funcs_test.go: added some tests

Also fixed mul() function that called doAdd() instead of doMul().

README.adoc

@@ -1,5 +1,5 @@
-= Expr
-Expressions calculator
+= README
+README about the Expressions calculator
 :authors: Celestino Amoroso
 :docinfo: shared
 :encoding: utf-8
@@ -63,35 +63,37 @@ package main
 import (
 	"fmt"
 	"strings"
-
 	"git.portale-stac.it/go-pkg/expr"
 )
 
 func main() {
 	ctx := expr.NewSimpleVarStore()
-	ctx.SetValue("var", int64(4))
+	ctx.SetVar("var", 4)
 
 	source := `(3-1)*(10/5) == var`
 
-    r := strings.NewReader(source)
-    scanner := expr.NewScanner(r, DefaultTranslations())
+	r := strings.NewReader(source)
+	scanner := expr.NewScanner(r, expr.DefaultTranslations())
 	parser := expr.NewParser(ctx)
 
 	if ast, err := parser.Parse(scanner); err == nil {
 		if result, err := ast.Eval(ctx); err == nil {
-            fmt.Printf("%q -> %v [%T]\n", source, result, result)
-        } else {
-            fmt.Println("Error calculating the expression:", err)
-        }
+			fmt.Printf("%q -> %v [%T]\n", source, result, result)
+		} else {
+			fmt.Println("Error calculating the expression:", err)
+		}
 	} else {
-        fmt.Println("Error parsing the expression:", err)
-    }
+		fmt.Println("Error parsing the expression:", err)
+	}
 }
 ----
+
 The above program is equivalent to the following one.
 
 [source,go]
 ----
+package main
+
 import (
 	"fmt"
 	"git.portale-stac.it/go-pkg/expr"
@@ -99,223 +101,47 @@ import (
 
 func main() {
 	ctx := expr.NewSimpleVarStore()
-	ctx.SetValue("var", int64(4))
+	ctx.SetVar("var", 4)
 
 	source := `(3-1)*(10/5) == var`
 
-    if result, err := expr.EvalString(ctx, source); err == nil {
-        fmt.Printf("%q -> %v [%T]\n", source, result, result)
-    } else {
-        fmt.Println("Error calculating the expression:", err)
-    }
+	if result, err := expr.EvalString(ctx, source); err == nil {
+		fmt.Printf("%q -> %v [%T]\n", source, result, result)
+	} else {
+		fmt.Println("Error calculating the expression:", err)
+	}
 }
 ----
 
-=== Data types
-_Expr_ supports numerical, string, relational, boolean expressions, and mixed-type lists.
+Here is another equivalent version.
 
-==== Numbers
-Numbers can be integers (GO int64) or float (GO float64). In mixed operations involving integers and floats, integers are automatically promoted to floats.
-
-.Arithmetic operators
-[cols="^1,^2,6,4"]
-|===
-| Symbol    | Operation     | Description               | Examples
-
-| [blue]`+` / [blue]`-` | _change sign_ | Change the sign of values | [blue]`-1` _[-1]_ +
-[blue]`-(+2)` _[-2]_
-
-| [blue]`+` | _sum_ | Add two values | [blue]`-1 + 2` _[1]_ +
-[blue]`4 + 0.5` _[4.5]_
-
-| [blue]`-` | _subtraction_ | Subtract the right value from the left one | [blue]`3 - 1` _[2]_ +
-[blue]`4 - 0.5` _[3.5]_
-
-| [blue]`*` | _product_ | Multiply two values | `-1 * 2` _[-2]_ +
-[blue]`4 * 0.5` _[2.0]_
-
-| [blue]`/` | _Division_ | Divide the left value by the right one | [blue]`-1 / 2` _[0]_ +
-[blue]`1.0 / 2` _[0.5]_
-
-| [blue]`./` | _Float division_ | Force float division | [blue]`-1 ./ 2` _[-0.5]_
-
-| [blue]`%` | _Modulo_ | Remainder of the integer division | [blue]`5 % 2` _[1]_
-
-|=== 
-
-==== String
-Strings are character sequences enclosed between two double quote [blue]`"`. Example: [blue]`"I'm a string"`.
-
-Some arithmetic operators can also be used with strings.
-
-.String operators
-[cols="^1,^2,6,4"]
-|===
-| Symbol    | Operation     | Description               | Examples
-
-| [blue]`+` | _concatenation_ | Join two strings or two _stringable_ values | [blue]`"one" + "two"` _["onetwo"]_ +
-[blue]`"one" + 2` _["one2"]_
-
-| [blue]`*` | _repeat_ | Make _n_ copy of a string  | [blue]`"one" * 2` _["oneone"]_
-|===
-
-
-==== Boolean
-Boolean data type has two values only: _true_ and _false_. Relational and Boolean expressions produce Boolean values.
-
-
-.Relational operators
-[cols="^1,^2,6,4"]
-|===
-| Symbol    | Operation     | Description               | Examples
-
-| [blue]`==` | _Equal_ | True if the left value is equal to the right one | [blue]`5 == 2` _[false]_ +
-[blue]`"a" == "a"` _[true]_
-| [blue]`!=` | _Not Equal_ | True if the left value is NOT equal to the right one | [blue]`5 != 2` _[true]_ +
-[blue]`"a" != "a"` _[false]_
-| [blue]`<` | _Less_ | True if the left value is less than the right one | [blue]`5 < 2` _[false]_ +
-[blue]`"a" < "b"` _[true]_
-| [blue]`\<=` | _Less or Equal_ | True if the left value is less than or equal to the right one | [blue]`5 \<= 2` _[false]_ +
-[blue]`"b" \<= "b"` _[true]_
-| [blue]`>` | _Greater_ | True if the left value is greater than the right one | [blue]`5 > 2` _[true]_ +
-[blue]`"a" < "b"` _[false]_
-| [blue]`>=` | _Greater or Equal_ | True if the left value is greater than or equal to the right one | [blue]`5 >= 2` _[true]_ +
-[blue]`"b" \<= "b"` _[true]_
-|===
-
-
-.Boolean operators
-[cols="^2,^2,5,4"]
-|===
-| Symbol    | Operation     | Description               | Examples
-
-| [blue]`NOT` | _Not_ | True if the right value is false | [blue]`NOT true` _[false]_ +
-[blue]`NOT (2 < 1)` _[true]_
-
-| [blue]`AND` / [blue]`&&` | _And_ | True if both left and right values are true  | [blue]`false && true` _[false]_ +
-[blue]`"a" < "b" AND NOT (2 < 1)` _[true]_
-
-| [blue]`OR` / [blue]`\|\|` | _Or_ | True if at least one of the left and right values integers true| [blue]`false or true` _[true]_ +
-[blue]`"a" == "b" OR (2 == 1)` _[false]_
-|===
-
-[CAUTION]
-====
-Currently, boolean operations are evaluated using _short cut evaluation_. This means that, if the left expression of operators [blue]`and` and [blue]`or` is sufficient to establish the result of the whole operation, the right expression would not evaluated at all.
-
-.Example
 [source,go]
 ----
-2 > (a=1) or (a=8) > 0; a // <1>
-----
-<1> This multi-expression returns _1_ because in the first expression the left value of [blue]`or` is _true_ and as a conseguence its right value is not computed. Therefore the _a_ variable only receives the integer _1_.
-====
+package main
 
-==== List
-#TODO: List operations#
+import (
+	"fmt"
+	"git.portale-stac.it/go-pkg/expr"
+)
 
-=== Variables
-#TODO: variables#
+func main() {
+	source := `(3-1)*(10/5) == var`
 
-=== Other operations
-
-==== [blue]`;` operator
-The semicolon operator [blue]`;` is an infixed operator. It evaluates the left expression first and then the right expression. The latter is the final result.
-
-IMPORTANT: Technically [blue]`;` is not treated as a real operator. It acts as a separator in lists of expressions.
-
-TIP: [blue]`;` can be used to set some variables before the final calculation.
-
-.Example
-[source,go]
-----
-a=1; b=2; c=3; a+b+c    // returns 6
+	if result, err := expr.EvalStringA(source, expr.Arg{"var", 4}); err == nil {
+		fmt.Printf("%q -> %v [%T]\n", source, result, result)
+	} else {
+		fmt.Println("Error calculating the expression:", err)
+	}
+}
 ----
 
-==== [blue]`but` operator
-[blue]`but` is an infixed operator. Its operands can be any type of expression. It evaluates the left expression first, then the right expression. The value of the right expression is the final result. Examples: [blue]`5 but 2` returns 2, [blue]`x=2*3 but x-1` returns 5.
+== Context of evaluation
+Unless helpers functions like _expr.EvalStringA()_ are used, a _context_ is required to compute an expession.
 
-[blue]`but` is very similar to [blue]`;`. The only difference is that [blue]`;` can't be used inside parenthesis [blue]`;(` and [blue]`)`.
-
-==== Assignment operator [blue]`=`
-The assignment operator [blue]`=` is used to define variable in the evaluation context or to change their value (see _ExprContext_).
-The value on the left side of [blue]`=` must be an identifier. The value on the right side can be any expression and it becomes the result of the assignment operation.
-
-.Example
-[source,go]
-----
-a=15+1    // returns 16
-----
-
-==== Selector operator [blue]`? : ::`
-The _selector operator_ is very similar to the _switch/case/default_ statement available in many programming languages.
-
-.Syntax
-[source,bnf]
-----
-<selector-operator> ::= <expression> "?" <selector-case> { ":" <selector-case> } ["::" <case-value>]
-<selector-case> ::= [<list>] <case-value>
-<case-value> ::= "{" <multi-expr> "}"
-<multi-expr> ::= <expr> {";" <expr>}
-----
-
-.Example
-[source,go]
-----
-1 ? {"a"} : {"b"}                           // returns "b"
-10 ? {"a"} : {"b"} :: {"c"}                 // returns "c"
-10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}      // returns "b"
-10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}  // error:  "... case list in default clause"
-10 ? {"a"} :[10] {x="b" but x} :: {"c"}     // returns "b"
-10 ? {"a"} :[10] {x="b"; x} :: {"c"}        // returns "b"
-10 ? {"a"} : {"b"}                          // error:  "... no case catches the value (10) of the selection expression
-----
-
-=== Priorities of operators
-The table below shows all supported operators by decreasing priorities.
-
-.Operators priorities
-[cols="^2,^2,^2,^5,<5"]
-|===
-| Priority | Operators     | Position | Operation | Operands and results
-
-1+|*FACT*| [blue]`!` | _Postfix_ | _Factorial_| _integer_ "!" -> _integer_
-1+|*SIGN*| [blue]`+`, [blue]`-` | _Prefix_ | _Change-sign_| ("+"\|"-") _number_ -> _number_
-.5+|*PROD*| [blue]`*` | _Infix_ | _Product_ | _number_ "*" _number_ -> _number_
-| [blue]`*` | _Infix_ | _String-repeat_ | _string_ "*" _integer_ -> _string_
-| [blue]`/` | _Infix_ | _Division_ | _number_ "/" _number_ -> _number_
-| [blue]`./` | _Infix_ | _Float-division_ | __number__ "./" _number_ -> _float_
-| [blue]`%` | _Infix_ | _Integer-remainder_ | _integer_ "%" _integer_ -> _integer_
-.5+|*SUM*| [blue]`+` | _Infix_ | _Sum_ | _number_ "+" _number_ -> _number_
-| [blue]`+` | _Infix_ |  _String-concat_ | (_string_\|_number_) "+" (_string_\|_number_) -> _string_
-| [blue]`+` | _Infix_ |  _List-join_ | _list_ "+" _list_ -> _list_
-| [blue]`-` | _Infix_ | _Subtraction_ | _number_ "-" _number_ -> _number_
-| [blue]`-` | _Infix_ | _List-difference_ | _list_ "-" _list_ -> _list_
-.6+|*RELATION*| [blue]`<` | _Infix_ | _less_ | _comparable_ "<" _comparable_ -> _boolean_
-| [blue]`\<=` | _Infix_ |  _less-equal_ | _comparable_ "\<=" _comparable_ -> _boolean_
-| [blue]`>` | _Infix_ |  _greater_ | _comparable_ ">" _comparable_ -> _boolean_
-| [blue]`>=` | _Infix_ |  _greater-equal_ | _comparable_ ">=" _comparable_ -> _boolean_
-| [blue]`==` | _Infix_ |  _equal_ | _comparable_ "==" _comparable_ -> _boolean_
-| [blue]`!=` | _Infix_ |  _not-equal_ | _comparable_ "!=" _comparable_ -> _boolean_
-.1+|*NOT*| [blue]`not` | _Prefix_ | _not_ | "not" _boolean_ -> _boolean_
-.2+|*AND*| [blue]`and` | _Infix_ | _and_ | _boolean_ "and" _boolean_ -> _boolean_
-| [blue]`&&` | _Infix_ | _and_ | _boolean_ "&&" _boolean_ -> _boolean_
-.2+|*OR*| [blue]`or` | _Infix_ | _or_ | _boolean_ "or" _boolean_ -> _boolean_
-| [blue]`||` | _Infix_ | _or_ | _boolean_ "||" _boolean_ -> _boolean_
-.1+|*ASSIGN*| [blue]`=` | _Infix_ | _assignment_ | _identifier_ "=" _any_ -> _any_
-.1+|*BUT*| [blue]`but` | _Infix_ | _but_ | _any_ "but" _any_ -> _any_
-|===
-
-=== Functions
-
-==== Function calls
-#TODO: function calls operations#
-
-==== Function definitions
-#TODO: function definitions operations#
-
-==== Builtins
-#TODO: builtins#
+A context is an object that implements the _expr.ExprContext_ interface. This interface specifies a set of function to handle variables and functions.
 
+Variables and functions can be added to a context both programmatically and ad an effect of the expression computation.
 
+== Expressions syntax
 
+See #TODO link to doc/Expr.html#

ast.go

@@ -5,13 +5,13 @@
 package expr
 
 import (
-	"errors"
 	"strings"
 )
 
 type Expr interface {
 	Eval(ctx ExprContext) (result any, err error)
 	eval(ctx ExprContext, preset bool) (result any, err error)
+	String() string
 }
 
 //-------- ast
@@ -60,10 +60,10 @@ func (self *ast) addToken(tk *Token) (err error) {
 }
 
 func (self *ast) addToken2(tk *Token) (t *term, err error) {
-	if t = newTerm(tk, nil); t != nil {
+	if t = newTerm(tk); t != nil {
 		err = self.addTerm(t)
 	} else {
-		err = tk.Errorf("No term constructor for token %q", tk.String())
+		err = tk.Errorf("unexpected token %q", tk.String())
 	}
 	return
 }
@@ -83,8 +83,9 @@ func (self *ast) insert(tree, node *term) (root *term, err error) {
 		if tree.isComplete() {
 			var subRoot *term
 			last := tree.removeLastChild()
-			subRoot, err = self.insert(last, node)
-			subRoot.setParent(tree)
+			if subRoot, err = self.insert(last, node); err == nil {
+				subRoot.setParent(tree)
+			}
 		} else {
 			node.setParent(tree)
 		}
@@ -118,7 +119,7 @@ func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
 		if self.forest != nil {
 			for _, root := range self.forest {
 				if result, err = root.compute(ctx); err == nil {
-					ctx.SetVar(control_last_result, result)
+					ctx.setVar(ControlLastResult, result)
 				} else {
 					//err = fmt.Errorf("error in expression nr %d: %v", i+1, err)
 					break
@@ -127,9 +128,10 @@ func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
 		}
 		if err == nil {
 			result, err = self.root.compute(ctx)
+			ctx.setVar(ControlLastResult, result)
 		}
-	} else {
-		err = errors.New("empty expression")
+		// } else {
+		// 	err = errors.New("empty expression")
 	}
 	return
 }

ast_test.go

@@ -44,7 +44,7 @@ func TestAddTokensBad(t *testing.T) {
 func TestAddUnknownTokens(t *testing.T) {
 	tk0 := NewToken(0, 0, SymPercent, "%")
 
-	wantErr := errors.New(`No term constructor for token "%"`)
+	wantErr := errors.New(`unexpected token "%"`)
 
 	tree := NewAst()
 	if gotErr := tree.addToken(tk0); gotErr != nil && gotErr.Error() != wantErr.Error() {

common-errors.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-errors.go
+package expr
+
+import (
+	"fmt"
+)
+
+// --- General errors
+
+func errCantConvert(funcName string, value any, kind string) error {
+	return fmt.Errorf("%s() can't convert %T to %s", funcName, value, kind)
+}
+
+func errExpectedGot(funcName string, kind string, value any) error {
+	return fmt.Errorf("%s() expected %s, got %T (%v)", funcName, kind, value, value)
+}
+
+func errDivisionByZero(funcName string) error {
+	return fmt.Errorf("%s() division by zero", funcName)
+}
+
+// --- Parameter errors
+
+func errOneParam(funcName string) error {
+	return fmt.Errorf("%s() requires exactly one param", funcName)
+}
+
+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 %T (%v) for parameter %q", funcName, 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 %T (%v)", funcName, paramName, paramType, paramValue, paramValue)
+}

common-params.go

@@ -0,0 +1,11 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-params.go
+package expr
+
+const (
+	paramParts     = "parts"
+	paramSeparator = "separator"
+	paramSource    = "source"
+)

common-type-names.go

@@ -0,0 +1,14 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// common-type-names.go
+package expr
+
+const (
+	typeBoolean  = "boolean"
+	typeFloat    = "decimal"
+	typeFraction = "fraction"
+	typeInt      = "integer"
+	typeNumber   = "number"
+	typeString   = "string"
+)

context-helpers.go

@@ -0,0 +1,43 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// context-helpers.go
+package expr
+
+func cloneContext(sourceCtx ExprContext) (clonedCtx ExprContext) {
+	if sourceCtx != nil {
+		clonedCtx = sourceCtx.Clone()
+	}
+	return
+}
+
+func exportVar(ctx ExprContext, name string, value any) {
+	if name[0] == '@' {
+		name = name[1:]
+	}
+	ctx.setVar(name, value)
+}
+
+func exportFunc(ctx ExprContext, name string, info ExprFunc) {
+	if name[0] == '@' {
+		name = name[1:]
+	}
+	ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
+}
+
+func exportObjects(destCtx, sourceCtx ExprContext) {
+	exportAll := isEnabled(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] == '@' }) {
+		// fmt.Printf("\tExporting %q\n", refName)
+		refValue, _ := sourceCtx.GetVar(refName)
+		exportVar(destCtx, refName, refValue)
+	}
+	// Export functions
+	for _, refName := range sourceCtx.EnumFuncs(func(name string) bool { return exportAll || name[0] == '@' }) {
+		if info, _ := sourceCtx.GetFuncInfo(refName); info != nil {
+			exportFunc(destCtx, refName, info)
+		}
+	}
+}

context.go

@@ -33,9 +33,10 @@ type ExprContext interface {
 	Clone() ExprContext
 	GetVar(varName string) (value any, exists bool)
 	SetVar(varName string, value any)
+	setVar(varName string, value any)
 	EnumVars(func(name string) (accept bool)) (varNames []string)
 	EnumFuncs(func(name string) (accept bool)) (funcNames []string)
-	GetFuncInfo(name string) ExprFunc
+	GetFuncInfo(name string) (item ExprFunc, exists bool)
 	Call(name string, args []any) (result any, err error)
 	RegisterFunc(name string, f Functor, minArgs, maxArgs int)
 }

control.go

@@ -1,13 +1,16 @@
-// preset.go
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// control.go
 package expr
 
 import "strings"
 
 // Preset control variables
 const (
-	control_last_result   = "_last"
-	control_bool_shortcut = "_bool_shortcut"
-	control_import_path   = "_import_path"
+	ControlLastResult   = "last"
+	ControlBoolShortcut = "_bool_shortcut"
+	ControlImportPath   = "_import_path"
 )
 
 // Other control variables
@@ -21,8 +24,8 @@ const (
 )
 
 func initDefaultVars(ctx ExprContext) {
-	ctx.SetVar(control_bool_shortcut, true)
-	ctx.SetVar(control_import_path, init_import_path)
+	ctx.SetVar(ControlBoolShortcut, true)
+	ctx.SetVar(ControlImportPath, init_import_path)
 }
 
 func enable(ctx ExprContext, name string) {

data-cursor.go

@@ -0,0 +1,154 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// data-cursors.go
+package expr
+
+import (
+	"errors"
+	"io"
+)
+
+type dataCursor struct {
+	ds          map[string]Functor
+	ctx         ExprContext
+	index       int
+	resource    any
+	nextFunc    Functor
+	cleanFunc   Functor
+	resetFunc   Functor
+	currentFunc Functor
+}
+
+func newDataCursor(ctx ExprContext, ds map[string]Functor) (dc *dataCursor) {
+	dc = &dataCursor{
+		ds:    ds,
+		index: -1,
+		ctx:   ctx.Clone(),
+	}
+	return
+}
+
+// func mapToString(m map[string]Functor) string {
+// 	var sb strings.Builder
+// 	sb.WriteByte('{')
+// 	for key, _ := range m {
+// 		if sb.Len() > 1 {
+// 			sb.WriteString(fmt.Sprintf(", %q: func(){}", key))
+// 		} else {
+// 			sb.WriteString(fmt.Sprintf("%q: func(){}", key))
+// 		}
+// 	}
+// 	sb.WriteByte('}')
+// 	return sb.String()
+// }
+
+func (dc *dataCursor) String() string {
+	return "$()"
+	/*
+	   var sb strings.Builder
+	   sb.WriteString(fmt.Sprintf(`$(
+	   index: %d,
+	   ds:    %s,
+	   ctx:   `, dc.index, mapToString(dc.ds)))
+	   CtxToBuilder(&sb, dc.ctx, 1)
+	   sb.WriteByte(')')
+	   return sb.String()
+	*/
+}
+
+func (dc *dataCursor) HasOperation(name string) (exists bool) {
+	exists = name == indexName
+	if !exists {
+		f, ok := dc.ds[name]
+		exists = ok && isFunctor(f)
+	}
+	return
+}
+
+func (dc *dataCursor) CallOperation(name string, args []any) (value any, err error) {
+	if name == indexName {
+		value = int64(dc.Index())
+	} else if functor, ok := dc.ds[name]; ok && isFunctor(functor) {
+		if functor == dc.cleanFunc {
+			value, err = dc.Clean()
+		} else if functor == dc.resetFunc {
+			value, err = dc.Reset()
+		} else {
+			ctx := cloneContext(dc.ctx)
+			value, err = functor.Invoke(ctx, name, []any{})
+			exportObjects(dc.ctx, ctx)
+		}
+	} else {
+		err = errNoOperation(name)
+	}
+	return
+}
+
+func (dc *dataCursor) Reset() (success bool, err error) {
+	if dc.resetFunc != nil {
+		if dc.resource != nil {
+			ctx := cloneContext(dc.ctx)
+			if _, err = dc.resetFunc.Invoke(ctx, resetName, []any{dc.resource}); err == nil {
+				dc.index = -1
+			}
+			exportObjects(dc.ctx, ctx)
+		} else {
+			err = errInvalidDataSource()
+		}
+	} else {
+		err = errNoOperation(resetName)
+	}
+	success = err == nil
+	return
+}
+
+func (dc *dataCursor) Clean() (success bool, err error) {
+	if dc.cleanFunc != nil {
+		if dc.resource != nil {
+			ctx := cloneContext(dc.ctx)
+			_, err = dc.cleanFunc.Invoke(ctx, cleanName, []any{dc.resource})
+			dc.resource = nil
+			exportObjects(dc.ctx, ctx)
+		} else {
+			err = errInvalidDataSource()
+		}
+	} else {
+		err = errors.New("no 'clean' function defined in the data-source")
+	}
+	success = err == nil
+	return
+}
+
+func (dc *dataCursor) Current() (item any, err error) { // must return io.EOF at the last item
+	ctx := cloneContext(dc.ctx)
+	if item, err = dc.currentFunc.Invoke(ctx, currentName, []any{}); err == nil && item == nil {
+		err = io.EOF
+	}
+	exportObjects(dc.ctx, ctx)
+	return
+}
+
+func (dc *dataCursor) Next() (item any, err error) { // must return io.EOF after the last item
+	if dc.resource != nil {
+		ctx := cloneContext(dc.ctx)
+		// fmt.Printf("Entering Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
+		if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{dc.resource}); err == nil {
+			if item == nil {
+				err = io.EOF
+			} else {
+				dc.index++
+			}
+		}
+		// fmt.Printf("Exiting Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
+		exportObjects(dc.ctx, ctx)
+		// fmt.Printf("Outer-Ctx [%p]: %s\n", dc.ctx, CtxToString(dc.ctx, 0))
+	} else {
+		err = errInvalidDataSource()
+	}
+	return
+}
+
+func (dc *dataCursor) Index() int {
+	return dc.index
+}

