Doc: concepts

t_list_test.go: new test cases added
operator-index.go: ConstLastIndex is checked
2024-06-19 09:38:02 +02:00 · 2024-06-19 09:24:50 +02:00 · 2024-06-19 09:24:19 +02:00 · 2024-06-19 09:22:40 +02:00 · 2024-06-19 09:20:02 +02:00 · 2024-06-19 09:17:46 +02:00
74 changed files with 1597 additions and 916 deletions
@@ -10,7 +10,6 @@ import (

 type Expr interface {
 	Eval(ctx ExprContext) (result any, err error)
-	eval(ctx ExprContext, preset bool) (result any, err error)
 	String() string
 }

@@ -106,16 +105,10 @@ func (self *ast) Finish() {
 }

 func (self *ast) Eval(ctx ExprContext) (result any, err error) {
-	return self.eval(ctx, true)
-}
-
-func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
 	self.Finish()

 	if self.root != nil {
-		if preset {
-			initDefaultVars(ctx)
-		}
+		// initDefaultVars(ctx)
 		if self.forest != nil {
 			for _, root := range self.forest {
 				if result, err = root.compute(ctx); err == nil {
@@ -0,0 +1,58 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// function.go
+package expr
+
+// ---- Linking with Expr functions
+type exprFunctor struct {
+	baseFunctor
+	params []ExprFuncParam
+	expr   Expr
+	defCtx ExprContext
+}
+
+// func newExprFunctor(e Expr, params []string, ctx ExprContext) *exprFunctor {
+// 	return &exprFunctor{expr: e, params: params, defCtx: ctx}
+// }
+
+func newExprFunctor(e Expr, params []ExprFuncParam, ctx ExprContext) *exprFunctor {
+	return &exprFunctor{expr: e, params: params, defCtx: ctx}
+}
+
+func (functor *exprFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
+	if functor.defCtx != nil {
+		ctx.Merge(functor.defCtx)
+	}
+
+	for i, p := range functor.params {
+		if i < len(args) {
+			arg := args[i]
+			if funcArg, ok := arg.(Functor); ok {
+				// ctx.RegisterFunc(p, functor, 0, -1)
+				paramSpecs := funcArg.GetParams()
+				ctx.RegisterFunc(p.Name(), funcArg, TypeAny, paramSpecs)
+			} else {
+				ctx.UnsafeSetVar(p.Name(), arg)
+			}
+		} else {
+			ctx.UnsafeSetVar(p.Name(), nil)
+		}
+	}
+	result, err = functor.expr.Eval(ctx)
+	return
+}
+
+// func CallExprFunction(parentCtx ExprContext, funcName string, params ...any) (v any, err error) {
+// 	ctx := cloneContext(parentCtx)
+// 	ctx.SetParent(parentCtx)
+
+// 	if err == nil {
+// 		if err = checkFunctionCall(ctx, funcName, &params); err == nil {
+// 			if v, err = ctx.Call(funcName, params); err == nil {
+// 				exportObjects(parentCtx, ctx)
+// 			}
+// 		}
+// 	}
+// 	return
+// }
@@ -0,0 +1,19 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// bind-go-function.go
+package expr
+
+// ---- Linking with Go functions
+type golangFunctor struct {
+	baseFunctor
+	f FuncTemplate
+}
+
+func NewGolangFunctor(f FuncTemplate) *golangFunctor {
+	return &golangFunctor{f: f}
+}
+
+func (functor *golangFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
+	return functor.f(ctx, name, args)
+}
@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.

-// func-builtins.go
+// builtin-base.go
 package expr

 import (
@@ -67,7 +67,7 @@ func boolFunc(ctx ExprContext, name string, args []any) (result any, err error)
 	case string:
 		result = len(v) > 0
 	default:
-		err = errCantConvert(name, v, "bool")
+		err = ErrCantConvert(name, v, "bool")
 	}
 	return
 }
@@ -90,7 +90,7 @@ func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 			result = int64(i)
 		}
 	default:
-		err = errCantConvert(name, v, "int")
+		err = ErrCantConvert(name, v, "int")
 	}
 	return
 }
@@ -115,7 +115,7 @@ func decFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	case *FractionType:
 		result = v.toFloat()
 	default:
-		err = errCantConvert(name, v, "float")
+		err = ErrCantConvert(name, v, "float")
 	}
 	return
 }
@@ -127,9 +127,9 @@ func fractFunc(ctx ExprContext, name string, args []any) (result any, err error)
 		if len(args) > 1 {
 			var ok bool
 			if den, ok = args[1].(int64); !ok {
-				err = errExpectedGot(name, "integer", args[1])
+				err = ErrExpectedGot(name, "integer", args[1])
 			} else if den == 0 {
-				err = errFuncDivisionByZero(name)
+				err = ErrFuncDivisionByZero(name)
 			}
 		}
 		if err == nil {
@@ -148,7 +148,7 @@ func fractFunc(ctx ExprContext, name string, args []any) (result any, err error)
 	case *FractionType:
 		result = v
 	default:
-		err = errCantConvert(name, v, "float")
+		err = ErrCantConvert(name, v, "float")
 	}
 	return
 }
@@ -159,28 +159,28 @@ func iteratorFunc(ctx ExprContext, name string, args []any) (result any, err err

 func ImportBuiltinsFuncs(ctx ExprContext) {
 	anyParams := []ExprFuncParam{
-		newFuncParam(paramValue),
+		NewFuncParam(ParamValue),
 	}

-	ctx.RegisterFunc("isNil", newGolangFunctor(isNilFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isInt", newGolangFunctor(isIntFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isFloat", newGolangFunctor(isFloatFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isBool", newGolangFunctor(isBoolFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isString", newGolangFunctor(isStringFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isFract", newGolangFunctor(isFractionFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isRational", newGolangFunctor(isRationalFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isList", newGolangFunctor(isListFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("isDict", newGolangFunctor(isDictionaryFunc), typeBoolean, anyParams)
+	ctx.RegisterFunc("isNil", NewGolangFunctor(isNilFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isInt", NewGolangFunctor(isIntFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isFloat", NewGolangFunctor(isFloatFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isBool", NewGolangFunctor(isBoolFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isString", NewGolangFunctor(isStringFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isFract", NewGolangFunctor(isFractionFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isRational", NewGolangFunctor(isRationalFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isList", NewGolangFunctor(isListFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("isDict", NewGolangFunctor(isDictionaryFunc), TypeBoolean, anyParams)

-	ctx.RegisterFunc("bool", newGolangFunctor(boolFunc), typeBoolean, anyParams)
-	ctx.RegisterFunc("int", newGolangFunctor(intFunc), typeInt, anyParams)
-	ctx.RegisterFunc("dec", newGolangFunctor(decFunc), typeFloat, anyParams)
-	ctx.RegisterFunc("fract", newGolangFunctor(fractFunc), typeFraction, []ExprFuncParam{
-		newFuncParam(paramValue),
-		newFuncParamFlagDef("denominator", pfOptional, 1),
+	ctx.RegisterFunc("bool", NewGolangFunctor(boolFunc), TypeBoolean, anyParams)
+	ctx.RegisterFunc("int", NewGolangFunctor(intFunc), TypeInt, anyParams)
+	ctx.RegisterFunc("dec", NewGolangFunctor(decFunc), TypeFloat, anyParams)
+	ctx.RegisterFunc("fract", NewGolangFunctor(fractFunc), TypeFraction, []ExprFuncParam{
+		NewFuncParam(ParamValue),
+		NewFuncParamFlagDef("denominator", PfDefault, 1),
 	})
 }

 func init() {
-	registerImport("base", ImportBuiltinsFuncs, "Base expression tools like isNil(), int(), etc.")
+	RegisterBuiltinModule("base", ImportBuiltinsFuncs, "Base expression tools like isNil(), int(), etc.")
 }
@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.

-// func-fmt.go
+// builtin-fmt.go
 package expr

 import "fmt"
@@ -23,14 +23,14 @@ func printLnFunc(ctx ExprContext, name string, args []any) (result any, err erro
 }

 func ImportFmtFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("print", newGolangFunctor(printFunc), typeInt, []ExprFuncParam{
-		newFuncParamFlag(paramItem, pfRepeat),
+	ctx.RegisterFunc("print", NewGolangFunctor(printFunc), TypeInt, []ExprFuncParam{
+		NewFuncParamFlag(ParamItem, PfRepeat),
 	})
-	ctx.RegisterFunc("println", newGolangFunctor(printLnFunc), typeInt, []ExprFuncParam{
-		newFuncParamFlag(paramItem, pfRepeat),
+	ctx.RegisterFunc("println", NewGolangFunctor(printLnFunc), TypeInt, []ExprFuncParam{
+		NewFuncParamFlag(ParamItem, PfRepeat),
 	})
 }

 func init() {
-	registerImport("fmt", ImportFmtFuncs, "String and console formatting functions")
+	RegisterBuiltinModule("fmt", ImportFmtFuncs, "String and console formatting functions")
 }
@@ -0,0 +1,75 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtin-import.go
+package expr
+
+import (
+	"io"
+	"os"
+)
+
+func importFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	return importGeneral(ctx, name, args)
+}
+
+func importAllFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	CtrlEnable(ctx, control_export_all)
+	return importGeneral(ctx, name, args)
+}
+
+func importGeneral(ctx ExprContext, name string, args []any) (result any, err error) {
+	dirList := buildSearchDirList("sources", ENV_EXPR_SOURCE_PATH)
+	result, err = doImport(ctx, name, dirList, NewArrayIterator(args))
+	return
+}
+
+func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (result any, err error) {
+	var v any
+	var sourceFilepath string
+
+	for v, err = it.Next(); err == nil; v, err = it.Next() {
+		if err = checkStringParamExpected(name, v, it.Index()); err != nil {
+			break
+		}
+		if sourceFilepath, err = makeFilepath(v.(string), dirList); err != nil {
+			break
+		}
+		var file *os.File
+		if file, err = os.Open(sourceFilepath); err == nil {
+			defer file.Close()
+			var expr *ast
+			scanner := NewScanner(file, DefaultTranslations())
+			parser := NewParser()
+			if expr, err = parser.parseGeneral(scanner, true, true); err == nil {
+				result, err = expr.Eval(ctx)
+			}
+			if err != nil {
+				break
+			}
+		} else {
+			break
+		}
+	}
+	if err != nil {
+		if err == io.EOF {
+			err = nil
+		} else {
+			result = nil
+		}
+	}
+	return
+}
+
+func ImportImportFuncs(ctx ExprContext) {
+	ctx.RegisterFunc("import", NewGolangFunctor(importFunc), TypeAny, []ExprFuncParam{
+		NewFuncParamFlag(ParamFilepath, PfRepeat),
+	})
+	ctx.RegisterFunc("importAll", NewGolangFunctor(importAllFunc), TypeAny, []ExprFuncParam{
+		NewFuncParamFlag(ParamFilepath, PfRepeat),
+	})
+}
+
+func init() {
+	RegisterBuiltinModule("import", ImportImportFuncs, "Functions import() and include()")
+}
@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.

-// funcs-math.go
+// builtin-math-arith.go
 package expr

 import (
@@ -167,15 +167,15 @@ func mulFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 }

 func ImportMathFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("add", &golangFunctor{f: addFunc}, typeNumber, []ExprFuncParam{
-		newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, int64(0)),
+	ctx.RegisterFunc("add", &golangFunctor{f: addFunc}, TypeNumber, []ExprFuncParam{
+		NewFuncParamFlagDef(ParamValue, PfDefault|PfRepeat, int64(0)),
 	})

-	ctx.RegisterFunc("mul", &golangFunctor{f: mulFunc}, typeNumber, []ExprFuncParam{
-		newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, int64(1)),
+	ctx.RegisterFunc("mul", &golangFunctor{f: mulFunc}, TypeNumber, []ExprFuncParam{
+		NewFuncParamFlagDef(ParamValue, PfDefault|PfRepeat, int64(1)),
 	})
 }

 func init() {
-	registerImport("math.arith", ImportMathFuncs, "Functions add() and mul()")
+	RegisterBuiltinModule("math.arith", ImportMathFuncs, "Functions add() and mul()")
 }
@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.

-// func-os.go
+// builtin-os-file.go
 package expr

 import (
@@ -68,7 +68,7 @@ func createFileFunc(ctx ExprContext, name string, args []any) (result any, err e
 			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
 		}
 	} else {
-		err = errMissingFilePath("createFile")
+		err = errMissingFilePath(name)
 	}
 	return
 }
@@ -80,7 +80,7 @@ func openFileFunc(ctx ExprContext, name string, args []any) (result any, err err
 			result = &osReader{fh: fh, reader: bufio.NewReader(fh)}
 		}
 	} else {
-		err = errMissingFilePath("openFile")
+		err = errMissingFilePath(name)
 	}
 	return
 }
@@ -92,7 +92,7 @@ func appendFileFunc(ctx ExprContext, name string, args []any) (result any, err e
 			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
 		}
 	} else {
-		err = errMissingFilePath("openFile")
+		err = errMissingFilePath(name)
 	}
 	return
 }
@@ -118,13 +118,13 @@ func closeFileFunc(ctx ExprContext, name string, args []any) (result any, err er
 		}
 	}
 	if err == nil && (handle == nil || invalidFileHandle != nil) {
-		err = errInvalidFileHandle("closeFileFunc", handle)
+		err = errInvalidFileHandle(name, handle)
 	}
 	result = err == nil
 	return
 }

-func writeFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+func fileWriteTextFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	var handle osHandle
 	var invalidFileHandle any
 	var ok bool
@@ -142,12 +142,12 @@ func writeFileFunc(ctx ExprContext, name string, args []any) (result any, err er
 	}

 	if err == nil && (handle == nil || invalidFileHandle != nil) {
-		err = errInvalidFileHandle("writeFileFunc", invalidFileHandle)
+		err = errInvalidFileHandle(name, invalidFileHandle)
 	}
 	return
 }

-func readFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+func fileReadTextFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	var handle osHandle
 	var invalidFileHandle any
 	var ok bool
@@ -165,50 +165,86 @@ func readFileFunc(ctx ExprContext, name string, args []any) (result any, err err
 				limit = s[0]
 			}

-			if v, err = r.reader.ReadString(limit); err == nil {
-				if len(v) > 0 && v[len(v)-1] == limit {
+			v, err = r.reader.ReadString(limit)
+			if err == io.EOF {
+				err = nil
+			}
+			if len(v) > 0 {
+				if v[len(v)-1] == limit {
 					result = v[0 : len(v)-1]
 				} else {
 					result = v
 				}
 			}
-			if err == io.EOF {
-				err = nil
-			}
 		} else {
 			invalidFileHandle = handle
 		}
 	}

 	if err == nil && (handle == nil || invalidFileHandle != nil) {
-		err = errInvalidFileHandle("readFileFunc", invalidFileHandle)
+		err = errInvalidFileHandle(name, invalidFileHandle)
+	}
+	return
+}
+
+func fileReadTextAllFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var handle osHandle
+	var invalidFileHandle any
+	var ok bool
+
+	result = nil
+	if handle, ok = args[0].(osHandle); !ok || args[0] == nil {
+		invalidFileHandle = args[0]
+	}
+
+	if handle != nil {
+		if r, ok := handle.(*osReader); ok {
+			var b []byte
+			b, err = io.ReadAll(r.reader)
+			result = string(b)
+		} else {
+			invalidFileHandle = handle
+		}
+	}
+
+	if err == nil && (handle == nil || invalidFileHandle != nil) {
+		err = errInvalidFileHandle(name, invalidFileHandle)
 	}
 	return
 }

 func ImportOsFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("openFile", newGolangFunctor(openFileFunc), typeHandle, []ExprFuncParam{
-		newFuncParam(paramFilepath),
+	ctx.RegisterFunc("fileOpen", NewGolangFunctor(openFileFunc), TypeHandle, []ExprFuncParam{
+		NewFuncParam(ParamFilepath),
 	})
-	ctx.RegisterFunc("appendFile", newGolangFunctor(appendFileFunc), typeHandle, []ExprFuncParam{
-		newFuncParam(paramFilepath),
+
+	ctx.RegisterFunc("fileAppend", NewGolangFunctor(appendFileFunc), TypeHandle, []ExprFuncParam{
+		NewFuncParam(ParamFilepath),
 	})
-	ctx.RegisterFunc("createFile", newGolangFunctor(createFileFunc), typeHandle, []ExprFuncParam{
-		newFuncParam(paramFilepath),
+
+	ctx.RegisterFunc("fileCreate", NewGolangFunctor(createFileFunc), TypeHandle, []ExprFuncParam{
+		NewFuncParam(ParamFilepath),
 	})
-	ctx.RegisterFunc("writeFile", newGolangFunctor(writeFileFunc), typeInt, []ExprFuncParam{
-		newFuncParam(typeHandle),
-		newFuncParamFlagDef(typeItem, pfOptional|pfRepeat, ""),
+
+	ctx.RegisterFunc("fileClose", NewGolangFunctor(closeFileFunc), TypeBoolean, []ExprFuncParam{
+		NewFuncParam(TypeHandle),
 	})
-	ctx.RegisterFunc("readFile", newGolangFunctor(readFileFunc), typeString, []ExprFuncParam{
-		newFuncParam(typeHandle),
-		newFuncParamFlagDef("limitCh", pfOptional, "\n"),
+
+	ctx.RegisterFunc("fileWriteText", NewGolangFunctor(fileWriteTextFunc), TypeInt, []ExprFuncParam{
+		NewFuncParam(TypeHandle),
+		NewFuncParamFlagDef(TypeItem, PfDefault|PfRepeat, ""),
 	})
-	ctx.RegisterFunc("closeFile", newGolangFunctor(closeFileFunc), typeBoolean, []ExprFuncParam{
-		newFuncParam(typeHandle),
+
+	ctx.RegisterFunc("fileReadText", NewGolangFunctor(fileReadTextFunc), TypeString, []ExprFuncParam{
+		NewFuncParam(TypeHandle),
+		NewFuncParamFlagDef("limitCh", PfDefault, "\n"),
+	})
+
+	ctx.RegisterFunc("fileReadTextAll", NewGolangFunctor(fileReadTextAllFunc), TypeString, []ExprFuncParam{
+		NewFuncParam(TypeHandle),
 	})
 }

 func init() {
-	registerImport("os.file", ImportOsFuncs, "Operating system file functions")
+	RegisterBuiltinModule("os.file", ImportOsFuncs, "Operating system file functions")
 }
@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.

