+1:2+0.5`, float64(2), nil},
 		/*  17 */ {`1:(2-2)`, nil, `[1:3] division by zero`},
-		/*  18 */ {`[0,1][1-1]:1`, kern.NewFraction(0, 1), nil},
+		/*  18 */ {`[0,1][1-1]:1`, fract.NewFraction(0, 1), nil},
 		/*  19 */ {`1:2 == 0.5`, true, nil},
 	}
 	// runTestSuiteSpec(t, section, inputs, 26)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestFractionToStringSimple(t *testing.T) {
-	source := kern.NewFraction(1, 2)
+	source := fract.NewFraction(1, 2)
 	want := "1:2"
 	got := source.ToString(0)
 	if got != want {
@@ -47,7 +48,7 @@ func TestFractionToStringSimple(t *testing.T) {
 }
 
 func TestFractionToStringMultiline(t *testing.T) {
-	source := kern.NewFraction(1, 2)
+	source := fract.NewFraction(1, 2)
 	want := "1\n-\n2"
 	got := source.ToString(kern.MultiLine)
 	if got != want {
@@ -56,7 +57,7 @@ func TestFractionToStringMultiline(t *testing.T) {
 }
 
 func TestToStringMultilineTty(t *testing.T) {
-	source := kern.NewFraction(-1, 2)
+	source := fract.NewFraction(-1, 2)
 	want := "\x1b[4m-1\x1b[0m\n 2"
 	got := source.ToString(kern.MultiLine | kern.TTY)
 	if got != want {

t_funcs_test.go

@@ -46,7 +46,7 @@ func TestFuncs(t *testing.T) {
 	// t.Setenv("EXPR_PATH", ".")
 
 	//runTestSuiteSpec(t, section, inputs, 19)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func TestFuncs2(t *testing.T) {
@@ -57,7 +57,7 @@ func TestFuncs2(t *testing.T) {
 		/*   3 */ {`builtin "iterator"; times=func(a,b){a*b}; run($(["1", "2", "3"]), times)`, nil, `operator(): missing params -- a, b`},
 	}
 	// runTestSuiteSpec(t, section, inputs, 4)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }
 
 func dummy(ctx kern.ExprContext, name string, args map[string]any) (result any, err error) {
@@ -102,6 +102,6 @@ func TestGoFunction(t *testing.T) {
 		kern.NewFuncParamFlagDef("name", kern.PfOptional|kern.PfDefault, "Celestino Amoroso"),
 	})
 
-	runCtxTestSuite(t, ctx, section, inputs)
+	RunCtxTestSuite(t, ctx, section, inputs)
 
 }

t_index_test.go

@@ -7,24 +7,48 @@ package expr
 import (
 	"testing"
 
-	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/list"
 )
 
 func TestCollections(t *testing.T) {
 	section := "Index"
 	inputs := []inputType{
-		/*   1 */ {`"abcdef"[1:3]`, "bc", nil},
+		/*   1 */ {`"abcdef"[1..3]`, "bc", nil},
-		/*   2 */ {`"abcdef"[:3]`, "abc", nil},
+		/*   2 */ {`"abcdef"[..3]`, "abc", nil},
-		/*   3 */ {`"abcdef"[1:]`, "bcdef", nil},
+		/*   3 */ {`"abcdef"[1..]`, "bcdef", nil},
-		/*   4 */ {`"abcdef"[:]`, "abcdef", nil},
+		/*   4 */ {`"abcdef"[..]`, "abcdef", nil},
-		/*   5 */ {`"abcdef"[1:2:3]`, nil, `[1:14] invalid range specification`},
+		/*   5 */ {`"abcdef"[1..2..3]`, `b`, nil},
-		/*   6 */ {`"abcdef"[((1>0)?{1}:{0}):3]`, "bc", nil},
+		/*   6 */ {`"abcdef"[((1>0)?{1}:{0})..3]`, "bc", nil},
-		/*   7 */ {`"abcdef"[[0,1][0]:1]`, "a", nil},
+		/*   7 */ {`"abcdef"[[0,1][0]..1]`, "a", nil},
-		/*   8 */ {`[0,1,2,3,4][:]`, kern.NewListA(int64(0), int64(1), int64(2), int64(3), int64(4)), nil},
+		/*   8 */ {`"abcdef"[..1]`, "a", nil},
+		/*   9 */ {`"abcdef"[..-1]`, "abcde", nil},
+		/*  10 */ {`"abcdef"[..-1..2]`, "ace", nil},
+		/*  11 */ {`"abcdef"[-3..-1..2]`, "d", nil},
+		/*  12 */ {`"abcdef"[3..0]`, "dcba", nil},
+		/*  13 */ {`"abcdef"[-1..0..2]`, "fdb", nil},
+		/*  14 */ {`[0,1,2,3,4][..]`, array.NewIntArrayA(0, 1, 2, 3, 4), nil},
+		/*  15 */ {`[0,1,2,3,4][2..3]`, array.NewIntArrayA(2), nil},
+		/*  16 */ {`[0,1,2,3,4][3..-1]`, array.NewIntArrayA(3), nil},
+		/*  17 */ {`[0,1,2,3,4][-3..-1]`, array.NewIntArrayA(2, 3), nil},
+		/*  18 */ {`[0,1,2,3,4][0..]`, array.NewIntArrayA(0, 1, 2, 3, 4), nil},
+		/*  19 */ {`[0,1,2,3,4][0..-1..2]`, array.NewIntArrayA(0, 2), nil},
+		/*  20 */ {`[0,1,2,3,4][-1..0..2]`, array.NewIntArrayA(4, 2), nil},
+		/*  21 */ {`[<0,1,2,3,4>][..]`, list.NewLinkedListA(0, 1, 2, 3, 4), nil},
+		/*  22 */ {`[<0,1,2,3,4>][2..3]`, list.NewLinkedListA(2), nil},
+		/*  23 */ {`[<0,1,2,3,4>][3..-1]`, list.NewLinkedListA(3), nil},
+		/*  24 */ {`[<0,1,2,3,4>][-3..-1]`, list.NewLinkedListA(2, 3), nil},
+		/*  25 */ {`[<0,1,2,3,4>][0..]`, list.NewLinkedListA(0, 1, 2, 3, 4), nil},
+		/*  26 */ {`[<0,1,2,3,4>][0..-1..2]`, list.NewLinkedListA(0, 2), nil},
+		/*  27 */ {`[<0,1,2,3,4>][-1..0..2]`, list.NewLinkedListA(4, 2), nil},
+		/*  28 */ {`[-1..0..2]`, nil, `[1:8] unexpected interval expression`},
+		/*  29 */ {`"abcdef"['x'..]`, nil, `[1:14] interval expression expected integer, got string (x)`},
+		/*  30 */ {`"abcdef"[1+..]`, nil, `[1:12] infix operator "+" requires two non-nil operands, got 1`},
+		/*  31 */ {`"abcdef"[1..4+]`, nil, `[1:15] infix operator "+" requires two non-nil operands, got 1`},
 	}
 
 	t.Setenv("EXPR_PATH", ".")
 
-	// runTestSuiteSpec(t, section, inputs, 5)
+	// RunTestSuiteSpec(t, section, inputs, 30)
-	runTestSuite(t, section, inputs)
+	RunTestSuite(t, section, inputs)
 }