dict_test.go

@@ -0,0 +1,103 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// dict_test.go
+package expr
+
+import (
+	"errors"
+
+	"strings"
+	"testing"
+)
+
+func TestDictParser(t *testing.T) {
+	section := "Dict"
+
+	type inputType struct {
+		source     string
+		wantResult any
+		wantErr    error
+	}
+
+	inputs := []inputType{
+		/*  1 */ {`{}`, map[any]any{}, nil},
+		/*  2 */ {`{123}`, nil, errors.New(`[1:6] expected ":", got "}"`)},
+		/*  3 */ {`{1:"one",2:"two",3:"three"}`, map[int64]any{int64(1): "one", int64(2): "two", int64(3): "three"}, nil},
+		/*  4 */ {`{1:"one",2:"two",3:"three"}.2`, "three", nil},
+		/*  5 */ {`#{1:"one",2:"two",3:"three"}`, int64(3), nil},
+		/*  6 */ {`{1:"one"} + {2:"two"}`, map[any]any{1: "one", 2: "two"}, nil},
+	}
+
+	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 := NewSimpleFuncStore()
+		ctx.SetVar("var1", int64(123))
+		ctx.SetVar("var2", "abc")
+		ImportMathFuncs(ctx)
+		parser := NewParser(ctx)
+
+		logTest(t, i+1, "Dict", 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)
+}

doc/Expr.adoc

@@ -0,0 +1,471 @@
+= Expr
+Expressions calculator
+:authors: Celestino Amoroso
+:docinfo: shared
+:encoding: utf-8
+:toc: right
+:toclevels: 4
+//:toc-title: Indice Generale
+:icons: font
+:icon-set: fi
+:numbered:
+//:table-caption: Tabella
+//:figure-caption: Diagramma
+:docinfo1:
+:sectlinks:
+:sectanchors:
+:source-highlighter: rouge
+// :rouge-style: ThankfulEyes
+:rouge-style: gruvbox
+// :rouge-style: colorful
+//:rouge-style: monokay
+
+toc::[]
+
+#TODO: Work in progress (last update on 2024/05/10, 06:52 a.m.)#
+
+== Expr
+_Expr_ is a GO package capable of analysing, interpreting and calculating expressions.
+
+=== Concepts and terminology
+#TODO#
+
+image::expression-diagram.png[]
+
+=== `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, beyond in additon to the automatic test suite based on the Go test framework, `dev-expr` provides an important aid for quickly testing of new features during their development.
+
+It cat work as a _REPL_, _**R**ead-**E**xecute-**P**rint-**L**oop_, or it can process expression acquired from files or standard input.
+
+The program can be downloaded from https://git.portale-stac.it/go-pkg/-/packages/generic/dev-expr/[dev-expr].
+
+Here are some examples of execution.
+
+.Run `dev-expr` in REPL mode and ask for help
+[source,shell]
+----
+# Assume the expr source directory. Type 'exit' or Ctrl+D to quit the program.
+
+[user]$ tools/expr -- Expressions calculator v1.7.0,2024/05/08 (celestino.amoroso@portale-stac.it)
+	Type help to get the list of command.
+	See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
+
+>>> help
+--- REPL commands:
+        base -- Set the integer output base: 2, 8, 10, or 16
+        exit -- Exit the program
+        help -- Show command list
+          ml -- Enable/Disable multi-line output
+        mods -- List builtin modules
+      source -- Load a file as input
+         tty -- Enable/Disable ansi output <1>
+
+--- Command line options:
+    -b <builtin>       Import builtin modules.
+                       <builtin> can be a list of module names or a glob-pattern.
+                       Use the special value 'all' or the pattern '*' to import all modules.
+    -e <expression>    Evaluate <expression> instead of standard-input
+    -i                 Force REPL operation when all -e occurences have been processed
+    -h, --help, help   Show this help menu
+    -m, --modules      List all builtin modules
+    -p                 Print prefix form
+    -t                 Print tree form <2>
+
+>>> 
+----
+
+<1> Only available for single fraction values
+<2> Work in progress
+
+.REPL examples
+[source,shell]
+----
+[user]$ tools/expr -- Expressions calculator v1.6.1,2024/05/06 (celestino.amoroso@portale-stac.it)
+        Type help to get the list of command.
+        See also https://git.portale-stac.it/go-pkg/expr/src/branch/main/README.adoc
+>>> 2+3
+5
+>>> 2+3*(4-1.5)
+9.5
+>>> 0xFD + 0b1 + 0o1 <1>
+255
+>>> 1|2 + 2|3 <2>
+7|6
+>>> ml <3>
+>>> 1|2 + 2|3
+7
+-
+6
+>>> 1+2 but 5|2+0.5 <4>
+3
+>>> 1+2; 5|2+0.5 <5>
+3
+>>>
+----
+
+<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.
+
+=== Numbers
+Numbers can be integers (GO int64) or float (GO float64). In mixed operations involving integers and floats, integers are automatically promoted to floats.
+
+.Arithmetic operators
+[cols="^1,^2,6,4"]
+|===
+| Symbol    | Operation     | Description               | Examples
+
+| [blue]`+` / [blue]`-` | _change sign_ | Change the sign of values | [blue]`-1` _[-1]_ +
+[blue]`-(+2)` _[-2]_
+
+| [blue]`+` | _sum_ | Add two values | [blue]`-1 + 2` _[1]_ +
+[blue]`4 + 0.5` _[4.5]_
+
+| [blue]`-` | _subtraction_ | Subtract the right value from the left one | [blue]`3 - 1` _[2]_ +
+[blue]`4 - 0.5` _[3.5]_
+
+| [blue]`*` | _product_ | Multiply two values | `-1 * 2` _[-2]_ +
+[blue]`4 * 0.5` _[2.0]_
+
+| [blue]`/` | _Division_ | Divide the left value by the right one | [blue]`-1 / 2` _[0]_ +
+[blue]`1.0 / 2` _[0.5]_
+
+| [blue]`./` | _Float division_ | Force float division | [blue]`-1 ./ 2` _[-0.5]_
+
+| [blue]`%` | _Modulo_ | Remainder of the integer division | [blue]`5 % 2` _[1]_
+
+|=== 
+
+=== Fractions
+_Expr_ also supports fractions. Fraction literals are made with two integers separated by a vertical bar `|`.
+
+.Examples
+// [source,go]
+// ----
+`>>>` [blue]`1 | 2` +
+[green]`1|2` +
+`>>>` [blue]`4|6` +
+[green]`2|3` [gray]_Fractions are always reduced to their lowest terms_ +
+`>>>` [blue]`1|2 + 2|3` +
+[green]`7|6` +
+`>>>` [blue]`1|2 * 2|3` +
+[green]`1|3` +
+`>>>` [blue]`1|2 / 1|3` +
+[green]`3|2` +
+`>>>` [blue]`1|2 ./ 1|3` [gray]_Force decimal division_ +
+[green]`1.5` +
+`>>>` [blue]`-1|2` +
+[green]`-1|2` +
+`>>>` [blue]`1|-2` [gray]_Wrong sign specification_ +
+[red]_Eval Error: [1:3] infix operator "|" requires two non-nil operands, got 1_ +
+`>>>` [blue]`1|(-2)` +
+[green]`-1|2`
+// ----
+
+Fractions can be used together with integers and floats in expressions.
+
+`>>>` [blue]`1|2 + 5` +
+[green]`11|2` +
+`>>>` [blue]`4 - 1|2` +
+[green]`7|2` +
+`>>>` [blue]`1.0 + 1|2` +
+[green]`1.5` +
+
+
+
+=== Strings
+Strings are character sequences enclosed between two double quote [blue]`"`. Example: [blue]`"I'm a string"`.
+
+Some arithmetic operators can also be used with strings.
+
+.String operators
+[cols="^1,^2,6,4"]
+|===
+| Symbol    | Operation     | Description               | Examples
+
+| [blue]`+` | _concatenation_ | Join two strings or two _stringable_ values | [blue]`"one" + "two"` _["onetwo"]_ +
+[blue]`"one" + 2` _["one2"]_
+
+| [blue]`*` | _repeat_ | Make _n_ copy of a string  | [blue]`"one" * 2` _["oneone"]_
+|===
+
+The items of strings can be accessed using the dot `.` operator.
+
+.Item access syntax
+[source,bnf]
+----
+<item> ::= <string-expr>"."<index-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`       [gray]_number of chars_ +
+[gren]`3` +
+`>>>` [blue]`#"abc"`   [gray]_number of chars_ +
+[green]`3` +
+
+=== Boolean
+Boolean data type has two values only: _true_ and _false_. Relational and Boolean expressions produce Boolean values.
+
+
+.Relational operators
+[cols="^1,^2,6,4"]
+|===
+| Symbol    | Operation     | Description               | Examples
+
+| [blue]`==` | _Equal_ | True if the left value is equal to the right one | [blue]`5 == 2` _[false]_ +
+[blue]`"a" == "a"` _[true]_
+| [blue]`!=` | _Not Equal_ | True if the left value is NOT equal to the right one | [blue]`5 != 2` _[true]_ +
+[blue]`"a" != "a"` _[false]_
+| [blue]`<` | _Less_ | True if the left value is less than the right one | [blue]`5 < 2` _[false]_ +
+[blue]`"a" < "b"` _[true]_
+| [blue]`\<=` | _Less or Equal_ | True if the left value is less than or equal to the right one | [blue]`5 \<= 2` _[false]_ +
+[blue]`"b" \<= "b"` _[true]_
+| [blue]`>` | _Greater_ | True if the left value is greater than the right one | [blue]`5 > 2` _[true]_ +
+[blue]`"a" < "b"` _[false]_
+| [blue]`>=` | _Greater or Equal_ | True if the left value is greater than or equal to the right one | [blue]`5 >= 2` _[true]_ +
+[blue]`"b" \<= "b"` _[true]_
+|===
+
+
+.Boolean operators
+[cols="^2,^2,5,4"]
+|===
+| Symbol    | Operation     | Description               | Examples
+
+| [blue]`NOT` | _Not_ | True if the right value is false | [blue]`NOT true` _[false]_ +
+[blue]`NOT (2 < 1)` _[true]_
+
+| [blue]`AND` / [blue]`&&` | _And_ | True if both left and right values are true  | [blue]`false && true` _[false]_ +
+[blue]`"a" < "b" AND NOT (2 < 1)` _[true]_
+
+| [blue]`OR` / [blue]`\|\|` | _Or_ | True if at least one of the left and right values integers true| [blue]`false or true` _[true]_ +
+[blue]`"a" == "b" OR (2 == 1)` _[false]_
+|===
+
+[CAUTION]
+====
+Currently, boolean operations are evaluated using _short cut evaluation_. This means that, if the left expression of operators [blue]`and` and [blue]`or` is sufficient to establish the result of the whole operation, the right expression would not evaluated at all.
+
+.Example
+[source,go]
+----
+2 > (a=1) or (a=8) > 0; a // <1>
+----
+<1> This multi-expression returns _1_ because in the first expression the left value of [blue]`or` is _true_ and as a conseguence its right value is not computed. Therefore the _a_ variable only receives the integer _1_.
+====
+
+=== Lists
+_Expr_ supports list of mixed-type values, also specified by normal expressions.
+
+.List examples
+[source,go]
+----
+[1, 2, 3]                   // List of integers
+["one", "two", "three"]     // List of strings
+["one", 2, false, 4.1]      // List of mixed-types
+["one"+1, 2.0*(9-2)]        // List of expressions
+[ [1,"one"], [2,"two"]]     // List of lists
+----
+
+.List operators
+[cols="^2,^2,5,4"]
+|===
+| Symbol    | Operation     | Description               | Examples
+
+| [blue]`+` | _Join_ | Joins two lists | [blue]`[1,2] + [3]` _[ [1,2,3] ]_
+
+| [blue]`-` | _Difference_ | Left list without elements in the right list  | [blue]`[1,2,3] - [2]` _[ [1,3] ]_
+|===
+
+The items of array can be accessed using the dot `.` operator.
+
+.Item access syntax
+[source,bnf]
+----
+<item> ::= <list-expr>"."<index-expr>
+----
+
+.Items of list
+`>>>` [blue]`[1,2,3].1` +
+[green]`2` +
+`>>>` [blue]`list=[1,2,3]; list.1` +
+[green]`2` +
+`>>>` [blue]`["one","two","three"].1` +
+[green]`two` +
+`>>>` [blue]`list=["one","two","three"]; list.(2-1)` +
+[green]`two` +
+`>>>` [blue]`list.(-1)` +
+[green]`three` +
+`>>>` [blue]`list.(10)` +
+[red]`Eval Error: [1:9] index 10 out of bounds` +
+`>>>` [blue]`#list` +
+[green]`3`
+
+
+
+== Dictionaries
+The _dictionary_ data-type is set of pairs _key/value_. It is also known as _map_ or _associative array_. Dictionary literals are sequences of pairs separated by comma `,`; sequences are enclosed between brace brackets.
+
+.Dictionary examples
+[source,go]
+----
+{1:"one", 2:"two"}
+{"one":1, "two": 2}
+{"sum":1+2+3, "prod":1*2*3}
+----
+
+WARNING: Support for dictionaries is still ongoing.
+
+== Variables
+A variable is an identifier with an assigned value. Variables are stored in the object that implements the Go _ExprContext_ interface, e.g. _SimpleVarStore_ or _SimpleFuncStore_.
+
+.Examples
+[source,go]
+----
+a=1
+x = 5.2 * (9-3)
+x = 1; y = 2*x
+----
+
+== Other operations
+
+=== [blue]`;` operator
+The semicolon operator [blue]`;` is an infixed pseudo-operator. It evaluates the left expression first and then the right expression. The latter is the final result.
+
+IMPORTANT: Technically [blue]`;` is not treated as a real operator. It acts as a separator in lists of expressions.
+
+TIP: [blue]`;` can be used to set some variables before the final calculation.
+
+.Example
+[source,go]
+----
+a=1; b=2; c=3; a+b+c    // returns 6
+----
+
+=== [blue]`but` operator
+[blue]`but` is an infixed operator. Its operands can be expressions of any type. It evaluates the left expression first, then the right expression. The value of the right expression is the final result. Examples: [blue]`5 but 2` returns 2, [blue]`x=2*3 but x-1` returns 5.
+
+[blue]`but` is very similar to [blue]`;`. The only difference is that [blue]`;` can't be used inside parenthesis [blue]`(` and [blue]`)`.
+
+=== Assignment operator [blue]`=`
+The assignment operator [blue]`=` is used to define variables in the evaluation context or to change their value (see _ExprContext_).
+The value on the left side of [blue]`=` must be an identifier. The value on the right side can be any expression and it becomes the result of the assignment operation.
+
+.Example
+[source,go]
+----
+a=15+1    // returns 16
+----
+
+=== Selector operator [blue]`? : ::`
+The _selector operator_ is very similar to the _switch/case/default_ statement available in many programming languages.
+
+.Syntax
+[source,bnf]
+----
+<selector-operator> ::= <select-expression> "?" <selector-case> { ":" <selector-case> } ["::" <default-multi-expression>]
+<selector-case> ::= [<match-list>] <case-value>
+<match-list> ::= "["<item>{","<items>}"]"
+<item> ::= <expression
+<case-multi-expression> ::= "{" <multi-expression> "}"
+<multi-expression> ::= <expression> {";" <expression>}
+----
+
+In other words, the selector operator evaluates the expression (`<select-expression>`) on the left-hand side of the `?` symbol; it then compares the result obtained with the values listed in the `<match-list>`'s. If the comparision finds a match with a value in a match-list, the associated  `<case-multi-expression>` is evaluted, and its result will be the final result of the selection operation.
+
+The match lists are optional. In that case, the position, from left to right, of the `<selector-case>` is used as match-list. Of course, that only works if the select-expression results in an integer.
+
+The `:` symbol (colon) is the separator of the selector-cases. Note that if the value of the select-expression does not match any match-list, an error will be issued. Therefore, it is strongly recommended to provide a default (multi-)expression introduced by the `::` symbol (double-colon). Also note that the default expression has no match-list.
+
+.Examples
+[source,go]
+----
+`>>>` [blue]`1 ? {"a"} : {"b"}`
+[green]`b`
+`>>>` [blue]`10 ? {"a"} : {"b"} :: {"c"}`
+[green]`c'
+[green]`>>>` [blue]`10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}`
+[green]`b`
+`>>>` [blue]`10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}`
+[red]`Parse Error: [1:34] case list in default clause`
+[green]`>>>` [blue]`10 ? {"a"} :[10] {x="b" but x} :: {"c"}`
+[green]`b`
+`>>>` [blue]`10 ? {"a"} :[10] {x="b"; x} :: {"c"}`
+[green]`b`
+`>>>` [blue]`10 ? {"a"} : {"b"}`
+[red]`Eval Error: [1:3] no case catches the value (10) of the selection expression`
+
+----
+
+== Priorities of operators
+The table below shows all supported operators by decreasing priorities.
+
+.Operators priorities
+[cols="^2,^2,^2,^5,^5"]
+|===
+| Priority | Operators     | Position | Operation | Operands and results
+
+.1+|*ITEM*| [blue]`.` | _Infix_ | _Item_| _collection_ `"."` _key_ -> _any_
+.2+|*INC*| [blue]`++` | _Postfix_ | _Post increment_| _integer-variable_ `"++"` -> _integer_
+| [blue]`++` | _Postfix_ | _Next item_ | _iterator_ `"++"` -> _any_
+.1+|*FACT*| [blue]`!` | _Postfix_ | _Factorial_| _integer_ `"!"` -> _integer_
+.3+|*SIGN*| [blue]`+`, [blue]`-` | _Prefix_ | _Change-sign_| (`"+"`\|`"-"`) _number_ -> _number_
+| [blue]`#` | _Prefix_ | _Lenght-of_ | `"#"` _collection_ -> _integer_
+| [blue]`#` | _Prefix_ | _Size-of_ | `"#"` _iterator_ -> _integer_
+.5+|*PROD*| [blue]`*` | _Infix_ | _Product_ | _number_ `"*"` _number_ -> _number_
+| [blue]`*` | _Infix_ | _String-repeat_ | _string_ `"*"` _integer_ -> _string_
+| [blue]`/` | _Infix_ | _Division_ | _number_ `"/"` _number_ -> _number_
+| [blue]`./` | _Infix_ | _Float-division_ | __number__ `"./"` _number_ -> _float_
+| [blue]`%` | _Infix_ | _Integer-remainder_ | _integer_ `"%"` _integer_ -> _integer_
+.5+|*SUM*| [blue]`+` | _Infix_ | _Sum_ | _number_ `"+"` _number_ -> _number_
+| [blue]`+` | _Infix_ |  _String-concat_ | (_string_\|_number_) `"+"` (_string_\|_number_) -> _string_
+| [blue]`+` | _Infix_ |  _List-join_ | _list_ `"+"` _list_ -> _list_
+| [blue]`-` | _Infix_ | _Subtraction_ | _number_ `"-"` _number_ -> _number_
+| [blue]`-` | _Infix_ | _List-difference_ | _list_ `"-"` _list_ -> _list_
+.6+|*RELATION*| [blue]`<` | _Infix_ | _less_ | _comparable_ `"<"` _comparable_ -> _boolean_
+| [blue]`\<=` | _Infix_ |  _less-equal_ | _comparable_ `"\<="` _comparable_ -> _boolean_
+| [blue]`>` | _Infix_ |  _greater_ | _comparable_ `">"` _comparable_ -> _boolean_
+| [blue]`>=` | _Infix_ |  _greater-equal_ | _comparable_ `">="` _comparable_ -> _boolean_
+| [blue]`==` | _Infix_ |  _equal_ | _comparable_ `"=="` _comparable_ -> _boolean_
+| [blue]`!=` | _Infix_ |  _not-equal_ | _comparable_ `"!="` _comparable_ -> _boolean_
+.1+|*NOT*| [blue]`not` | _Prefix_ | _not_ | `"not"` _boolean_ -> _boolean_
+.2+|*AND*| [blue]`and` | _Infix_ | _and_ | _boolean_ `"and"` _boolean_ -> _boolean_
+| [blue]`&&` | _Infix_ | _and_ | _boolean_ `"&&"` _boolean_ -> _boolean_
+.2+|*OR*| [blue]`or` | _Infix_ | _or_ | _boolean_ `"or"` _boolean_ -> _boolean_
+| [blue]`\|\|` | _Infix_ | _or_ | _boolean_ `"\|\|"` _boolean_ -> _boolean_
+.1+|*ASSIGN*| [blue]`=` | _Infix_ | _assignment_ | _identifier_ "=" _any_ -> _any_
+.1+|*BUT*| [blue]`but` | _Infix_ | _but_ | _any_ "but" _any_ -> _any_
+|===
+
+== Functions
+Functions in _Expr_ are very similar to functions in many programming languages.
+
+In _Expr_ functions compute values in a local context (scope) that do not make effects on the calling context. This is the normal behavior. Using the reference operator [blue]`@` it is possibile to export local definition to the calling context.
+
+=== Function calls
+#TODO: function calls operations#
+
+=== Function definitions
+#TODO: function definitions operations#
+
+== Builtins
+#TODO: builtins#
+
+=== Builtin functions
+
+=== [blue]_import()_
+[blue]_import([grey]#<source-file>#)_ loads the multi-expression contained in the specified source and returns its value.
+
+
+

expr_test.go

@@ -0,0 +1,82 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// expr_test.go
+package expr
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestExpr(t *testing.T) {
+	type inputType struct {
+		source     string
+		wantResult any
+		wantErr    error
+	}
+
+	inputs := []inputType{
+		/*   1 */ {`0?{}`, nil, nil},
+		/*   2 */ {`fact=func(n){(n)?{1}::{n*fact(n-1)}}; fact(5)`, int64(120), nil},
+		/*   3 */ {`f=openFile("test-file.txt"); line=readFile(f); closeFile(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},
+		/*   10 */ {`
+		ds={
+			"init":func(end){@end=end; @current=0 but true},
+			"current":func(){current},
+			"next":func(){
+				((next=current+1) <= end) ? [true] {@current=next but current} :: {nil}
+			}
+		};
+		it=$(ds,3);
+		it++;
+		it++
+`, int64(1), nil},
+	}
+
+	succeeded := 0
+	failed := 0
+
+	for i, input := range inputs {
+		var expr Expr
+		var gotResult any
+		var gotErr error
+
+		ctx := NewSimpleFuncStore()
+		// ImportMathFuncs(ctx)
+		// ImportImportFunc(ctx)
+		ImportOsFuncs(ctx)
+		parser := NewParser(ctx)
+
+		logTest(t, i+1, "Expr", 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 != input.wantResult {
+			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("test count: %d, succeeded count: %d, failed count: %d", len(inputs), succeeded, failed)
+}

file-reader.expr

@@ -0,0 +1,33 @@
+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)

formatter.go

@@ -0,0 +1,20 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// formatter.go
+package expr
+
+type FmtOpt uint16
+
+const (
+	TTY FmtOpt = 1 << iota
+	MultiLine
+	Base2
+	Base8
+	Base10
+	Base16
+)
+
+type Formatter interface {
+	ToString(options FmtOpt) string
+}