-// func-string.go
+// builtin-string.go
 package expr

 import (
@@ -21,7 +21,7 @@ func doJoinStr(funcName string, sep string, it Iterator) (result any, err error)
 		if s, ok := v.(string); ok {
 			sb.WriteString(s)
 		} else {
-			err = errExpectedGot(funcName, typeString, v)
+			err = ErrExpectedGot(funcName, TypeString, v)
 			return
 		}
 	}
@@ -45,13 +45,13 @@ func joinStrFunc(ctx ExprContext, name string, args []any) (result any, err erro
 			} else if it, ok := args[1].(Iterator); ok {
 				result, err = doJoinStr(name, sep, it)
 			} else {
-				err = errInvalidParameterValue(name, paramParts, args[1])
+				err = ErrInvalidParameterValue(name, ParamParts, args[1])
 			}
 		} else {
 			result, err = doJoinStr(name, sep, NewArrayIterator(args[1:]))
 		}
 	} else {
-		err = errWrongParamType(name, paramSeparator, typeString, args[0])
+		err = ErrWrongParamType(name, ParamSeparator, TypeString, args[0])
 	}
 	return
 }
@@ -63,14 +63,14 @@ func subStrFunc(ctx ExprContext, name string, args []any) (result any, err error
 	var ok bool

 	if source, ok = args[0].(string); !ok {
-		return nil, errWrongParamType(name, paramSource, typeString, args[0])
+		return nil, ErrWrongParamType(name, ParamSource, TypeString, args[0])
 	}

-	if start, err = toInt(args[1], name+"()"); err != nil {
+	if start, err = ToInt(args[1], name+"()"); err != nil {
 		return
 	}

-	if count, err = toInt(args[2], name+"()"); err != nil {
+	if count, err = ToInt(args[2], name+"()"); err != nil {
 		return
 	}

@@ -91,7 +91,7 @@ func trimStrFunc(ctx ExprContext, name string, args []any) (result any, err erro
 	var ok bool

 	if source, ok = args[0].(string); !ok {
-		return nil, errWrongParamType(name, paramSource, typeString, args[0])
+		return nil, ErrWrongParamType(name, ParamSource, TypeString, args[0])
 	}
 	result = strings.TrimSpace(source)
 	return
@@ -104,7 +104,7 @@ func startsWithStrFunc(ctx ExprContext, name string, args []any) (result any, er
 	result = false

 	if source, ok = args[0].(string); !ok {
-		return result, errWrongParamType(name, paramSource, typeString, args[0])
+		return result, ErrWrongParamType(name, ParamSource, TypeString, args[0])
 	}
 	for i, targetSpec := range args[1:] {
 		if target, ok := targetSpec.(string); ok {
@@ -127,7 +127,7 @@ func endsWithStrFunc(ctx ExprContext, name string, args []any) (result any, err
 	result = false

 	if source, ok = args[0].(string); !ok {
-		return result, errWrongParamType(name, paramSource, typeString, args[0])
+		return result, ErrWrongParamType(name, ParamSource, TypeString, args[0])
 	}
 	for i, targetSpec := range args[1:] {
 		if target, ok := targetSpec.(string); ok {
@@ -150,7 +150,7 @@ func splitStrFunc(ctx ExprContext, name string, args []any) (result any, err err
 	var ok bool

 	if source, ok = args[0].(string); !ok {
-		return result, errWrongParamType(name, paramSource, typeString, args[0])
+		return result, ErrWrongParamType(name, ParamSource, TypeString, args[0])
 	}

 	if sep, ok = args[1].(string); !ok {
@@ -182,42 +182,42 @@ func splitStrFunc(ctx ExprContext, name string, args []any) (result any, err err

 // Import above functions in the context
 func ImportStringFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("joinStr", newGolangFunctor(joinStrFunc), typeString, []ExprFuncParam{
-		newFuncParam(paramSeparator),
-		newFuncParamFlag(paramItem, pfRepeat),
+	ctx.RegisterFunc("strJoin", NewGolangFunctor(joinStrFunc), TypeString, []ExprFuncParam{
+		NewFuncParam(ParamSeparator),
+		NewFuncParamFlag(ParamItem, PfRepeat),
 	})

-	ctx.RegisterFunc("subStr", newGolangFunctor(subStrFunc), typeString, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParamFlagDef(paramStart, pfOptional, int64(0)),
-		newFuncParamFlagDef(paramCount, pfOptional, int64(-1)),
+	ctx.RegisterFunc("strSub", NewGolangFunctor(subStrFunc), TypeString, []ExprFuncParam{
+		NewFuncParam(ParamSource),
+		NewFuncParamFlagDef(ParamStart, PfDefault, int64(0)),
+		NewFuncParamFlagDef(ParamCount, PfDefault, int64(-1)),
 	})

-	ctx.RegisterFunc("splitStr", newGolangFunctor(splitStrFunc), "list of "+typeString, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParamFlagDef(paramSeparator, pfOptional, ""),
-		newFuncParamFlagDef(paramCount, pfOptional, int64(-1)),
+	ctx.RegisterFunc("strSplit", NewGolangFunctor(splitStrFunc), "list of "+TypeString, []ExprFuncParam{
+		NewFuncParam(ParamSource),
+		NewFuncParamFlagDef(ParamSeparator, PfDefault, ""),
+		NewFuncParamFlagDef(ParamCount, PfDefault, int64(-1)),
 	})

-	ctx.RegisterFunc("trimStr", newGolangFunctor(trimStrFunc), typeString, []ExprFuncParam{
-		newFuncParam(paramSource),
+	ctx.RegisterFunc("strTrim", NewGolangFunctor(trimStrFunc), TypeString, []ExprFuncParam{
+		NewFuncParam(ParamSource),
 	})

-	ctx.RegisterFunc("startsWithStr", newGolangFunctor(startsWithStrFunc), typeBoolean, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParam(paramPrefix),
-		newFuncParamFlag("other "+paramPrefix, pfRepeat),
+	ctx.RegisterFunc("strStartsWith", NewGolangFunctor(startsWithStrFunc), TypeBoolean, []ExprFuncParam{
+		NewFuncParam(ParamSource),
+		NewFuncParam(ParamPrefix),
+		NewFuncParamFlag("other "+ParamPrefix, PfRepeat),
 	})

-	ctx.RegisterFunc("endsWithStr", newGolangFunctor(endsWithStrFunc), typeBoolean, []ExprFuncParam{
-		newFuncParam(paramSource),
-		newFuncParam(paramSuffix),
-		newFuncParamFlag("other "+paramSuffix, pfRepeat),
+	ctx.RegisterFunc("strEndsWith", NewGolangFunctor(endsWithStrFunc), TypeBoolean, []ExprFuncParam{
+		NewFuncParam(ParamSource),
+		NewFuncParam(ParamSuffix),
+		NewFuncParamFlag("other "+ParamSuffix, PfRepeat),
 	})
 }

 // Register the import function in the import-register.
 // That will allow to import all function of this module by the "builtin" operator."
 func init() {
-	registerImport("string", ImportStringFuncs, "string utilities")
+	RegisterBuiltinModule("string", ImportStringFuncs, "string utilities")
 }
@@ -0,0 +1,48 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// builtins-register.go
+package expr
+
+import (
+	"fmt"
+)
+
+type builtinModule struct {
+	importFunc  func(ExprContext)
+	description string
+	imported    bool
+}
+
+func newBuiltinModule(importFunc func(ExprContext), description string) *builtinModule {
+	return &builtinModule{importFunc, description, false}
+}
+
+var builtinModuleRegister map[string]*builtinModule
+
+func RegisterBuiltinModule(name string, importFunc func(ExprContext), description string) {
+	if builtinModuleRegister == nil {
+		builtinModuleRegister = make(map[string]*builtinModule)
+	}
+	if _, exists := builtinModuleRegister[name]; exists {
+		panic(fmt.Errorf("module %q already registered", name))
+	}
+	builtinModuleRegister[name] = newBuiltinModule(importFunc, description)
+}
+
+func IterateBuiltinModules(op func(name, description string, imported bool) bool) {
+	if op != nil {
+		for name, mod := range builtinModuleRegister {
+			if !op(name, mod.description, mod.imported) {
+				break
+			}
+		}
+	}
+}
+
+// ----
+func init() {
+	if builtinModuleRegister == nil {
+		builtinModuleRegister = make(map[string]*builtinModule)
+	}
+}
@@ -8,7 +8,7 @@ import (
 	"fmt"
 )

-func errTooFewParams(funcName string, minArgs, maxArgs, argCount int) (err error) {
+func ErrTooFewParams(funcName string, minArgs, maxArgs, argCount int) (err error) {
 	if maxArgs < 0 {
 		err = fmt.Errorf("%s(): too few params -- expected %d or more, got %d", funcName, minArgs, argCount)
 	} else {
@@ -17,39 +17,39 @@ func errTooFewParams(funcName string, minArgs, maxArgs, argCount int) (err error
 	return
 }

-func errTooMuchParams(funcName string, maxArgs, argCount int) (err error) {
+func ErrTooMuchParams(funcName string, maxArgs, argCount int) (err error) {
 	err = fmt.Errorf("%s(): too much params -- expected %d, got %d", funcName, maxArgs, argCount)
 	return
 }

 // --- General errors

-func errCantConvert(funcName string, value any, kind string) error {
-	return fmt.Errorf("%s(): can't convert %s to %s", funcName, typeName(value), kind)
+func ErrCantConvert(funcName string, value any, kind string) error {
+	return fmt.Errorf("%s(): can't convert %s to %s", funcName, TypeName(value), kind)
 }

-func errExpectedGot(funcName string, kind string, value any) error {
-	return fmt.Errorf("%s() expected %s, got %s (%v)", funcName, kind, typeName(value), value)
+func ErrExpectedGot(funcName string, kind string, value any) error {
+	return fmt.Errorf("%s(): expected %s, got %s (%v)", funcName, kind, TypeName(value), value)
 }

-func errFuncDivisionByZero(funcName string) error {
+func ErrFuncDivisionByZero(funcName string) error {
 	return fmt.Errorf("%s(): division by zero", funcName)
 }

-func errDivisionByZero() error {
+func ErrDivisionByZero() error {
 	return fmt.Errorf("division by zero")
 }

 // --- Parameter errors

-func errMissingRequiredParameter(funcName, paramName string) error {
-	return fmt.Errorf("%s() missing required parameter %q", funcName, paramName)
+func ErrMissingRequiredParameter(funcName, paramName string) error {
+	return fmt.Errorf("%s(): missing required parameter %q", funcName, paramName)
 }

-func errInvalidParameterValue(funcName, paramName string, paramValue any) error {
-	return fmt.Errorf("%s() invalid value %s (%v) for parameter %q", funcName, typeName(paramValue), paramValue, paramName)
+func ErrInvalidParameterValue(funcName, paramName string, paramValue any) error {
+	return fmt.Errorf("%s(): invalid value %s (%v) for parameter %q", funcName, TypeName(paramValue), paramValue, paramName)
 }

-func errWrongParamType(funcName, paramName, paramType string, paramValue any) error {
-	return fmt.Errorf("%s() the %q parameter must be a %s, got a %s (%v)", funcName, paramName, paramType, typeName(paramValue), paramValue)
+func ErrWrongParamType(funcName, paramName, paramType string, paramValue any) error {
+	return fmt.Errorf("%s(): the %q parameter must be a %s, got a %s (%v)", funcName, paramName, paramType, TypeName(paramValue), paramValue)
 }
@@ -5,17 +5,23 @@
 package expr

 const (
-	paramCount     = "count"
-	paramItem      = "item"
-	paramParts     = "parts"
-	paramSeparator = "separator"
-	paramSource    = "source"
-	paramSuffix    = "suffix"
-	paramPrefix    = "prefix"
-	paramStart     = "start"
-	paramEnd       = "end"
-	paramValue     = "value"
-	paramEllipsis  = "..."
-	paramFilepath  = "filepath"
-	paramDirpath   = "dirpath"
+	ParamCount     = "count"
+	ParamItem      = "item"
+	ParamParts     = "parts"
+	ParamSeparator = "separator"
+	ParamSource    = "source"
+	ParamSuffix    = "suffix"
+	ParamPrefix    = "prefix"
+	ParamStart     = "start"
+	ParamEnd       = "end"
+	ParamValue     = "value"
+	ParamName      = "name"
+	ParamEllipsis  = "..."
+	ParamFilepath  = "filepath"
+	ParamDirpath   = "dirpath"
 )
+
+// to be moved in its own source file
+const (
+	ConstLastIndex = 0xFFFF_FFFF
+)
@@ -5,14 +5,16 @@
 package expr

 const (
-	typeAny      = "any"
-	typeBoolean  = "boolean"
-	typeFloat    = "float"
-	typeFraction = "fraction"
-	typeHandle   = "handle"
-	typeInt      = "integer"
-	typeItem     = "item"
-	typeNumber   = "number"
-	typePair     = "pair"
-	typeString   = "string"
+	TypeAny      = "any"
+	TypeBoolean  = "boolean"
+	TypeFloat    = "float"
+	TypeFraction = "fraction"
+	TypeHandle   = "handle"
+	TypeInt      = "integer"
+	TypeItem     = "item"
+	TypeNumber   = "number"
+	TypePair     = "pair"
+	TypeString   = "string"
+	TypeListOf = "list-of-"
+	TypeListOfStrings = "list-of-strings"
 )
@@ -22,13 +22,11 @@ func exportFunc(ctx ExprContext, name string, info ExprFunc) {
 	if name[0] == '@' {
 		name = name[1:]
 	}
-	// ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
-	// ctx.RegisterFuncInfo(name, info)
 	ctx.RegisterFunc(name, info.Functor(), info.ReturnType(), info.Params())
 }

 func exportObjects(destCtx, sourceCtx ExprContext) {
-	exportAll := isEnabled(sourceCtx, control_export_all)
+	exportAll := CtrlIsEnabled(sourceCtx, control_export_all)
 	// fmt.Printf("Exporting from sourceCtx [%p] to destCtx [%p] -- exportAll=%t\n", sourceCtx, destCtx, exportAll)
 	// Export variables
 	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return exportAll || name[0] == '@' }) {
@@ -43,3 +41,9 @@ func exportObjects(destCtx, sourceCtx ExprContext) {
 		}
 	}
 }
+
+func exportObjectsToParent(sourceCtx ExprContext) {
+	if parentCtx := sourceCtx.GetParent(); parentCtx != nil {
+		exportObjects(parentCtx, sourceCtx)
+	}
+}
@@ -16,6 +16,7 @@ type Functor interface {
 type ExprFuncParam interface {
 	Name() string
 	Type() string
+	IsDefault() bool
 	IsOptional() bool
 	IsRepeat() bool
 	DefaultValue() any
@@ -36,7 +37,10 @@ type ExprFunc interface {
 type ExprContext interface {
 	Clone() ExprContext
 	Merge(ctx ExprContext)
+	SetParent(ctx ExprContext)
+	GetParent() (ctx ExprContext)
 	GetVar(varName string) (value any, exists bool)
+	GetLast() any
 	SetVar(varName string, value any)
 	UnsafeSetVar(varName string, value any)
 	EnumVars(func(name string) (accept bool)) (varNames []string)
@@ -4,13 +4,13 @@
 // control.go
 package expr

-import "strings"
-
 // Preset control variables
 const (
-	ControlLastResult   = "last"
-	ControlBoolShortcut = "_bool_shortcut"
-	ControlImportPath   = "_import_path"
+	ControlPreset        = "_preset"
+	ControlLastResult    = "last"
+	ControlBoolShortcut  = "_bool_shortcut"
+	ControlSearchPath    = "_search_path"
+	ControlParentContext = "_parent_context"
 )

 // Other control variables
@@ -20,43 +20,14 @@ const (

 // Initial values
 const (
-	init_import_path = "~/.local/lib/go-pkg/expr:/usr/local/lib/go-pkg/expr:/usr/lib/go-pkg/expr"
+	init_search_path = "~/.local/lib/go-pkg/expr:/usr/local/lib/go-pkg/expr:/usr/lib/go-pkg/expr"
 )

 func initDefaultVars(ctx ExprContext) {
+	if _, exists := ctx.GetVar(ControlPreset); exists {
+		return
+	}
+	ctx.SetVar(ControlPreset, true)
 	ctx.SetVar(ControlBoolShortcut, true)
-	ctx.SetVar(ControlImportPath, init_import_path)
-}
-
-func enable(ctx ExprContext, name string) {
-	if strings.HasPrefix(name, "_") {
-		ctx.SetVar(name, true)
-	} else {
-		ctx.SetVar("_"+name, true)
-	}
-}
-
-func disable(ctx ExprContext, name string) {
-	if strings.HasPrefix(name, "_") {
-		ctx.SetVar(name, false)
-	} else {
-		ctx.SetVar("_"+name, false)
-	}
-}
-
-func isEnabled(ctx ExprContext, name string) (status bool) {
-	if v, exists := ctx.GetVar(name); exists {
-		if b, ok := v.(bool); ok {
-			status = b
-		}
-	}
-	return
-}
-
-func getControlString(ctx ExprContext, name string) (s string, exists bool) {
-	var v any
-	if v, exists = ctx.GetVar(name); exists {
-		s, exists = v.(string)
-	}
-	return
+	ctx.SetVar(ControlSearchPath, init_search_path)
 }
@@ -12,6 +12,12 @@ import (

 type DictType map[any]any

+func MakeDict() (dict *DictType) {
+	d := make(DictType)
+	dict = &d
+	return
+}
+
 func newDict(dictAny map[any]*term) (dict *DictType) {
 	var d DictType
 	if dictAny != nil {
@@ -26,42 +32,52 @@ func newDict(dictAny map[any]*term) (dict *DictType) {
 	return
 }

-func (dict *DictType) toMultiLine(sb *strings.Builder, indent int) {
-	sb.WriteString(strings.Repeat("\t", indent))
-	sb.WriteString("{\n")
+func (dict *DictType) toMultiLine(sb *strings.Builder, opt FmtOpt) {
+	indent := GetFormatIndent(opt)
+	flags := GetFormatFlags(opt)
+	//sb.WriteString(strings.Repeat("  ", indent))
+	sb.WriteByte('{')

-	first := true
-	for name, value := range *dict {
-		if first {
-			first = false
-		} else {
-			sb.WriteByte(',')
-			sb.WriteByte('\n')
-		}
+	if len(*dict) > 0 {
+		innerOpt := MakeFormatOptions(flags, indent+1)
+		nest := strings.Repeat("  ", indent+1)
+		sb.WriteByte('\n')

-		sb.WriteString(strings.Repeat("\t", indent+1))
-		if key, ok := name.(string); ok {
-			sb.WriteString(string('"') + key + string('"'))
-		} else {
-			sb.WriteString(fmt.Sprintf("%v", name))
-		}
-		sb.WriteString(": ")
-		if f, ok := value.(Formatter); ok {
-			sb.WriteString(f.ToString(MultiLine))
-		} else if _, ok = value.(Functor); ok {
-			sb.WriteString("func(){}")
-		} else {
-			sb.WriteString(fmt.Sprintf("%v", value))
+		first := true
+		for name, value := range *dict {
+			if first {
+				first = false
+			} else {
+				sb.WriteByte(',')
+				sb.WriteByte('\n')
+			}
+
+			sb.WriteString(nest)
+			if key, ok := name.(string); ok {
+				sb.WriteString(string('"') + key + string('"'))
+			} else {
+				sb.WriteString(fmt.Sprintf("%v", name))
+			}
+			sb.WriteString(": ")
+			if f, ok := value.(Formatter); ok {
+				sb.WriteString(f.ToString(innerOpt))
+			} else if _, ok = value.(Functor); ok {
+				sb.WriteString("func(){}")
+			} else {
+				sb.WriteString(fmt.Sprintf("%v", value))
+			}
 		}
+		sb.WriteByte('\n')
+		sb.WriteString(strings.Repeat("  ", indent))
 	}
-	sb.WriteString(strings.Repeat("\t", indent))
-	sb.WriteString("\n}")
+	sb.WriteString("}")
 }

 func (dict *DictType) ToString(opt FmtOpt) string {
 	var sb strings.Builder
-	if opt&MultiLine != 0 {
-		dict.toMultiLine(&sb, 0)
+	flags := GetFormatFlags(opt)
+	if flags&MultiLine != 0 {
+		dict.toMultiLine(&sb, opt)
 	} else {
 		sb.WriteByte('{')
 		first := true
@@ -124,7 +140,12 @@ func (dict *DictType) merge(second *DictType) {
 }

 func (dict *DictType) setItem(key any, value any) (err error) {
-	(*dict)[key]=value
+	(*dict)[key] = value
 	return
 }

+////////////////
+
+type DictFormat interface {
+	ToDict() *DictType
+}
@@ -22,18 +22,45 @@ Expressions calculator

 toc::[]

-#TODO: Work in progress (last update on 2024/06/02, 08:18 a.m.)#
+#TODO: Work in progress (last update on 2024/06/17, 16:31 a.m.)#

 == Expr
 _Expr_ is a GO package capable of analysing, interpreting and calculating expressions.