func-base.go

@@ -0,0 +1,179 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-builtins.go
+package expr
+
+import (
+	"math"
+	"strconv"
+)
+
+func isNilFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	if len(args) == 1 {
+		result = args[0] == nil
+	} else {
+		err = errOneParam(name)
+	}
+	return
+}
+
+func isIntFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsInteger(args[0])
+	return
+}
+
+func isFloatFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsFloat(args[0])
+	return
+}
+
+func isBoolFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsBool(args[0])
+	return
+}
+
+func isStringFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsString(args[0])
+	return
+}
+
+func isFractionFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsFract(args[0])
+	return
+}
+
+func isRationalFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsRational(args[0])
+	return
+}
+
+func isListFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsList(args[0])
+	return
+}
+
+func isDictionaryFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	result = IsDict(args[0])
+	return
+}
+
+func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		result = v
+	case float64:
+		result = int64(math.Trunc(v))
+	case bool:
+		if v {
+			result = int64(1)
+		} else {
+			result = int64(0)
+		}
+	case string:
+		var i int
+		if i, err = strconv.Atoi(v); err == nil {
+			result = int64(i)
+		}
+	default:
+		err = errCantConvert(name, v, "int")
+	}
+	return
+}
+
+func decFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		result = float64(v)
+	case float64:
+		result = v
+	case bool:
+		if v {
+			result = float64(1)
+		} else {
+			result = float64(0)
+		}
+	case string:
+		var f float64
+		if f, err = strconv.ParseFloat(v, 64); err == nil {
+			result = f
+		}
+	case *fraction:
+		result = v.toFloat()
+	default:
+		err = errCantConvert(name, v, "float")
+	}
+	return
+}
+
+func fractFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		var den int64 = 1
+		if len(args) > 1 {
+			var ok bool
+			if den, ok = args[1].(int64); !ok {
+				err = errExpectedGot(name, "integer", args[1])
+			} else if den == 0 {
+				err = errDivisionByZero(name)
+			}
+		}
+		if err == nil {
+			result = newFraction(v, den)
+		}
+	case float64:
+		result, err = float64ToFraction(v)
+		// var n, d int64
+		// if n, d, err = float64ToFraction(v); err == nil {
+		//	result = newFraction(n, d)
+		// }
+	case bool:
+		if v {
+			result = newFraction(1, 1)
+		} else {
+			result = newFraction(0, 1)
+		}
+	case string:
+		result, err = makeGeneratingFraction(v)
+		// var f float64
+		// // TODO temporary implementation
+		// if f, err = strconv.ParseFloat(v, 64); err == nil {
+		// 	var n, d int64
+		// 	if n, d, err = float64ToFraction(f); err == nil {
+		// 		result = newFraction(n, d)
+		// 	}
+		// } else {
+		// 	errors.New("convertion from string to float is ongoing")
+		// }
+	case *fraction:
+		result = v
+	default:
+		err = errCantConvert(name, v, "float")
+	}
+	return
+}
+
+func iteratorFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	return
+}
+
+func ImportBuiltinsFuncs(ctx ExprContext) {
+	ctx.RegisterFunc("isNil", &simpleFunctor{f: isNilFunc}, 1, 1)
+	ctx.RegisterFunc("isInt", &simpleFunctor{f: isIntFunc}, 1, 1)
+	ctx.RegisterFunc("isFloat", &simpleFunctor{f: isFloatFunc}, 1, 1)
+	ctx.RegisterFunc("isBool", &simpleFunctor{f: isBoolFunc}, 1, 1)
+	ctx.RegisterFunc("isString", &simpleFunctor{f: isStringFunc}, 1, 1)
+	ctx.RegisterFunc("isFraction", &simpleFunctor{f: isFractionFunc}, 1, 1)
+	ctx.RegisterFunc("isFract", &simpleFunctor{f: isFractionFunc}, 1, 1)
+	ctx.RegisterFunc("isRational", &simpleFunctor{f: isRationalFunc}, 1, 1)
+	ctx.RegisterFunc("isList", &simpleFunctor{f: isListFunc}, 1, 1)
+	ctx.RegisterFunc("isDictionary", &simpleFunctor{f: isDictionaryFunc}, 1, 1)
+	ctx.RegisterFunc("isDict", &simpleFunctor{f: isDictionaryFunc}, 1, 1)
+	ctx.RegisterFunc("int", &simpleFunctor{f: intFunc}, 1, 1)
+	ctx.RegisterFunc("dec", &simpleFunctor{f: decFunc}, 1, 1)
+	ctx.RegisterFunc("fract", &simpleFunctor{f: fractFunc}, 1, 2)
+}
+
+func init() {
+	registerImport("base", ImportBuiltinsFuncs, "Base expression tools like isNil(), int(), etc.")
+}

func-import.go

@@ -1,3 +1,6 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // func-import.go
 package expr
 
@@ -17,7 +20,7 @@ func importFunc(ctx ExprContext, name string, args []any) (result any, err error
 	return importGeneral(ctx, name, args)
 }
 
-func includeFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+func importAllFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	enable(ctx, control_export_all)
 	return importGeneral(ctx, name, args)
 }
@@ -27,12 +30,12 @@ func importGeneral(ctx ExprContext, name string, args []any) (result any, err er
 
 	dirList = addEnvImportDirs(dirList)
 	dirList = addPresetImportDirs(ctx, dirList)
-	result, err = doImport(ctx, name, dirList, NewFlatArrayIterator(args))
+	result, err = doImport(ctx, name, dirList, NewArrayIterator(args))
 	return
 }
 
 func checkStringParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(isString(paramValue) /*|| isList(paramValue)*/) {
+	if !(IsString(paramValue) /*|| isList(paramValue)*/) {
 		err = fmt.Errorf("%s(): param nr %d has wrong type %T, string expected", funcName, paramPos+1, paramValue)
 	}
 	return
@@ -51,7 +54,7 @@ func addEnvImportDirs(dirList []string) []string {
 }
 
 func addPresetImportDirs(ctx ExprContext, dirList []string) []string {
-	if dirSpec, exists := getControlString(ctx, control_import_path); exists {
+	if dirSpec, exists := getControlString(ctx, ControlImportPath); exists {
 		dirs := strings.Split(dirSpec, ":")
 		if dirList == nil {
 			dirList = dirs
@@ -133,7 +136,11 @@ func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (resu
 	return
 }
 
-func importImportFunc(ctx ExprContext) {
+func ImportImportFuncs(ctx ExprContext) {
 	ctx.RegisterFunc("import", &simpleFunctor{f: importFunc}, 1, -1)
-	ctx.RegisterFunc("include", &simpleFunctor{f: includeFunc}, 1, -1)
+	ctx.RegisterFunc("importAll", &simpleFunctor{f: importAllFunc}, 1, -1)
+}
+
+func init() {
+	registerImport("import", ImportImportFuncs, "Functions import() and include()")
 }

func-math.go

@@ -1,3 +1,6 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // funcs-math.go
 package expr
 
@@ -6,36 +9,65 @@ import (
 	"io"
 )
 
-func checkNumberParamExpected(funcName string, paramValue any, paramPos int) (err error) {
-	if !(isNumber(paramValue) || isList(paramValue)) {
-		err = fmt.Errorf("%s(): param nr %d has wrong type %T, number expected", funcName, paramPos+1, paramValue)
+func checkNumberParamExpected(funcName string, paramValue any, paramPos, level, subPos int) (err error) {
+	if !(IsNumber(paramValue) || isFraction(paramValue)) /*|| isList(paramValue)*/ {
+		err = fmt.Errorf("%s(): param nr %d (%d in %d) has wrong type %T, number expected",
+			funcName, paramPos+1, subPos+1, level, paramValue)
 	}
 	return
 }
 
-func doAdd(ctx ExprContext, name string, it Iterator) (result any, err error) {
-	var sumAsFloat = false
+func doAdd(ctx ExprContext, name string, it Iterator, count, level int) (result any, err error) {
+	var sumAsFloat, sumAsFract bool
 	var floatSum float64 = 0.0
 	var intSum int64 = 0
+	var fractSum *fraction
 	var v any
 
+	level++
+
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if err = checkNumberParamExpected(name, v, it.Index()); err != nil {
+		if list, ok := v.(*ListType); ok {
+			v = NewListIterator(list, nil)
+		}
+		if subIter, ok := v.(Iterator); ok {
+			if v, err = doAdd(ctx, name, subIter, count, level); err != nil {
+				break
+			}
+			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(cleanName) {
+				if _, err = extIter.CallOperation(cleanName, nil); err != nil {
+					return
+				}
+			}
+		} else if err = checkNumberParamExpected(name, v, count, level, it.Index()); err != nil {
 			break
 		}
+		count++
 
-		if array, ok := v.([]any); ok {
-			if v, err = doAdd(ctx, name, NewFlatArrayIterator(array)); err != nil {
-				break
+		if !sumAsFloat {
+			if IsFloat(v) {
+				sumAsFloat = true
+				if sumAsFract {
+					floatSum = fractSum.toFloat()
+				} else {
+					floatSum = float64(intSum)
+				}
+			} else if !sumAsFract && isFraction(v) {
+				fractSum = newFraction(intSum, 1)
+				sumAsFract = true
 			}
 		}
 
-		if !sumAsFloat && isFloat(v) {
-			sumAsFloat = true
-			floatSum = float64(intSum)
-		}
 		if sumAsFloat {
 			floatSum += numAsFloat(v)
+		} else if sumAsFract {
+			var item *fraction
+			var ok bool
+			if item, ok = v.(*fraction); !ok {
+				iv, _ := v.(int64)
+				item = newFraction(iv, 1)
+			}
+			fractSum = sumFract(fractSum, item)
 		} else {
 			iv, _ := v.(int64)
 			intSum += iv
@@ -45,6 +77,8 @@ func doAdd(ctx ExprContext, name string, it Iterator) (result any, err error) {
 		err = nil
 		if sumAsFloat {
 			result = floatSum
+		} else if sumAsFract {
+			result = fractSum
 		} else {
 			result = intSum
 		}
@@ -53,33 +87,62 @@ func doAdd(ctx ExprContext, name string, it Iterator) (result any, err error) {
 }
 
 func addFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result, err = doAdd(ctx, name, NewFlatArrayIterator(args))
+	result, err = doAdd(ctx, name, NewArrayIterator(args), 0, -1)
 	return
 }
 
-func doMul(ctx ExprContext, name string, it Iterator) (result any, err error) {
-	var mulAsFloat = false
+func doMul(ctx ExprContext, name string, it Iterator, count, level int) (result any, err error) {
+	var mulAsFloat, mulAsFract bool
 	var floatProd float64 = 1.0
 	var intProd int64 = 1
+	var fractProd *fraction
 	var v any
 
+	level++
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		if err = checkNumberParamExpected(name, v, it.Index()); err != nil {
-			break
+		if list, ok := v.(*ListType); ok {
+			v = NewListIterator(list, nil)
 		}
-
-		if array, ok := v.([]any); ok {
-			if v, err = doAdd(ctx, name, NewFlatArrayIterator(array)); err != nil {
+		if subIter, ok := v.(Iterator); ok {
+			if v, err = doMul(ctx, name, subIter, count, level); err != nil {
+				break
+			}
+			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(cleanName) {
+				if _, err = extIter.CallOperation(cleanName, nil); err != nil {
+					return
+				}
+			}
+		} else {
+			if err = checkNumberParamExpected(name, v, count, level, it.Index()); err != nil {
 				break
 			}
 		}
+		count++
 
-		if !mulAsFloat && isFloat(v) {
-			mulAsFloat = true
-			floatProd = float64(intProd)
+		if !mulAsFloat {
+			if IsFloat(v) {
+				mulAsFloat = true
+				if mulAsFract {
+					floatProd = fractProd.toFloat()
+				} else {
+					floatProd = float64(intProd)
+				}
+			} else if !mulAsFract && isFraction(v) {
+				fractProd = newFraction(intProd, 1)
+				mulAsFract = true
+			}
 		}
+
 		if mulAsFloat {
 			floatProd *= numAsFloat(v)
+		} else if mulAsFract {
+			var item *fraction
+			var ok bool
+			if item, ok = v.(*fraction); !ok {
+				iv, _ := v.(int64)
+				item = newFraction(iv, 1)
+			}
+			fractProd = mulFract(fractProd, item)
 		} else {
 			iv, _ := v.(int64)
 			intProd *= iv
@@ -89,6 +152,8 @@ func doMul(ctx ExprContext, name string, it Iterator) (result any, err error) {
 		err = nil
 		if mulAsFloat {
 			result = floatProd
+		} else if mulAsFract {
+			result = fractProd
 		} else {
 			result = intProd
 		}
@@ -97,11 +162,15 @@ func doMul(ctx ExprContext, name string, it Iterator) (result any, err error) {
 }
 
 func mulFunc(ctx ExprContext, name string, args []any) (result any, err error) {
-	result, err = doMul(ctx, name, NewFlatArrayIterator(args))
+	result, err = doMul(ctx, name, NewArrayIterator(args), 0, -1)
 	return
 }
 
-func importMathFuncs(ctx ExprContext) {
+func ImportMathFuncs(ctx ExprContext) {
 	ctx.RegisterFunc("add", &simpleFunctor{f: addFunc}, 0, -1)
 	ctx.RegisterFunc("mul", &simpleFunctor{f: mulFunc}, 0, -1)
 }
+
+func init() {
+	registerImport("math.arith", ImportMathFuncs, "Functions add() and mul()")
+}

func-os.go

@@ -0,0 +1,171 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-os.go
+package expr
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+)
+
+type osHandle interface {
+	getFile() *os.File
+}
+
+type osWriter struct {
+	fh     *os.File
+	writer *bufio.Writer
+}
+
+func (h *osWriter) getFile() *os.File {
+	return h.fh
+}
+
+type osReader struct {
+	fh     *os.File
+	reader *bufio.Reader
+}
+
+func (h *osReader) getFile() *os.File {
+	return h.fh
+}
+
+func createFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var filePath string
+	if len(args) > 0 {
+		filePath, _ = args[0].(string)
+	}
+
+	if len(filePath) > 0 {
+		var fh *os.File
+		if fh, err = os.Create(filePath); err == nil {
+			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
+		}
+	} else {
+		err = fmt.Errorf("%s(): missing the file path", name)
+	}
+	return
+}
+
+func openFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var filePath string
+	if len(args) > 0 {
+		filePath, _ = args[0].(string)
+	}
+
+	if len(filePath) > 0 {
+		var fh *os.File
+		if fh, err = os.Open(filePath); err == nil {
+			result = &osReader{fh: fh, reader: bufio.NewReader(fh)}
+		}
+	} else {
+		err = fmt.Errorf("%s(): missing the file path", name)
+	}
+	return
+}
+
+func appendFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var filePath string
+	if len(args) > 0 {
+		filePath, _ = args[0].(string)
+	}
+
+	if len(filePath) > 0 {
+		var fh *os.File
+		if fh, err = os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0660); err == nil {
+			result = &osWriter{fh: fh, writer: bufio.NewWriter(fh)}
+		}
+	} else {
+		err = fmt.Errorf("%s(): missing the file path", name)
+	}
+	return
+}
+
+func closeFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var handle osHandle
+
+	if len(args) > 0 {
+		handle, _ = args[0].(osHandle)
+	}
+
+	if handle != nil {
+		if fh := handle.getFile(); fh != nil {
+			if w, ok := handle.(*osWriter); ok {
+				err = w.writer.Flush()
+			}
+			if err == nil {
+				err = fh.Close()
+			}
+		}
+	} else {
+		err = fmt.Errorf("%s(): invalid file handle", name)
+	}
+	result = err == nil
+	return
+}
+
+func writeFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var handle osHandle
+
+	if len(args) > 0 {
+		handle, _ = args[0].(osHandle)
+	}
+
+	if handle != nil {
+		if fh := handle.getFile(); fh != nil {
+			if w, ok := handle.(*osWriter); ok {
+				result, err = fmt.Fprint(w.writer, args[1:]...)
+			}
+		}
+	}
+	return
+}
+
+func readFileFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var handle osHandle
+	result = nil
+	if len(args) > 0 {
+		handle, _ = args[0].(osHandle)
+	}
+
+	if handle != nil {
+		if fh := handle.getFile(); fh != nil {
+			if r, ok := handle.(*osReader); ok {
+				var limit byte = '\n'
+				var v string
+				if len(args) > 1 {
+					if s, ok := args[1].(string); ok && len(s) > 0 {
+						limit = s[0]
+					}
+				}
+				if v, err = r.reader.ReadString(limit); err == nil {
+					if len(v) > 0 && v[len(v)-1] == limit {
+						result = v[0 : len(v)-1]
+					} else {
+						result = v
+					}
+				}
+				if err == io.EOF {
+					err = nil
+				}
+			}
+		}
+	}
+	return
+}
+
+func ImportOsFuncs(ctx ExprContext) {
+	ctx.RegisterFunc("openFile", &simpleFunctor{f: openFileFunc}, 1, 1)
+	ctx.RegisterFunc("appendFile", &simpleFunctor{f: appendFileFunc}, 1, 1)
+	ctx.RegisterFunc("createFile", &simpleFunctor{f: createFileFunc}, 1, 1)
+	ctx.RegisterFunc("writeFile", &simpleFunctor{f: writeFileFunc}, 1, -1)
+	ctx.RegisterFunc("readFile", &simpleFunctor{f: readFileFunc}, 1, 2)
+	ctx.RegisterFunc("closeFile", &simpleFunctor{f: closeFileFunc}, 1, 1)
+}
+
+func init() {
+	registerImport("os.file", ImportOsFuncs, "Operating system file functions")
+}

func-string.go

@@ -0,0 +1,211 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-string.go
+package expr
+
+import (
+	"fmt"
+	"io"
+	"strings"
+)
+
+// --- Start of function definitions
+func doJoinStr(funcName string, sep string, it Iterator) (result any, err error) {
+	var sb strings.Builder
+	var v any
+	for v, err = it.Next(); err == nil; v, err = it.Next() {
+		if it.Index() > 0 {
+			sb.WriteString(sep)
+		}
+		if s, ok := v.(string); ok {
+			sb.WriteString(s)
+		} else {
+			err = errExpectedGot(funcName, typeString, v)
+			return
+		}
+	}
+	if err == nil || err == io.EOF {
+		err = nil
+		result = sb.String()
+	}
+	return
+}
+
+func joinStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	if len(args) < 1 {
+		return nil, errMissingRequiredParameter(name, paramSeparator)
+	}
+	if sep, ok := args[0].(string); ok {
+		if len(args) == 1 {
+			result = ""
+		} else if len(args) == 2 {
+			if ls, ok := args[1].(*ListType); ok {
+				result, err = doJoinStr(name, sep, NewListIterator(ls, nil))
+			} else if it, ok := args[1].(Iterator); ok {
+				result, err = doJoinStr(name, sep, it)
+			} else {
+				err = errInvalidParameterValue(name, paramParts, args[1])
+			}
+		} else {
+			result, err = doJoinStr(name, sep, NewArrayIterator(args[1:]))
+		}
+	} else {
+		err = errWrongParamType(name, paramSeparator, typeString, args[0])
+	}
+	return
+}
+
+func subStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var start = 0
+	var count = -1
+	var source string
+	var ok bool
+
+	if len(args) < 1 {
+		return nil, errMissingRequiredParameter(name, paramSource)
+	}
+	if source, ok = args[0].(string); !ok {
+		return nil, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	if len(args) > 1 {
+		if start, err = toInt(args[1], name+"()"); err != nil {
+			return
+		}
+		if len(args) > 2 {
+			if count, err = toInt(args[2], name+"()"); err != nil {
+				return
+			}
+		}
+		if start < 0 {
+			start = len(source) + start
+		}
+	}
+	if count < 0 {
+		count = len(source) - start
+	}
+	end := min(start+count, len(source))
+	result = source[start:end]
+	return
+}
+
+func trimStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source string
+	var ok bool
+
+	if len(args) < 1 {
+		return nil, errMissingRequiredParameter(name, paramSource)
+	}
+	if source, ok = args[0].(string); !ok {
+		return nil, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	result = strings.TrimSpace(source)
+	return
+}
+
+func startsWithStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source string
+	var ok bool
+
+	result = false
+	if len(args) < 1 {
+		return result, errMissingRequiredParameter(name, paramSource)
+	}
+	if source, ok = args[0].(string); !ok {
+		return result, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	for i, targetSpec := range args[1:] {
+		if target, ok := targetSpec.(string); ok {
+			if strings.HasPrefix(source, target) {
+				result = true
+				break
+			}
+		} else {
+			err = fmt.Errorf("target item nr %d is %T, expected string", i+1, targetSpec)
+			break
+		}
+	}
+	return
+}
+
+func endsWithStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source string
+	var ok bool
+
+	result = false
+	if len(args) < 1 {
+		return result, errMissingRequiredParameter(name, paramSource)
+	}
+	if source, ok = args[0].(string); !ok {
+		return result, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	for i, targetSpec := range args[1:] {
+		if target, ok := targetSpec.(string); ok {
+			if strings.HasSuffix(source, target) {
+				result = true
+				break
+			}
+		} else {
+			err = fmt.Errorf("target item nr %d is %T, expected string", i+1, targetSpec)
+			break
+		}
+	}
+	return
+}
+
+func splitStrFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	var source, sep string
+	var count int = -1
+	var parts []string
+	var ok bool
+
+	if len(args) < 1 {
+		return result, errMissingRequiredParameter(name, paramSource)
+	}
+	if source, ok = args[0].(string); !ok {
+		return result, errWrongParamType(name, paramSource, typeString, args[0])
+	}
+	if len(args) >= 2 {
+		if sep, ok = args[1].(string); !ok {
+			return nil, fmt.Errorf("separator param must be string, got %T (%v)", args[1], args[1])
+		}
+		if len(args) >= 3 {
+			if count64, ok := args[2].(int64); ok { // TODO replace type assertion with toInt()
+				count = int(count64)
+			} else {
+				return nil, fmt.Errorf("part count must be integer, got %T (%v)", args[2], args[2])
+			}
+		}
+	}
+	if count > 0 {
+		parts = strings.SplitN(source, sep, count)
+	} else if count < 0 {
+		parts = strings.Split(source, sep)
+	} else {
+		parts = []string{}
+	}
+	list := make(ListType, len(parts))
+	for i, part := range parts {
+		list[i] = part
+	}
+	result = &list
+	return
+}
+
+// --- End of function definitions
+
+// Import above functions in the context
+func ImportStringFuncs(ctx ExprContext) {
+	ctx.RegisterFunc("joinStr", &simpleFunctor{f: joinStrFunc}, 1, -1)
+	ctx.RegisterFunc("subStr", &simpleFunctor{f: subStrFunc}, 1, -1)
+	ctx.RegisterFunc("splitStr", &simpleFunctor{f: splitStrFunc}, 2, -1)
+	ctx.RegisterFunc("trimStr", &simpleFunctor{f: trimStrFunc}, 1, -1)
+	ctx.RegisterFunc("startsWithStr", &simpleFunctor{f: startsWithStrFunc}, 2, -1)
+	ctx.RegisterFunc("endsWithStr", &simpleFunctor{f: endsWithStrFunc}, 2, -1)
+}
+
+// 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")
+}