+
 === Concepts and terminology
-#TODO#
+
+Expressions are texts containing sequences of operations represented by a syntax very similar to that of most programming languages. _Expr_ package provides these macro functions:
+
+* *_Scanner_* -- Its input is a text. It scans expression text characters to produce a flow of logical symbol and related attributes, aka tokens.
+* *_Parser_* -- Parser input is the token flow coming from the scanner. It analyses the token flow verifyng if it complies with the _Expr_ syntax. If that is the case, the Parser generates the Abstract Syntax Tree (AST). This is tree data structure that represents the components of an expressions and how they are related one each other.
+* *_Calculator_*. Its input is the AST. It computes the parsed expression contained in the AST and returns the result or an error.

 image::expression-diagram.png[]

+==== Variables
+_Expr_ supports variables. The result of an expression can be stored in a variable and reused in other espressions simply specifying the name of the variable as an operand.
+
+==== Multi-expression
+An input text valid for _Expr_ can contain more than an expression. Expressions are separated by [blue]`;` (semicolon). When an input contains two or more expressions it is called _multi-expression_.
+
+_Expr_ parses and computes each expression of a multi-espression, from the left to the right. If all expressions are computed without errors, it only returns the value of the last, the right most.
+
+The result of each expression of a multi-expression is stored in an automatic variable named _last_. In this way, each expression can refer to the result of the previous one without the need to assign that value to a new dedicated variable.
+
+==== Calculation context
+All objects, such as variables and functions, created during the calculation of an expression are stored in a memory called _context_.
+
+The expression context is analogous to the stack-frame of other programming languages. When a function is called, a new context is allocated to store local definitions.
+
+Function contexts are created by cloning the calling context. More details on this topic are given later in this document.
+
+_Expr_ creates and keeps a inner _global context_ where it stores imported functions, either from builtin or plugin modules. To perform calculations, the calling program must provide its own context; this is the _main context_. All calculations take place in this context. As mentioned eralier, when a function is called, a new context is created by cloning the calling context. The createt context can be called _function context_.
+
+Imported functions are registerd in the _global context_. When an expression first calls an imported function, that function is linked to the current context; this can be the _main context_ or a _function context_.
+
 === `dev-expr` test tool
-`dev-expr` is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose.  In fact, in additon to the automatic verification test suite based on the Go test framework, `dev-expr` provides an important aid for quickly testing of new features during their development.
+`dev-expr` is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose.  In fact, in additon to the automatic verification test suite based on the Go test framework, `dev-expr` provided an important aid for quickly testing of new features during their development.

 `dev-expr` can work as a _REPL_, _**R**ead-**E**xecute-**P**rint-**L**oop_, or it can process expression acquired from files or standard input.

@@ -47,11 +74,10 @@ Here are some examples of execution.
 # Type 'exit' or Ctrl+D to quit the program.

 [user]$ ./dev-expr
-expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@portale-stac.it)
-	Based on the Expr package v0.10.0
+dev-expr -- Expressions calculator v1.10.0(build 14),2024/06/17 (celestino.amoroso@portale-stac.it)
+	Based on the Expr package v0.19.0
 	Type help to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
-
 >>> help
 --- REPL commands:
      source -- Load a file as input
@@ -61,6 +87,7 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
        help -- Show command list
          ml -- Enable/Disable multi-line output
        mods -- List builtin modules
+      output -- Enable/Disable printing expression results. Options 'on', 'off', 'status'

 --- Command line options:
    -b <builtin>       Import builtin modules.
@@ -70,9 +97,10 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
    -i                 Force REPL operation when all -e occurences have been processed
    -h, --help, help   Show this help menu
    -m, --modules      List all builtin modules
+    --noout            Disable printing of expression results
    -p                 Print prefix form
    -t                 Print tree form <2>
-
+    -v, --version      Show program version
 >>> 
 ----

@@ -83,8 +111,8 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
 [source,shell]
 ----
 [user]$ ./dev-expr
-expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@portale-stac.it)
-	Based on the Expr package v0.10.0
+dev-expr -- Expressions calculator v1.10.0(build 14),2024/06/17 (celestino.amoroso@portale-stac.it)
+	Based on the Expr package v0.19.0
 	Type help to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc

@@ -101,21 +129,21 @@ expr -- Expressions calculator v1.7.1(build 2),2024/05/16 (celestino.amoroso@por
 7
 -
 6
->>> 1+2 but 5|2+0.5 <4>
+>>> 4+2 but 5|2+0.5 <4>
 3
->>> 1+2; 5|2+0.5 <5>
+>>> 4+2; 5|2+0.5 <5>
 3
 >>>
 ----

-<1> Number bases: 0x = hexadecimal, 0o = octal, 0b = binary.
-<2> Fractions: numerator | denominator.
+<1> Number bases: 0x = _hexadecimal_, 0o = _octal_, 0b = _binary_.
+<2> Fractions: _numerator_ | _denominator_.
 <3> Activate multi-line output of fractions.
 <4> But operator, see <<_but_operator>>.
 <5> Multi-expression: the same result of the previous single expression but this it is obtained with two separated calculations.

 == Data types
-_Expr_ supports numerical, string, relational, boolean expressions, and mixed-type lists.
+_Expr_ has its type system which is a subset of Golang's type system. It supports numerical, string, relational, boolean expressions, and mixed-type lists and maps.

 === Numbers
 _Expr_ supports three type of numbers:
@@ -272,25 +300,31 @@ Some arithmetic operators can also be used with strings.
 | [blue]`*` | _repeat_ | Make _n_ copy of a string  | [blue]`"one" * 2` -> _"oneone"_
 |===

-The items of strings can be accessed using the dot `.` operator.
+The items of strings can be accessed using the square `[]` operator.

 .Item access syntax
 ====
-_item_ = _string-expr_ "**.**" _integer-expr_
+_item_ = _string-expr_ "**[**" _integer-expr_ "**]**" 
+====
+
+.Sub string syntax
+====
+_sub-string_ = _string-expr_ "**[**" _integer-expr_ "**:**" _integer-expr_ "**]**" 
 ====

 .String examples
-`>>>` [blue]`s="abc"`  [gray]_// assign the string to variable s_ +
-[green]`abc` +
-`>>>` [blue]`s.1`      [gray]_// char at position 1 (starting from 0)_ +
-[green]`b` +
-`>>>` [blue]`s.(-1)`   [gray]_// char at position -1, the rightmost one_ +
-[green]`c` +
+`>>>` [blue]`s="abcd"`  [gray]_// assign the string to variable s_ +
+[green]`"abcd"` +
+`>>>` [blue]`s[1]`      [gray]_// char at position 1 (starting from 0)_ +
+[green]`"b"` +
+`>>>` [blue]`s.[-1]`    [gray]_// char at position -1, the rightmost one_ +
+[green]`"d"` +
 `>>>` [blue]`\#s`       [gray]_// number of chars_ +
-[gren]`3` +
-`>>>` [blue]`#"abc"`   [gray]_// number of chars_ +
-[green]`3`
-
+[gren]`4` +
+`>>>` [blue]`#"abc"`    [gray]_// number of chars_ +
+[green]`3` +
+`>>>` [blue]`s[1:3]`    [gray]_// chars from position 1 to position 3 excluded_ +
+[grean]`"bc"`

 === Booleans
 Boolean data type has two values only: [blue]_true_ and [blue]_false_. Relational and boolean expressions result in boolean values.
@@ -535,7 +535,13 @@ pre.rouge .ss {
 <ul class="sectlevel1">
 <li><a href="#_expr">1. Expr</a>
 <ul class="sectlevel2">
-<li><a href="#_concepts_and_terminology">1.1. Concepts and terminology</a></li>
+<li><a href="#_concepts_and_terminology">1.1. Concepts and terminology</a>
+<ul class="sectlevel3">
+<li><a href="#_variables">1.1.1. Variables</a></li>
+<li><a href="#_multi_expression">1.1.2. Multi-expression</a></li>
+<li><a href="#_calculation_context">1.1.3. Calculation context</a></li>
+</ul>
+</li>
 <li><a href="#_dev_expr_test_tool">1.2. <code>dev-expr</code> test tool</a></li>
 </ul>
 </li>
@@ -554,7 +560,7 @@ pre.rouge .ss {
 <li><a href="#_dictionaries">2.5. Dictionaries</a></li>
 </ul>
 </li>
-<li><a href="#_variables">3. Variables</a></li>
+<li><a href="#_variables_2">3. Variables</a></li>
 <li><a href="#_other_operations">4. Other operations</a>
 <ul class="sectlevel2">
 <li><a href="#_operator">4.1. <code class="blue">;</code> operator</a></li>
@@ -585,7 +591,7 @@ pre.rouge .ss {
 <div class="sectionbody">
 <!-- toc disabled -->
 <div class="paragraph">
-<p><mark>TODO: Work in progress (last update on 2024/06/02, 08:18 a.m.)</mark></p>
+<p><mark>TODO: Work in progress (last update on 2024/06/17, 16:31 a.m.)</mark></p>
 </div>
 </div>
 </div>
@@ -598,18 +604,67 @@ pre.rouge .ss {
 <div class="sect2">
 <h3 id="_concepts_and_terminology"><a class="anchor" href="#_concepts_and_terminology"></a><a class="link" href="#_concepts_and_terminology">1.1. Concepts and terminology</a></h3>
 <div class="paragraph">
-<p><mark>TODO</mark></p>
+<p>Expressions are texts containing sequences of operations represented by a syntax very similar to that of most programming languages. <em>Expr</em> package provides these macro functions:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><strong><em>Scanner</em></strong>&#8201;&#8212;&#8201;Its input is a text. It scans expression text characters to produce a flow of logical symbol and related attributes, aka tokens.</p>
+</li>
+<li>
+<p><strong><em>Parser</em></strong>&#8201;&#8212;&#8201;Parser input is the token flow coming from the scanner. It analyses the token flow verifyng if it complies with the <em>Expr</em> syntax. If that is the case, the Parser generates the Abstract Syntax Tree (AST). This is tree data structure that represents the components of an expressions and how they are related one each other.</p>
+</li>
+<li>
+<p><strong><em>Calculator</em></strong>. Its input is the AST. It computes the parsed expression contained in the AST and returns the result or an error.</p>
+</li>
+</ul>
 </div>
 <div class="imageblock">
 <div class="content">
 <img src="expression-diagram.png" alt="expression diagram">
 </div>
 </div>
+<div class="sect3">
+<h4 id="_variables"><a class="anchor" href="#_variables"></a><a class="link" href="#_variables">1.1.1. Variables</a></h4>
+<div class="paragraph">
+<p><em>Expr</em> supports variables. The result of an expression can be stored in a variable and reused in other espressions simply specifying the name of the variable as an operand.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="_multi_expression"><a class="anchor" href="#_multi_expression"></a><a class="link" href="#_multi_expression">1.1.2. Multi-expression</a></h4>
+<div class="paragraph">
+<p>An input text valid for <em>Expr</em> can contain more than an expression. Expressions are separated by <code class="blue">;</code> (semicolon). When an input contains two or more expressions it is called <em>multi-expression</em>.</p>
+</div>
+<div class="paragraph">
+<p><em>Expr</em> parses and computes each expression of a multi-espression, from the left to the right. If all expressions are computed without errors, it only returns the value of the last, the right most.</p>
+</div>
+<div class="paragraph">
+<p>The result of each expression of a multi-expression is stored in an automatic variable named <em>last</em>. In this way, each expression can refer to the result of the previous one without the need to assign that value to a new dedicated variable.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="_calculation_context"><a class="anchor" href="#_calculation_context"></a><a class="link" href="#_calculation_context">1.1.3. Calculation context</a></h4>
+<div class="paragraph">
+<p>All objects, such as variables and functions, created during the calculation of an expression are stored in a memory called <em>context</em>.</p>
+</div>
+<div class="paragraph">
+<p>The expression context is analogous to the stack-frame of other programming languages. When a function is called, a new context is allocated to store local definitions.</p>
+</div>
+<div class="paragraph">
+<p>Function contexts are created by cloning the calling context. More details on this topic are given later in this document.</p>
+</div>
+<div class="paragraph">
+<p><em>Expr</em> creates and keeps a inner <em>global context</em> where it stores imported functions, either from builtin or plugin modules. To perform calculations, the calling program must provide its own context; this is the <em>main context</em>. All calculations take place in this context. As mentioned eralier, when a function is called, a new context is created by cloning the calling context. The createt context can be called <em>function context</em>.</p>
+</div>
+<div class="paragraph">
+<p>Imported functions are registerd in the <em>global context</em>. When an expression first calls an imported function, that function is linked to the current context; this can be the <em>main context</em> or a <em>function context</em>.</p>
+</div>
+</div>
 </div>
 <div class="sect2">
 <h3 id="_dev_expr_test_tool"><a class="anchor" href="#_dev_expr_test_tool"></a><a class="link" href="#_dev_expr_test_tool">1.2. <code>dev-expr</code> test tool</a></h3>
 <div class="paragraph">
-<p><code>dev-expr</code> is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose.  In fact, in additon to the automatic verification test suite based on the Go test framework, <code>dev-expr</code> provides an important aid for quickly testing of new features during their development.</p>
+<p><code>dev-expr</code> is a simple program that can be used to evaluate expressions interactively. As its name suggests, it was created for testing purpose.  In fact, in additon to the automatic verification test suite based on the Go test framework, <code>dev-expr</code> provided an important aid for quickly testing of new features during their development.</p>
 </div>
 <div class="paragraph">
 <p><code>dev-expr</code> can work as a <em>REPL</em>, <em><strong>R</strong>ead-<strong>E</strong>xecute-<strong>P</strong>rint-<strong>L</strong>oop</em>, or it can process expression acquired from files or standard input.</p>
@@ -626,11 +681,10 @@ pre.rouge .ss {
 <pre class="rouge highlight"><code data-lang="shell"><span class="c"># Type 'exit' or Ctrl+D to quit the program.</span>

 <span class="o">[</span>user]<span class="nv">$ </span>./dev-expr
-<span class="nb">expr</span> <span class="nt">--</span> Expressions calculator v1.7.1<span class="o">(</span>build 2<span class="o">)</span>,2024/05/16 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
-	Based on the Expr package v0.10.0
+dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o">(</span>build 14<span class="o">)</span>,2024/06/17 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
+	Based on the Expr package v0.19.0
 	Type <span class="nb">help </span>to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
-
 <span class="o">&gt;&gt;&gt;</span> <span class="nb">help</span>
 <span class="nt">---</span> REPL commands:
      <span class="nb">source</span> <span class="nt">--</span> Load a file as input
@@ -640,6 +694,7 @@ pre.rouge .ss {
        <span class="nb">help</span> <span class="nt">--</span> Show <span class="nb">command </span>list
          ml <span class="nt">--</span> Enable/Disable multi-line output
        mods <span class="nt">--</span> List <span class="nb">builtin </span>modules
+      output <span class="nt">--</span> Enable/Disable printing expression results. Options <span class="s1">'on'</span>, <span class="s1">'off'</span>, <span class="s1">'status'</span>

 <span class="nt">---</span> Command line options:
    <span class="nt">-b</span> &lt;<span class="nb">builtin</span><span class="o">&gt;</span>       Import <span class="nb">builtin </span>modules.
@@ -649,9 +704,10 @@ pre.rouge .ss {
    <span class="nt">-i</span>                 Force REPL operation when all <span class="nt">-e</span> occurences have been processed
    <span class="nt">-h</span>, <span class="nt">--help</span>, <span class="nb">help   </span>Show this <span class="nb">help </span>menu
    <span class="nt">-m</span>, <span class="nt">--modules</span>      List all <span class="nb">builtin </span>modules
+    <span class="nt">--noout</span>            Disable printing of expression results
    <span class="nt">-p</span>                 Print prefix form
    <span class="nt">-t</span>                 Print tree form <i class="conum" data-value="2"></i><b>(2)</b>
-
+    <span class="nt">-v</span>, <span class="nt">--version</span>      Show program version
 <span class="o">&gt;&gt;&gt;</span></code></pre>
 </div>
 </div>
@@ -671,8 +727,8 @@ pre.rouge .ss {
 <div class="title">REPL examples</div>
 <div class="content">
 <pre class="rouge highlight"><code data-lang="shell"><span class="o">[</span>user]<span class="nv">$ </span>./dev-expr
-<span class="nb">expr</span> <span class="nt">--</span> Expressions calculator v1.7.1<span class="o">(</span>build 2<span class="o">)</span>,2024/05/16 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
-	Based on the Expr package v0.10.0
+dev-expr <span class="nt">--</span> Expressions calculator v1.10.0<span class="o">(</span>build 14<span class="o">)</span>,2024/06/17 <span class="o">(</span>celestino.amoroso@portale-stac.it<span class="o">)</span>
+	Based on the Expr package v0.19.0
 	Type <span class="nb">help </span>to get the list of available commands
 	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc

@@ -689,9 +745,9 @@ pre.rouge .ss {
 7
 -
 6
-<span class="o">&gt;&gt;&gt;</span> 1+2 but 5|2+0.5 <i class="conum" data-value="4"></i><b>(4)</b>
+<span class="o">&gt;&gt;&gt;</span> 4+2 but 5|2+0.5 <i class="conum" data-value="4"></i><b>(4)</b>
 3
-<span class="o">&gt;&gt;&gt;</span> 1+2<span class="p">;</span> 5|2+0.5 <i class="conum" data-value="5"></i><b>(5)</b>
+<span class="o">&gt;&gt;&gt;</span> 4+2<span class="p">;</span> 5|2+0.5 <i class="conum" data-value="5"></i><b>(5)</b>
 3
 <span class="o">&gt;&gt;&gt;</span></code></pre>
 </div>
@@ -700,11 +756,11 @@ pre.rouge .ss {
 <table>
 <tr>
 <td><i class="conum" data-value="1"></i><b>1</b></td>
-<td>Number bases: 0x = hexadecimal, 0o = octal, 0b = binary.</td>
+<td>Number bases: 0x = <em>hexadecimal</em>, 0o = <em>octal</em>, 0b = <em>binary</em>.</td>
 </tr>
 <tr>
 <td><i class="conum" data-value="2"></i><b>2</b></td>
-<td>Fractions: numerator | denominator.</td>
+<td>Fractions: <em>numerator</em> | <em>denominator</em>.</td>
 </tr>
 <tr>
 <td><i class="conum" data-value="3"></i><b>3</b></td>
@@ -727,7 +783,7 @@ pre.rouge .ss {
 <h2 id="_data_types"><a class="anchor" href="#_data_types"></a><a class="link" href="#_data_types">2. Data types</a></h2>
 <div class="sectionbody">
 <div class="paragraph">
-<p><em>Expr</em> supports numerical, string, relational, boolean expressions, and mixed-type lists.</p>
+<p><em>Expr</em> has its type system which is a subset of Golang&#8217;s type system. It supports numerical, string, relational, boolean expressions, and mixed-type lists and maps.</p>
 </div>
 <div class="sect2">
 <h3 id="_numbers"><a class="anchor" href="#_numbers"></a><a class="link" href="#_numbers">2.1. Numbers</a></h3>
@@ -1011,28 +1067,38 @@ pre.rouge .ss {
 </tbody>
 </table>
 <div class="paragraph">
-<p>The items of strings can be accessed using the dot <code>.</code> operator.</p>
+<p>The items of strings can be accessed using the square <code>[]</code> operator.</p>
 </div>
 <div class="exampleblock">
 <div class="title">Example 4. Item access syntax</div>
 <div class="content">
 <div class="paragraph">
-<p><em>item</em> = <em>string-expr</em> "<strong>.</strong>" <em>integer-expr</em></p>
+<p><em>item</em> = <em>string-expr</em> "<strong>[</strong>" <em>integer-expr</em> "<strong>]</strong>"</p>
+</div>
+</div>
+</div>
+<div class="exampleblock">
+<div class="title">Example 5. Sub string syntax</div>
+<div class="content">
+<div class="paragraph">
+<p><em>sub-string</em> = <em>string-expr</em> "<strong>[</strong>" <em>integer-expr</em> "<strong>:</strong>" <em>integer-expr</em> "<strong>]</strong>"</p>
 </div>
 </div>
 </div>
 <div class="paragraph">
 <div class="title">String examples</div>
-<p><code>&gt;&gt;&gt;</code> <code class="blue">s="abc"</code>  <em class="gray">// assign the string to variable s</em><br>
-<code class="green">abc</code><br>
-<code>&gt;&gt;&gt;</code> <code class="blue">s.1</code>      <em class="gray">// char at position 1 (starting from 0)</em><br>
-<code class="green">b</code><br>
-<code>&gt;&gt;&gt;</code> <code class="blue">s.(-1)</code>   <em class="gray">// char at position -1, the rightmost one</em><br>
-<code class="green">c</code><br>
+<p><code>&gt;&gt;&gt;</code> <code class="blue">s="abcd"</code>  <em class="gray">// assign the string to variable s</em><br>
+<code class="green">"abcd"</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">s[1]</code>      <em class="gray">// char at position 1 (starting from 0)</em><br>
+<code class="green">"b"</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">s.[-1]</code>    <em class="gray">// char at position -1, the rightmost one</em><br>
+<code class="green">"d"</code><br>
 <code>&gt;&gt;&gt;</code> <code class="blue">#s</code>       <em class="gray">// number of chars</em><br>
-<code class="gren">3</code><br>
-<code>&gt;&gt;&gt;</code> <code class="blue">#"abc"</code>   <em class="gray">// number of chars</em><br>
-<code class="green">3</code></p>
+<code class="gren">4</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">#"abc"</code>    <em class="gray">// number of chars</em><br>
+<code class="green">3</code><br>
+<code>&gt;&gt;&gt;</code> <code class="blue">s[1:3]</code>    <em class="gray">// chars from position 1 to position 3 excluded</em><br>
+<code class="grean">"bc"</code></p>
 </div>
 </div>
 <div class="sect2">
@@ -1179,7 +1245,7 @@ pre.rouge .ss {
 <p><em>Expr</em> supports list of mixed-type values, also specified by normal expressions. Internally, <em>Expr</em>'s lists are Go arrays.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 5. List literal syntax</div>
+<div class="title">Example 6. List literal syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><strong><em>list</em></strong> = <em>empty-list</em> | <em>non-empty-list</em><br>
@@ -1261,7 +1327,7 @@ pre.rouge .ss {
 <p>The items of array can be accessed using the dot <code>.</code> operator.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 6. Item access syntax</div>
+<div class="title">Example 7. Item access syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><em>item</em> = <em>list-expr</em> "<strong>.</strong>" <em>integer-expr</em></p>
@@ -1297,7 +1363,7 @@ pre.rouge .ss {
 <p>Dictionary literals are sequences of pairs separated by comma <code class="blue">,</code> enclosed between brace brackets.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 7. Dict literal syntax</div>
+<div class="title">Example 8. Dict literal syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><strong><em>dict</em></strong> = <em>empty-dict</em> | <em>non-empty-dict</em><br>
@@ -1357,13 +1423,13 @@ pre.rouge .ss {
 </div>
 </div>
 <div class="sect1">
-<h2 id="_variables"><a class="anchor" href="#_variables"></a><a class="link" href="#_variables">3. Variables</a></h2>
+<h2 id="_variables_2"><a class="anchor" href="#_variables_2"></a><a class="link" href="#_variables_2">3. Variables</a></h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p><em>Expr</em>, like most programming languages, supports variables. A variable is an identifier with an assigned value. Variables are stored in <em>contexts</em>.</p>
 </div>
 <div class="exampleblock">
-<div class="title">Example 8. Variable literal syntax</div>
+<div class="title">Example 9. Variable literal syntax</div>
 <div class="content">
 <div class="paragraph">
 <p><strong><em>variable</em></strong> = <em>identifier</em> "<strong>=</strong>" <em>any-value</em><br>
@@ -1884,7 +1950,7 @@ These operators have a high priority, in particular higher than the operator <co
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2024-06-03 06:26:03 +0200
+Last updated 2024-06-19 09:33:41 +0200
 </div>
 </div>
 </body>
@@ -1,33 +0,0 @@
-builtin ["os.file", "base"];
-
-readInt=func(fh){
-	line=readFile(fh);
-	line ? [nil] {nil} :: {int(line)}
-};
-
-ds={
-	"init":func(filename){
-		fh=openFile(filename);
-		fh ? [nil] {nil} :: { @current=readInt(fh); @prev=@current };
-		fh
-	},
-	"current":func(){
-		prev
-	},
-	"next":func(fh){
-		current ? 
-			[nil] {current}
-			:: {@prev=current; @current=readInt(fh) but current}
-	},
-	"clean":func(fh){
-		closeFile(fh)
-	}
-}
-
-//;f=$(ds, "int.list")
-/*
-;f++
-;f++
-;f++
-*/
-//;add(f)
@@ -6,7 +6,7 @@ package expr

 import "fmt"

-type FmtOpt uint16
+type FmtOpt uint32 // lower 16 bits hold a bit-mask, higher 16 bits hold an indentation number

 const (
 	TTY FmtOpt = 1 << iota
@@ -30,6 +30,18 @@ func TruncateString(s string) (trunc string) {
 	return
 }

+func MakeFormatOptions(flags FmtOpt, indent int) FmtOpt {
+	return FmtOpt(indent<<16) | flags
+}
+
+func GetFormatFlags(opt FmtOpt) FmtOpt {
+	return opt & 0xFFFF
+}
+
+func GetFormatIndent(opt FmtOpt) int {
+	return int(opt >> 16)
+}
+
 type Formatter interface {
 	ToString(options FmtOpt) string
 }
@@ -51,7 +63,7 @@ type Typer interface {
 	TypeName() string
 }

-func typeName(v any) (name string) {
+func TypeName(v any) (name string) {
 	if v == nil {
 		name = "nil"
 	} else if typer, ok := v.(Typer); ok {
@@ -70,7 +70,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 			}
 			for _, c := range dec[0:lsd] {
 				if c < '0' || c > '9' {
-					return nil, errExpectedGot("fract", "digit", c)
+					return nil, ErrExpectedGot("fract", "digit", c)
 				}
 				num = num*10 + int64(c-'0')
 				den = den * 10
@@ -81,7 +81,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 			mul := int64(1)
 			for _, c := range subParts[0] {
 				if c < '0' || c > '9' {
-					return nil, errExpectedGot("fract", "digit", c)
+					return nil, ErrExpectedGot("fract", "digit", c)
 				}
 				num = num*10 + int64(c-'0')
 				sub = sub*10 + int64(c-'0')
@@ -94,7 +94,7 @@ func makeGeneratingFraction(s string) (f *FractionType, err error) {
 				p := subParts[1][0 : len(subParts[1])-1]
 				for _, c := range p {
 					if c < '0' || c > '9' {
-						return nil, errExpectedGot("fract", "digit", c)
+						return nil, ErrExpectedGot("fract", "digit", c)
 					}
 					num = num*10 + int64(c-'0')
 					den = den*10 + 9
@@ -212,7 +212,7 @@ func anyToFract(v any) (f *FractionType, err error) {
 		}
 	}
 	if f == nil {
-		err = errExpectedGot("fract", typeFraction, v)
+		err = ErrExpectedGot("fract", TypeFraction, v)
 	}
 	return
 }
@@ -1,150 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-import.go
-package expr
-
-import (
-	"errors"
-	"fmt"
-	"io"
-	"os"
-	"path"
-	"path/filepath"
-	"strings"
-)
-
-const ENV_EXPR_PATH = "EXPR_PATH"
-
-func importFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	return importGeneral(ctx, name, args)
-}
-
-func importAllFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	enable(ctx, control_export_all)
-	return importGeneral(ctx, name, args)
-}
-
-func importGeneral(ctx ExprContext, name string, args []any) (result any, err error) {
-	var dirList []string
-
-	dirList = addEnvImportDirs(dirList)
-	dirList = addPresetImportDirs(ctx, dirList)
-	result, err = doImport(ctx, name, dirList, NewArrayIterator(args))
-	return
-}
-
-func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(IsString(paramValue) /*|| isList(paramValue)*/) {
-		err = fmt.Errorf("%s(): param nr %d has wrong type %T, string expected", funcName, paramPos+1, paramValue)
-	}
-	return
-}
-
-func addEnvImportDirs(dirList []string) []string {
-	if dirSpec, exists := os.LookupEnv(ENV_EXPR_PATH); exists {
-		dirs := strings.Split(dirSpec, ":")
-		if dirList == nil {
-			dirList = dirs
-		} else {
-			dirList = append(dirList, dirs...)
-		}
-	}
-	return dirList
-}
-
-func addPresetImportDirs(ctx ExprContext, dirList []string) []string {
-	if dirSpec, exists := getControlString(ctx, ControlImportPath); exists {
-		dirs := strings.Split(dirSpec, ":")
-		if dirList == nil {
-			dirList = dirs
-		} else {
-			dirList = append(dirList, dirs...)
-		}
-	}
-	return dirList
-}
-
-func isFile(filePath string) bool {
-	info, err := os.Stat(filePath)
-	return (err == nil || errors.Is(err, os.ErrExist)) && info.Mode().IsRegular()
-}
-
-func searchAmongPath(filename string, dirList []string) (filePath string) {
-	for _, dir := range dirList {
-		if fullPath := path.Join(dir, filename); isFile(fullPath) {
-			filePath = fullPath
-			break
-		}
-	}
-	return
-}
-
-func isPathRelative(filePath string) bool {
-	unixPath := filepath.ToSlash(filePath)
-	return strings.HasPrefix(unixPath, "./") || strings.HasPrefix(unixPath, "../")
-}
-
-func makeFilepath(filename string, dirList []string) (filePath string, err error) {
-	if path.IsAbs(filename) || isPathRelative(filename) {
-		if isFile(filename) {
-			filePath = filename
-		}
-	} else {
-		filePath = searchAmongPath(filename, dirList)
-	}
-	if len(filePath) == 0 {
-		err = fmt.Errorf("source file %q not found", filename)
-	}
-	return
-}
-
-func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (result any, err error) {
-	var v any
-	var sourceFilepath string
-
-	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if err = checkStringParamExpected(name, v, it.Index()); err != nil {
-			break
-		}
-		if sourceFilepath, err = makeFilepath(v.(string), dirList); err != nil {
-			break
-		}
-		var file *os.File
-		if file, err = os.Open(sourceFilepath); err == nil {
-			defer file.Close()
-			var expr *ast
-			scanner := NewScanner(file, DefaultTranslations())
-			parser := NewParser(ctx)
-			if expr, err = parser.parseGeneral(scanner, true, true); err == nil {
-				result, err = expr.eval(ctx, false)
-			}
-			if err != nil {
-				break
-			}
-		} else {
-			break
-		}
-	}
-	if err != nil {
-		if err == io.EOF {
-			err = nil
-		} else {
-			result = nil
-		}
-	}
-	return
-}
-
-func ImportImportFuncs(ctx ExprContext) {
-	ctx.RegisterFunc("import", newGolangFunctor(importFunc), typeAny, []ExprFuncParam{
-		newFuncParamFlag(paramFilepath, pfRepeat),
-	})
-	ctx.RegisterFunc("importAll", newGolangFunctor(importAllFunc), typeAny, []ExprFuncParam{
-		newFuncParamFlag(paramFilepath, pfRepeat),
-	})
-}
-
-func init() {
-	registerImport("import", ImportImportFuncs, "Functions import() and include()")
-}
@@ -21,7 +21,7 @@ func (functor *baseFunctor) ToString(opt FmtOpt) (s string) {
 	if functor.info != nil {
 		s = functor.info.ToString(opt)
 	} else {
-		s = "func() {<body>}"
+		s = "func() {}"
 	}
 	return s
 }
@@ -42,65 +42,13 @@ func (functor *baseFunctor) GetFunc() ExprFunc {
 	return functor.info
 }

-// ---- Linking with Go functions
-type golangFunctor struct {
-	baseFunctor
-	f FuncTemplate
-}
-
-func newGolangFunctor(f FuncTemplate) *golangFunctor {
-	return &golangFunctor{f: f}
-}
-
-func (functor *golangFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
-	return functor.f(ctx, name, args)
-}
-
-// ---- Linking with Expr functions
-type exprFunctor struct {
-	baseFunctor
-	params []ExprFuncParam
-	expr   Expr
-	defCtx ExprContext
-}
-
-// func newExprFunctor(e Expr, params []string, ctx ExprContext) *exprFunctor {
-// 	return &exprFunctor{expr: e, params: params, defCtx: ctx}
-// }
-
-func newExprFunctor(e Expr, params []ExprFuncParam, ctx ExprContext) *exprFunctor {
-	return &exprFunctor{expr: e, params: params, defCtx: ctx}
-}
-
-func (functor *exprFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
-	if functor.defCtx != nil {
-		ctx.Merge(functor.defCtx)
-	}
-
-	for i, p := range functor.params {
-		if i < len(args) {
-			arg := args[i]
-			if funcArg, ok := arg.(Functor); ok {
-				// ctx.RegisterFunc(p, functor, 0, -1)
-				paramSpecs := funcArg.GetParams()
-				ctx.RegisterFunc(p.Name(), funcArg, typeAny, paramSpecs)
-			} else {
-				ctx.UnsafeSetVar(p.Name(), arg)
-			}
-		} else {
-			ctx.UnsafeSetVar(p.Name(), nil)
-		}
-	}
-	result, err = functor.expr.eval(ctx, false)
-	return
-}
-
 // ---- Function Parameters
 type paramFlags uint16

 const (
-	pfOptional paramFlags = 1 << iota
-	pfRepeat
+	PfDefault paramFlags = 1 << iota
+	PfOptional
+	PfRepeat
 )

 type funcParamInfo struct {
@@ -109,15 +57,15 @@ type funcParamInfo struct {
 	defaultValue any
 }

-func newFuncParam(name string) ExprFuncParam {
+func NewFuncParam(name string) ExprFuncParam {
 	return &funcParamInfo{name: name}
 }

-func newFuncParamFlag(name string, flags paramFlags) ExprFuncParam {
+func NewFuncParamFlag(name string, flags paramFlags) ExprFuncParam {
 	return &funcParamInfo{name: name, flags: flags}
 }

-func newFuncParamFlagDef(name string, flags paramFlags, defValue any) *funcParamInfo {
+func NewFuncParamFlagDef(name string, flags paramFlags, defValue any) *funcParamInfo {
 	return &funcParamInfo{name: name, flags: flags, defaultValue: defValue}
 }

@@ -126,15 +74,19 @@ func (param *funcParamInfo) Name() string {
 }

 func (param *funcParamInfo) Type() string {
-	return "any"
+	return TypeAny
+}
+
+func (param *funcParamInfo) IsDefault() bool {
+	return (param.flags & PfDefault) != 0
 }

 func (param *funcParamInfo) IsOptional() bool {
-	return (param.flags & pfOptional) != 0
+	return (param.flags & PfOptional) != 0
 }

 func (param *funcParamInfo) IsRepeat() bool {
-	return (param.flags & pfRepeat) != 0
+	return (param.flags & PfRepeat) != 0
 }

 func (param *funcParamInfo) DefaultValue() any {
@@ -159,7 +111,7 @@ func newFuncInfo(name string, functor Functor, returnType string, params []ExprF
 			if maxArgs == -1 {
 				return nil, fmt.Errorf("no more params can be specified after the ellipsis symbol: %q", p.Name())
 			}
-			if p.IsOptional() {
+			if p.IsDefault() || p.IsOptional() {
 				maxArgs++
 			} else if maxArgs == minArgs {
 				minArgs++
@@ -207,7 +159,7 @@ func (info *funcInfo) ToString(opt FmtOpt) string {
 			}
 			sb.WriteString(p.Name())

-			if p.IsOptional() {
+			if p.IsDefault() {
 				sb.WriteByte('=')
 				if s, ok := p.DefaultValue().(string); ok {
 					sb.WriteByte('"')
@@ -226,9 +178,9 @@ func (info *funcInfo) ToString(opt FmtOpt) string {
 	if len(info.returnType) > 0 {
 		sb.WriteString(info.returnType)
 	} else {
-		sb.WriteString(typeAny)
+		sb.WriteString(TypeAny)
 	}
-	sb.WriteString(" {<body>}")
+	sb.WriteString(" {}")
 	return sb.String()
 }

@@ -247,3 +199,42 @@ func (info *funcInfo) MaxArgs() int {
 func (info *funcInfo) Functor() Functor {
 	return info.functor
 }
+
+// ----- Call a function ---
+
+func checkFunctionCall(ctx ExprContext, name string, varParams *[]any) (err error) {
+	if info, exists, owner := GetFuncInfo(ctx, name); exists {
+		passedCount := len(*varParams)
+		if info.MinArgs() > passedCount {
+			err = ErrTooFewParams(name, info.MinArgs(), info.MaxArgs(), passedCount)
+		}
+		for i, p := range info.Params() {
+			if i >= passedCount {
+				if !p.IsDefault() {
+					break
+				}
+				*varParams = append(*varParams, p.DefaultValue())
+			}
+		}
+		if err == nil && info.MaxArgs() >= 0 && info.MaxArgs() < len(*varParams) {
+			err = ErrTooMuchParams(name, info.MaxArgs(), len(*varParams))
+		}
+		if err == nil && owner != ctx {
+			ctx.RegisterFuncInfo(info)
+		}
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}
+
+func CallFunction(parentCtx ExprContext, name string, params []any) (result any, err error) {
+	ctx := cloneContext(parentCtx)
+	ctx.SetParent(parentCtx)
+
+	if err = checkFunctionCall(ctx, name, &params); err == nil {
+		result, err = ctx.Call(name, params)
+		exportObjectsToParent(ctx)
+	}
+	return
+}
@@ -4,13 +4,16 @@
 // global-context.go
 package expr