funcs_test.go

@@ -0,0 +1,86 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// funcs_test.go
+package expr
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestFuncs(t *testing.T) {
+	inputs := []inputType{
+		/*   1 */ {`isNil(nil)`, true, nil},
+		/*   2 */ {`v=nil; isNil(v)`, true, nil},
+		/*   3 */ {`v=5; isNil(v)`, false, nil},
+		/*   4 */ {`int(true)`, int64(1), nil},
+		/*   5 */ {`int(false)`, int64(0), nil},
+		/*   6 */ {`int(3.1)`, int64(3), nil},
+		/*   7 */ {`int(3.9)`, int64(3), nil},
+		/*   8 */ {`int("432")`, int64(432), nil},
+		/*   9 */ {`int("1.5")`, nil, errors.New(`strconv.Atoi: parsing "1.5": invalid syntax`)},
+		/*  10 */ {`int("432", 4)`, nil, errors.New(`too much params -- expected 1, got 2`)},
+		/*  11 */ {`int(nil)`, nil, errors.New(`int() can't convert <nil> to int`)},
+		/*  12 */ {`two=func(){2}; two()`, int64(2), nil},
+		/*  13 */ {`double=func(x) {2*x}; (double(3))`, int64(6), nil},
+		/*  14 */ {`double=func(x){2*x}; double(3)`, int64(6), nil},
+		/*  15 */ {`double=func(x){2*x}; a=5; double(3+a) + 1`, int64(17), nil},
+		/*  16 */ {`double=func(x){2*x}; a=5; two=func() {2}; (double(3+a) + 1) * two()`, int64(34), nil},
+		/*  17 */ {`builtin "import"; import("./test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
+		/*  18 */ {`builtin "import"; import("test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
+		/*  19 */ {`@x="hello"; @x`, nil, errors.New(`[1:3] variable references are not allowed in top level expressions: "@x"`)},
+		/*  20 */ {`f=func(){@x="hello"}; f(); x`, "hello", nil},
+		/*  21 */ {`f=func(@y){@y=@y+1}; f(2); y`, int64(3), nil},
+		/*  22 */ {`f=func(@y){g=func(){@x=5}; @y=@y+g()}; f(2); y+x`, nil, errors.New(`undefined variable or function "x"`)},
+		/*  23 */ {`f=func(@y){g=func(){@x=5}; @z=g(); @y=@y+@z}; f(2); y+z`, int64(12), nil},
+		/*  24 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @y=@y+@z}; f(2); y+z`, int64(12), nil},
+		/*  25 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @x=@y+@z}; f(2); y+x`, int64(9), nil},
+		/*  26 */ {`builtin "import"; importAll("./test-funcs.expr"); six()`, int64(6), nil},
+		/*  27 */ {`builtin "import"; import("./sample-export-all.expr"); six()`, int64(6), nil},
+		/*  28 */ {`builtin "string"; joinStr("-", "one", "two", "three")`, "one-two-three", nil},
+		/*  29 */ {`builtin "string"; joinStr("-", ["one", "two", "three"])`, "one-two-three", nil},
+		/*  30 */ {`builtin "string"; ls= ["one", "two", "three"]; joinStr("-", ls)`, "one-two-three", nil},
+		/*  31 */ {`builtin "string"; ls= ["one", "two", "three"]; joinStr(1, ls)`, nil, errors.New(`joinStr() the "separator" parameter must be a string, got a int64 (1)`)},
+		/*  32 */ {`builtin "string"; ls= ["one", 2, "three"]; joinStr("-", ls)`, nil, errors.New(`joinStr() expected string, got int64 (2)`)},
+		/*  33 */ {`builtin "string"; "<"+trimStr("  bye bye  ")+">"`, "<bye bye>", nil},
+		/*  34 */ {`builtin "string"; subStr("0123456789", 1,2)`, "12", nil},
+		/*  35 */ {`builtin "string"; subStr("0123456789", -3,2)`, "78", nil},
+		/*  36 */ {`builtin "string"; subStr("0123456789", -3)`, "789", nil},
+		/*  37 */ {`builtin "string"; subStr("0123456789")`, "0123456789", nil},
+		/*  38 */ {`builtin "string"; startsWithStr("0123456789", "xyz", "012")`, true, nil},
+		/*  39 */ {`builtin "string"; startsWithStr("0123456789", "xyz", "0125")`, false, nil},
+		/*  40 */ {`builtin "string"; startsWithStr("0123456789")`, nil, errors.New(`too few params -- expected 2 or more, got 1`)},
+		/*  41 */ {`builtin "string"; endsWithStr("0123456789", "xyz", "789")`, true, nil},
+		/*  42 */ {`builtin "string"; endsWithStr("0123456789", "xyz", "0125")`, false, nil},
+		/*  43 */ {`builtin "string"; endsWithStr("0123456789")`, nil, errors.New(`too few params -- expected 2 or more, got 1`)},
+		/*  44 */ {`builtin "string"; splitStr("one-two-three", "-", )`, newListA("one", "two", "three"), nil},
+		/*  45 */ {`isInt(2+1)`, true, nil},
+		/*  46 */ {`isInt(3.1)`, false, nil},
+		/*  47 */ {`isFloat(3.1)`, true, nil},
+		/*  48 */ {`isString("3.1")`, true, nil},
+		/*  49 */ {`isString("3" + 1)`, true, nil},
+		/*  50 */ {`isList(["3",  1])`, true, nil},
+		/*  51 */ {`isDict({"a":"3",  "b":1})`, true, nil},
+		/*  52 */ {`isFract(1|3)`, true, nil},
+		/*  53 */ {`isFract(3|1)`, false, nil},
+		/*  54 */ {`isRational(3|1)`, true, nil},
+		/*  55 */ {`builtin "math.arith"; add(1,2)`, int64(3), nil},
+		/*  56 */ {`fract("2.2(3)")`, newFraction(67, 30), nil},
+		/*  57 */ {`fract("1.21(3)")`, newFraction(91, 75), nil},
+		/*  58 */ {`fract(1.21(3))`, newFraction(91, 75), nil},
+		/*  59 */ {`fract(1.21)`, newFraction(121, 100), nil},
+		/*  60 */ {`dec(2)`, float64(2), nil},
+		/*  61 */ {`dec(2.0)`, float64(2), nil},
+		/*  62 */ {`dec("2.0")`, float64(2), nil},
+		/*  63 */ {`dec(true)`, float64(1), nil},
+		/*  64 */ {`dec(true")`, nil, errors.New("[1:11] missing string termination \"")},
+		/*  65 */ {`builtin "string"; joinStr("-", [1, "two", "three"])`, nil, errors.New(`joinStr() expected string, got int64 (1)`)},
+		// /*  64 */ {`string(true)`, "true", nil},
+	}
+
+	t.Setenv("EXPR_PATH", ".")
+
+	//parserTest(t, "Func", inputs[54:55])
+	parserTest(t, "Func", inputs)
+}

global-context.go

@@ -0,0 +1,54 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// global-context.go
+package expr
+
+import "path/filepath"
+
+var globalCtx *SimpleFuncStore
+
+func ImportInContext(name string) (exists bool) {
+	var mod *module
+	if mod, exists = moduleRegister[name]; exists {
+		mod.importFunc(globalCtx)
+		mod.imported = true
+	}
+	return
+}
+
+func ImportInContextByGlobPattern(pattern string) (count int, err error) {
+	var matched bool
+	for name, mod := range moduleRegister {
+		if matched, err = filepath.Match(pattern, name); err == nil {
+			if matched {
+				count++
+				mod.importFunc(globalCtx)
+				mod.imported = true
+			}
+		} else {
+			break
+		}
+	}
+	return
+}
+
+func GetVar(ctx ExprContext, name string) (value any, exists bool) {
+	if value, exists = ctx.GetVar(name); !exists {
+		value, exists = globalCtx.GetVar(name)
+	}
+	return
+}
+
+func GetFuncInfo(ctx ExprContext, name string) (item ExprFunc, exists bool, ownerCtx ExprContext) {
+	if item, exists = ctx.GetFuncInfo(name); exists {
+		ownerCtx = ctx
+	} else if item, exists = globalCtx.GetFuncInfo(name); exists {
+		ownerCtx = globalCtx
+	}
+	return
+}
+
+func init() {
+	globalCtx = NewSimpleFuncStore()
+}

graph.go

@@ -0,0 +1,122 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// graph.go
+package expr
+
+import (
+	"fmt"
+	"strings"
+)
+
+func BuildGraph(root *term) (g string) {
+	//var sb strings.Builder
+	g = fmt.Sprintf("tree: %v", root)
+
+	r := NewReticle(root)
+	fmt.Println(r)
+	return
+}
+
+type NodeRef struct {
+	node  *term
+	pos   int
+	label string
+}
+
+type Level []*NodeRef
+
+type Reticle struct {
+	levels      []Level
+	left, right int
+	colsWidth   []int
+}
+
+func NewExprReticle(e Expr) *Reticle {
+	tree, _ := e.(*ast)
+	return NewReticle(tree.root)
+}
+
+func NewReticle(tree *term) *Reticle {
+	r := &Reticle{levels: make([]Level, 0)}
+	r.build(tree, 0, 0)
+	r.computeCharWidth()
+	return r
+}
+
+func (r *Reticle) computeCharWidth() {
+	numCol := r.right - r.left + 1
+	r.colsWidth = make([]int, numCol)
+	for _, level := range r.levels {
+		for _, ref := range level {
+			c := ref.pos - r.left
+			if v := ref.node.value(); v != nil {
+				ref.label = fmt.Sprintf("%v", v)
+			} else {
+				ref.label = ref.node.source()
+			}
+			r.colsWidth[c] = max(r.colsWidth[c], len(ref.label)+2) // +2 to make room for brakets
+		}
+	}
+}
+
+func (r *Reticle) build(node *term, depth, pos int) {
+	var level Level
+	if node == nil {
+		return
+	}
+	if len(r.levels) == depth {
+		level = make(Level, 0)
+		r.levels = append(r.levels, level)
+	} else {
+		level = r.levels[depth]
+	}
+	ref := &NodeRef{node: node, pos: pos}
+	level = append(level, ref)
+	if r.left > pos {
+		r.left = pos
+	}
+	if r.right < pos {
+		r.right = pos
+	}
+	if node.children != nil {
+		halfPos := len(node.children) / 2
+		childPos := pos - halfPos - 1
+		for _, child := range node.children {
+			childPos++
+			if childPos == pos && (len(node.children)&1) == 0 {
+				childPos++
+			}
+			r.build(child, depth+1, childPos)
+		}
+	}
+	r.levels[depth] = level
+}
+
+func (r *Reticle) nodeInLevel(level []*NodeRef, index int) (node *NodeRef) {
+	for _, ref := range level {
+		if ref.pos-r.left == index {
+			node = ref
+			break
+		}
+	}
+	return
+}
+
+func (r *Reticle) String() string {
+	var sb strings.Builder
+	for _, level := range r.levels {
+		for j, w := range r.colsWidth {
+			var label string
+			if ref := r.nodeInLevel(level, j); ref != nil {
+				s := "(" + ref.label + ")"
+				label = fmt.Sprintf("%[1]*s", -w, fmt.Sprintf("%[1]*s", (w+len(s))/2, s))
+			} else {
+				label = strings.Repeat(" ", w)
+			}
+			sb.WriteString(label)
+		}
+		sb.WriteByte('\n')
+	}
+	return sb.String()
+}

graph_test.go

@@ -0,0 +1,33 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// graph_test.go
+package expr
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestGraph(t *testing.T) {
+	// tk0 := NewToken(0, 0, SymChangeSign, "-")
+	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
+	tk2 := NewToken(0, 0, SymPlus, "+")
+	tk3 := NewValueToken(0, 0, SymInteger, "200", 200)
+
+	tree := NewAst()
+	// tree.addToken(tk0)
+	tree.addToken(tk1)
+	tree.addToken(tk2)
+	tree.addToken(tk3)
+	tk4 := NewToken(0, 0, SymPlus, "-")
+	tk5 := NewValueToken(0, 0, SymInteger, "50", 50)
+	tree.addToken(tk4)
+	tree.addToken(tk5)
+
+	g := BuildGraph(tree.root)
+	fmt.Println(g)
+}

helpers.go

@@ -1,8 +1,13 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // helpers.go
 package expr
 
 import (
 	"fmt"
+	"io"
+	"os"
 	"strings"
 )
 
@@ -19,35 +24,35 @@ func EvalString(ctx ExprContext, source string) (result any, err error) {
 	return
 }
 
-type EvalArg struct {
-	name  string
-	value any
+type Arg struct {
+	Name  string
+	Value any
 }
 
-func EvalStringA(source string, args ...EvalArg) (result any, err error) {
+func EvalStringA(source string, args ...Arg) (result any, err error) {
 	return EvalStringV(source, args)
 }
 
-func EvalStringV(source string, args []EvalArg) (result any, err error) {
+func EvalStringV(source string, args []Arg) (result any, err error) {
 	ctx := NewSimpleFuncStore()
 	for _, arg := range args {
-		if isFunc(arg.value) {
-			if f, ok := arg.value.(FuncTemplate); ok {
+		if isFunc(arg.Value) {
+			if f, ok := arg.Value.(FuncTemplate); ok {
 				functor := &simpleFunctor{f: f}
-				ctx.RegisterFunc(arg.name, functor, 0, -1)
+				ctx.RegisterFunc(arg.Name, functor, 0, -1)
 			} else {
-				err = fmt.Errorf("invalid function specification: %q", arg.name)
+				err = fmt.Errorf("invalid function specification: %q", arg.Name)
 			}
-		} else if integer, ok := anyInteger(arg.value); ok {
-			ctx.SetVar(arg.name, integer)
-		} else if float, ok := anyFloat(arg.value); ok {
-			ctx.SetVar(arg.name, float)
-		} else if _, ok := arg.value.(string); ok {
-			ctx.SetVar(arg.name, arg.value)
-		} else if _, ok := arg.value.(bool); ok {
-			ctx.SetVar(arg.name, arg.value)
+		} else if integer, ok := anyInteger(arg.Value); ok {
+			ctx.SetVar(arg.Name, integer)
+		} else if float, ok := anyFloat(arg.Value); ok {
+			ctx.SetVar(arg.Name, float)
+		} else if _, ok := arg.Value.(string); ok {
+			ctx.SetVar(arg.Name, arg.Value)
+		} else if _, ok := arg.Value.(bool); ok {
+			ctx.SetVar(arg.Name, arg.Value)
 		} else {
-			err = fmt.Errorf("unsupported type %T specified for item %q", arg.value, arg.name)
+			err = fmt.Errorf("unsupported type %T specified for item %q", arg.Value, arg.Name)
 		}
 	}
 
@@ -56,3 +61,24 @@ func EvalStringV(source string, args []EvalArg) (result any, err error) {
 	}
 	return
 }
+
+func EvalStream(ctx ExprContext, r io.Reader) (result any, err error) {
+	var tree *ast
+	scanner := NewScanner(r, DefaultTranslations())
+	parser := NewParser(ctx)
+
+	if tree, err = parser.Parse(scanner); err == nil {
+		result, err = tree.Eval(ctx)
+	}
+	return
+}
+
+func EvalFile(ctx ExprContext, filePath string) (result any, err error) {
+	var fh *os.File
+	if fh, err = os.Open(filePath); err != nil {
+		return nil, err
+	}
+	defer fh.Close()
+	result, err = EvalStream(ctx, fh)
+	return
+}

helpers_test.go

@@ -1,3 +1,6 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // helpers_test.go
 package expr
 
@@ -24,7 +27,7 @@ func subtract(ctx ExprContext, name string, args []any) (result any, err error)
 func TestEvalStringA(t *testing.T) {
 
 	source := `a + b * subtract(4,2)`
-	args := []EvalArg{
+	args := []Arg{
 		{"a", uint8(1)},
 		{"b", int8(2)},
 		{"subtract", FuncTemplate(subtract)},
@@ -45,7 +48,6 @@ func TestEvalStringA(t *testing.T) {
 		t.Errorf("Source %q got %v, want %v", source, gotResult, wantResult)
 		t.Errorf("Error: %v", gotErr)
 	}
-	fmt.Println("Hello World!")
 }
 
 func TestEvalString(t *testing.T) {
@@ -76,5 +78,4 @@ func TestEvalString(t *testing.T) {
 		t.Errorf("Source %q got %v, want %v", source, gotResult, wantResult)
 		t.Errorf("Error: %v", gotErr)
 	}
-	fmt.Println("Hello World!")
 }

int.list

@@ -0,0 +1,4 @@
+10
+20
+5
+12

it-range.go

@@ -1,3 +1,6 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // it-range.go
 package expr
 

iter-list.go

@@ -0,0 +1,132 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iter-list.go
+package expr
+
+import (
+	"fmt"
+	"io"
+)
+
+type ListIterator struct {
+	a     *ListType
+	count int
+	index int
+	start int
+	stop  int
+	step  int
+}
+
+func NewListIterator(list *ListType, args []any) (it *ListIterator) {
+	var argc int = 0
+	listLen := len(([]any)(*list))
+	if args != nil {
+		argc = len(args)
+	}
+	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 < 0 {
+				i = listLen + i
+			}
+			it.start = i
+		}
+		if argc >= 2 {
+			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 < 0 {
+						i = -i
+					}
+					if it.start > it.stop {
+						it.step = -i
+					} else {
+						it.step = i
+					}
+				}
+			}
+		}
+	}
+	it.index = it.start - it.step
+	return
+}
+
+func NewArrayIterator(array []any) (it *ListIterator) {
+	it = &ListIterator{a: (*ListType)(&array), count: 0, index: -1, start: 0, stop: len(array) - 1, step: 1}
+	return
+}
+
+func NewAnyIterator(value any) (it *ListIterator) {
+	if value == nil {
+		it = NewArrayIterator([]any{})
+	} else if list, ok := value.(*ListType); ok {
+		it = NewListIterator(list, nil)
+	} else if array, ok := value.([]any); ok {
+		it = NewArrayIterator(array)
+	} else if it1, ok := value.(*ListIterator); ok {
+		it = it1
+	} else {
+		it = NewArrayIterator([]any{value})
+	}
+	return
+}
+
+func (it *ListIterator) String() string {
+	var l = 0
+	if it.a != nil {
+		l = len(*it.a)
+	}
+	return fmt.Sprintf("$(#%d)", l)
+}
+
+func (it *ListIterator) HasOperation(name string) bool {
+	yes := name == resetName || name == indexName || name == countName
+	return yes
+}
+
+func (it *ListIterator) CallOperation(name string, args []any) (v any, err error) {
+	switch name {
+	case resetName:
+		v, err = it.Reset()
+	case indexName:
+		v = int64(it.Index())
+	case countName:
+		v = it.count
+	default:
+		err = errNoOperation(name)
+	}
+	return
+}
+
+func (it *ListIterator) Current() (item any, err error) {
+	a := *(it.a)
+	if it.index >= 0 && it.index <= it.stop {
+		item = a[it.index]
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (it *ListIterator) Next() (item any, err error) {
+	it.index += it.step
+	if item, err = it.Current(); err != io.EOF {
+		it.count++
+	}
+	return
+}
+
+func (it *ListIterator) Index() int {
+	return it.index
+}
+
+func (it *ListIterator) Reset() (bool, error) {
+	it.index = it.start
+	return true, nil
+}

iterator.expr

@@ -0,0 +1,18 @@
+ds={
+	"init":func(end){@end=end; @current=0; @prev=@current},
+	"current":func(){prev},
+	"next":func(){
+		(current <= end) ? [true] {@current=current+1; @prev=current} :: {nil}
+	},
+	"reset":func(){@current=0; @prev=@current}
+}
+
+// Example
+//;
+//it=$(ds,3);
+//it++;
+//it."reset"
+//it++;
+//it++;
+//add(it)
+

iterator.go

@@ -1,37 +1,42 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // iterator.go
 package expr
 
-import "io"
+import (
+	"errors"
+	"fmt"
+)
+
+// Operator names
+
+const (
+	initName    = "init"
+	cleanName   = "clean"
+	resetName   = "reset"
+	nextName    = "next"
+	currentName = "current"
+	indexName   = "index"
+	countName   = "count"
+)
 
 type Iterator interface {
-	Reset()
 	Next() (item any, err error) // must return io.EOF after the last item
+	Current() (item any, err error)
 	Index() int
 }
 
-type FlatArrayIterator struct {
-	a     []any
-	index int
+type ExtIterator interface {
+	Iterator
+	HasOperation(name string) bool
+	CallOperation(name string, args []any) (value any, err error)
 }
 
-func NewFlatArrayIterator(array []any) *FlatArrayIterator {
-	return &FlatArrayIterator{a: array, index: 0}
+func errNoOperation(name string) error {
+	return fmt.Errorf("no %q function defined in the data-source", name)
 }
 
-func (it *FlatArrayIterator) Reset() {
-	it.index = 0
-}
-
-func (it *FlatArrayIterator) Next() (item any, err error) {
-	if it.index < len(it.a) {
-		item = it.a[it.index]
-		it.index++
-	} else {
-		err = io.EOF
-	}
-	return
-}
-
-func (it *FlatArrayIterator) Index() int {
-	return it.index - 1
+func errInvalidDataSource() error {
+	return errors.New("invalid data-source")
 }

iterator_test.go

@@ -0,0 +1,26 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iterator_test.go
+package expr
+
+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=$(ds,"int.list"); it.clean`, true, nil},
+		/*  11 */ {`it=$(1,2,3); it++`, int64(1), nil},
+	}
+	// inputs1 := []inputType{
+	// 	/*   1 */ {`0?{}`, nil, nil},
+	// }
+	parserTest(t, "Iterator", inputs)
+}

list_test.go

@@ -0,0 +1,119 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// list_test.go
+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 */ {`[]`, []any{}, nil},
+		/*   2 */ {`[1,2,3]`, []any{int64(1), int64(2), int64(3)}, nil},
+		/*   3 */ {`[1,2,"hello"]`, []any{int64(1), int64(2), "hello"}, nil},
+		/*   4 */ {`[1+2, not true, "hello"]`, []any{int64(3), false, "hello"}, nil},
+		/*   5 */ {`[1,2]+[3]`, []any{int64(1), int64(2), int64(3)}, nil},
+		/*   6 */ {`[1,4,3,2]-[3]`, []any{int64(1), int64(4), int64(2)}, nil},
+		/*   7 */ {`add([1,4,3,2])`, int64(10), nil},
+		/*   8 */ {`add([1,[2,2],3,2])`, int64(10), nil},
+		/*   9 */ {`mul([1,4,3.0,2])`, float64(24.0), nil},
+		/*  10 */ {`add([1,"hello"])`, nil, errors.New(`add(): param nr 2 (2 in 1) has wrong type string, number expected`)},
+		/*  11 */ {`[a=1,b=2,c=3] but a+b+c`, int64(6), nil},
+		/*  12 */ {`[1,2,3] << 2+2`, []any{int64(1), int64(2), int64(3), int64(4)}, nil},
+		/*  13 */ {`2-1 >> [2,3]`, []any{int64(1), int64(2), int64(3)}, nil},
+		/*  14 */ {`[1,2,3].1`, int64(2), nil},
+		/*  15 */ {`ls=[1,2,3] but ls.1`, int64(2), nil},
+		/*  16 */ {`ls=[1,2,3] but ls.(-1)`, int64(3), nil},
+		/*  17 */ {`list=["one","two","three"]; list.10`, nil, errors.New(`[1:36] index 10 out of bounds`)},
+		/*  18 */ {`["a", "b", "c"]`, newListA("a", "b", "c"), nil},
+		/*  19 */ {`["a", "b", "c"]`, newList([]any{"a", "b", "c"}), nil},
+		/*  20 */ {`#["a", "b", "c"]`, int64(3), 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},
+	}
+
+	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 := NewSimpleFuncStore()
+		ctx.SetVar("var1", int64(123))
+		ctx.SetVar("var2", "abc")
+		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)
+}

module-register.go

@@ -0,0 +1,73 @@
+// 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 ImportInContext(ctx ExprContext, name string) (exists bool) {
+// 	var mod *module
+// 	if mod, exists = moduleRegister[name]; exists {
+// 		mod.importFunc(ctx)
+// 		mod.imported = true
+// 	}
+// 	return
+// }
+
+// func ImportInContextByGlobPattern(ctx ExprContext, pattern string) (count int, err error) {
+// 	var matched bool
+// 	for name, mod := range moduleRegister {
+// 		if matched, err = filepath.Match(pattern, name); err == nil {
+// 			if matched {
+// 				count++
+// 				mod.importFunc(ctx)
+// 				mod.imported = true
+// 			}
+// 		} else {
+// 			break
+// 		}
+// 	}
+// 	return
+// }
+
+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)
+	}
+}

operand-const.go

@@ -1,73 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// operand-const.go
-package expr
-
-// -------- bool const term
-func newBoolTerm(tk *Token) *term {
-	return &term{
-		tk: *tk,
-		// class:    classConst,
-		// kind:     kindBool,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- integer const term
-func newIntegerTerm(tk *Token) *term {
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- float const term
-func newFloatTerm(tk *Token) *term {
-	return &term{
-		tk: *tk,
-		// class:    classConst,
-		// kind:     kindFloat,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- string const term
-func newStringTerm(tk *Token) *term {
-	return &term{
-		tk: *tk,
-		// class:    classConst,
-		// kind:     kindString,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- eval func
-func evalConst(ctx ExprContext, self *term) (v any, err error) {
-	v = self.tk.Value
-	return
-}
-
-// init
-func init() {
-	registerTermConstructor(SymString, newStringTerm)
-	registerTermConstructor(SymInteger, newIntegerTerm)
-	registerTermConstructor(SymFloat, newFloatTerm)
-	registerTermConstructor(SymBool, newBoolTerm)
-}

operand-dict.go

@@ -0,0 +1,34 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-dict.go
+package expr
+
+// -------- dict term
+func newDictTerm(args map[any]*term) *term {
+	return &term{
+		tk:       *NewValueToken(0, 0, SymDict, "{}", args),
+		parent:   nil,
+		children: nil,
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalDict,
+	}
+}
+
+// -------- dict func
+func evalDict(ctx ExprContext, self *term) (v any, err error) {
+	dict, _ := self.value().(map[any]*term)
+	items := make(map[any]any, len(dict))
+	for key, tree := range dict {
+		var param any
+		if param, err = tree.compute(ctx); err != nil {
+			break
+		}
+		items[key] = param
+	}
+	if err == nil {
+		v = items
+	}
+	return
+}

operand-expr.go

@@ -27,8 +27,3 @@ func evalExpr(ctx ExprContext, self *term) (v any, err error) {
 	}
 	return
 }
-
-// init
-// func init() {
-// 	registerTermConstructor(SymExpression, newExprTerm)
-// }

operand-func.go

@@ -6,14 +6,13 @@ package expr
 
 import (
 	"errors"
+	"fmt"
 )
 
 // -------- function call term
 func newFuncCallTerm(tk *Token, args []*term) *term {
 	return &term{
-		tk: *tk,
-		// class:    classVar,
-		// kind:     kindUnknown,
+		tk:       *tk,
 		parent:   nil,
 		children: args,
 		position: posLeaf,
@@ -23,9 +22,31 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 }
 
 // -------- eval func call
+func checkFunctionCall(ctx ExprContext, name string, params []any) (err error) {
+	if info, exists, owner := GetFuncInfo(ctx, name); exists {
+		if info.MinArgs() > len(params) {
+			if info.MaxArgs() < 0 {
+				err = fmt.Errorf("too few params -- expected %d or more, got %d", info.MinArgs(), len(params))
+			} else {
+				err = fmt.Errorf("too few params -- expected %d, got %d", info.MinArgs(), len(params))
+			}
+		}
+		if err == nil && info.MaxArgs() >= 0 && info.MaxArgs() < len(params) {
+			err = fmt.Errorf("too much params -- expected %d, got %d", info.MaxArgs(), len(params))
+		}
+		if err == nil && owner != ctx {
+			ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
+		}
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}
+
 func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
-	ctx := parentCtx.Clone()
+	ctx := cloneContext(parentCtx)
 	name, _ := self.tk.Value.(string)
+	// fmt.Printf("Call %s(), context: %p\n", name, ctx)
 	params := make([]any, len(self.children))
 	for i, tree := range self.children {
 		var param any
@@ -35,44 +56,21 @@ func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 		params[i] = param
 	}
 	if err == nil {
-		if v, err = ctx.Call(name, params); err == nil {
-			exportAll := isEnabled(ctx, control_export_all)
-			// Export variables
-			for _, refName := range ctx.EnumVars(func(name string) bool { return exportAll || name[0] == '@' }) {
-				refValue, _ := ctx.GetVar(refName)
-				exportVar(parentCtx, refName, refValue)
-			}
-			// Export functions
-			for _, refName := range ctx.EnumFuncs(func(name string) bool { return exportAll || name[0] == '@' }) {
-				if info := ctx.GetFuncInfo(refName); info != nil {
-					exportFunc(parentCtx, refName, info)
-				}
+		if err = checkFunctionCall(ctx, name, params); err == nil {
+			if v, err = ctx.Call(name, params); err == nil {
+				exportObjects(parentCtx, ctx)
 			}
 		}
 	}
 	return
 }
 
-func exportVar(ctx ExprContext, name string, value any) {
-	if name[0] == '@' {
-		name = name[1:]
-	}
-	ctx.SetVar(name, value)
-}
-
-func exportFunc(ctx ExprContext, name string, info ExprFunc) {
-	if name[0] == '@' {
-		name = name[1:]
-	}
-	ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
-}
-
 // -------- function definition term
 func newFuncDefTerm(tk *Token, args []*term) *term {
 	return &term{
-		tk:       *tk,
+		tk:       *tk, // value is the expression body
 		parent:   nil,
-		children: args, // arg[0]=formal-param-list, arg[1]=*ast
+		children: args, // function params
 		position: posLeaf,
 		priority: priValue,
 		evalFunc: evalFuncDef,
@@ -89,9 +87,14 @@ type funcDefFunctor struct {
 func (functor *funcDefFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
 	for i, p := range functor.params {
 		if i < len(args) {
-			ctx.SetVar(p, args[i])
+			arg := args[i]
+			if functor, ok := arg.(Functor); ok {
+				ctx.RegisterFunc(p, functor, 0, -1)
+			} else {
+				ctx.setVar(p, arg)
+			}
 		} else {
-			ctx.SetVar(p, nil)
+			ctx.setVar(p, nil)
 		}
 	}
 	result, err = functor.expr.eval(ctx, false)
@@ -104,12 +107,6 @@ func evalFuncDef(ctx ExprContext, self *term) (v any, err error) {
 		paramList := make([]string, 0, len(self.children))
 		for _, param := range self.children {
 			paramList = append(paramList, param.source())
-			// if paramName, ok := param.value().(string); ok {
-			// 	paramList = append(paramList, paramName)
-			// } else {
-			// 	err = fmt.Errorf("invalid function definition: formal param nr %d must be an identifier", i+1)
-			// 	break
-			// }
 		}
 		v = &funcDefFunctor{
 			params: paramList,

operand-iterator.go

@@ -0,0 +1,184 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-iterator.go
+package expr
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+)
+
+// -------- iterator term
+
+func newDsIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
+	tk.Sym = SymIterator
+
+	children := make([]*term, 0, 1+len(args))
+	children = append(children, dsTerm)
+	children = append(children, args...)
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: children,
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalIterator,
+	}
+}
+
+func newIteratorTerm(tk *Token, args []*term) *term {
+	tk.Sym = SymIterator
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: args,
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalIterator,
+	}
+}
+
+// -------- eval iterator
+
+func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
+	values = make([]any, len(a))
+	for i, t := range a {
+		var value any
+		if value, err = t.compute(ctx); err == nil {
+			values[i] = value
+		} else {
+			break
+		}
+	}
+	return
+}
+
+func evalFirstChild(ctx ExprContext, self *term) (value any, err error) {
+	if len(self.children) < 1 || self.children[0] == nil {
+		err = self.Errorf("missing the data-source parameter")
+		return
+	}
+
+	value, err = self.children[0].compute(ctx)
+	return
+}
+
+func getDataSourceDict(ctx ExprContext, self *term, firstChildValue any) (ds map[string]Functor, err error) {
+	if dictAny, ok := firstChildValue.(map[any]any); ok {
+		requiredFields := []string{currentName, nextName}
+		fieldsMask := 0b11
+		foundFields := 0
+		ds = make(map[string]Functor)
+		for keyAny, item := range dictAny {
+			if key, ok := keyAny.(string); ok {
+				if functor, ok := item.(*funcDefFunctor); ok {
+					ds[key] = functor
+					if index := slices.Index(requiredFields, key); index >= 0 {
+						foundFields |= 1 << index
+					}
+				}
+			}
+		}
+		// check required functions
+		if foundFields != fieldsMask {
+			missingFields := make([]string, 0, len(requiredFields))
+			for index, field := range requiredFields {
+				if (foundFields & (1 << index)) == 0 {
+					missingFields = append(missingFields, field)
+				}
+			}
+			err = fmt.Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
+		}
+	}
+	return
+}
+
+func evalIterator(ctx ExprContext, self *term) (v any, err error) {
+	var firstChildValue any
+	var ds map[string]Functor
+
+	if firstChildValue, err = evalFirstChild(ctx, self); err != nil {
+		return
+	}
+
+	if ds, err = getDataSourceDict(ctx, self, firstChildValue); err != nil {
+		return
+	}
+
+	if ds != nil {
+		dc := newDataCursor(ctx, ds)
+		if initFunc, exists := ds[initName]; exists && initFunc != nil {
+			var args []any
+			if len(self.children) > 1 {
+				if args, err = evalTermArray(ctx, self.children[1:]); err != nil {
+					return
+				}
+			} else {
+				args = []any{}
+			}
+
+			initCtx := dc.ctx.Clone()
+			if dc.resource, err = initFunc.Invoke(initCtx, initName, args); err != nil {
+				return
+			}
+			exportObjects(dc.ctx, initCtx)
+		}
+
+		dc.nextFunc, _ = ds[nextName]
+		dc.currentFunc, _ = ds[currentName]
+		dc.cleanFunc, _ = ds[cleanName]
+		dc.resetFunc, _ = ds[resetName]
+
+		v = dc
+	} else if list, ok := firstChildValue.(*ListType); ok {
+		var args []any
+		if args, err = evalSibling(ctx, self.children, nil); err == nil {
+			v = NewListIterator(list, args)
+		}
+	} else {
+		var list []any
+		if list, err = evalSibling(ctx, self.children, firstChildValue); err == nil {
+			v = NewArrayIterator(list)
+		}
+	}
+	return
+}
+
+// func evalChildren(ctx ExprContext, terms []*term, firstChildValue any) (list *ListType, err error) {
+// 	items := make(ListType, len(terms))
+// 	for i, tree := range terms {
+// 		var param any
+// 		if i == 0 && firstChildValue != nil {
+// 			param = firstChildValue
+// 		} else if param, err = tree.compute(ctx); err != nil {
+// 			break
+// 		}
+// 		items[i] = param
+// 	}
+// 	if err == nil {
+// 		list = &items
+// 	}
+// 	return
+// }
+
+func evalSibling(ctx ExprContext, terms []*term, firstChildValue any) (list []any, err error) {
+	items := make([]any, 0, len(terms))
+	for i, tree := range terms {
+		var param any
+		if i == 0 {
+			if firstChildValue == nil {
+				continue
+			}
+			param = firstChildValue
+		} else if param, err = tree.compute(ctx); err != nil {
+			break
+		}
+		items = append(items, param)
+	}
+	if err == nil {
+		list = items
+	}
+	return
+}

operand-list.go

@@ -4,12 +4,74 @@
 // operand-list.go
 package expr
 
+import (
+	"fmt"
+	"strings"
+)
+
+type ListType []any
+
+func (ls *ListType) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	sb.WriteByte('[')
+	if len(*ls) > 0 {
+		if opt&MultiLine != 0 {
+			sb.WriteString("\n  ")
+		}
+		for i, item := range []any(*ls) {
+			if i > 0 {
+				if opt&MultiLine != 0 {
+					sb.WriteString(",\n  ")
+				} else {
+					sb.WriteString(", ")
+				}
+			}
+			if s, ok := item.(string); ok {
+				sb.WriteByte('"')
+				sb.WriteString(s)
+				sb.WriteByte('"')
+			} else {
+				sb.WriteString(fmt.Sprintf("%v", item))
+			}
+		}
+		if opt&MultiLine != 0 {
+			sb.WriteByte('\n')
+		}
+	}
+	sb.WriteByte(']')
+	return sb.String()
+}
+
+func (ls *ListType) String() string {
+	return ls.ToString(0)
+}
+
+func newListA(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 {
+			ls[i] = item
+		}
+		list = &ls
+	}
+	return
+}
+
+
 // -------- list term
+func newListTermA(args ...*term) *term {
+	return newListTerm(args)
+}
+
 func newListTerm(args []*term) *term {
 	return &term{
-		tk:       *NewToken(0, 0, SymList, "[]"),
+		tk:       *NewValueToken(0, 0, SymList, "[]", args),
 		parent:   nil,
-		children: args,
+		children: nil,
 		position: posLeaf,
 		priority: priValue,
 		evalFunc: evalList,
@@ -18,8 +80,9 @@ func newListTerm(args []*term) *term {
 
 // -------- list func
 func evalList(ctx ExprContext, self *term) (v any, err error) {
-	items := make([]any, len(self.children))
-	for i, tree := range self.children {
+	list, _ := self.value().([]*term)
+	items := make(ListType, len(list))
+	for i, tree := range list {
 		var param any
 		if param, err = tree.compute(ctx); err != nil {
 			break
@@ -27,7 +90,7 @@ func evalList(ctx ExprContext, self *term) (v any, err error) {
 		items[i] = param
 	}
 	if err == nil {
-		v = items
+		v = &items
 	}
 	return
 }

operand-literal.go

@@ -0,0 +1,33 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-literal.go
+package expr
+
+// -------- literal term
+func newLiteralTerm(tk *Token) *term {
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: nil,
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalLiteral,
+	}
+}
+
+// -------- eval func
+func evalLiteral(ctx ExprContext, self *term) (v any, err error) {
+	v = self.tk.Value
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymString, newLiteralTerm)
+	registerTermConstructor(SymInteger, newLiteralTerm)
+	registerTermConstructor(SymFloat, newLiteralTerm)
+	registerTermConstructor(SymFraction, newLiteralTerm)
+	registerTermConstructor(SymBool, newLiteralTerm)
+	registerTermConstructor(SymKwNil, newLiteralTerm)
+}

operand-selector-case.go

@@ -4,7 +4,10 @@
 // operand-selector-case.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 // -------- selector case term
 
@@ -13,6 +16,18 @@ type selectorCase struct {
 	caseExpr   Expr
 }
 
+func (sc *selectorCase) String() string {
+	var sb strings.Builder
+	if sc.filterList != nil {
+		sc.filterList.toString(&sb)
+		sb.WriteByte(' ')
+	}
+	sb.WriteByte('{')
+	sb.WriteString(sc.caseExpr.String())
+	sb.WriteByte('}')
+	return sb.String()
+}
+
 func newSelectorCaseTerm(row, col int, filterList *term, caseExpr Expr) *term {
 	tk := NewValueToken(row, col, SymSelectorCase, "", &selectorCase{filterList: filterList, caseExpr: caseExpr})
 	return &term{

operand-var.go

@@ -23,8 +23,13 @@ func newVarTerm(tk *Token) *term {
 // -------- eval func
 func evalVar(ctx ExprContext, self *term) (v any, err error) {
 	var exists bool
-	if v, exists = ctx.GetVar(self.tk.source); !exists {
-		err = fmt.Errorf("undefined variable %q", self.tk.source)
+	name := self.source()
+	if v, exists = GetVar(ctx, name); !exists {
+		if info, exists, _ := GetFuncInfo(ctx, name); exists {
+			v = info.Functor()
+		} else {
+			err = fmt.Errorf("undefined variable or function %q", name)
+		}
 	}
 	return
 }

operator-assign.go

@@ -1,5 +1,5 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
+// All rights reserightChilded.
 
 // operator-assign.go
 package expr
@@ -27,11 +27,24 @@ func evalAssign(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if v, err = self.children[1].compute(ctx); err == nil {
+	rightChild := self.children[1]
+
+	if v, err = rightChild.compute(ctx); err == nil {
 		if functor, ok := v.(Functor); ok {
-			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
+			var minArgs, maxArgs int = 0, -1
+
+			funcName := rightChild.source()
+			if info, exists := ctx.GetFuncInfo(funcName); exists {
+				minArgs = info.MinArgs()
+				maxArgs = info.MaxArgs()
+			} else if funcDef, ok := functor.(*funcDefFunctor); ok {
+				l := len(funcDef.params)
+				minArgs = l
+				maxArgs = l
+			}
+			ctx.RegisterFunc(leftTerm.source(), functor, minArgs, maxArgs)
 		} else {
-			ctx.SetVar(leftTerm.tk.source, v)
+			ctx.setVar(leftTerm.source(), v)
 		}
 	}
 	return

operator-bool.go

@@ -48,7 +48,7 @@ func newAndTerm(tk *Token) (inst *term) {
 }
 
 func evalAnd(ctx ExprContext, self *term) (v any, err error) {
-	if isEnabled(ctx, control_bool_shortcut) {
+	if isEnabled(ctx, ControlBoolShortcut) {
 		v, err = evalAndWithShortcut(ctx, self)
 	} else {
 		v, err = evalAndWithoutShortcut(ctx, self)
@@ -117,7 +117,7 @@ func newOrTerm(tk *Token) (inst *term) {
 }
 
 func evalOr(ctx ExprContext, self *term) (v any, err error) {
-	if isEnabled(ctx, control_bool_shortcut) {
+	if isEnabled(ctx, ControlBoolShortcut) {
 		v, err = evalOrWithShortcut(ctx, self)
 	} else {
 		v, err = evalOrWithoutShortcut(ctx, self)

operator-builtin.go

@@ -0,0 +1,61 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-builtin.go
+package expr
+
+import "io"
+
+//-------- builtin term
+
+func newBuiltinTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priSign,
+		evalFunc: evalBuiltin,
+	}
+}
+
+func evalBuiltin(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	count := 0
+	if IsString(childValue) {
+		module, _ := childValue.(string)
+		count, err = ImportInContextByGlobPattern(module)
+	} else {
+		var moduleSpec any
+		it := NewAnyIterator(childValue)
+		for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
+			if module, ok := moduleSpec.(string); ok {
+				if ImportInContext(module) {
+					count++
+				} else {
+					err = self.Errorf("unknown module %q", module)
+					break
+				}
+			} else {
+				err = self.Errorf("expected string at item nr %d, got %T", it.Index()+1, moduleSpec)
+				break
+			}
+		}
+		if err == io.EOF {
+			err = nil
+		}
+	}
+	if err == nil {
+		v = int64(count)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymKwBuiltin, newBuiltinTerm)
+}

operator-coalesce.go

@@ -34,11 +34,11 @@ func evalNullCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
 		v = leftValue
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if _, ok := rightValue.(Functor); ok {
-			err = errCoalesceNoFunc(self.children[1])
-		} else {
-			v = rightValue
-		}
+		// if _, ok := rightValue.(Functor); ok {
+		// 	err = errCoalesceNoFunc(self.children[1])
+		// } else {
+		v = rightValue
+		// }
 	}
 	return
 }
@@ -71,20 +71,20 @@ func evalAssignCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
 		v = leftValue
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if _, ok := rightValue.(Functor); ok {
-			err = errCoalesceNoFunc(self.children[1])
+		if functor, ok := rightValue.(Functor); ok {
+			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
 		} else {
 			v = rightValue
-			ctx.SetVar(leftTerm.source(), rightValue)
+			ctx.setVar(leftTerm.source(), rightValue)
 		}
 	}
 	return
 }
 
 // utils
-func errCoalesceNoFunc(t *term) error {
-	return t.Errorf("the right operand of a coalescing operation cannot be a function definition")
-}
+// func errCoalesceNoFunc(t *term) error {
+// 	return t.Errorf("the right operand of a coalescing operation cannot be a function definition")
+// }
 
 // init
 func init() {

operator-context.go

@@ -0,0 +1,57 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-context-value.go
+package expr
+
+//-------- context term
+
+func newContextTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priIncDec,
+		evalFunc: evalContextValue,
+	}
+}
+
+func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+
+	var sourceCtx ExprContext
+	if len(self.children) == 0 {
+		sourceCtx = ctx
+	} else if childValue, err = self.evalPrefix(ctx); err == nil {
+		if dc, ok := childValue.(*dataCursor); ok {
+			sourceCtx = dc.ctx
+		}
+	} else {
+		return
+	}
+
+	if sourceCtx != nil {
+		if formatter, ok := ctx.(Formatter); ok {
+			v = formatter.ToString(0)
+		} else {
+			keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+			d := make(map[string]any)
+			for _, key := range keys {
+				d[key], _ = sourceCtx.GetVar(key)
+			}
+			keys = sourceCtx.EnumFuncs(func(name string) bool { return true })
+			for _, key := range keys {
+				d[key], _ = sourceCtx.GetFuncInfo(key)
+			}
+			v = d
+		}
+	} else {
+		err = self.errIncompatibleType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymDoubleDollar, newContextTerm)
+}

operator-dot.go

@@ -0,0 +1,101 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-dot.go
+package expr
+
+import "fmt"
+
+// -------- dot term
+func newDotTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priDot,
+		evalFunc: evalDot,
+	}
+}
+
+func verifyIndex(ctx ExprContext, indexTerm *term, maxValue int) (index int, err error) {
+	var v int
+	var indexValue any
+	if indexValue, err = indexTerm.compute(ctx); err == nil {
+		if v, err = indexTerm.toInt(indexValue, "index expression value must be integer"); err == nil {
+			if v < 0 && v >= -maxValue {
+				v = maxValue + v
+			}
+			if v >= 0 && v < maxValue {
+				index = v
+			} else {
+				err = indexTerm.Errorf("index %d out of bounds", v)
+			}
+		}
+	}
+	return
+}
+
+func evalDot(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if err = self.checkOperands(); err != nil {
+		return
+	}
+	if leftValue, err = self.children[0].compute(ctx); err != nil {
+		return
+	}
+
+	indexTerm := self.children[1]
+
+	switch unboxedValue := leftValue.(type) {
+	case *ListType:
+		var index int
+		array := ([]any)(*unboxedValue)
+		if index, err = verifyIndex(ctx, indexTerm, len(array)); err == nil {
+			v = array[index]
+		}
+	case string:
+		var index int
+		if index, err = verifyIndex(ctx, indexTerm, len(unboxedValue)); err == nil {
+			v = string(unboxedValue[index])
+		}
+	case map[any]any:
+		var ok bool
+		var indexValue any
+		if indexValue, err = indexTerm.compute(ctx); err == nil {
+			if v, ok = unboxedValue[indexValue]; !ok {
+				err = fmt.Errorf("key %v does not belong to the dictionary", rightValue)
+			}
+		}
+	// case *dataCursor:
+	// 	if indexTerm.symbol() == SymIdentifier {
+	// 		opName := indexTerm.source()
+	// 		if opName == resetName {
+	// 			_, err = unboxedValue.Reset()
+	// 		} else if opName == cleanName {
+	// 			_, err = unboxedValue.Clean()
+	// 		} else {
+	// 			err = indexTerm.Errorf("iterators do not support command %q", opName)
+	// 		}
+	// 		v = err == nil
+	// 	}
+	case ExtIterator:
+		if indexTerm.symbol() == SymIdentifier {
+			opName := indexTerm.source()
+			if unboxedValue.HasOperation(opName) {
+				v, err = unboxedValue.CallOperation(opName, []any{})
+			} else {
+				err = indexTerm.Errorf("this iterator do not support the %q command", opName)
+				v = false
+			}
+		}
+	default:
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymDot, newDotTerm)
+}

operator-fact.go

@@ -25,7 +25,7 @@ func evalFact(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isInteger(leftValue) {
+	if IsInteger(leftValue) {
 		if i, _ := leftValue.(int64); i >= 0 {
 			f := int64(1)
 			for k := int64(1); k <= i; k++ {