-import "path/filepath"
+import (
+	"path/filepath"
+	"strings"
+)

 var globalCtx *SimpleStore

 func ImportInContext(name string) (exists bool) {
-	var mod *module
-	if mod, exists = moduleRegister[name]; exists {
+	var mod *builtinModule
+	if mod, exists = builtinModuleRegister[name]; exists {
 		mod.importFunc(globalCtx)
 		mod.imported = true
 	}
@@ -19,7 +22,7 @@ func ImportInContext(name string) (exists bool) {

 func ImportInContextByGlobPattern(pattern string) (count int, err error) {
 	var matched bool
-	for name, mod := range moduleRegister {
+	for name, mod := range builtinModuleRegister {
 		if matched, err = filepath.Match(pattern, name); err == nil {
 			if matched {
 				count++
@@ -63,7 +66,78 @@ func GetFuncInfo(ctx ExprContext, name string) (item ExprFunc, exists bool, owne
 	return
 }

+func GlobalCtrlSet(name string, newValue any) (currentValue any) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	currentValue, _ = globalCtx.GetVar(name)
+
+	globalCtx.SetVar(name, newValue)
+	return currentValue
+}
+
+func GlobalCtrlGet(name string) (currentValue any) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	currentValue, _ = globalCtx.GetVar(name)
+	return currentValue
+}
+
+func CtrlEnable(ctx ExprContext, name string) (currentStatus bool) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	if v, exists := ctx.GetVar(name); exists && IsBool(v) {
+		currentStatus, _ = v.(bool)
+	}
+
+	ctx.SetVar(name, true)
+	return currentStatus
+}
+
+func CtrlDisable(ctx ExprContext, name string) (currentStatus bool) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	if v, exists := ctx.GetVar(name); exists && IsBool(v) {
+		currentStatus, _ = v.(bool)
+	}
+
+	ctx.SetVar(name, false)
+	return currentStatus
+}
+
+func CtrlIsEnabled(ctx ExprContext, name string) (status bool) {
+	var v any
+	var exists bool
+
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+
+	if v, exists = ctx.GetVar(name); !exists {
+		v, exists = globalCtx.GetVar(name)
+	}
+
+	if exists {
+		if b, ok := v.(bool); ok {
+			status = b
+		}
+	}
+	return
+}
+
+func getControlString(name string) (s string, exists bool) {
+	var v any
+	if v, exists = globalCtx.GetVar(name); exists {
+		s, exists = v.(string)
+	}
+	return
+}
+
 func init() {
 	globalCtx = NewSimpleStore()
+	initDefaultVars(globalCtx)
 	ImportBuiltinsFuncs(globalCtx)
 }
@@ -16,10 +16,10 @@ func EvalString(ctx ExprContext, source string) (result any, err error) {

 	r := strings.NewReader(source)
 	scanner := NewScanner(r, DefaultTranslations())
-	parser := NewParser(ctx)
+	parser := NewParser()

 	if tree, err = parser.Parse(scanner); err == nil {
-		result, err = tree.eval(ctx, true)
+		result, err = tree.Eval(ctx)
 	}
 	return
 }
@@ -38,10 +38,10 @@ func EvalStringV(source string, args []Arg) (result any, err error) {
 	for _, arg := range args {
 		if isFunc(arg.Value) {
 			if f, ok := arg.Value.(FuncTemplate); ok {
-				functor := newGolangFunctor(f)
+				functor := NewGolangFunctor(f)
 				// ctx.RegisterFunc(arg.Name, functor, 0, -1)
-				ctx.RegisterFunc(arg.Name, functor, typeAny, []ExprFuncParam{
-					newFuncParamFlagDef(paramValue, pfOptional|pfRepeat, 0),
+				ctx.RegisterFunc(arg.Name, functor, TypeAny, []ExprFuncParam{
+					NewFuncParamFlagDef(ParamValue, PfDefault|PfRepeat, 0),
 				})
 			} else {
 				err = fmt.Errorf("invalid function specification: %q", arg.Name)
@@ -68,7 +68,7 @@ func EvalStringV(source string, args []Arg) (result any, err error) {
 func EvalStream(ctx ExprContext, r io.Reader) (result any, err error) {
 	var tree *ast
 	scanner := NewScanner(r, DefaultTranslations())
-	parser := NewParser(ctx)
+	parser := NewParser()

 	if tree, err = parser.Parse(scanner); err == nil {
 		result, err = tree.Eval(ctx)
@@ -0,0 +1,104 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// import-utils.go
+package expr
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+)
+
+const (
+	ENV_EXPR_SOURCE_PATH = "EXPR_PATH"
+	ENV_EXPR_PLUGIN_PATH = "EXPR_PLUGIN_PATH"
+)
+
+func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
+	if !(IsString(paramValue) /*|| isList(paramValue)*/) {
+		err = fmt.Errorf("%s(): param nr %d has wrong type %s, string expected", funcName, paramPos+1, TypeName(paramValue))
+	}
+	return
+}
+
+func addSourceEnvImportDirs(varName string, dirList []string) []string {
+	return addEnvImportDirs(ENV_EXPR_SOURCE_PATH, dirList)
+}
+
+func addPluginEnvImportDirs(varName string, dirList []string) []string {
+	return addEnvImportDirs(ENV_EXPR_PLUGIN_PATH, dirList)
+}
+
+func addEnvImportDirs(envVarName string, dirList []string) []string {
+	if dirSpec, exists := os.LookupEnv(envVarName); exists {
+		dirs := strings.Split(dirSpec, ":")
+		if dirList == nil {
+			dirList = dirs
+		} else {
+			dirList = append(dirList, dirs...)
+		}
+	}
+	return dirList
+}
+
+func addSearchDirs(endingPath string, dirList []string) []string {
+	if dirSpec, exists := getControlString(ControlSearchPath); exists {
+		dirs := strings.Split(dirSpec, ":")
+		if dirList == nil {
+			dirList = dirs
+		} else {
+			if len(endingPath) > 0 {
+				for _, d := range dirs {
+					dirList = append(dirList, path.Join(d, endingPath))
+				}
+			} else {
+				dirList = append(dirList, dirs...)
+			}
+		}
+	}
+	return dirList
+}
+
+func buildSearchDirList(endingPath, envVarName string) (dirList []string) {
+	dirList = addEnvImportDirs(envVarName, dirList)
+	dirList = addSearchDirs(endingPath, dirList)
+	return
+}
+
+func isFile(filePath string) bool {
+	info, err := os.Stat(filePath)
+	return (err == nil || errors.Is(err, os.ErrExist)) && info.Mode().IsRegular()
+}
+
+func searchAmongPath(filename string, dirList []string) (filePath string) {
+	for _, dir := range dirList {
+		if fullPath := path.Join(dir, filename); isFile(fullPath) {
+			filePath = fullPath
+			break
+		}
+	}
+	return
+}
+
+func isPathRelative(filePath string) bool {
+	unixPath := filepath.ToSlash(filePath)
+	return strings.HasPrefix(unixPath, "./") || strings.HasPrefix(unixPath, "../")
+}
+
+func makeFilepath(filename string, dirList []string) (filePath string, err error) {
+	if path.IsAbs(filename) || isPathRelative(filename) {
+		if isFile(filename) {
+			filePath = filename
+		}
+	} else {
+		filePath = searchAmongPath(filename, dirList)
+	}
+	if len(filePath) == 0 {
+		err = fmt.Errorf("file %q not found", filename)
+	}
+	return
+}
@@ -26,21 +26,21 @@ func NewListIterator(list *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 := toInt(args[0], "start index"); err == nil {
+		if i, err := ToInt(args[0], "start index"); err == nil {
 			if i < 0 {
 				i = listLen + i
 			}
 			it.start = i
 		}
 		if argc >= 2 {
-			if i, err := toInt(args[1], "stop index"); err == nil {
+			if i, err := ToInt(args[1], "stop index"); err == nil {
 				if i < 0 {
 					i = listLen + i
 				}
 				it.stop = i
 			}
 			if argc >= 3 {
-				if i, err := toInt(args[2], "step"); err == nil {
+				if i, err := ToInt(args[2], "step"); err == nil {
 					if i < 0 {
 						i = -i
 					}
@@ -20,6 +20,10 @@ func newListA(listAny ...any) (list *ListType) {
 }

 func newList(listAny []any) (list *ListType) {
+	return NewList(listAny)
+}
+
+func NewList(listAny []any) (list *ListType) {
 	if listAny != nil {
 		ls := make(ListType, len(listAny))
 		for i, item := range listAny {
@@ -30,17 +34,42 @@ func newList(listAny []any) (list *ListType) {
 	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 {
-		if opt&MultiLine != 0 {
-			sb.WriteString("\n  ")
+                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 opt&MultiLine != 0 {
-					sb.WriteString(",\n  ")
+				if flags&MultiLine != 0 {
+					sb.WriteString(",\n")
+					sb.WriteString(nest)
 				} else {
 					sb.WriteString(", ")
 				}
@@ -49,17 +78,20 @@ func (ls *ListType) ToString(opt FmtOpt) (s string) {
 				sb.WriteByte('"')
 				sb.WriteString(s)
 				sb.WriteByte('"')
+			} else if formatter, ok := item.(Formatter); ok {
+				sb.WriteString(formatter.ToString(innerOpt))
 			} else {
 				sb.WriteString(fmt.Sprintf("%v", item))
 			}
 		}
-		if opt&MultiLine != 0 {
+		if flags&MultiLine != 0 {
 			sb.WriteByte('\n')
+			sb.WriteString(strings.Repeat("  ", indent))
 		}
 	}
 	sb.WriteByte(']')
 	s = sb.String()
-	if opt&Truncate != 0 && len(s) > TruncateSize {
+	if flags&Truncate != 0 && len(s) > TruncateSize {
 		s = TruncateString(s)
 	}
 	return
@@ -1,48 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// module-register.go
-package expr
-
-import (
-	"fmt"
-)
-
-type module struct {
-	importFunc  func(ExprContext)
-	description string
-	imported    bool
-}
-
-func newModule(importFunc func(ExprContext), description string) *module {
-	return &module{importFunc, description, false}
-}
-
-var moduleRegister map[string]*module
-
-func registerImport(name string, importFunc func(ExprContext), description string) {
-	if moduleRegister == nil {
-		moduleRegister = make(map[string]*module)
-	}
-	if _, exists := moduleRegister[name]; exists {
-		panic(fmt.Errorf("module %q already registered", name))
-	}
-	moduleRegister[name] = newModule(importFunc, description)
-}
-
-func IterateModules(op func(name, description string, imported bool) bool) {
-	if op != nil {
-		for name, mod := range moduleRegister {
-			if !op(name, mod.description, mod.imported) {
-				break
-			}
-		}
-	}
-}
-
-// ----
-func init() {
-	if moduleRegister == nil {
-		moduleRegister = make(map[string]*module)
-	}
-}
@@ -6,7 +6,6 @@ package expr

 import (
 	"errors"
-	"fmt"
 )

 // -------- function call term
@@ -22,34 +21,7 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 }

 // -------- eval func call
-func checkFunctionCall(ctx ExprContext, name string, varParams *[]any) (err error) {
-	if info, exists, owner := GetFuncInfo(ctx, name); exists {
-		passedCount := len(*varParams)
-		if info.MinArgs() > passedCount {
-			err = errTooFewParams(name, info.MinArgs(), info.MaxArgs(), passedCount)
-		}
-		for i, p := range info.Params() {
-			if i >= passedCount {
-				if !p.IsOptional() {
-					break
-				}
-				*varParams = append(*varParams, p.DefaultValue())
-			}
-		}
-		if err == nil && info.MaxArgs() >= 0 && info.MaxArgs() < len(*varParams) {
-			err = errTooMuchParams(name, info.MaxArgs(), len(*varParams))
-		}
-		if err == nil && owner != ctx {
-			ctx.RegisterFuncInfo(info)
-		}
-	} else {
-		err = fmt.Errorf("unknown function %s()", name)
-	}
-	return
-}
-
-func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
-	ctx := cloneContext(parentCtx)
+func evalFuncCall(ctx ExprContext, self *term) (v any, err error) {
 	name, _ := self.tk.Value.(string)
 	params := make([]any, len(self.children), len(self.children)+5)
 	for i, tree := range self.children {
@@ -61,11 +33,7 @@ func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 	}

 	if err == nil {
-		if err = checkFunctionCall(ctx, name, &params); err == nil {
-			if v, err = ctx.Call(name, params); err == nil {
-				exportObjects(parentCtx, ctx)
-			}
-		}
+		v, err = CallFunction(ctx, name, params)
 	}
 	return
 }
@@ -91,12 +59,12 @@ func evalFuncDef(ctx ExprContext, self *term) (v any, err error) {
 			var defValue any
 			flags := paramFlags(0)
 			if len(param.children) > 0 {
-				flags |= pfOptional
+				flags |= PfDefault
 				if defValue, err = param.children[0].compute(ctx); err != nil {
 					return
 				}
 			}
-			info := newFuncParamFlagDef(param.source(), flags, defValue)
+			info := NewFuncParamFlagDef(param.source(), flags, defValue)
 			paramList = append(paramList, info)
 		}
 		v = newExprFunctor(expr, paramList, ctx)
@@ -28,7 +28,7 @@ func assignCollectionItem(ctx ExprContext, collectionTerm, keyListTerm *term, va
 	if keyListValue, err = keyListTerm.compute(ctx); err != nil {
 		return
 	} else if keyList, ok = keyListValue.(*ListType); !ok || len(*keyList) != 1 {
-		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, typeName(keyListValue))
+		err = keyListTerm.Errorf("index/key specification expected, got %v [%s]", keyListValue, TypeName(keyListValue))
 		return
 	}
 	if keyValue = (*keyList)[0]; keyValue == nil {
@@ -41,7 +41,7 @@ func assignCollectionItem(ctx ExprContext, collectionTerm, keyListTerm *term, va
 		if index, ok := keyValue.(int64); ok {
 			err = collection.setItem(index, value)
 		} else {
-			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, typeName(keyValue))
+			err = keyListTerm.Errorf("integer expected, got %v [%s]", keyValue, TypeName(keyValue))
 		}
 	case *DictType:
 		err = collection.setItem(keyValue, value)
@@ -81,7 +81,7 @@ func evalAssign(ctx ExprContext, self *term) (v any, err error) {
 			} else if funcDef, ok := functor.(*exprFunctor); ok {
 				paramSpecs := ForAll(funcDef.params, func(p ExprFuncParam) ExprFuncParam { return p })

-				ctx.RegisterFunc(leftTerm.source(), functor, typeAny, paramSpecs)
+				ctx.RegisterFunc(leftTerm.source(), functor, TypeAny, paramSpecs)
 			} else {
 				err = self.Errorf("unknown function %s()", rightChild.source())
 			}
@@ -25,7 +25,7 @@ func evalNot(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}

-	if b, ok := toBool(rightValue); ok {
+	if b, ok := ToBool(rightValue); ok {
 		v = !b
 	} else {
 		err = self.errIncompatibleType(rightValue)
@@ -48,7 +48,7 @@ func newAndTerm(tk *Token) (inst *term) {
 }

 func evalAnd(ctx ExprContext, self *term) (v any, err error) {
-	if isEnabled(ctx, ControlBoolShortcut) {
+	if CtrlIsEnabled(ctx, ControlBoolShortcut) {
 		v, err = evalAndWithShortcut(ctx, self)
 	} else {
 		v, err = evalAndWithoutShortcut(ctx, self)
@@ -65,8 +65,8 @@ func evalAndWithoutShortcut(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}

-	leftBool, lok = toBool(leftValue)
-	rightBool, rok = toBool(rightValue)
+	leftBool, lok = ToBool(leftValue)
+	rightBool, rok = ToBool(rightValue)

 	if lok && rok {
 		v = leftBool && rightBool
@@ -87,13 +87,13 @@ func evalAndWithShortcut(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}

-	if leftBool, lok := toBool(leftValue); !lok {
+	if leftBool, lok := ToBool(leftValue); !lok {
 		err = fmt.Errorf("got %T as left operand type of 'and' operator, it must be bool", leftBool)
 		return
 	} else if !leftBool {
 		v = false
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if rightBool, rok := toBool(rightValue); rok {
+		if rightBool, rok := ToBool(rightValue); rok {
 			v = rightBool
 		} else {
 			err = self.errIncompatibleTypes(leftValue, rightValue)
@@ -117,7 +117,7 @@ func newOrTerm(tk *Token) (inst *term) {
 }

 func evalOr(ctx ExprContext, self *term) (v any, err error) {
-	if isEnabled(ctx, ControlBoolShortcut) {
+	if CtrlIsEnabled(ctx, ControlBoolShortcut) {
 		v, err = evalOrWithShortcut(ctx, self)
 	} else {
 		v, err = evalOrWithoutShortcut(ctx, self)
@@ -134,8 +134,8 @@ func evalOrWithoutShortcut(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}

-	leftBool, lok = toBool(leftValue)
-	rightBool, rok = toBool(rightValue)
+	leftBool, lok = ToBool(leftValue)
+	rightBool, rok = ToBool(rightValue)

 	if lok && rok {
 		v = leftBool || rightBool
@@ -156,13 +156,13 @@ func evalOrWithShortcut(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}

-	if leftBool, lok := toBool(leftValue); !lok {
+	if leftBool, lok := ToBool(leftValue); !lok {
 		err = fmt.Errorf("got %T as left operand type of 'or' operator, it must be bool", leftBool)
 		return
 	} else if leftBool {
 		v = true
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if rightBool, rok := toBool(rightValue); rok {
+		if rightBool, rok := ToBool(rightValue); rok {
 			v = rightBool
 		} else {
 			err = self.errIncompatibleTypes(leftValue, rightValue)
@@ -37,11 +37,11 @@ func evalBuiltin(ctx ExprContext, self *term) (v any, err error) {
 				if ImportInContext(module) {
 					count++
 				} else {
-					err = self.Errorf("unknown module %q", module)
+					err = self.Errorf("unknown builtin module %q", module)
 					break
 				}
 			} else {
-				err = self.Errorf("expected string at item nr %d, got %T", it.Index()+1, moduleSpec)
+				err = self.Errorf("expected string at item nr %d, got %s", it.Index()+1, TypeName(moduleSpec))
 				break
 			}
 		}
@@ -67,8 +67,8 @@ func evalAssignCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
 		if functor, ok := rightValue.(Functor); ok {
 			//ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
-			ctx.RegisterFunc(leftTerm.source(), functor, typeAny, []ExprFuncParam{
-				newFuncParamFlag(paramValue, pfOptional|pfRepeat),
+			ctx.RegisterFunc(leftTerm.source(), functor, TypeAny, []ExprFuncParam{
+				NewFuncParamFlag(ParamValue, PfDefault|PfRepeat),
 			})
 		} else {
 			v = rightValue
@@ -31,10 +31,13 @@ func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
 	}

 	if sourceCtx != nil {
-		if formatter, ok := sourceCtx.(Formatter); ok {
+		if formatter, ok := sourceCtx.(DictFormat); ok {
+			v = formatter.ToDict()
+		} else if formatter, ok := sourceCtx.(Formatter); ok {
 			v = formatter.ToString(0)
 		} else {
-			keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+			// keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+			keys := sourceCtx.EnumVars(nil)
 			d := make(map[string]any)
 			for _, key := range keys {
 				d[key], _ = sourceCtx.GetVar(key)
@@ -17,7 +17,7 @@ func newExportAllTerm(tk *Token) (inst *term) {
 }

 func evalExportAll(ctx ExprContext, self *term) (v any, err error) {
-	enable(ctx, control_export_all)
+	CtrlEnable(ctx, control_export_all)
 	return
 }