operator-fraction.go

@@ -0,0 +1,411 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-fraction.go
+package expr
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+)
+
+type fraction struct {
+	num, den int64
+}
+
+func newFraction(num, den int64) *fraction {
+	/*	if den < 0 {
+		den = -den
+		num = -num
+	}*/
+	num, den = simplifyIntegers(num, den)
+	return &fraction{num, den}
+}
+
+func float64ToFraction(f float64) (fract *fraction, err error) {
+	var sign string
+	intPart, decPart := math.Modf(f)
+	if decPart < 0.0 {
+		sign="-"
+		intPart = -intPart
+		decPart = -decPart
+	}
+	dec := fmt.Sprintf("%.12f", decPart)
+	s := fmt.Sprintf("%s%.f%s", sign, intPart, dec[1:])
+	// fmt.Printf("S: '%s'\n",s)
+	return makeGeneratingFraction(s)
+}
+
+// Based on https://cs.opensource.google/go/go/+/refs/tags/go1.22.3:src/math/big/rat.go;l=39
+/*
+func _float64ToFraction(f float64) (num, den int64, err error) {
+	const expMask = 1<<11 - 1
+	bits := math.Float64bits(f)
+	mantissa := bits & (1<<52 - 1)
+	exp := int((bits >> 52) & expMask)
+	switch exp {
+	case expMask: // non-finite
+		err = errors.New("infite")
+		return
+	case 0: // denormal
+		exp -= 1022
+	default: // normal
+		mantissa |= 1 << 52
+		exp -= 1023
+	}
+
+	shift := 52 - exp
+
+	// Optimization (?): partially pre-normalise.
+	for mantissa&1 == 0 && shift > 0 {
+		mantissa >>= 1
+		shift--
+	}
+
+	if f < 0 {
+		num = -int64(mantissa)
+	} else {
+		num = int64(mantissa)
+	}
+	den = int64(1)
+
+	if shift > 0 {
+		den = den << shift
+	} else {
+		num = num << (-shift)
+	}
+	return
+}
+*/
+
+func makeGeneratingFraction(s string) (f *fraction, err error) {
+	var num, den int64
+	var sign int64 = 1
+	var parts []string
+	if len(s) == 0 {
+		goto exit
+	}
+	if s[0] == '-' {
+		sign=int64(-1)
+		s = s[1:]
+	} else if s[0] == '+' {
+		s = s[1:]
+	}
+	parts = strings.SplitN(s, ".", 2)
+	if num, err = strconv.ParseInt(parts[0], 10, 64); err != nil {
+		return
+	}
+	if len(parts) == 1 {
+		f = newFraction(sign*num, 1)
+	} else if len(parts) == 2 {
+		subParts := strings.SplitN(parts[1], "(", 2)
+		if len(subParts) == 1 {
+			den = 1
+			dec := parts[1]
+			lsd := len(dec)
+			for i:=lsd-1; i>= 0 && dec[i]=='0'; i-- {
+				lsd--
+			}
+			for _, c := range dec[0:lsd] {
+				if c < '0' || c > '9' {
+					return nil, errExpectedGot("fract", "digit", c)
+				}
+				num = num*10 + int64(c-'0')
+				den = den * 10
+			}
+			f = newFraction(sign*num, den)
+		} else if len(subParts) == 2 {
+			sub := num
+			mul := int64(1)
+			for _, c := range subParts[0] {
+				if c < '0' || c > '9' {
+					return nil, errExpectedGot("fract", "digit", c)
+				}
+				num = num*10 + int64(c-'0')
+				sub = sub*10 + int64(c-'0')
+				mul *= 10
+			}
+			if len(subParts) == 2 {
+				if s[len(s)-1] != ')' {
+					goto exit
+				}
+				p := subParts[1][0 : len(subParts[1])-1]
+				for _, c := range p {
+					if c < '0' || c > '9' {
+						return nil, errExpectedGot("fract", "digit", c)
+					}
+					num = num*10 + int64(c-'0')
+					den = den*10 + 9
+				}
+				den *= mul
+			}
+			num -= sub
+			f = newFraction(sign*num, den)
+		}
+	}
+exit:
+	if f == nil {
+		err = errors.New("bad syntax")
+	}
+	return
+}
+
+func (f *fraction) toFloat() float64 {
+	return float64(f.num) / float64(f.den)
+}
+
+func (f *fraction) String() string {
+	return f.ToString(0)
+}
+
+func (f *fraction) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	if opt&MultiLine == 0 {
+		sb.WriteString(fmt.Sprintf("%d|%d", f.num, f.den))
+	} else {
+		var s, num string
+		if f.num < 0 && opt&TTY == 0 {
+			num = strconv.FormatInt(-f.num, 10)
+			s = "-"
+		} else {
+			num = strconv.FormatInt(f.num, 10)
+		}
+		den := strconv.FormatInt(f.den, 10)
+		size := max(len(num), len(den))
+		if opt&TTY != 0 {
+			sb.WriteString(fmt.Sprintf("\x1b[4m%[1]*s\x1b[0m\n", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, s+num)))
+		} else {
+			if len(s) > 0 {
+				sb.WriteString("  ")
+			}
+			sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(num))/2, num)))
+			sb.WriteByte('\n')
+			if len(s) > 0 {
+				sb.WriteString(s)
+				sb.WriteByte(' ')
+			}
+			sb.WriteString(strings.Repeat("-", size))
+			sb.WriteByte('\n')
+			if len(s) > 0 {
+				sb.WriteString("  ")
+			}
+		}
+		sb.WriteString(fmt.Sprintf("%[1]*s", -size, fmt.Sprintf("%[1]*s", (size+len(den))/2, den)))
+	}
+
+	return sb.String()
+}
+
+// -------- fraction term
+func newFractionTerm(tk *Token) *term {
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priFraction,
+		evalFunc: evalFraction,
+	}
+}
+
+// -------- eval func
+func evalFraction(ctx ExprContext, self *term) (v any, err error) {
+	var numValue, denValue any
+	var num, den int64
+	var ok bool
+
+	if numValue, denValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+	if num, ok = numValue.(int64); !ok {
+		err = fmt.Errorf("numerator must be integer, got %T (%v)", numValue, numValue)
+		return
+	}
+	if den, ok = denValue.(int64); !ok {
+		err = fmt.Errorf("denominator must be integer, got %T (%v)", denValue, denValue)
+		return
+	}
+	if den == 0 {
+		err = errors.New("division by zero")
+		return
+	}
+
+	if den < 0 {
+		den = -den
+		num = -num
+	}
+	g := gcd(num, den)
+	num = num / g
+	den = den / g
+	if den == 1 {
+		v = num
+	} else {
+		v = &fraction{num, den}
+	}
+	return
+}
+
+func gcd(a, b int64) (g int64) {
+	if a < 0 {
+		a = -a
+	}
+	if b < 0 {
+		b = -b
+	}
+	if a < b {
+		a, b = b, a
+	}
+	r := a % b
+	for r > 0 {
+		a, b = b, r
+		r = a % b
+	}
+	g = b
+	return
+}
+
+func lcm(a, b int64) (l int64) {
+	g := gcd(a, b)
+	l = a * b / g
+	return
+}
+
+func sumFract(f1, f2 *fraction) (sum *fraction) {
+	m := lcm(f1.den, f2.den)
+	sum = newFraction(f1.num*(m/f1.den)+f2.num*(m/f2.den), m)
+	return
+}
+
+func mulFract(f1, f2 *fraction) (prod *fraction) {
+	prod = newFraction(f1.num*f2.num, f1.den*f2.den)
+	return
+}
+
+func anyToFract(v any) (f *fraction, err error) {
+	var ok bool
+	if f, ok = v.(*fraction); !ok {
+		if n, ok := v.(int64); ok {
+			f = intToFraction(n)
+		}
+	}
+	if f == nil {
+		err = errExpectedGot("fract", typeFraction, v)
+	}
+	return
+}
+
+func anyPairToFract(v1, v2 any) (f1, f2 *fraction, err error) {
+	if f1, err = anyToFract(v1); err != nil {
+		return
+	}
+	if f2, err = anyToFract(v2); err != nil {
+		return
+	}
+	return
+}
+
+func sumAnyFract(af1, af2 any) (sum any, err error) {
+	var f1, f2 *fraction
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	f := sumFract(f1, f2)
+	if f.num == 0 {
+		sum = 0
+	} else {
+		sum = simplifyFraction(f)
+	}
+	return
+}
+
+func subAnyFract(af1, af2 any) (sum any, err error) {
+	var f1, f2 *fraction
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	f2.num = -f2.num
+	f := sumFract(f1, f2)
+	if f.num == 0 {
+		sum = 0
+	} else {
+		sum = simplifyFraction(f)
+	}
+	return
+}
+
+func mulAnyFract(af1, af2 any) (prod any, err error) {
+	var f1, f2 *fraction
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	if f1.num == 0 || f2.num == 0 {
+		prod = 0
+	} else {
+		f := &fraction{f1.num * f2.num, f1.den * f2.den}
+		prod = simplifyFraction(f)
+	}
+	return
+}
+
+func divAnyFract(af1, af2 any) (quot any, err error) {
+	var f1, f2 *fraction
+	if f1, f2, err = anyPairToFract(af1, af2); err != nil {
+		return
+	}
+	if f2.num == 0 {
+		err = errors.New("division by zero")
+		return
+		return
+	}
+	if f1.num == 0 || f2.den == 0 {
+		quot = 0
+	} else {
+		f := &fraction{f1.num * f2.den, f1.den * f2.num}
+		quot = simplifyFraction(f)
+	}
+	return
+}
+
+func simplifyFraction(f *fraction) (v any) {
+	f.num, f.den = simplifyIntegers(f.num, f.den)
+	if f.den == 1 {
+		v = f.num
+	} else {
+		v = &fraction{f.num, f.den}
+	}
+	return v
+}
+
+func simplifyIntegers(num, den int64) (a, b int64) {
+	if num == 0 {
+		return 0, 1
+	}
+	if den == 0 {
+		panic("fraction with denominator == 0")
+	}
+	if den < 0 {
+		den = -den
+		num = -num
+	}
+	g := gcd(num, den)
+	a = num / g
+	b = den / g
+	return
+}
+
+func intToFraction(n int64) *fraction {
+	return &fraction{n, 1}
+}
+
+func isFraction(v any) (ok bool) {
+	_, ok = v.(*fraction)
+	return ok
+}
+
+// init
+func init() {
+	registerTermConstructor(SymVertBar, newFractionTerm)
+}

operator-include.go

@@ -0,0 +1,57 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-include.go
+package expr
+
+//-------- include term
+
+func newIncludeTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priSign,
+		evalFunc: evalInclude,
+	}
+}
+
+func evalInclude(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	count := 0
+	if IsList(childValue) {
+		list, _ := childValue.([]any)
+		for i, filePathSpec := range list {
+			if filePath, ok := filePathSpec.(string); ok {
+				if v, err = EvalFile(ctx, filePath); err == nil {
+					count++
+				} else {
+					err = self.Errorf("can't load file %q", filePath)
+					break
+				}
+			} else {
+				err = self.Errorf("expected string at item nr %d, got %T", i+1, filePathSpec)
+				break
+			}
+		}
+	} else if IsString(childValue) {
+		filePath, _ := childValue.(string)
+		v, err = EvalFile(ctx, filePath)
+	} else {
+		err = self.errIncompatibleType(childValue)
+	}
+	if err == nil {
+		v = count
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymKwInclude, newIncludeTerm)
+}

operator-insert.go

@@ -0,0 +1,67 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-insert.go
+package expr
+
+//-------- insert term
+
+func newInsertTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priAssign,
+		evalFunc: evalInsert,
+	}
+}
+
+func newAppendTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priAssign,
+		evalFunc: evalAppend,
+	}
+}
+
+func evalInsert(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	if IsList(rightValue) {
+		list, _ := rightValue.(*ListType)
+		newList := append(ListType{leftValue}, *list...)
+		v = &newList
+	} else {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+func evalAppend(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	if IsList(leftValue) {
+		list, _ := leftValue.(*ListType)
+		newList := append(*list, rightValue)
+		v = &newList
+	} else {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymInsert, newInsertTerm)
+	registerTermConstructor(SymAppend, newAppendTerm)
+}

operator-iter-value.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-iter-value.go
+package expr
+
+//-------- iter value term
+
+func newIterValueTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priIterValue,
+		evalFunc: evalIterValue,
+	}
+}
+
+func evalIterValue(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	if it, ok := childValue.(Iterator); ok {
+		v, err = it.Current()
+	} else {
+		err = self.errIncompatibleType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymOpenClosedRound, newIterValueTerm)
+}

operator-length.go

@@ -0,0 +1,51 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-length.go
+package expr
+
+//-------- length term
+
+func newLengthTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priSign,
+		evalFunc: evalLength,
+	}
+}
+
+func evalLength(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+
+	if childValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	if IsList(childValue) {
+		ls, _ := childValue.(*ListType)
+		v = int64(len(*ls))
+	} else if IsString(childValue) {
+		s, _ := childValue.(string)
+		v = int64(len(s))
+	} else if IsDict(childValue) {
+		m, _ := childValue.(map[any]any)
+		v = int64(len(m))
+	} else if it, ok := childValue.(Iterator); ok {
+		if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(countName) {
+			count, _ := extIt.CallOperation(countName, nil)
+			v, _ = toInt(count, "")
+		} else {
+			v = int64(it.Index() + 1)
+		}
+	} else {
+		err = self.errIncompatibleType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymHash, newLengthTerm)
+}

operator-post-inc.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-post-inc.go
+package expr
+
+// -------- post increment term
+
+func newPostIncTerm(tk *Token) *term {
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: make([]*term, 0, 1),
+		position: posPostfix,
+		priority: priIncDec,
+		evalFunc: evalPostInc,
+	}
+}
+
+func evalPostInc(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+	if childValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	if it, ok := childValue.(Iterator); ok {
+		v, err = it.Next()
+	} else if IsInteger(childValue) && self.children[0].symbol() == SymIdentifier {
+		v = childValue
+		i, _ := childValue.(int64)
+		ctx.SetVar(self.children[0].source(), i+1)
+	} else {
+		err = self.errIncompatibleType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymDoublePlus, newPostIncTerm)
+}

operator-prod.go

@@ -30,13 +30,15 @@ func evalMultiply(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isString(leftValue) && isInteger(rightValue) {
+	if IsString(leftValue) && IsInteger(rightValue) {
 		s, _ := leftValue.(string)
 		n, _ := rightValue.(int64)
 		v = strings.Repeat(s, int(n))
-	} else if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+	} else if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			v = numAsFloat(leftValue) * numAsFloat(rightValue)
+		} else if isFraction(leftValue) || isFraction(rightValue) {
+			v, err = mulAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
@@ -69,14 +71,16 @@ func evalDivide(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			d := numAsFloat(rightValue)
 			if d == 0.0 {
 				err = errors.New("division by zero")
 			} else {
 				v = numAsFloat(leftValue) / d
 			}
+		} else if isFraction(leftValue) || isFraction(rightValue) {
+			v, err = divAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			if rightInt, _ := rightValue.(int64); rightInt == 0 {
@@ -110,7 +114,7 @@ func evalDivideAsFloat(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
+	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
 		d := numAsFloat(rightValue)
 		if d == 0.0 {
 			err = errors.New("division by zero")
@@ -144,7 +148,7 @@ func evalReminder(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isInteger(leftValue) && isInteger(rightValue) {
+	if IsInteger(leftValue) && IsInteger(rightValue) {
 		rightInt, _ := rightValue.(int64)
 		if rightInt == 0 {
 			err = errors.New("division by zero")

operator-rel.go

@@ -25,15 +25,15 @@ func evalEqual(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isInteger(leftValue) && isInteger(rightValue) {
+	if IsNumber(leftValue) && IsNumber(rightValue) {
+		if IsInteger(leftValue) && IsInteger(rightValue) {
 			li, _ := leftValue.(int64)
 			ri, _ := rightValue.(int64)
 			v = li == ri
 		} else {
 			v = numAsFloat(leftValue) == numAsFloat(rightValue)
 		}
-	} else if isString(leftValue) && isString(rightValue) {
+	} else if IsString(leftValue) && IsString(rightValue) {
 		ls, _ := leftValue.(string)
 		rs, _ := rightValue.(string)
 		v = ls == rs
@@ -111,15 +111,15 @@ func evalLess(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isInteger(leftValue) && isInteger(rightValue) {
+	if IsNumber(leftValue) && IsNumber(rightValue) {
+		if IsInteger(leftValue) && IsInteger(rightValue) {
 			li, _ := leftValue.(int64)
 			ri, _ := rightValue.(int64)
 			v = li < ri
 		} else {
 			v = numAsFloat(leftValue) < numAsFloat(rightValue)
 		}
-	} else if isString(leftValue) && isString(rightValue) {
+	} else if IsString(leftValue) && IsString(rightValue) {
 		ls, _ := leftValue.(string)
 		rs, _ := rightValue.(string)
 		v = ls < rs
@@ -148,15 +148,15 @@ func evalLessEqual(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isInteger(leftValue) && isInteger(rightValue) {
+	if IsNumber(leftValue) && IsNumber(rightValue) {
+		if IsInteger(leftValue) && IsInteger(rightValue) {
 			li, _ := leftValue.(int64)
 			ri, _ := rightValue.(int64)
 			v = li <= ri
 		} else {
 			v = numAsFloat(leftValue) <= numAsFloat(rightValue)
 		}
-	} else if isString(leftValue) && isString(rightValue) {
+	} else if IsString(leftValue) && IsString(rightValue) {
 		ls, _ := leftValue.(string)
 		rs, _ := rightValue.(string)
 		v = ls <= rs

operator-selector.go

@@ -4,31 +4,33 @@
 // operator-selector.go
 package expr
 
-//-------- export all term
+//-------- selector term
 
 func newSelectorTerm(tk *Token) (inst *term) {
 	return &term{
 		tk:       *tk,
 		children: make([]*term, 0, 3),
-		position: posMultifix,
+		position: posInfix,
 		priority: priSelector,
 		evalFunc: evalSelector,
 	}
 }
 
-func isSelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (selectedValue any, err error) {
+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)
-	} else {
-		filterList := caseData.filterList.children
+		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)
+			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)
+					match = true
 					break
 				}
 			}
@@ -39,7 +41,7 @@ func isSelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (sel
 
 func evalSelector(ctx ExprContext, self *term) (v any, err error) {
 	var exprValue any
-	// var caseList []*term
+	var match bool
 
 	if err = self.checkOperands(); err != nil {
 		return
@@ -49,14 +51,15 @@ func evalSelector(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	caseList := self.children[1:]
+	caseListTerm := self.children[1]
+	caseList, _ := caseListTerm.value().([]*term)
 	for i, caseTerm := range caseList {
 		caseSel := caseTerm.value()
-		if v, err = isSelectorCase(ctx, exprValue, caseSel, i); err != nil || v != nil {
+		if match, v, err = trySelectorCase(ctx, exprValue, caseSel, i); err != nil || match {
 			break
 		}
 	}
-	if err == nil && v == nil {
+	if err == nil && !match {
 		err = exprTerm.tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
 	}
 	return

operator-sign.go

@@ -35,14 +35,14 @@ func evalSign(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isFloat(rightValue) {
+	if IsFloat(rightValue) {
 		if self.tk.Sym == SymChangeSign {
 			f, _ := rightValue.(float64)
 			v = -f
 		} else {
 			v = rightValue
 		}
-	} else if isInteger(rightValue) {
+	} else if IsInteger(rightValue) {
 		if self.tk.Sym == SymChangeSign {
 			i, _ := rightValue.(int64)
 			v = -i

operator-sum.go

@@ -28,33 +28,47 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if (isString(leftValue) && isNumberString(rightValue)) || (isString(rightValue) && isNumberString(leftValue)) {
+	if (IsString(leftValue) && isNumberString(rightValue)) || (IsString(rightValue) && isNumberString(leftValue)) {
 		v = fmt.Sprintf("%v%v", leftValue, rightValue)
-	} else if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+	} else if IsNumber(leftValue) && IsNumber(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			v = numAsFloat(leftValue) + numAsFloat(rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt + rightInt
 		}
-	} else if isList(leftValue) || isList(rightValue) {
-		var leftList, rightList []any
+	} else if IsList(leftValue) || IsList(rightValue) {
+		var leftList, rightList *ListType
 		var ok bool
-		if leftList, ok = leftValue.([]any); !ok {
-			leftList = []any{leftValue}
+		if leftList, ok = leftValue.(*ListType); !ok {
+			leftList = &ListType{leftValue}
 		}
-		if rightList, ok = rightValue.([]any); !ok {
-			rightList = []any{rightValue}
+		if rightList, ok = rightValue.(*ListType); !ok {
+			rightList = &ListType{rightValue}
 		}
-		sumList := make([]any, 0, len(leftList)+len(rightList))
-		for _, item := range leftList {
+		sumList := make(ListType, 0, len(*leftList)+len(*rightList))
+		for _, item := range *leftList {
 			sumList = append(sumList, item)
 		}
-		for _, item := range rightList {
+		for _, item := range *rightList {
 			sumList = append(sumList, item)
 		}
-		v = sumList
+		v = &sumList
+	} else if isFraction(leftValue) || isFraction(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
+			v = numAsFloat(leftValue) + numAsFloat(rightValue)
+		} else {
+			v, err = sumAnyFract(leftValue, rightValue)
+		}
+	} else if IsDict(leftValue) && IsDict(rightValue) {
+		leftDict, _ := leftValue.(map[any]any)
+		rightDict, _ := rightValue.(map[any]any)
+		c := CloneMap(leftDict)
+		for key, value := range rightDict {
+			c[key] = value
+		}
+		v = c
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -65,9 +79,7 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 
 func newMinusTerm(tk *Token) (inst *term) {
 	return &term{
-		tk: *tk,
-		// class:    classOperator,
-		// kind:     kindUnknown,
+		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priSum,
@@ -82,24 +94,26 @@ func evalMinus(ctx ExprContext, self *term) (v any, err error) {
 		return
 	}
 
-	if isNumber(leftValue) && isNumber(rightValue) {
-		if isFloat(leftValue) || isFloat(rightValue) {
+	if isNumOrFract(leftValue) && isNumOrFract(rightValue) {
+		if IsFloat(leftValue) || IsFloat(rightValue) {
 			v = numAsFloat(leftValue) - numAsFloat(rightValue)
+		} else if isFraction(leftValue) || isFraction(rightValue) {
+			v, err = subAnyFract(leftValue, rightValue)
 		} else {
 			leftInt, _ := leftValue.(int64)
 			rightInt, _ := rightValue.(int64)
 			v = leftInt - rightInt
 		}
-	} else if isList(leftValue) && isList(rightValue) {
-		leftList, _ := leftValue.([]any)
-		rightList, _ := rightValue.([]any)
-		diffList := make([]any, 0, len(leftList)-len(rightList))
-		for _, item := range leftList {
-			if slices.Index(rightList, item) < 0 {
+	} else if IsList(leftValue) && IsList(rightValue) {
+		leftList, _ := leftValue.(*ListType)
+		rightList, _ := rightValue.(*ListType)
+		diffList := make(ListType, 0, len(*leftList)-len(*rightList))
+		for _, item := range *leftList {
+			if slices.Index(*rightList, item) < 0 {
 				diffList = append(diffList, item)
 			}
 		}
-		v = diffList
+		v = &diffList
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}

parser.go

@@ -58,34 +58,94 @@ func (self *parser) parseFuncCall(scanner *scanner, allowVarRef bool, tk *Token)
 	return
 }
 