@@ -23,7 +23,7 @@ func verifyKey(indexTerm *term, indexList *ListType) (index any, err error) {
 func verifyIndex(indexTerm *term, indexList *ListType, maxValue int) (index int, err error) {
 	var v int

-	if v, err = toInt((*indexList)[0], "index expression"); err == nil {
+	if v, err = ToInt((*indexList)[0], "index expression"); err == nil {
 		if v < 0 && v >= -maxValue {
 			v = maxValue + v
 		}
@@ -40,11 +40,14 @@ func verifyRange(indexTerm *term, indexList *ListType, maxValue int) (startIndex
 	v, _ := ((*indexList)[0]).(*intPair)
 	startIndex = v.a
 	endIndex = v.b
+	if endIndex == ConstLastIndex {
+		endIndex = maxValue
+	}
 	if startIndex < 0 && startIndex >= -maxValue {
 		startIndex = maxValue + startIndex
 	}
 	if endIndex < 0 && endIndex >= -maxValue {
-		endIndex = maxValue + endIndex + 1
+		endIndex = maxValue + endIndex
 	}
 	if startIndex < 0 || startIndex > maxValue {
 		err = indexTerm.Errorf("range start-index %d is out of bounds", startIndex)
@@ -87,13 +90,14 @@ func evalIndex(ctx ExprContext, self *term) (v any, err error) {
 				v = string(unboxedValue[index])
 			}
 		case *DictType:
-			var ok bool
+/* 			var ok bool
 			var indexValue any
 			if indexValue, err = verifyKey(indexTerm, indexList); err == nil {
 				if v, ok = (*unboxedValue)[indexValue]; !ok {
 					err = indexTerm.Errorf("key %v does not belong to the dictionary", rightValue)
 				}
-			}
+			} */
+			v, err = getDictItem(unboxedValue, indexTerm, indexList, rightValue)
 		default:
 			err = self.errIncompatibleTypes(leftValue, rightValue)
 		}
@@ -113,6 +117,29 @@ func evalIndex(ctx ExprContext, self *term) (v any, err error) {
 		default:
 			err = self.errIncompatibleTypes(leftValue, rightValue)
 		}
+	} else if IsDict(leftValue) {
+		d := leftValue.(*DictType)
+
+		/* 		var ok bool
+		   		var indexValue any
+		   		if indexValue, err = verifyKey(indexTerm, indexList); err == nil {
+		   			if v, ok = (*d)[indexValue]; !ok {
+		   				err = indexTerm.Errorf("key %v does not belong to the dictionary", rightValue)
+		   			}
+		   		}*/
+		v, err = getDictItem(d, indexTerm, indexList, rightValue)
+	}
+	return
+}
+
+func getDictItem(d *DictType, indexTerm *term, indexList *ListType, rightValue any) (v any, err error) {
+	var ok bool
+	var indexValue any
+
+	if indexValue, err = verifyKey(indexTerm, indexList); err == nil {
+		if v, ok = (*d)[indexValue]; !ok {
+			err = indexTerm.Errorf("key %v does not belong to the dictionary", rightValue)
+		}
 	}
 	return
 }
@@ -36,7 +36,7 @@ func evalLength(ctx ExprContext, self *term) (v any, err error) {
 	} else if it, ok := childValue.(Iterator); ok {
 		if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(countName) {
 			count, _ := extIt.CallOperation(countName, nil)
-			v, _ = toInt(count, "")
+			v, _ = ToInt(count, "")
 		} else {
 			v = int64(it.Index() + 1)
 		}
@@ -0,0 +1,58 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-plugin.go
+package expr
+
+import (
+	"io"
+)
+
+//-------- plugin term
+
+func newPluginTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priSign,
+		evalFunc: evalPlugin,
+	}
+}
+
+func evalPlugin(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+	var moduleSpec any
+
+	if childValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	dirList := buildSearchDirList("plugin", ENV_EXPR_PLUGIN_PATH)
+	count := 0
+	it := NewAnyIterator(childValue)
+	for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
+		if module, ok := moduleSpec.(string); ok {
+			if err = importPlugin(dirList, module); err != nil {
+				break
+			}
+			count++
+		} else {
+			err = self.Errorf("expected string as item nr %d, got %s", it.Index()+1, TypeName(moduleSpec))
+			break
+		}
+	}
+	if err == io.EOF {
+		err = nil
+	}
+
+	if err == nil {
+		v = int64(count)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymKwPlugin, newPluginTerm)
+}
@@ -12,7 +12,7 @@ type intPair struct {
 }

 func (p *intPair) TypeName() string {
-	return typePair
+	return TypePair
 }

 func (p *intPair) ToString(opt FmtOpt) string {
@@ -29,7 +29,7 @@ func newRangeTerm(tk *Token) (inst *term) {
 		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
-		priority: priDot,
+		priority: priRange,
 		evalFunc: evalRange,
 	}
 }
@@ -47,7 +47,7 @@ func evalRange(ctx ExprContext, self *term) (v any, err error) {
 		if leftValue, err = self.children[0].compute(ctx); err != nil {
 			return
 		}
-		rightValue = int64(-1)
+		rightValue = int64(ConstLastIndex)
 	} else if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
 		return
 	}
@@ -70,7 +70,7 @@ func newNotEqualTerm(tk *Token) (inst *term) {

 func evalNotEqual(ctx ExprContext, self *term) (v any, err error) {
 	if v, err = evalEqual(ctx, self); err == nil {
-		b, _ := toBool(v)
+		b, _ := ToBool(v)
 		v = !b
 	}
 	return
@@ -19,17 +19,17 @@ func newSelectorTerm(tk *Token) (inst *term) {
 func trySelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (match bool, selectedValue any, err error) {
 	caseData, _ := caseSel.(*selectorCase)
 	if caseData.filterList == nil {
-		selectedValue, err = caseData.caseExpr.eval(ctx, false)
+		selectedValue, err = caseData.caseExpr.Eval(ctx)
 		match = true
 	} else if filterList, ok := caseData.filterList.value().([]*term); ok {
 		if len(filterList) == 0 && exprValue == int64(caseIndex) {
-			selectedValue, err = caseData.caseExpr.eval(ctx, false)
+			selectedValue, err = caseData.caseExpr.Eval(ctx)
 			match = true
 		} else {
 			var caseValue any
 			for _, caseTerm := range filterList {
 				if caseValue, err = caseTerm.compute(ctx); err != nil || caseValue == exprValue {
-					selectedValue, err = caseData.caseExpr.eval(ctx, false)
+					selectedValue, err = caseData.caseExpr.Eval(ctx)
 					match = true
 					break
 				}
@@ -11,13 +11,10 @@ import (
 //-------- parser

 type parser struct {
-	ctx ExprContext
 }

-func NewParser(ctx ExprContext) (p *parser) {
-	p = &parser{
-		ctx: ctx,
-	}
+func NewParser() (p *parser) {
+	p = &parser{}
 	return p
 }

@@ -328,6 +325,14 @@ func couldBeACollection(t *term) bool {
 	return sym == SymList || sym == SymString || sym == SymDict || sym == SymExpression || sym == SymVariable
 }

+// func areSymbolsOutOfCtx(tk *Token, ctxTerm *term, syms ...Symbol) bool {
+// 	var areOut = false
+// 	if ctxTerm != nil {
+// 		areOut = tk.IsOneOf(syms)
+// 	}
+// 	return areOut
+// }
+
 func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef bool, termSymbols ...Symbol) (tree *ast, err error) {
 	var selectorTerm *term = nil
 	var currentTerm *term = nil
@@ -335,7 +340,7 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 	tree = NewAst()
 	firstToken := true
 	// lastSym := SymUnknown
-	for tk = scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); tk = scanner.Next() {
+	for tk = scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); /*&& !areSymbolsOutOfCtx(tk, selectorTerm, SymColon, SymDoubleColon)*/ tk = scanner.Next() {
 		if tk.Sym == SymComment {
 			continue
 		}
@@ -441,6 +446,10 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 			} else {
 				currentTerm, err = tree.addToken2(tk)
 			}
+			if tk.IsSymbol(SymColon) {
+				// Colon outside a selector term acts like a separator
+				firstToken = true
+			}
 		default:
 			currentTerm, err = tree.addToken2(tk)
 		}
@@ -0,0 +1,107 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// plugin.go
+package expr
+
+import (
+	"fmt"
+	"os"
+	"plugin"
+	"strings"
+)
+
+var pluginRegister map[string]*plugin.Plugin
+
+func registerPlugin(name string, p *plugin.Plugin) (err error) {
+	if pluginExists(name) {
+		err = fmt.Errorf("plugin %q already loaded", name)
+	} else {
+		pluginRegister[name] = p
+	}
+	return
+}
+
+func pluginExists(name string) (exists bool) {
+	_, exists = pluginRegister[name]
+	return
+}
+
+func makePluginName(name string) (decorated string) {
+	var template string
+	if execName, err := os.Executable(); err != nil || strings.Index(execName, "debug") < 0 {
+		template = "expr-%s-plugin.so"
+	} else {
+		template = "expr-%s-plugin.so.debug"
+	}
+	decorated = fmt.Sprintf(template, name)
+	return
+}
+
+func importPlugin( /*ctx ExprContext,*/ dirList []string, name string) (err error) {
+	var filePath string
+	var p *plugin.Plugin
+	var sym plugin.Symbol
+	var moduleName string
+	var importFunc func(ExprContext)
+	var ok bool
+
+	decoratedName := makePluginName(name)
+
+	if filePath, err = makeFilepath(decoratedName, dirList); err != nil {
+		return
+	}
+
+	if p, err = plugin.Open(filePath); err != nil {
+		return
+	}
+
+	if sym, err = p.Lookup("MODULE_NAME"); err != nil {
+		return
+	}
+
+	if moduleName = *sym.(*string); moduleName == "" {
+		err = fmt.Errorf("plugin %q does not provide a valid module name", decoratedName)
+		return
+	}
+
+	if sym, err = p.Lookup("DEPENDENCIES"); err != nil {
+		return
+	}
+	if deps := *sym.(*[]string); len(deps) > 0 {
+		// var count int
+		if err = loadModules(dirList, deps); err != nil {
+			return
+		}
+	}
+
+	if sym, err = p.Lookup("ImportFuncs"); err != nil {
+		return
+	}
+
+	if importFunc, ok = sym.(func(ExprContext)); !ok {
+		err = fmt.Errorf("plugin %q does not provide a valid import function", decoratedName)
+		return
+	}
+
+	registerPlugin(moduleName, p)
+	importFunc(globalCtx)
+
+	return
+}
+
+func loadModules(dirList []string, moduleNames []string) (err error) {
+	for _, name := range moduleNames {
+		if err1 := importPlugin(dirList, name); err1 != nil {
+			if !ImportInContext(name) {
+				err = err1
+				break
+			}
+		}
+	}
+	return
+}
+
+func init() {
+	pluginRegister = make(map[string]*plugin.Plugin)
+}
@@ -178,13 +178,18 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 				tk = self.makeToken(SymDot, ch)
 			}
 		case '\'':
-			tk = self.makeToken(SymQuote, ch)
+			if escape {
+				tk = self.makeToken(SymQuote, ch)
+				escape = false
+			} else {
+				tk = self.fetchString(ch)
+			}
 		case '"':
 			if escape {
 				tk = self.makeToken(SymDoubleQuote, ch)
 				escape = false
 			} else {
-				tk = self.fetchString()
+				tk = self.fetchString(ch)
 			}
 		case '`':
 			tk = self.makeToken(SymBackTick, ch)
@@ -533,7 +538,7 @@ func (self *scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (tk
 	return
 }

-func (self *scanner) fetchString() (tk *Token) {
+func (self *scanner) fetchString(termCh byte) (tk *Token) {
 	var err error
 	var ch, prev byte
 	var sb strings.Builder
@@ -554,7 +559,7 @@ func (self *scanner) fetchString() (tk *Token) {
 				sb.WriteByte(ch)
 			}
 			prev = 0
-		} else if ch == '"' {
+		} else if ch == termCh {
 			break
 		} else {
 			prev = ch
@@ -7,10 +7,11 @@ package expr
 import (
 	"fmt"
 	"slices"
-	"strings"
+	// "strings"
 )

 type SimpleStore struct {
+	parent    ExprContext
 	varStore  map[string]any
 	funcStore map[string]ExprFunc
 }
@@ -26,6 +27,14 @@ func NewSimpleStore() *SimpleStore {
 func filterRefName(name string) bool  { return name[0] != '@' }
 func filterPrivName(name string) bool { return name[0] != '_' }

+func (ctx *SimpleStore) SetParent(parentCtx ExprContext) {
+	ctx.parent = parentCtx
+}
+
+func (ctx *SimpleStore) GetParent() ExprContext {
+	return ctx.parent
+}
+
 func (ctx *SimpleStore) Clone() ExprContext {
 	return &SimpleStore{
 		varStore:  CloneFilteredMap(ctx.varStore, filterRefName),
@@ -42,10 +51,11 @@ func (ctx *SimpleStore) Merge(src ExprContext) {
 	}
 }

+/*
 func varsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
 	sb.WriteString("vars: {\n")
 	first := true
-	for _, name := range ctx.EnumVars(filterPrivName) {
+	for _, name := range ctx.EnumVars(nil) {
 		if first {
 			first = false
 		} else {
@@ -68,7 +78,7 @@ func varsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
 		}
 	}
 	sb.WriteString(strings.Repeat("\t", indent))
-	sb.WriteString("\n}\n")
+	sb.WriteString("\n}")
 }

 func varsCtxToString(ctx ExprContext, indent int) string {
@@ -97,21 +107,70 @@ func funcsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
 			sb.WriteString(fmt.Sprintf("%v", value))
 		}
 	}
-	sb.WriteString("\n}\n")
+	sb.WriteString("\n}")
 }

 func (ctx *SimpleStore) ToString(opt FmtOpt) string {
 	var sb strings.Builder
 	varsCtxToBuilder(&sb, ctx, 0)
+	sb.WriteByte('\n')
 	funcsCtxToBuilder(&sb, ctx, 0)
 	return sb.String()
 }
+*/
+
+func (ctx *SimpleStore) ToString(opt FmtOpt) string {
+	dict := ctx.ToDict()
+	return dict.ToString(opt)
+}
+
+func (ctx *SimpleStore) varsToDict(dict *DictType) *DictType {
+	names := ctx.EnumVars(nil)
+	slices.Sort(names)
+	for _, name := range ctx.EnumVars(nil) {
+		value, _ := ctx.GetVar(name)
+		if f, ok := value.(Formatter); ok {
+			(*dict)[name] = f.ToString(0)
+		} else if _, ok = value.(Functor); ok {
+			(*dict)[name] = "func(){}"
+		} else {
+			(*dict)[name] = fmt.Sprintf("%v", value)
+		}
+	}
+	return dict
+}
+
+func (ctx *SimpleStore) funcsToDict(dict *DictType) *DictType {
+	names := ctx.EnumFuncs(func(name string) bool { return true })
+	slices.Sort(names)
+	for _, name := range names {
+		value, _ := ctx.GetFuncInfo(name)
+		if formatter, ok := value.(Formatter); ok {
+			(*dict)[name] = formatter.ToString(0)
+		} else {
+			(*dict)[name] = fmt.Sprintf("%v", value)
+		}
+	}
+	return dict
+}
+
+func (ctx *SimpleStore) ToDict() (dict *DictType) {
+	dict = MakeDict()
+	(*dict)["variables"] = ctx.varsToDict(MakeDict())
+	(*dict)["functions"] = ctx.funcsToDict(MakeDict())
+	return
+}

 func (ctx *SimpleStore) GetVar(varName string) (v any, exists bool) {
 	v, exists = ctx.varStore[varName]
 	return
 }

+func (ctx *SimpleStore) GetLast() (v any) {
+	v = ctx.varStore["last"]
+	return
+}
+
 func (ctx *SimpleStore) UnsafeSetVar(varName string, value any) {
 	// fmt.Printf("[%p] setVar(%v, %v)\n", ctx, varName, value)
 	ctx.varStore[varName] = value
@@ -101,6 +101,7 @@ const (
 	SymKwBut
 	SymKwFunc
 	SymKwBuiltin
+	SymKwPlugin
 	SymKwIn
 	SymKwInclude
 	SymKwNil
@@ -113,6 +114,7 @@ func init() {
 	keywords = map[string]Symbol{
 		"AND":     SymKwAnd,
 		"BUILTIN": SymKwBuiltin,
+		"PLUGIN":  SymKwPlugin,
 		"BUT":     SymKwBut,
 		"FUNC":    SymKwFunc,
 		"IN":      SymKwIn,
@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.

-// t_func-base_test.go
+// t_builtin-base_test.go
 package expr

 import (
@@ -10,7 +10,7 @@ import (
 )

 func TestFuncBase(t *testing.T) {
-	section := "Func-Base"
+	section := "Builtin-Base"

 	inputs := []inputType{
 		/*   1 */ {`isNil(nil)`, true, nil},
@@ -0,0 +1,24 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_builtin-import_test.go
+package expr
+
+import (
+	"testing"
+)
+
+func TestFuncImport(t *testing.T) {
+	section := "Builtin-Import"
+	inputs := []inputType{
+		/*   1 */ {`builtin "import"; import("./test-resources/test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
+		/*   2 */ {`builtin "import"; import("test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
+		/*   3 */ {`builtin "import"; importAll("./test-resources/test-funcs.expr"); six()`, int64(6), nil},
+		/*   4 */ {`builtin "import"; import("./test-resources/sample-export-all.expr"); six()`, int64(6), nil},
+	}
+
+	t.Setenv("EXPR_PATH", "test-resources")
+
+	// parserTestSpec(t, section, inputs, 69)
+	parserTest(t, section, inputs)
+}
@@ -1,7 +1,7 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.

-// t_func-math-arith_test.go
+// t_builtin-math-arith_test.go
 package expr

 import (
@@ -10,7 +10,7 @@ import (
 )

 func TestFuncMathArith(t *testing.T) {
-	section := "Func-Math-Arith"
+	section := "Builtin-Math-Arith"
 	inputs := []inputType{
 		/*   1 */ {`builtin "math.arith"; add(1,2)`, int64(3), nil},
 		/*   2 */ {`builtin "math.arith"; add(1,2,3)`, int64(6), nil},
@@ -0,0 +1,29 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_builtin-os-file_test.go
+package expr
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestFuncOs(t *testing.T) {
+	section := "Builtin-OS-File"
+	inputs := []inputType{
+		/*   1 */ {`builtin "os.file"`, int64(1), nil},
+		/*   2 */ {`builtin "os.file"; handle=fileOpen("/etc/hosts"); fileClose(handle)`, true, nil},
+		/*   3 */ {`builtin "os.file"; handle=fileOpen("/etc/hostsX")`, nil, errors.New(`open /etc/hostsX: no such file or directory`)},
+		/*   4 */ {`builtin "os.file"; handle=fileCreate("/tmp/dummy"); fileClose(handle)`, true, nil},
+		/*   5 */ {`builtin "os.file"; handle=fileAppend("/tmp/dummy"); fileWriteText(handle, "bye-bye"); fileClose(handle)`, true, nil},
+		/*   6 */ {`builtin "os.file"; handle=fileOpen("/tmp/dummy"); word=fileReadText(handle, "-"); fileClose(handle);word`, "bye", nil},
+		/*   7 */ {`builtin "os.file"; word=fileReadText(nil, "-")`, nil, errors.New(`fileReadText(): invalid file handle`)},
+		/*   7 */ {`builtin "os.file"; fileWriteText(nil, "bye")`, nil, errors.New(`fileWriteText(): invalid file handle`)},
+	}
+
+	// t.Setenv("EXPR_PATH", ".")
+
+	// parserTestSpec(t, section, inputs, 69)
+	parserTest(t, section, inputs)
+}
@@ -0,0 +1,69 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_builtin-string_test.go
+package expr
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestFuncString(t *testing.T) {
+	section := "Builtin-String"
+
+	inputs := []inputType{
+		/*   1 */ {`builtin "string"; strJoin("-", "one", "two", "three")`, "one-two-three", nil},
+		/*   2 */ {`builtin "string"; strJoin("-", ["one", "two", "three"])`, "one-two-three", nil},
+		/*   3 */ {`builtin "string"; ls= ["one", "two", "three"]; strJoin("-", ls)`, "one-two-three", nil},
+		/*   4 */ {`builtin "string"; ls= ["one", "two", "three"]; strJoin(1, ls)`, nil, errors.New(`strJoin(): the "separator" parameter must be a string, got a integer (1)`)},
+		/*   5 */ {`builtin "string"; ls= ["one", 2, "three"]; strJoin("-", ls)`, nil, errors.New(`strJoin(): expected string, got integer (2)`)},
+		/*   6 */ {`builtin "string"; "<"+strTrim("  bye bye  ")+">"`, "<bye bye>", nil},
+		/*   7 */ {`builtin "string"; strSub("0123456789", 1,2)`, "12", nil},
+		/*   8 */ {`builtin "string"; strSub("0123456789", -3,2)`, "78", nil},
+		/*   9 */ {`builtin "string"; strSub("0123456789", -3)`, "789", nil},
+		/*  10 */ {`builtin "string"; strSub("0123456789")`, "0123456789", nil},
+		/*  11 */ {`builtin "string"; strStartsWith("0123456789", "xyz", "012")`, true, nil},
+		/*  12 */ {`builtin "string"; strStartsWith("0123456789", "xyz", "0125")`, false, nil},
+		/*  13 */ {`builtin "string"; strStartsWith("0123456789")`, nil, errors.New(`strStartsWith(): too few params -- expected 2 or more, got 1`)},
+		/*  14 */ {`builtin "string"; strEndsWith("0123456789", "xyz", "789")`, true, nil},
+		/*  15 */ {`builtin "string"; strEndsWith("0123456789", "xyz", "0125")`, false, nil},
+		/*  16 */ {`builtin "string"; strEndsWith("0123456789")`, nil, errors.New(`strEndsWith(): too few params -- expected 2 or more, got 1`)},
+		/*  17 */ {`builtin "string"; strSplit("one-two-three", "-")`, newListA("one", "two", "three"), nil},
+		/*  18 */ {`builtin "string"; strJoin("-", [1, "two", "three"])`, nil, errors.New(`strJoin(): expected string, got integer (1)`)},
+		/*  19 */ {`builtin "string"; strJoin()`, nil, errors.New(`strJoin(): too few params -- expected 1 or more, got 0`)},
+
+		/*  69 */ /*{`builtin "string"; $$global`, `vars: {
+		}
+		funcs: {
+		    	add(any=0 ...) -> number,
+		    	dec(any) -> decimal,
+		    	endsWithStr(source, suffix) -> boolean,
+		    	fract(any, denominator=1) -> fraction,
+		    	import( ...) -> any,
+		    	importAll( ...) -> any,
+		    	int(any) -> integer,
+		    	isBool(any) -> boolean,
+		    	isDec(any) -> boolean,
+		    	isDict(any) -> boolean,
+		    	isFloat(any) -> boolean,
+		    	isFract(any) -> boolean,
+		    	isInt(any) -> boolean,
+		    	isList(any) -> boolean,
+		    	isNil(any) -> boolean,
+		    	isString(any) -> boolean,
+		    	joinStr(separator, item="" ...) -> string,
+		    	mul(any=1 ...) -> number,
+		    	splitStr(source, separator="", count=-1) -> list of string,
+		    	startsWithStr(source, prefix) -> boolean,
+		    	subStr(source, start=0, count=-1) -> string,
+		    	trimStr(source) -> string
+		}
+		`, nil},*/
+	}
+
+	//t.Setenv("EXPR_PATH", ".")
+
+	// parserTestSpec(t, section, inputs, 19)
+	parserTest(t, section, inputs)
+}
@@ -31,6 +31,7 @@ func TestDictParser(t *testing.T) {
 		/*  8 */ {`D={"a":1, "b":2}; D["a"]=9; D`, map[any]any{"a": 9, "b": 2}, nil},
 		/*  9 */ {`D={"a":1, "b":2}; D["z"]=9; D`, map[any]any{"z": 9, "a": 1, "b": 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},
 	}

 	succeeded := 0
@@ -49,7 +50,7 @@ func TestDictParser(t *testing.T) {
 		ctx.SetVar("var1", int64(123))
 		ctx.SetVar("var2", "abc")
 		ImportMathFuncs(ctx)
-		parser := NewParser(ctx)
+		parser := NewParser()

 		logTest(t, i+1, "Dict", input.source, input.wantResult, input.wantErr)

@@ -110,7 +111,7 @@ func TestDictToStringMultiLine(t *testing.T) {
 	var good bool
 	section := "dict-ToString-ML"
 	want := `{
-	"first": 1
+  "first": 1
 }`
 	args := map[any]*term{
 		"first": newLiteralTerm(NewValueToken(0, 0, SymInteger, "1", 1)),
@@ -14,7 +14,7 @@ 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=openFile("test-file.txt"); line=readFile(f); closeFile(f); line`, "uno", nil},
+		/*   3 */ {`builtin "os.file"; f=fileOpen("test-file.txt"); line=fileReadText(f); fileClose(f); line`, "uno", nil},
 		/*   4 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
 		/*   5 */ {`1 ? {1} : [1+0] {3*(1+1)}`, int64(6), nil},
 		/*   6 */ {`
@@ -1,24 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// t_func-import_test.go
-package expr
-
-import (
-	"testing"
-)
-
-func TestFuncImport(t *testing.T) {
-	section := "Func-Import"
-	inputs := []inputType{
-		/*   1 */ {`builtin "import"; import("./test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
-		/*   2 */ {`builtin "import"; import("test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
-		/*   3 */ {`builtin "import"; importAll("./test-funcs.expr"); six()`, int64(6), nil},
-		/*   4 */ {`builtin "import"; import("./sample-export-all.expr"); six()`, int64(6), nil},
-	}
-
-	t.Setenv("EXPR_PATH", ".")
-
-	// parserTestSpec(t, section, inputs, 69)
-	parserTest(t, section, inputs)
-}
@@ -1,29 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// t_func-os_test.go
-package expr
-
-import (
-	"errors"
-	"testing"
-)
-
-func TestFuncOs(t *testing.T) {
-	section := "Func-OS"
-	inputs := []inputType{
-		/*   1 */ {`builtin "os.file"`, int64(1), nil},
-		/*   2 */ {`builtin "os.file"; handle=openFile("/etc/hosts"); closeFile(handle)`, true, nil},
-		/*   3 */ {`builtin "os.file"; handle=openFile("/etc/hostsX")`, nil, errors.New(`open /etc/hostsX: no such file or directory`)},
-		/*   4 */ {`builtin "os.file"; handle=createFile("/tmp/dummy"); closeFile(handle)`, true, nil},
-		/*   5 */ {`builtin "os.file"; handle=appendFile("/tmp/dummy"); writeFile(handle, "bye-bye"); closeFile(handle)`, true, nil},
-		/*   6 */ {`builtin "os.file"; handle=openFile("/tmp/dummy"); word=readFile(handle, "-"); closeFile(handle);word`, "bye", nil},
-		/*   7 */ {`builtin "os.file"; word=readFile(nil, "-")`, nil, errors.New(`readFileFunc(): invalid file handle`)},
-		/*   7 */ {`builtin "os.file"; writeFile(nil, "bye")`, nil, errors.New(`writeFileFunc(): invalid file handle`)},
-	}
-
-	// t.Setenv("EXPR_PATH", ".")
-
-	// parserTestSpec(t, section, inputs, 69)
-	parserTest(t, section, inputs)
-}
@@ -1,69 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// t_func-string_test.go
-package expr
-
-import (
-	"errors"
-	"testing"
-)
-
-func TestFuncString(t *testing.T) {
-	section := "Func-String"
-
-	inputs := []inputType{
-		/*   1 */ {`builtin "string"; joinStr("-", "one", "two", "three")`, "one-two-three", nil},
-		/*   2 */ {`builtin "string"; joinStr("-", ["one", "two", "three"])`, "one-two-three", nil},
-		/*   3 */ {`builtin "string"; ls= ["one", "two", "three"]; joinStr("-", ls)`, "one-two-three", nil},
-		/*   4 */ {`builtin "string"; ls= ["one", "two", "three"]; joinStr(1, ls)`, nil, errors.New(`joinStr() the "separator" parameter must be a string, got a integer (1)`)},
-		/*   5 */ {`builtin "string"; ls= ["one", 2, "three"]; joinStr("-", ls)`, nil, errors.New(`joinStr() expected string, got integer (2)`)},
-		/*   6 */ {`builtin "string"; "<"+trimStr("  bye bye  ")+">"`, "<bye bye>", nil},
-		/*   7 */ {`builtin "string"; subStr("0123456789", 1,2)`, "12", nil},
-		/*   8 */ {`builtin "string"; subStr("0123456789", -3,2)`, "78", nil},
-		/*   9 */ {`builtin "string"; subStr("0123456789", -3)`, "789", nil},
-		/*  10 */ {`builtin "string"; subStr("0123456789")`, "0123456789", nil},
-		/*  11 */ {`builtin "string"; startsWithStr("0123456789", "xyz", "012")`, true, nil},
-		/*  12 */ {`builtin "string"; startsWithStr("0123456789", "xyz", "0125")`, false, nil},
-		/*  13 */ {`builtin "string"; startsWithStr("0123456789")`, nil, errors.New(`startsWithStr(): too few params -- expected 2 or more, got 1`)},
-		/*  14 */ {`builtin "string"; endsWithStr("0123456789", "xyz", "789")`, true, nil},
-		/*  15 */ {`builtin "string"; endsWithStr("0123456789", "xyz", "0125")`, false, nil},
-		/*  16 */ {`builtin "string"; endsWithStr("0123456789")`, nil, errors.New(`endsWithStr(): too few params -- expected 2 or more, got 1`)},
-		/*  17 */ {`builtin "string"; splitStr("one-two-three", "-")`, newListA("one", "two", "three"), nil},
-		/*  18 */ {`builtin "string"; joinStr("-", [1, "two", "three"])`, nil, errors.New(`joinStr() expected string, got integer (1)`)},
-		/*  19 */ {`builtin "string"; joinStr()`, nil, errors.New(`joinStr(): too few params -- expected 1 or more, got 0`)},
-
-		/*  69 */ /*{`builtin "string"; $$global`, `vars: {
-		}
-		funcs: {
-		    	add(any=0 ...) -> number,
-		    	dec(any) -> decimal,
-		    	endsWithStr(source, suffix) -> boolean,
-		    	fract(any, denominator=1) -> fraction,
-		    	import( ...) -> any,
-		    	importAll( ...) -> any,
-		    	int(any) -> integer,
-		    	isBool(any) -> boolean,
-		    	isDec(any) -> boolean,
-		    	isDict(any) -> boolean,
-		    	isFloat(any) -> boolean,
-		    	isFract(any) -> boolean,
-		    	isInt(any) -> boolean,
-		    	isList(any) -> boolean,
-		    	isNil(any) -> boolean,
-		    	isString(any) -> boolean,
-		    	joinStr(separator, item="" ...) -> string,
-		    	mul(any=1 ...) -> number,
-		    	splitStr(source, separator="", count=-1) -> list of string,
-		    	startsWithStr(source, prefix) -> boolean,
-		    	subStr(source, start=0, count=-1) -> string,
-		    	trimStr(source) -> string
-		}
-		`, nil},*/
-	}
-
-	//t.Setenv("EXPR_PATH", ".")
-
-	// parserTestSpec(t, section, inputs, 19)
-	parserTest(t, section, inputs)
-}
@@ -43,8 +43,8 @@ func dummy(ctx ExprContext, name string, args []any) (result any, err error) {
 }

 func TestFunctionToStringSimple(t *testing.T) {
-	source := newGolangFunctor(dummy)
-	want := "func() {<body>}"
+	source := NewGolangFunctor(dummy)
+	want := "func() {}"
 	got := source.ToString(0)
 	if got != want {
 		t.Errorf(`(func() -> result = %v [%T], want = %v [%T]`, got, got, want, want)
@@ -52,7 +52,7 @@ func TestFunctionToStringSimple(t *testing.T) {
 }

 func TestFunctionGetFunc(t *testing.T) {
-	source := newGolangFunctor(dummy)
+	source := NewGolangFunctor(dummy)
 	want := ExprFunc(nil)
 	got := source.GetFunc()
 	if got != want {
@@ -0,0 +1,162 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_iter-list_test.go
+package expr
+
+import (
+	"io"
+	"testing"
+)
+
+func TestNewListIterator(t *testing.T) {
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{1, 3, 1})
+	if item, err := it.Next(); err != nil {
+		t.Errorf("error: %v", err)
+	} else if item != "b" {
+		t.Errorf("expcted %q, got %q", "b", item)
+	} else {
+		t.Logf("Next: %v", item)
+	}
+}
+
+func TestNewListIterator2(t *testing.T) {
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{3, 1, -1})
+	if item, err := it.Next(); err != nil {
+		t.Errorf("error: %v", err)
+	} else if item != "d" {
+		t.Errorf("expcted %q, got %q", "d", item)
+	} else {
+		t.Logf("Next: %v", item)
+	}
+}
+
+func TestNewListIterator3(t *testing.T) {
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{1, -1, 1})
+	if item, err := it.Next(); err != nil {
+		t.Errorf("error: %v", err)
+	} else if item != "b" {
+		t.Errorf("expcted %q, got %q", "b", item)
+	} else {
+		t.Logf("Next: %v", item)
+	}
+}
+
+func TestNewIterList2(t *testing.T) {
+	list := []any{"a", "b", "c", "d"}
+	it := NewArrayIterator(list)
+	if item, err := it.Next(); err != nil {
+		t.Errorf("error: %v", err)
+	} else if item != "a" {
+		t.Errorf("expcted %q, got %q", "a", item)
+	} else {
+		t.Logf("Next: %v", item)
+	}
+}
+
+func TestNewIterList3(t *testing.T) {
+	list := []any{"a", "b", "c", "d"}
+	it := NewAnyIterator(list)
+	if item, err := it.Next(); err != nil {
+		t.Errorf("error: %v", err)
+	} else if item != "a" {
+		t.Errorf("expcted %q, got %q", "a", item)
+	} else {
+		t.Logf("Next: %v", item)
+	}
+}
+
+func TestNewIterList4(t *testing.T) {
+	list := any(nil)
+	it := NewAnyIterator(list)
+	if _, err := it.Next(); err != io.EOF {
+		t.Errorf("error: %v", err)
+	}
+}
+
+func TestNewIterList5(t *testing.T) {
+	list := "123"
+	it := NewAnyIterator(list)
+	if item, err := it.Next(); err != nil {
+		t.Errorf("error: %v", err)
+	} else if item != "123" {
+		t.Errorf("expcted %q, got %q", "123", item)
+	} else {
+		t.Logf("Next: %v", item)
+	}
+}
+
+func TestNewIterList6(t *testing.T) {
+	list := newListA("a", "b", "c", "d")
+	it1 := NewAnyIterator(list)
+	it := NewAnyIterator(it1)
+	if item, err := it.Next(); err != nil {
+		t.Errorf("error: %v", err)
+	} else if item != "a" {
+		t.Errorf("expcted %q, got %q", "a", item)
+	} else {
+		t.Logf("Next: %v", item)
+	}
+}
+func TestNewString(t *testing.T) {
+	list := "123"
+	it := NewAnyIterator(list)
+	if s := it.String(); s != "$(#1)" {
+		t.Errorf("expected $(#1), got %s", s)
+	}
+}
+
+func TestHasOperation(t *testing.T) {
+
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{1, 3, 1})
+	hasOp := it.HasOperation("reset")
+	if !hasOp {
+		t.Errorf("HasOperation(reset) must be true, got false")
+	}
+}
+
+func TestCallOperationReset(t *testing.T) {
+
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{1, 3, 1})
+	if v, err := it.CallOperation("reset", nil); err != nil {
+		t.Errorf("Error on CallOperation(reset): %v", err)
+	} else {
+		t.Logf("Reset result: %v", v)
+	}
+}
+
+func TestCallOperationIndex(t *testing.T) {
+
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{1, 3, 1})
+	if v, err := it.CallOperation("index", nil); err != nil {
+		t.Errorf("Error on CallOperation(index): %v", err)
+	} else {
+		t.Logf("Index result: %v", v)
+	}
+}
+
+func TestCallOperationCount(t *testing.T) {
+
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{1, 3, 1})
+	if v, err := it.CallOperation("count", nil); err != nil {
+		t.Errorf("Error on CallOperation(count): %v", err)
+	} else {
+		t.Logf("Count result: %v", v)
+	}
+}
+
+func TestCallOperationUnknown(t *testing.T) {
+
+	list := newListA("a", "b", "c", "d")
+	it := NewListIterator(list, []any{1, 3, 1})
+	if v, err := it.CallOperation("unknown", nil); err == nil {
+		t.Errorf("Expected error on CallOperation(unknown), got %v", v)
+	}
+}
@@ -8,15 +8,15 @@ import "testing"

 func TestIteratorParser(t *testing.T) {
 	inputs := []inputType{
-		/*   1 */ {`include "iterator.expr"; it=$(ds,3); ()it`, int64(0), nil},
-		/*   2 */ {`include "iterator.expr"; it=$(ds,3); it++; it++`, int64(1), nil},
-		/*   3 */ {`include "iterator.expr"; it=$(ds,3); it++; it++; #it`, int64(2), nil},
-		/*   4 */ {`include "iterator.expr"; it=$(ds,3); it++; it++; it.reset; ()it`, int64(0), nil},
-		/*   5 */ {`builtin "math.arith"; include "iterator.expr"; it=$(ds,3); add(it)`, int64(6), nil},
-		/*   6 */ {`builtin "math.arith"; include "iterator.expr"; it=$(ds,3); mul(it)`, int64(0), nil},
-		/*   7 */ {`builtin "math.arith"; include "file-reader.expr"; it=$(ds,"int.list"); mul(it)`, int64(12000), nil},
-		/*   8 */ {`include "file-reader.expr"; it=$(ds,"int.list"); it++; it.index`, int64(0), nil},
-		/*  10 */ {`include "file-reader.expr"; it=$(ds,"int.list"); it.clean`, true, nil},
+		/*   1 */ {`include "test-resources/iterator.expr"; it=$(ds,3); ()it`, int64(0), nil},
+		/*   2 */ {`include "test-resources/iterator.expr"; it=$(ds,3); it++; it++`, int64(1), nil},
+		/*   3 */ {`include "test-resources/iterator.expr"; it=$(ds,3); it++; it++; #it`, int64(2), nil},
+		/*   4 */ {`include "test-resources/iterator.expr"; it=$(ds,3); it++; it++; it.reset; ()it`, int64(0), nil},
+		/*   5 */ {`builtin "math.arith"; include "test-resources/iterator.expr"; it=$(ds,3); add(it)`, int64(6), nil},
+		/*   6 */ {`builtin "math.arith"; include "test-resources/iterator.expr"; it=$(ds,3); mul(it)`, int64(0), nil},
+		/*   7 */ {`builtin "math.arith"; include "test-resources/file-reader.expr"; it=$(ds,"test-resources/int.list"); mul(it)`, int64(12000), nil},
+		/*   8 */ {`include "test-resources/file-reader.expr"; it=$(ds,"test-resources/int.list"); it++; it.index`, int64(0), nil},
+		/*  10 */ {`include "test-resources/file-reader.expr"; it=$(ds,"test-resources/int.list"); it.clean`, true, nil},
 		/*  11 */ {`it=$(1,2,3); it++`, int64(1), nil},
 	}
 	// inputs1 := []inputType{
@@ -6,19 +6,12 @@ package expr

 import (
 	"errors"
-	"strings"
 	"testing"
 )

 func TestListParser(t *testing.T) {
 	section := "List"