+// func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
+// 	// Example: "add = func(x,y) {x+y}
+// 	var body *ast
+// 	args := make([]*term, 0)
+// 	lastSym := SymUnknown
+// 	itemExpected := false
+// 	tk := scanner.Previous()
+// 	for lastSym != SymClosedRound && lastSym != SymEos {
+// 		var subTree *ast
+// 		if subTree, err = self.parseItem(scanner, true, SymComma, SymClosedRound); err == nil {
+// 			if subTree.root != nil {
+// 				if subTree.root.symbol() == SymIdentifier {
+// 					args = append(args, subTree.root)
+// 				} else {
+// 					err = tk.ErrorExpectedGotString("param-name", subTree.root.String())
+// 				}
+// 			} else if itemExpected {
+// 				prev := scanner.Previous()
+// 				err = prev.ErrorExpectedGot("function-param")
+// 				break
+// 			}
+// 		} else {
+// 			break
+// 		}
+// 		lastSym = scanner.Previous().Sym
+// 		itemExpected = lastSym == SymComma
+// 	}
+
+// 	if err == nil && lastSym != SymClosedRound {
+// 		err = tk.ErrorExpectedGot(")")
+// 	}
+// 	if err == nil {
+// 		tk = scanner.Next()
+// 		if tk.Sym == SymOpenBrace {
+// 			body, err = self.parseGeneral(scanner, true, true, SymClosedBrace)
+// 		} else {
+// 			err = tk.ErrorExpectedGot("{")
+// 		}
+// 	}
+// 	if err == nil {
+// 		// TODO Check arguments
+// 		if scanner.Previous().Sym != SymClosedBrace {
+// 			err = scanner.Previous().ErrorExpectedGot("}")
+// 		} else {
+// 			tk = scanner.makeValueToken(SymExpression, "", body)
+// 			tree = newFuncDefTerm(tk, args)
+// 		}
+// 	}
+// 	return
+// }
+
 func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	// Example: "add = func(x,y) {x+y}
 	var body *ast
 	args := make([]*term, 0)
-	tk := scanner.Next()
-	for tk.Sym != SymClosedRound && tk.Sym != SymEos {
-		if tk.Sym == SymIdentifier {
-			t := newTerm(tk, nil)
-			args = append(args, t)
-		} else {
-			err = tk.Errorf("invalid param %q, variable identifier expected", tk.source)
+	lastSym := SymUnknown
+	itemExpected := false
+	tk := scanner.Previous()
+	for lastSym != SymClosedRound && lastSym != SymEos {
+		tk = scanner.Next()
+		if tk.IsSymbol(SymIdentifier) {
+			param := newTerm(tk)
+			args = append(args, param)
+			tk = scanner.Next()
+		} else if itemExpected {
+			prev := scanner.Previous()
+			err = prev.ErrorExpectedGot("function-param")
 			break
 		}
-		tk = scanner.Next()
+		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
 	}
-	if err == nil && tk.Sym != SymClosedRound {
-		err = tk.Errorf("unterminate function params list")
+
+	if err == nil && lastSym != SymClosedRound {
+		err = tk.ErrorExpectedGot(")")
 	}
 	if err == nil {
 		tk = scanner.Next()
-		if tk.Sym == SymOpenBrace {
+		if tk.IsSymbol(SymOpenBrace) {
 			body, err = self.parseGeneral(scanner, true, true, SymClosedBrace)
+		} else {
+			err = tk.ErrorExpectedGot("{")
 		}
 	}
 	if err == nil {
 		// TODO Check arguments
 		if scanner.Previous().Sym != SymClosedBrace {
-			err = scanner.Previous().Errorf("not properly terminated function body")
+			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
 			tk = scanner.makeValueToken(SymExpression, "", body)
 			tree = newFuncDefTerm(tk, args)
@@ -97,21 +157,27 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
 	args := make([]*term, 0)
 	lastSym := SymUnknown
+	itemExpected := false
 	for lastSym != SymClosedSquare && lastSym != SymEos {
 		var subTree *ast
 		if subTree, err = self.parseItem(scanner, allowVarRef, SymComma, SymClosedSquare); err == nil {
 			if subTree.root != nil {
 				args = append(args, subTree.root)
+			} else if itemExpected {
+				prev := scanner.Previous()
+				err = prev.ErrorExpectedGot("list-item")
+				break
 			}
 		} else {
 			break
 		}
 		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
 	}
 	if err == nil {
 		// TODO Check arguments
 		if lastSym != SymClosedSquare {
-			err = scanner.Previous().Errorf("unterminate items list")
+			err = scanner.Previous().ErrorExpectedGot("]")
 		} else {
 			subtree = newListTerm(args)
 		}
@@ -119,6 +185,103 @@ func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term
 	return
 }
 
+func (self *parser) parseIterDef(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
+	tk := scanner.Previous()
+	args := make([]*term, 0)
+	lastSym := SymUnknown
+	itemExpected := false
+	for lastSym != SymClosedRound && lastSym != SymEos {
+		var subTree *ast
+		if subTree, err = self.parseItem(scanner, allowVarRef, SymComma, SymClosedRound); err == nil {
+			if subTree.root != nil {
+				args = append(args, subTree.root)
+			} else if itemExpected {
+				prev := scanner.Previous()
+				err = prev.ErrorExpectedGot("iterator-param")
+				break
+			}
+		} else {
+			break
+		}
+		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
+	}
+	if err == nil {
+		// TODO Check arguments
+		if lastSym != SymClosedRound {
+			err = scanner.Previous().ErrorExpectedGot(")")
+		} else {
+			subtree = newIteratorTerm(tk, args)
+		}
+	}
+	return
+}
+
+func (self *parser) parseDictKey(scanner *scanner, allowVarRef bool) (key any, err error) {
+	tk := scanner.Next()
+	if tk.Sym == SymError {
+		err = tk.Error()
+		return
+	}
+	if tk.Sym == SymClosedBrace || tk.Sym == SymEos {
+		return
+	}
+	if tk.Sym == SymInteger || tk.Sym == SymString {
+		tkSep := scanner.Next()
+		if tkSep.Sym != SymColon {
+			err = tkSep.ErrorExpectedGot(":")
+		} else {
+			key = tk.Value
+		}
+	} else {
+		// err = tk.Errorf("expected dictionary key or closed brace, got %q", tk)
+		err = tk.ErrorExpectedGot("dictionary-key or }")
+	}
+	return
+}
+
+func (self *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
+	args := make(map[any]*term, 0)
+	lastSym := SymUnknown
+	itemExpected := false
+	for lastSym != SymClosedBrace && lastSym != SymEos {
+		var subTree *ast
+		var key any
+		if key, err = self.parseDictKey(scanner, allowVarRef); err != nil {
+			break
+		} else if key == nil {
+			tk := scanner.Previous()
+			lastSym = tk.Sym
+			if itemExpected {
+				err = tk.ErrorExpectedGot("dictionary-key")
+			}
+			break
+		}
+		if subTree, err = self.parseItem(scanner, allowVarRef, SymComma, SymClosedBrace); err == nil {
+			if subTree.root != nil {
+				args[key] = subTree.root
+			} else if key != nil {
+				prev := scanner.Previous()
+				err = prev.ErrorExpectedGot("dictionary-value")
+				break
+			}
+		} else {
+			break
+		}
+		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
+	}
+	if err == nil {
+		// TODO Check arguments
+		if lastSym != SymClosedBrace {
+			err = scanner.Previous().ErrorExpectedGot("}")
+		} else {
+			subtree = newDictTerm(args)
+		}
+	}
+	return
+}
+
 func (self *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaultCase bool) (caseTerm *term, err error) {
 	var filterList *term
 	var caseExpr *ast
@@ -145,7 +308,7 @@ func (self *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaul
 			return
 		}
 	} else {
-		err = tk.Errorf("selector-case expected, got %q", tk.source)
+		err = tk.ErrorExpectedGot("{")
 	}
 
 	if err == nil {
@@ -154,6 +317,19 @@ func (self *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaul
 	return
 }
 
+func addSelectorCase(selectorTerm, caseTerm *term) {
+	if len(selectorTerm.children) < 2 {
+		caseListTerm := newListTermA(caseTerm)
+		selectorTerm.children = append(selectorTerm.children, caseListTerm)
+	} else {
+		caseListTerm := selectorTerm.children[1]
+		caseList, _ := caseListTerm.value().([]*term)
+		caseList = append(caseList, caseTerm)
+		caseListTerm.tk.Value = caseList
+	}
+	caseTerm.parent = selectorTerm
+}
+
 func (self *parser) parseSelector(scanner *scanner, tree *ast, allowVarRef bool) (selectorTerm *term, err error) {
 	var caseTerm *term
 	tk := scanner.makeToken(SymSelector, '?')
@@ -162,8 +338,7 @@ func (self *parser) parseSelector(scanner *scanner, tree *ast, allowVarRef bool)
 	}
 
 	if caseTerm, err = self.parseSelectorCase(scanner, allowVarRef, false); err == nil {
-		selectorTerm.children = append(selectorTerm.children, caseTerm)
-		caseTerm.parent = selectorTerm
+		addSelectorCase(selectorTerm, caseTerm)
 	}
 	return
 }
@@ -179,14 +354,14 @@ func (self *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, e
 func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef bool, termSymbols ...Symbol) (tree *ast, err error) {
 	var selectorTerm *term = nil
 	var currentTerm *term = nil
+	var tk *Token
 	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); tk = scanner.Next() {
 		if tk.Sym == SymComment {
 			continue
 		}
-		//resetSelector := true
 
 		if tk.Sym == SymSemiColon {
 			if allowForest {
@@ -229,6 +404,12 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 				err = tree.addTerm(listTerm)
 				currentTerm = listTerm
 			}
+		case SymOpenBrace:
+			var mapTerm *term
+			if mapTerm, err = self.parseDictionary(scanner, allowVarRef); err == nil {
+				err = tree.addTerm(mapTerm)
+				currentTerm = mapTerm
+			}
 		case SymEqual:
 			if err = checkPrevSymbol(lastSym, SymIdentifier, tk); err == nil {
 				currentTerm, err = tree.addToken2(tk)
@@ -239,6 +420,12 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 				err = tree.addTerm(funcDefTerm)
 				currentTerm = funcDefTerm
 			}
+		case SymDollarRound:
+			var iterDefTerm *term
+			if iterDefTerm, err = self.parseIterDef(scanner, allowVarRef); err == nil {
+				err = tree.addTerm(iterDefTerm)
+				currentTerm = iterDefTerm
+			}
 		case SymIdentifier:
 			if tk.source[0] == '@' && !allowVarRef {
 				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.source)
@@ -246,9 +433,7 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 				currentTerm, err = tree.addToken2(tk)
 			}
 		case SymQuestion:
-			/*if selectorTerm != nil {
-				err = tk.Errorf("nested selectors must be enclosed in parentheses")
-			} else*/if selectorTerm, err = self.parseSelector(scanner, tree, allowVarRef); err == nil {
+			if selectorTerm, err = self.parseSelector(scanner, tree, allowVarRef); err == nil {
 				currentTerm = selectorTerm
 			}
 		case SymColon, SymDoubleColon:
@@ -256,27 +441,25 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 			if selectorTerm == nil {
 				err = tk.Errorf("selector-case outside of a selector context")
 			} else if caseTerm, err = self.parseSelectorCase(scanner, allowVarRef, tk.Sym == SymDoubleColon); err == nil {
-				selectorTerm.children = append(selectorTerm.children, caseTerm)
-				caseTerm.parent = selectorTerm
+				addSelectorCase(selectorTerm, caseTerm)
 				currentTerm = caseTerm
 				if tk.Sym == SymDoubleColon {
 					selectorTerm = nil
 				}
 			}
-			//resetSelector = tk.Sym == SymDoubleColon
 		default:
 			currentTerm, err = tree.addToken2(tk)
 		}
 
-		if currentTerm != nil && currentTerm.parent != nil && currentTerm.parent.tk.Sym != SymSelector {
+		if currentTerm != nil && currentTerm.tk.Sym != SymSelector && currentTerm.parent != nil && currentTerm.parent.tk.Sym != SymSelector {
 			selectorTerm = nil
 
 		}
-		// if resetSelector {
-		// 	selectorTree = nil
-		// }
 		lastSym = tk.Sym
 	}
+	if err == nil {
+		err = tk.Error()
+	}
 	return
 }
 

parser_test.go

@@ -6,18 +6,18 @@ package expr
 
 import (
 	"errors"
-	"fmt"
+	"reflect"
 	"strings"
 	"testing"
 )
 
-func TestParser(t *testing.T) {
-	type inputType struct {
-		source     string
-		wantResult any
-		wantErr    error
-	}
+type inputType struct {
+	source     string
+	wantResult any
+	wantErr    error
+}
 
+func TestGeneralParser(t *testing.T) {
 	inputs := []inputType{
 		/*   1 */ {`1+/*5*/2`, int64(3), nil},
 		/*   2 */ {`3 == 4`, false, nil},
@@ -35,10 +35,10 @@ func TestParser(t *testing.T) {
 		/*  14 */ {`not true`, false, nil},
 		/*  15 */ {`true and false`, false, nil},
 		/*  16 */ {`true or false`, true, nil},
-		/*  17 */ {`"uno" + "due"`, `unodue`, nil},
-		/*  18 */ {`"uno" + 2`, `uno2`, nil},
-		/*  19 */ {`"uno" + (2+1)`, `uno3`, nil},
-		/*  20 */ {`"uno" * (2+1)`, `unounouno`, nil},
+		/*  *17 */ {`"uno" + "due"`, `unodue`, nil},
+		/*  *18 */ {`"uno" + 2`, `uno2`, nil},
+		/*  *19 */ {`"uno" + (2+1)`, `uno3`, nil},
+		/*  *20 */ {`"uno" * (2+1)`, `unounouno`, nil},
 		/*  21 */ {"1", int64(1), nil},
 		/*  22 */ {"1.5", float64(1.5), nil},
 		/*  23 */ {"1.5*2", float64(3.0), nil},
@@ -51,133 +51,133 @@ func TestParser(t *testing.T) {
 		/*  30 */ {"-(-2+1)", int64(1), nil},
 		/*  31 */ {"(1+1)*5", int64(10), nil},
 		/*  32 */ {"200 / (1+1) - 1", int64(99), nil},
-		/*  33 */ {`add(1,2,3)`, int64(6), nil},
-		/*  34 */ {`mulX(1,2,3)`, nil, errors.New(`unknown function mulX()`)},
-		/*  35 */ {`add(1+4,3+2,5*(3-2))`, int64(15), nil},
-		/*  36 */ {`add(add(1+4),3+2,5*(3-2))`, int64(15), nil},
-		/*  37 */ {`add(add(1,4),/*3+2,*/5*(3-2))`, int64(10), nil},
-		/*  38 */ {`1+(1+(1+(1)+1)+1)+1`, int64(7), nil},
-		/*  39 */ {`(((1)))`, int64(1), nil},
-		/*  40 */ {`"uno_" + var2`, `uno_abc`, nil},
-		/*  41 */ {`0 || 0.0 && "hello"`, false, nil},
-		/*  42 */ {`"s" + true`, nil, errors.New(`[1:6] left operand 's' [string] and right operand 'true' [bool] are not compatible with operator "+"`)},
-		/*  43 */ {`+false`, nil, errors.New(`[1:2] prefix/postfix operator "+" do not support operand 'false' [bool]`)},
-		/*  44 */ {`false // very simple expression`, false, nil},
-		/*  45 */ {`1 + // Missing right operator`, nil, errors.New(`[1:4] infix operator "+" requires two not nil operands, got 1`)},
-		/*  46 */ {"", nil, errors.New(`empty expression`)},
-		/*  47 */ {"4!", int64(24), nil},
-		/*  48 */ {"(-4)!", nil, errors.New(`factorial of a negative integer (-4) is not allowed`)},
-		/*  49 */ {"-4!", int64(-24), nil},
-		/*  50 */ {"1.5 < 7", true, nil},
-		/*  51 */ {"1.5 > 7", false, nil},
-		/*  52 */ {"1.5 <= 7", true, nil},
-		/*  53 */ {"1.5 >= 7", false, nil},
-		/*  54 */ {"1.5 != 7", true, nil},
-		/*  55 */ {"1.5 == 7", false, nil},
-		/*  56 */ {`"1.5" < "7"`, true, nil},
-		/*  57 */ {`"1.5" > "7"`, false, nil},
-		/*  58 */ {`"1.5" == "7"`, false, nil},
-		/*  59 */ {`"1.5" != "7"`, true, nil},
-		/*  60 */ {"1.5 < ", nil, errors.New(`[1:6] infix operator "<" requires two not nil operands, got 1`)},
-		/*  61 */ {"1.5 > ", nil, errors.New(`[1:6] infix operator ">" requires two not nil operands, got 1`)},
-		/*  62 */ {"1.5 <= ", nil, errors.New(`[1:6] infix operator "<=" requires two not nil operands, got 1`)},
-		/*  63 */ {"1.5 >= ", nil, errors.New(`[1:6] infix operator ">=" requires two not nil operands, got 1`)},
-		/*  64 */ {"1.5 != ", nil, errors.New(`[1:6] infix operator "!=" requires two not nil operands, got 1`)},
-		/*  65 */ {"1.5 == ", nil, errors.New(`[1:6] infix operator "==" requires two not nil operands, got 1`)},
-		/*  66 */ {`"1.5" < `, nil, errors.New(`[1:8] infix operator "<" requires two not nil operands, got 1`)},
-		/*  67 */ {`"1.5" > `, nil, errors.New(`[1:8] infix operator ">" requires two not nil operands, got 1`)},
-		/*  68 */ {`"1.5" == `, nil, errors.New(`[1:8] infix operator "==" requires two not nil operands, got 1`)},
-		/*  69 */ {`"1.5" != `, nil, errors.New(`[1:8] infix operator "!=" requires two not nil operands, got 1`)},
-		/*  70 */ {"+1.5", float64(1.5), nil},
-		/*  71 */ {"+", nil, errors.New(`[1:2] prefix operator "+" requires one not nil operand`)},
-		/*  72 */ {"4 / 0", nil, errors.New(`division by zero`)},
-		/*  73 */ {"4.0 / 0", nil, errors.New(`division by zero`)},
-		/*  74 */ {"4.0 / \n2", float64(2.0), nil},
-		/*  75 */ {`123`, int64(123), nil},
-		/*  76 */ {`1.`, float64(1.0), nil},
-		/*  77 */ {`1.E-2`, float64(0.01), nil},
-		/*  78 */ {`1E2`, float64(100), nil},
-		/*  79 */ {`1 / 2`, int64(0), nil},
-		/*  80 */ {`1.0 / 2`, float64(0.5), nil},
-		/*  81 */ {`1 ./ 2`, float64(0.5), nil},
-		/*  82 */ {`5 % 2`, int64(1), nil},
-		/*  83 */ {`5 % (-2)`, int64(1), nil},
-		/*  84 */ {`-5 % 2`, int64(-1), nil},
-		/*  85 */ {`5 % 2.0`, nil, errors.New(`[1:4] left operand '5' [int64] and right operand '2' [float64] are not compatible with operator "%"`)},
-		/*  86 */ {`"a" < "b" AND NOT (2 < 1)`, true, nil},
-		/*  87 */ {`"a" < "b" AND NOT (2 == 1)`, true, nil},
-		/*  88 */ {`"a" < "b" AND ~ 2 == 1`, true, nil},
-		/*  89 */ {`~ 2 > 1`, false, nil},
-		/*  90 */ {`~ true && true`, false, nil},
-		/*  91 */ {`~ false || true`, true, nil},
-		/*  92 */ {`false but true`, true, nil},
-		/*  93 */ {`2+3 but 5*2`, int64(10), nil},
-		/*  94 */ {`add(1,2) but var2`, "abc", nil},
-		/*  95 */ {`x=2`, int64(2), nil},
-		/*  96 */ {`x=2 but x*10`, int64(20), nil},
-		/*  97 */ {`false and true`, false, nil},
-		/*  98 */ {`false and (x==2)`, false, nil},
-		/*  99 */ {`false and (x=2 but x==2) or x==2`, nil, errors.New(`undefined variable "x"`)},
-		/* 100 */ {`false or true`, true, nil},
-		/* 101 */ {`false or (x==2)`, nil, errors.New(`undefined variable "x"`)},
-		/* 102 */ {`a=5; a`, int64(5), nil},
-		/* 103 */ {`a=5; b=2; add(a, b*3)`, int64(11), nil},
-		/* 104 */ {`2=5`, nil, errors.New(`assign operator ("=") must be preceded by a variable`)},
-		/* 105 */ {`2+a=5`, nil, errors.New(`[1:3] left operand of "=" must be a variable`)},
-		/* 106 */ {`2+(a=5)`, int64(7), nil},
-		/* 107 */ {`two=func(){2}; two()`, int64(2), nil},
-		/* 108 */ {`double=func(x) {2*x}; (double(3))`, int64(6), nil},
-		/* 109 */ {`double=func(x){2*x}; double(3)`, int64(6), nil},
-		/* 110 */ {`double=func(x){2*x}; a=5; double(3+a) + 1`, int64(17), nil},
-		/* 111 */ {`double=func(x){2*x}; a=5; two=func() {2}; (double(3+a) + 1) * two()`, int64(34), nil},
-		/* 112 */ {`import("./test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
-		/* 113 */ {`import("test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
-		/* 114 */ {`x ?? "default"`, "default", nil},
-		/* 115 */ {`x="hello"; x ?? "default"`, "hello", nil},
-		/* 116 */ {`x ?? func(){}"`, nil, errors.New(`[1:15] the right operand of a coalescing operation cannot be a function definition`)},
-		/* 117 */ {`x ?= "default"; x`, "default", nil},
-		/* 118 */ {`x="hello"; x ?= "default"; x`, "hello", nil},
-		/* 119 */ {`@x="hello"; @x`, nil, errors.New(`[1:3] variable references are not allowed in top level expressions: "@x"`)},
-		/* 120 */ {`f=func(){@x="hello"}; f(); x`, "hello", nil},
-		/* 121 */ {`f=func(@y){@y=@y+1}; f(2); y`, int64(3), nil},
-		/* 122 */ {`f=func(@y){g=func(){@x=5}; @y=@y+g()}; f(2); y+x`, nil, errors.New(`undefined variable "x"`)},
-		/* 123 */ {`f=func(@y){g=func(){@x=5}; @z=g(); @y=@y+@z}; f(2); y+z`, int64(12), nil},
-		/* 124 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @y=@y+@z}; f(2); y+z`, int64(12), nil},
-		/* 125 */ {`f=func(@y){g=func(){@x=5}; g(); @z=x; @x=@y+@z}; f(2); y+x`, int64(9), nil},
-		/* 126 */ {`include("./test-funcs.expr"); six()`, int64(6), nil},
-		/* 127 */ {`import("./sample-export-all.expr"); six()`, int64(6), nil},
-		/* 128 */ {`1 ? {"a"} : {"b"}`, "b", nil},
-		/* 129 */ {`10 ? {"a"} : {"b"} :: {"c"}`, "c", nil},
-		/* 130 */ {`10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}`, "b", nil},
-		/* 131 */ {`10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}`, nil, errors.New(`[1:34] case list in default clause`)},
-		/* 132 */ {`10 ? {"a"} :[10] {x="b" but x} :: {"c"}`, "b", nil},
-		/* 133 */ {`10 ? {"a"} :[10] {x="b"; x} :: {"c"}`, "b", nil},
-		/* 134 */ {`10 ? {"a"} : {"b"}`, nil, errors.New(`[1:3] no case catches the value (10) of the selection expression`)},
-		/* 135 */ {`10 ? {"a"} :: {"b"} : {"c"}`, nil, errors.New(`[1:22] selector-case outside of a selector context`)},
-		/* 136 */ {`1 ? {"a"} : {"b"} ? ["a"] {"A"} :["b"] {"B"}`, "B", nil},
+		/*  33 */ {`1+(1+(1+(1)+1)+1)+1`, int64(7), nil},
+		/*  34 */ {`(((1)))`, int64(1), nil},
+		/*  35 */ {`var2="abc"; "uno_" + var2`, `uno_abc`, nil},
+		/*  36 */ {`0 || 0.0 && "hello"`, false, nil},
+		/*  37 */ {`"s" + true`, nil, errors.New(`[1:6] left operand 's' [string] and right operand 'true' [bool] are not compatible with operator "+"`)},
+		/*  38 */ {`+false`, nil, errors.New(`[1:2] prefix/postfix operator "+" do not support operand 'false' [bool]`)},
+		/*  39 */ {`false // very simple expression`, false, nil},
+		/*  40 */ {`1 + // Missing right operator`, nil, errors.New(`[1:4] infix operator "+" requires two non-nil operands, got 1`)},
+		/*  41 */ {"", nil, nil},
+		/*  42 */ {"4!", int64(24), nil},
+		/*  43 */ {"(-4)!", nil, errors.New(`factorial of a negative integer (-4) is not allowed`)},
+		/*  44 */ {"-4!", int64(-24), nil},
+		/*  45 */ {"1.5 < 7", true, nil},
+		/*  46 */ {"1.5 > 7", false, nil},
+		/*  47 */ {"1.5 <= 7", true, nil},
+		/*  48 */ {"1.5 >= 7", false, nil},
+		/*  49 */ {"1.5 != 7", true, nil},
+		/*  50 */ {"1.5 == 7", false, nil},
+		/*  51 */ {`"1.5" < "7"`, true, nil},
+		/*  52 */ {`"1.5" > "7"`, false, nil},
+		/*  53 */ {`"1.5" == "7"`, false, nil},
+		/*  54 */ {`"1.5" != "7"`, true, nil},
+		/*  55 */ {"1.5 < ", nil, errors.New(`[1:6] infix operator "<" requires two non-nil operands, got 1`)},
+		/*  56 */ {"1.5 > ", nil, errors.New(`[1:6] infix operator ">" requires two non-nil operands, got 1`)},
+		/*  57 */ {"1.5 <= ", nil, errors.New(`[1:6] infix operator "<=" requires two non-nil operands, got 1`)},
+		/*  58 */ {"1.5 >= ", nil, errors.New(`[1:6] infix operator ">=" requires two non-nil operands, got 1`)},
+		/*  59 */ {"1.5 != ", nil, errors.New(`[1:6] infix operator "!=" requires two non-nil operands, got 1`)},
+		/*  60 */ {"1.5 == ", nil, errors.New(`[1:6] infix operator "==" requires two non-nil operands, got 1`)},
+		/*  61 */ {`"1.5" < `, nil, errors.New(`[1:8] infix operator "<" requires two non-nil operands, got 1`)},
+		/*  62 */ {`"1.5" > `, nil, errors.New(`[1:8] infix operator ">" requires two non-nil operands, got 1`)},
+		/*  63 */ {`"1.5" == `, nil, errors.New(`[1:8] infix operator "==" requires two non-nil operands, got 1`)},
+		/*  64 */ {`"1.5" != `, nil, errors.New(`[1:8] infix operator "!=" requires two non-nil operands, got 1`)},
+		/*  65 */ {"+1.5", float64(1.5), nil},
+		/*  66 */ {"+", nil, errors.New(`[1:2] prefix operator "+" requires one not nil operand`)},
+		/*  67 */ {"4 / 0", nil, errors.New(`division by zero`)},
+		/*  68 */ {"4.0 / 0", nil, errors.New(`division by zero`)},
+		/*  69 */ {"4.0 / \n2", float64(2.0), nil},
+		/*  70 */ {`123`, int64(123), nil},
+		/*  71 */ {`1.`, float64(1.0), nil},
+		/*  72 */ {`1.E-2`, float64(0.01), nil},
+		/*  73 */ {`1E2`, float64(100), nil},
+		/*  74 */ {`1 / 2`, int64(0), nil},
+		/*  75 */ {`1.0 / 2`, float64(0.5), nil},
+		/*  76 */ {`1 ./ 2`, float64(0.5), nil},
+		/*  77 */ {`5 % 2`, int64(1), nil},
+		/*  78 */ {`5 % (-2)`, int64(1), nil},
+		/*  79 */ {`-5 % 2`, int64(-1), nil},
+		/*  80 */ {`5 % 2.0`, nil, errors.New(`[1:4] left operand '5' [int64] and right operand '2' [float64] are not compatible with operator "%"`)},
+		/*  81 */ {`"a" < "b" AND NOT (2 < 1)`, true, nil},
+		/*  82 */ {`"a" < "b" AND NOT (2 == 1)`, true, nil},
+		/*  83 */ {`"a" < "b" AND ~ 2 == 1`, true, nil},
+		/*  84 */ {`~ 2 > 1`, false, nil},
+		/*  85 */ {`~ true && true`, false, nil},
+		/*  86 */ {`~ false || true`, true, nil},
+		/*  87 */ {`false but true`, true, nil},
+		/*  88 */ {`2+3 but 5*2`, int64(10), nil},
+		/*  89 */ {`x=2`, int64(2), nil},
+		/*  90 */ {`x=2 but x*10`, int64(20), nil},
+		/*  91 */ {`false and true`, false, nil},
+		/*  92 */ {`false and (x==2)`, false, nil},
+		/*  93 */ {`false and (x=2 but x==2) or x==2`, nil, errors.New(`undefined variable or function "x"`)},
+		/*  94 */ {`false or true`, true, nil},
+		/*  95 */ {`false or (x==2)`, nil, errors.New(`undefined variable or function "x"`)},
+		/*  96 */ {`a=5; a`, int64(5), nil},
+		/*  97 */ {`2=5`, nil, errors.New(`assign operator ("=") must be preceded by a variable`)},
+		/*  98 */ {`2+a=5`, nil, errors.New(`[1:3] left operand of "=" must be a variable`)},
+		/*  99 */ {`2+(a=5)`, int64(7), nil},
+		/* 100 */ {`x ?? "default"`, "default", nil},
+		/* 101 */ {`x="hello"; x ?? "default"`, "hello", nil},
+		/* 102 */ {`y=x ?? func(){4}; y()`, int64(4), nil},
+		/* 103 */ {`x ?= "default"; x`, "default", nil},
+		/* 104 */ {`x="hello"; x ?= "default"; x`, "hello", nil},
+		/* 105 */ {`1 ? {"a"} : {"b"}`, "b", nil},
+		/* 106 */ {`10 ? {"a"} : {"b"} :: {"c"}`, "c", nil},
+		/* 107 */ {`10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}`, "b", nil},
+		/* 108 */ {`10 ? {"a"} :[true, 2+8] {"b"} ::[10] {"c"}`, nil, errors.New(`[1:34] case list in default clause`)},
+		/* 109 */ {`10 ? {"a"} :[10] {x="b" but x} :: {"c"}`, "b", nil},
+		/* 110 */ {`10 ? {"a"} :[10] {x="b"; x} :: {"c"}`, "b", nil},
+		/* 111 */ {`10 ? {"a"} : {"b"}`, nil, errors.New(`[1:3] no case catches the value (10) of the selection expression`)},
+		/* 112 */ {`10 ? {"a"} :: {"b"} : {"c"}`, nil, errors.New(`[1:22] selector-case outside of a selector context`)},
+		/* 113 */ {`1 ? {"a"} : {"b"} ? ["a"] {"A"} :["b"] {"B"}`, "B", nil},
+		/* 114 */ {`2 + 1 ? {"a"} : {"b"} * 3`, "2bbb", nil},
+		/* 115 */ {`nil`, nil, nil},
+		/* 116 */ {`null`, nil, errors.New(`undefined variable or function "null"`)},
+		/* 117 */ {`{"key"}`, nil, errors.New(`[1:8] expected ":", got "}"`)},
+		/* 118 */ {`{"key":}`, nil, errors.New(`[1:9] expected "dictionary-value", got "}"`)},
+		/* 119 */ {`{}`, map[any]any{}, nil},
+		/* 120 */ {`1|2`, newFraction(1, 2), nil},
+		/* 121 */ {`1|2 + 1`, newFraction(3, 2), nil},
+		/* 122 */ {`1|2 - 1`, newFraction(-1, 2), nil},
+		/* 123 */ {`1|2 * 1`, newFraction(1, 2), nil},
+		/* 124 */ {`1|2 * 2|3`, newFraction(2, 6), nil},
+		/* 125 */ {`1|2 / 2|3`, newFraction(3, 4), nil},
+		/* 126 */ {`builtin "math.arith"; add(1,2,3)`, int64(6), nil},
+		/* 127 */ {`builtin "math.arith"; mulX(1,2,3)`, nil, errors.New(`unknown function mulX()`)},
+		/* 128 */ {`builtin "math.arith"; add(1+4,3+2,5*(3-2))`, int64(15), nil},
+		/* 129 */ {`builtin "math.arith"; add(add(1+4),3+2,5*(3-2))`, int64(15), nil},
+		/* 130 */ {`builtin "math.arith"; add(add(1,4),/*3+2,*/5*(3-2))`, int64(10), nil},
+		/* 131 */ {`builtin "math.arith"; a=5; b=2; add(a, b*3)`, int64(11), nil},
+		/* 132 */ {`builtin "math.arith"; var2="abc"; add(1,2) but var2`, "abc", nil},
+		/* 133 */ {`builtin "math.arith"; add(1|2, 2|3)`, newFraction(7, 6), nil},
+		/* 134 */ {`builtin "math.arith"; add(1|2, 1.0, 2)`, float64(3.5), nil},
+		/* 135 */ {`builtin "math.arith"; mul(1|2, 2|3)`, newFraction(2, 6), nil},
+		/* 136 */ {`builtin "math.arith"; mul(1|2, 1.0, 2)`, float64(1.0), nil},
+		/* 137 */ {`builtin "os.file"`, int64(1), nil},
+		/* 138 */ {`v=10; v++; v`, int64(11), nil},
+		/* 139 */ {`1+1|2+0.5`, float64(2), nil},
 	}
-	check_env_expr_path := 113
+
+	// t.Setenv("EXPR_PATH", ".")
+	parserTest(t, "General", inputs)
+}
+
+func parserTest(t *testing.T, section string, inputs []inputType) {
 