-	/*	type inputType struct {
-			source     string
-			wantResult any
-			wantErr    error
-		}
-	*/
 	inputs := []inputType{
 		/*   1 */ {`[]`, newListA(), nil},
 		/*   2 */ {`[1,2,3]`, newListA(int64(1), int64(2), int64(3)), nil},
@@ -56,82 +49,14 @@ func TestListParser(t *testing.T) {
 		/*  35 */ {`L=[1,2]; L[5]=9; L`, nil, errors.New(`index 5 out of bounds (0, 1)`)},
 		/*  36 */ {`L=[1,2]; L[]=9; L`, nil, errors.New(`[1:12] index/key specification expected, got [] [list]`)},
 		/*  37 */ {`L=[1,2]; L[nil]=9;`, nil, errors.New(`[1:12] index/key is nil`)},
-		// /*  8 */ {`[int(x)|x=csv("test.csv",1,all(),1)]`, []any{int64(10), int64(40), int64(20)}, nil},
-		// /*  9 */ {`sum(@[int(x)|x=csv("test.csv",1,all(),1)])`, []any{int64(10), int64(40), int64(20)}, nil},
+		/*  38 */ {`[0,1,2,3,4][2:3]`, newListA(int64(2)), nil},
+		/*  39 */ {`[0,1,2,3,4][3:-1]`, newListA(int64(3)), nil},
+		/*  40 */ {`[0,1,2,3,4][-3:-1]`, newListA(int64(2), int64(3)), nil},
+		/*  41 */ {`[0,1,2,3,4][0:]`, newListA(int64(0), int64(1), int64(2), int64(3), int64(4)), nil},
 	}

 	// t.Setenv("EXPR_PATH", ".")

 	// parserTestSpec(t, section, inputs, 17)
 	parserTest(t, section, inputs)
-	return
-	succeeded := 0
-	failed := 0
-
-	// inputs1 := []inputType{
-	// 	/*  7 */ {`add([1,4,3,2])`, int64(10), nil},
-	// }
-
-	for i, input := range inputs {
-		var expr *ast
-		var gotResult any
-		var gotErr error
-
-		ctx := NewSimpleStore()
-		ImportMathFuncs(ctx)
-		parser := NewParser(ctx)
-
-		logTest(t, i+1, "List", input.source, input.wantResult, input.wantErr)
-
-		r := strings.NewReader(input.source)
-		scanner := NewScanner(r, DefaultTranslations())
-
-		good := true
-		if expr, gotErr = parser.Parse(scanner); gotErr == nil {
-			gotResult, gotErr = expr.Eval(ctx)
-		}
-
-		if (gotResult == nil && input.wantResult != nil) || (gotResult != nil && input.wantResult == nil) {
-			t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
-			good = false
-		}
-
-		if gotList, okGot := gotResult.([]any); okGot {
-			if wantList, okWant := input.wantResult.([]any); okWant {
-				if (gotList == nil && wantList != nil) || (gotList != nil && wantList == nil) {
-					t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
-					good = false
-				} else {
-					equal := len(gotList) == len(wantList)
-					if equal {
-						for i, gotItem := range gotList {
-							wantItem := wantList[i]
-							equal = gotItem == wantItem
-							if !equal {
-								break
-							}
-						}
-					}
-					if !equal {
-						t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
-						good = false
-					}
-				}
-			}
-		}
-
-		if gotErr != input.wantErr {
-			if input.wantErr == nil || gotErr == nil || (gotErr.Error() != input.wantErr.Error()) {
-				t.Errorf("%d: %q  -> err = <%v>, want <%v>", i+1, input.source, gotErr, input.wantErr)
-				good = false
-			}
-		}
-
-		if good {
-			succeeded++
-		} else {
-			failed++
-		}
-	}
-	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(inputs), succeeded, failed)
 }
@@ -12,7 +12,7 @@ func TestIterateModules(t *testing.T) {
 	section := "Module-Register"

 	mods := make([]string, 0, 100)
-	IterateModules(func(name, description string, imported bool) bool {
+	IterateBuiltinModules(func(name, description string, imported bool) bool {
 		mods = append(mods, name)
 		return true
 	})
@@ -188,7 +188,7 @@ func doTest(t *testing.T, section string, input *inputType, count int) (good boo
 	var gotErr error

 	ctx := NewSimpleStore()
-	parser := NewParser(ctx)
+	parser := NewParser()

 	logTest(t, count, section, input.source, input.wantResult, input.wantErr)

@@ -203,7 +203,7 @@ func doTest(t *testing.T, section string, input *inputType, count int) (good boo
 	eq := reflect.DeepEqual(gotResult, input.wantResult)

 	if !eq /*gotResult != input.wantResult*/ {
-		t.Errorf("%d: %q -> result = %v [%s], want = %v [%s]", count, input.source, gotResult, typeName(gotResult), input.wantResult, typeName(input.wantResult))
+		t.Errorf("%d: %q -> result = %v [%s], want = %v [%s]", count, input.source, gotResult, TypeName(gotResult), input.wantResult, TypeName(input.wantResult))
 		good = false
 	}

@@ -45,7 +45,7 @@ func TestScanner(t *testing.T) {
 		/* 22 */ {"@", SymAt, nil, nil},
 		/* 23 */ {`#`, SymHash, nil, nil},
 		/* 24 */ {`%`, SymPercent, nil, nil},
-		/* 25 */ {`'`, SymQuote, nil, nil},
+		/* 25 */ {`\'`, SymQuote, nil, nil},
 		/* 26 */ {`\"`, SymDoubleQuote, nil, nil},
 		/* 27 */ {`_`, SymUndescore, nil, nil},
 		/* 28 */ {`<>`, SymLessGreater, nil, nil},
@@ -63,7 +63,7 @@ func TestIsString(t *testing.T) {
 	}

 	count++
-	b, ok := toBool(true)
+	b, ok := ToBool(true)
 	if !(ok && b) {
 		t.Errorf("%d: toBool(true) b=%v, ok=%v -> result = false, want true", count, b, ok)
 		failed++
@@ -72,7 +72,7 @@ func TestIsString(t *testing.T) {
 	}

 	count++
-	b, ok = toBool("abc")
+	b, ok = ToBool("abc")
 	if !(ok && b) {
 		t.Errorf("%d: toBool(\"abc\") b=%v, ok=%v -> result = false, want true", count, b, ok)
 		failed++
@@ -81,7 +81,7 @@ func TestIsString(t *testing.T) {
 	}

 	count++
-	b, ok = toBool([]int{})
+	b, ok = ToBool([]int{})
 	if ok {
 		t.Errorf("%d: toBool([]) b=%v, ok=%v -> result = true, want false", count, b, ok)
 		failed++
@@ -97,7 +97,7 @@ func TestToIntOk(t *testing.T) {
 	wantValue := int(64)
 	wantErr := error(nil)

-	gotValue, gotErr := toInt(source, "test")
+	gotValue, gotErr := ToInt(source, "test")

 	if gotErr != nil || gotValue != wantValue {
 		t.Errorf("toInt(%v, \"test\") gotValue=%v, gotErr=%v -> wantValue=%v, wantErr=%v",
@@ -110,7 +110,7 @@ func TestToIntErr(t *testing.T) {
 	wantValue := 0
 	wantErr := errors.New(`test expected integer, got uint64 (64)`)

-	gotValue, gotErr := toInt(source, "test")
+	gotValue, gotErr := ToInt(source, "test")

 	if gotErr.Error() != wantErr.Error() || gotValue != wantValue {
 		t.Errorf("toInt(%v, \"test\") gotValue=%v, gotErr=%v -> wantValue=%v, wantErr=%v",
@@ -156,15 +156,15 @@ func (self *term) toInt(computedValue any, valueDescription string) (i int, err
 	if index64, ok := computedValue.(int64); ok {
 		i = int(index64)
 	} else {
-		err = self.Errorf("%s, got %s (%v)", valueDescription, typeName(computedValue), computedValue)
+		err = self.Errorf("%s, got %s (%v)", valueDescription, TypeName(computedValue), computedValue)
 	}
 	return
 }

 func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
-	leftType := typeName(leftValue)
+	leftType := TypeName(leftValue)
 	leftText := getFormatted(leftValue, Truncate)
-	rightType := typeName(rightValue)
+	rightType := TypeName(rightValue)
 	rightText := getFormatted(rightValue, Truncate)
 	return self.tk.Errorf(
 		"left operand '%s' [%s] and right operand '%s' [%s] are not compatible with operator %q",
@@ -176,7 +176,7 @@ func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
 func (self *term) errIncompatibleType(value any) error {
 	return self.tk.Errorf(
 		"prefix/postfix operator %q do not support operand '%v' [%s]",
-		self.source(), value, typeName(value))
+		self.source(), value, TypeName(value))
 }

 func (self *term) Errorf(template string, args ...any) (err error) {
@@ -0,0 +1,32 @@
+builtin ["os.file", "base"];
+
+readInt=func(fh){
+	line=fileReadText(fh);
+	line ? [nil] {nil} :: {int(line)}
+};
+
+ds={
+	"init":func(filename){
+		fh=fileOpen(filename);
+		fh ? [nil] {nil} :: { @current=readInt(fh) };
+		fh
+	},
+	"current":func(){
+		current
+	},
+	"next":func(fh){
+		@current=readInt(fh);
+		current
+	},
+	"clean":func(fh){
+		fileClose(fh)
+	}
+}
+
+//;f=$(ds, "int.list")
+
+//;f++
+//;f++
+//;f++
+//*/
+//;add(f)
@@ -60,7 +60,11 @@ func (tk *Token) IsError() bool {
 }

 func (tk *Token) IsTerm(termSymbols []Symbol) bool {
-	return tk.IsEos() || tk.IsError() || (termSymbols != nil && slices.Index(termSymbols, tk.Sym) >= 0)
+	return tk.IsEos() || tk.IsError() || tk.IsOneOf(termSymbols)
+}
+
+func (tk *Token) IsOneOf(termSymbols []Symbol) bool {
+	return termSymbols != nil && slices.Index(termSymbols, tk.Sym) >= 0
 }

 func (tk *Token) IsSymbol(sym Symbol) bool {
@@ -86,7 +86,7 @@ func numAsFloat(v any) (f float64) {
 	return
 }

-func toBool(v any) (b bool, ok bool) {
+func ToBool(v any) (b bool, ok bool) {
 	ok = true
 	switch x := v.(type) {
 	case string:
@@ -201,13 +201,13 @@ func CloneFilteredMap[K comparable, V any](source map[K]V, filter func(key K) (a
 	return CopyFilteredMap(dest, source, filter)
 }

-func toInt(value any, description string) (i int, err error) {
+func ToInt(value any, description string) (i int, err error) {
 	if valueInt64, ok := value.(int64); ok {
 		i = int(valueInt64)
 	} else if valueInt, ok := value.(int); ok {
 		i = valueInt
 	} else {
-		err = fmt.Errorf("%s expected integer, got %s (%v)", description, typeName(value), value)
+		err = fmt.Errorf("%s expected integer, got %s (%v)", description, TypeName(value), value)
 	}
 	return
 }
Author	SHA1	Message	Date
camoroso	531cb1c249	Doc: concepts	2024-06-19 09:38:02 +02:00
camoroso	d1b468f35b	t_list_test.go: new test cases added	2024-06-19 09:24:50 +02:00
camoroso	ff9cf80c66	operator-index.go: ConstLastIndex is checked	2024-06-19 09:24:19 +02:00
camoroso	d63b18fd76	parser.go: SymColon resets the firstToken flag; that is needed to specify range indeces that can define negative limits	2024-06-19 09:22:40 +02:00
camoroso	019470faf1	operator-range.go: Fixed priority bug; when range only has the left limit, right limit is set to ConstLastIndex constant	2024-06-19 09:20:02 +02:00
camoroso	302430d57d	common-params.go: added the constant ConstLastIndex	2024-06-19 09:17:46 +02:00
camoroso	62ef0d699d	token.go: new function IsOneOf()	2024-06-19 09:16:19 +02:00
camoroso	866de759dd	file-reader.expr: simpler implementation	2024-06-17 14:07:39 +02:00
camoroso	b1d6b6de44	refactored dict's item access	2024-06-17 14:06:33 +02:00
camoroso	7e357eea62	changed to comply new builtin-os-file.go's function names	2024-06-17 09:54:20 +02:00
camoroso	d6b4c79736	operator-index.go: dict item access by generic keys implemented	2024-06-17 09:05:23 +02:00
camoroso	d066344af8	builtin-os-file.go: changed read and write function names; added fileReadTextAll	2024-06-17 06:59:15 +02:00
camoroso	f41dba069e	plugin.go: support Liteide and VScode to debug executable file name	2024-06-17 06:57:47 +02:00
camoroso	703ecf6829	Added utility function GetLast() to context	2024-06-17 06:56:32 +02:00
camoroso	ba479a1b99	Function call moved from operand-func.go to function.go	2024-06-17 06:54:50 +02:00
camoroso	24e6a293b0	common-params.go: ParamName added	2024-06-12 11:16:57 +02:00
camoroso	28f464c4dc	plugins.go: If the main program's file name ends with '.debug', plugins will be loaded from file with name ending with '.debug'	2024-06-12 11:15:31 +02:00
camoroso	9fb611aa20	Formatter option is now composed of two data: flags (lower 16 bits) and indentation size (higher 16 bits). DictType and ListType formatter use both indent and flag options. Simple-store now makes a DictType from its data and its ToString() function returns dict.ToString()	2024-06-11 16:32:01 +02:00
camoroso	56d6d06d15	simple-store.go: newline removed after context last brace in ToString()	2024-06-10 20:58:38 +02:00
camoroso	d9f7e5b1ad	common-errors.go: exported all error functions. builtin-string.go: renamed all functions from somthingStr() to strSomething()	2024-06-10 20:37:58 +02:00
camoroso	0f54e01ef3	t_scanner_test.go: Test nr 25 changed because now single-quotes can enclose strings	2024-06-10 20:36:03 +02:00
camoroso	63f5db00b3	all test file on builtin functions have been renamed from t_func-_test.go to t_builtin-_test.go	2024-06-10 20:34:11 +02:00
camoroso	9745a5d909	utils.go: toInt() -> ToInt(); toBool() -> ToBool()	2024-06-10 19:03:39 +02:00
camoroso	0bb4c96481	scanner.go: Strings can be enclosed between two single-quotes too	2024-06-10 18:52:13 +02:00
camoroso	1757298eb4	formatter.go: typeName() renamed as TypeName()	2024-06-10 09:37:27 +02:00
camoroso	54041552d4	dict-type.go: added MakeDict() constructor	2024-06-10 09:35:48 +02:00
camoroso	5302907dcf	external plugins can now request for dependencies	2024-06-09 17:12:57 +02:00
camoroso	eb4b17f078	moved all test expression files in the test-resources forlder	2024-06-09 16:02:07 +02:00
camoroso	33d70d6d1a	splitted go and expr function bindings in dedicated source files	2024-06-09 10:41:06 +02:00
camoroso	9df9ad5dd1	func-.go modules renamed as builtin-.go. Also changed and exported some identiefier relatet to the builtin feature	2024-06-09 10:28:51 +02:00
camoroso	34dc828ead	exported some identifier	2024-06-09 10:13:37 +02:00
camoroso	29bc2c62a3	first plugin support. Module organization requires a better structure to decouple definitions and implementations	2024-06-09 07:41:56 +02:00
camoroso	8eb2d77ea3	improved position of some common functions	2024-06-09 07:38:29 +02:00
camoroso	53bcf90d2a	operator-builtin.go: some error messages improved	2024-06-09 07:36:12 +02:00
camoroso	f347b15146	Control vars are now stored in the globalCtx only. However, it is still allowed to store control var in a local context in special situation	2024-06-08 05:49:28 +02:00
camoroso	115ce26ce9	IsOptional() function of ExprFuncParam renamed as IdDefault(). A new IsOptional() function created to check if a param is optional without requiring a default value	2024-06-07 09:45:02 +02:00
camoroso	227944b3fb	Removed eval() function from ast interface and implementation. Check on preset control variables is now done in initDefaultVars()	2024-06-07 09:41:10 +02:00
camoroso	0d01afcc9f	member ctx removed from struct parser because it is unused	2024-06-07 09:03:42 +02:00
camoroso	00c76b41f1	list-type.go: two special constructors, MakeList() and ListFromStrigns(), added	2024-06-07 09:02:14 +02:00
camoroso	08e0979cdd	import-utils.go: addPresetDirs() replaced by addSearchDirs()	2024-06-07 09:01:18 +02:00
camoroso	f04f5822ec	common-type-names.go: added type name list-of	2024-06-07 08:59:04 +02:00
camoroso	80d47879e9	t_list_test.go: removed commented code	2024-06-07 08:54:59 +02:00
camoroso	985eb3d19d	Merge branch 'main' into feat_plugin	2024-06-06 05:33:56 +02:00
camoroso	45734ab393	new test file t_iter-list.go	2024-06-06 05:33:35 +02:00
camoroso	c100cf349d	some identier exported; new file import-utils.go	2024-06-06 05:31:35 +02:00