 	succeeded := 0
 	failed := 0
 
-	// inputs1 := []inputType{
-	// 	{`1 ? {"a"} : {"b"} ? ["a"] {"A"} :["b"] {"B"}`, "B", nil},
-	// }
-
 	for i, input := range inputs {
 		var expr Expr
 		var gotResult any
 		var gotErr error
 
 		ctx := NewSimpleFuncStore()
-		ctx.SetVar("var1", int64(123))
-		ctx.SetVar("var2", "abc")
-		importMathFuncs(ctx)
-		importImportFunc(ctx)
 		parser := NewParser(ctx)
 
-		logTest(t, i+1, input.source, input.wantResult, input.wantErr)
+		logTest(t, i+1, section, input.source, input.wantResult, input.wantErr)
 
 		r := strings.NewReader(input.source)
 		scanner := NewScanner(r, DefaultTranslations())
@@ -187,7 +187,9 @@ func TestParser(t *testing.T) {
 			gotResult, gotErr = expr.Eval(ctx)
 		}
 
-		if gotResult != input.wantResult {
+		eq := reflect.DeepEqual(gotResult, input.wantResult)
+
+		if !eq /*gotResult != input.wantResult*/ {
 			t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
 			good = false
 		}
@@ -203,114 +205,15 @@ func TestParser(t *testing.T) {
 			succeeded++
 		} else {
 			failed++
-			if i+1 == check_env_expr_path {
-				t.Logf(`NOTICE: Test nr %d requires EXPR_PATH environment variable with value "."`, check_env_expr_path)
-			}
 		}
 	}
-	t.Log(fmt.Sprintf("test count: %d, succeeded count: %d, failed count: %d", len(inputs), succeeded, failed))
+	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(inputs), succeeded, failed)
 }
 
-func TestListParser(t *testing.T) {
-	type inputType struct {
-		source     string
-		wantResult any
-		wantErr    error
-	}
-
-	// inputs1 := []inputType{
-	// 	{`add(1,2,3)`, int64(6), nil},
-	// }
-
-	inputs := []inputType{
-		/*  1 */ {`[]`, []any{}, nil},
-		/*  2 */ {`[1,2,3]`, []any{int64(1), int64(2), int64(3)}, nil},
-		/*  3 */ {`[1,2,"hello"]`, []any{int64(1), int64(2), "hello"}, nil},
-		/*  4 */ {`[1+2, not true, "hello"]`, []any{int64(3), false, "hello"}, nil},
-		/*  5 */ {`[1,2]+[3]`, []any{int64(1), int64(2), int64(3)}, nil},
-		/*  6 */ {`[1,4,3,2]-[3]`, []any{int64(1), int64(4), int64(2)}, nil},
-		/*  7 */ {`add([1,4,3,2])`, int64(10), nil},
-		/*  8 */ {`add([1,[2,2],3,2])`, int64(10), nil},
-		/*  9 */ {`mul([1,4,3.0,2])`, float64(24.0), nil},
-		/* 10 */ {`add([1,"hello"])`, nil, errors.New(`add(): param nr 2 has wrong type string, number expected`)},
-		/* 11 */ {`[a=1,b=2,c=3] but a+b+c`, int64(6), 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},
-	}
-
-	succeeded := 0
-	failed := 0
-
-	for i, input := range inputs {
-		var expr *ast
-		var gotResult any
-		var gotErr error
-
-		ctx := NewSimpleFuncStore()
-		ctx.SetVar("var1", int64(123))
-		ctx.SetVar("var2", "abc")
-		importMathFuncs(ctx)
-		parser := NewParser(ctx)
-
-		logTest(t, i+1, 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.Log(fmt.Sprintf("test count: %d, succeeded count: %d, failed count: %d", len(inputs), succeeded, failed))
-}
-
-func logTest(t *testing.T, n int, source string, wantResult any, wantErr error) {
+func logTest(t *testing.T, n int, section, source string, wantResult any, wantErr error) {
 	if wantErr == nil {
-		t.Log(fmt.Sprintf("[+]Test nr %3d -- %q  --> %v", n, source, wantResult))
+		t.Logf("[+]%s nr %3d -- %q  --> %v", section, n, source, wantResult)
 	} else {
-		t.Log(fmt.Sprintf("[-]Test nr %3d -- %q  --> %v", n, source, wantErr))
+		t.Logf("[-]%s nr %3d -- %q  --> %v", section, n, source, wantErr)
 	}
 }

scanner.go

@@ -86,13 +86,14 @@ func (self *scanner) Next() (tk *Token) {
 }
 
 func (self *scanner) fetchNextToken() (tk *Token) {
+	var ch byte
 	if err := self.skipBlanks(); err != nil {
 		return self.makeErrorToken(err)
 	}
 
 	escape := false
 	for {
-		ch, _ := self.readChar()
+		ch, _ = self.readChar()
 		switch ch {
 		case '+':
 			if next, _ := self.peek(); next == '+' {
@@ -143,6 +144,8 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 			}
 		case ',':
 			tk = self.makeToken(SymComma, ch)
+		case '^':
+			tk = self.makeToken(SymCaret, ch)
 		case ':':
 			if next, _ := self.peek(); next == ':' {
 				tk = self.moveOn(SymDoubleColon, ch, next)
@@ -152,10 +155,17 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 		case ';':
 			tk = self.makeToken(SymSemiColon, ch)
 		case '.':
-			if next, _ := self.peek(); next >= '0' && next <= '9' {
-				tk = self.parseNumber(ch)
-			} else if next == '/' {
+			//if next, _ := self.peek(); next >= '0' && next <= '9' {
+			//	tk = self.parseNumber(ch)
+			//} else if next == '/' {
+			if next, _ := self.peek(); next == '/' {
 				tk = self.moveOn(SymDotSlash, ch, next)
+			} else if next == '.' {
+				if next1, _ := self.peek(); next1 == '.' {
+					tk = self.moveOn(SymTripleDot, ch, next, next1)
+				} else {
+					tk = self.moveOn(SymDoubleDot, ch, next)
+				}
 			} else {
 				tk = self.makeToken(SymDot, ch)
 			}
@@ -219,6 +229,8 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 		case '<':
 			if next, _ := self.peek(); next == '=' {
 				tk = self.moveOn(SymLessOrEqual, ch, next)
+			} else if next == '<' {
+				tk = self.moveOn(SymAppend, ch, next)
 			} else if next == '>' {
 				tk = self.moveOn(SymLessGreater, ch, next)
 			} else {
@@ -227,13 +239,26 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 		case '>':
 			if next, _ := self.peek(); next == '=' {
 				tk = self.moveOn(SymGreaterOrEqual, ch, next)
+			} else if next == '>' {
+				tk = self.moveOn(SymInsert, ch, next)
 			} else {
 				tk = self.makeToken(SymGreater, ch)
 			}
 		case '$':
-			tk = self.makeToken(SymDollar, ch)
+			if next, _ := self.peek(); next == '(' {
+				tk = self.moveOn(SymDollarRound, ch, next)
+				tk.source += ")"
+			} else if next == '$' {
+				tk = self.moveOn(SymDoubleDollar, ch, next)
+			} else {
+				tk = self.makeToken(SymDollar, ch)
+			}
 		case '(':
-			tk = self.makeToken(SymOpenRound, ch)
+			if next, _ := self.peek(); next == ')' {
+				tk = self.moveOn(SymOpenClosedRound, ch, next)
+			} else {
+				tk = self.makeToken(SymOpenRound, ch)
+			}
 		case ')':
 			tk = self.makeToken(SymClosedRound, ch)
 		case '[':
@@ -266,6 +291,9 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 			break
 		}
 	}
+	if tk == nil {
+		tk = NewErrorToken(self.row, self.column, fmt.Errorf("unknown symbol '%c'", ch))
+	}
 	return
 }
 
@@ -276,62 +304,135 @@ func (self *scanner) sync(err error) error {
 	return err
 }
 
+func isBinaryDigit(ch byte) bool {
+	return ch == '0' || ch == '1'
+}
+
+func isOctalDigit(ch byte) bool {
+	return ch >= '0' && ch <= '7'
+}
+
+func isDecimalDigit(ch byte) bool {
+	return ch >= '0' && ch <= '9'
+}
+
+func isHexDigit(ch byte) bool {
+	return (ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'f') || (ch >= 'A' && ch <= 'F')
+}
+
+func (self *scanner) initBase(sb *strings.Builder, currentFirstCh byte) (firstCh byte, numBase int, digitFunc func(byte) bool, err error) {
+	var ch byte
+	var digitType string
+	firstCh = currentFirstCh
+	digitFunc = isDecimalDigit
+	numBase = 10
+
+	if ch, err = self.peek(); err == nil {
+		if ch == 'b' || ch == 'B' {
+			numBase = 2
+			digitType = "binary"
+			self.readChar()
+			digitFunc = isBinaryDigit
+			firstCh, err = self.readChar()
+		} else if ch == 'o' || ch == 'O' {
+			numBase = 8
+			digitType = "octal"
+			self.readChar()
+			digitFunc = isOctalDigit
+			firstCh, err = self.readChar()
+		} else if ch == 'x' || ch == 'X' {
+			numBase = 16
+			digitType = "hex"
+			self.readChar()
+			digitFunc = isHexDigit
+			firstCh, err = self.readChar()
+		}
+		if err == nil && !digitFunc(firstCh) {
+			if len(digitType) == 0 {
+				digitType = "decimal"
+			}
+			err = fmt.Errorf("expected %s digit, got '%c'", digitType, firstCh)
+		}
+	} else if err == io.EOF {
+		err = nil
+	}
+	return
+}
+
 func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sym Symbol = SymInteger
-	var value any
 	var sb strings.Builder
+	var isDigit func(byte) bool = isDecimalDigit
+	var numBase = 10
 
-	for ch = firstCh; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
+	if firstCh == '0' {
+		firstCh, numBase, isDigit, err = self.initBase(&sb, firstCh)
+	}
+	for ch = firstCh; err == nil && isDigit(ch); ch, err = self.readChar() {
 		sb.WriteByte(ch)
 	}
-	if ch == '.' {
-		sym = SymFloat
-		sb.WriteByte(ch)
-		ch, err = self.readChar()
-		if ch >= '0' && ch <= '9' {
-			for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
-				sb.WriteByte(ch)
-			}
-		}
-	}
-	if ch == 'e' || ch == 'E' {
-		sym = SymFloat
-		sb.WriteByte(ch)
-		if ch, err = self.readChar(); err == nil {
-			if ch == '+' || ch == '-' {
-				sb.WriteByte(ch)
-				ch, err = self.readChar()
-			}
+
+	if numBase == 10 {
+		if err == nil && ch == '.' {
+			sym = SymFloat
+			sb.WriteByte(ch)
+			ch, err = self.readChar()
 			if ch >= '0' && ch <= '9' {
 				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
 					sb.WriteByte(ch)
 				}
-				//err = self.sync(err)
-			} else {
-				err = errors.New("expected integer exponent")
 			}
 		}
-		// } else {
-		// err = self.sync(err)
+		if err == nil {
+			if ch == 'e' || ch == 'E' {
+				sym = SymFloat
+				sb.WriteByte(ch)
+				if ch, err = self.readChar(); err == nil {
+					if ch == '+' || ch == '-' {
+						sb.WriteByte(ch)
+						ch, err = self.readChar()
+					}
+					if ch >= '0' && ch <= '9' {
+						for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
+							sb.WriteByte(ch)
+						}
+					} else {
+						err = fmt.Errorf("[%d:%d] expected integer exponent, got %c", self.row, self.column, ch)
+					}
+				}
+			} else if ch == '(' {
+				sym = SymFraction
+				sb.WriteByte(ch)
+				ch, err = self.readChar()
+				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
+					sb.WriteByte(ch)
+				}
+				if err == nil {
+					if ch != ')' {
+						err = fmt.Errorf("[%d:%d] expected ')', got '%c'", self.row, self.column, ch)
+					} else {
+						sb.WriteByte(ch)
+						_, err = self.readChar()
+					}
+				}
+			}
+		}
 	}
 
 	if err != nil && err != io.EOF {
 		tk = self.makeErrorToken(err)
 	} else {
+		var value any
 		err = self.sync(err)
 		txt := sb.String()
 		if sym == SymFloat {
 			value, err = strconv.ParseFloat(txt, 64)
-		} else if strings.HasPrefix(txt, "0x") {
-			value, err = strconv.ParseInt(txt, 16, 64)
-		} else if strings.HasPrefix(txt, "0o") {
-			value, err = strconv.ParseInt(txt, 8, 64)
-		} else if strings.HasPrefix(txt, "0b") {
-			value, err = strconv.ParseInt(txt, 2, 64)
+		} else if sym == SymFraction {
+			value, err = makeGeneratingFraction(txt)
 		} else {
-			value, err = strconv.ParseInt(txt, 10, 64)
+			value, err = strconv.ParseInt(txt, numBase, 64)
 		}
 		if err == nil {
 			tk = self.makeValueToken(sym, txt, value)

scanner_test.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"errors"
 	"fmt"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -36,7 +37,7 @@ func TestScanner(t *testing.T) {
 		/* 14 */ {`:`, SymColon, nil, nil},
 		/* 15 */ {`;`, SymSemiColon, nil, nil},
 		/* 16 */ {`.`, SymDot, nil, nil},
-		/* 17 */ {`.5`, SymFloat, float64(0.5), nil},
+		/* 17 */ {`0.5`, SymFloat, float64(0.5), nil},
 		/* 18 */ {`\\`, SymBackSlash, nil, nil},
 		/* 19 */ {"`", SymBackTick, nil, nil},
 		/* 20 */ {"?", SymQuestion, nil, nil},
@@ -55,15 +56,18 @@ func TestScanner(t *testing.T) {
 		/* 33 */ {`(`, SymOpenRound, nil, nil},
 		/* 34 */ {`)`, SymClosedRound, nil, nil},
 		/* 35 */ {`1E+2`, SymFloat, float64(100), nil},
-		/* 36 */ {`1E+x`, SymError, errors.New("expected integer exponent"), nil},
+		/* 36 */ {`1E+x`, SymError, errors.New("[1:5] expected integer exponent, got x"), nil},
 		/* 37 */ {`$`, SymDollar, nil, nil},
 		/* 38 */ {`\`, SymError, errors.New("incomplete escape sequence"), nil},
 		/* 39 */ {`"string"`, SymString, "string", nil},
-		/* 39 */ {`identifier`, SymIdentifier, "identifier", nil},
+		/* 40 */ {`identifier`, SymIdentifier, "identifier", nil},
+		/* 41 */ {`1.2(3)`, SymFraction, newFraction(37, 30), nil},
 	}
 
 	for i, input := range inputs {
-
+		// if i != 40 {
+		// 	continue
+		// }
 		if input.wantErr == nil {
 			t.Log(fmt.Sprintf("[+]Test nr %2d -- %q", i+1, input.source))
 		} else {
@@ -74,8 +78,9 @@ func TestScanner(t *testing.T) {
 		scanner := NewScanner(r, nil)
 
 		if tk := scanner.Next(); tk == nil {
-			t.Errorf("%d: %q -> got = (nil), want %v (value %v [%T)", i+1, input.source, input.wantSym, input.wantValue, input.wantValue)
-		} else if tk.Sym != input.wantSym || tk.Value != input.wantValue {
+			t.Errorf("%d: %q -> got = (nil), want %v (value %v [%T])", i+1, input.source, input.wantSym, input.wantValue, input.wantValue)
+			// } else if tk.Sym != input.wantSym || tk.Value != input.wantValue {
+		} else if tk.Sym != input.wantSym || !reflect.DeepEqual(tk.Value, input.wantValue) {
 			if tk.Sym == SymError && input.wantSym == tk.Sym {
 				if tkErr, tkOk := tk.Value.(error); tkOk {
 					if inputErr, inputOk := input.wantValue.(error); inputOk {
@@ -86,7 +91,7 @@ func TestScanner(t *testing.T) {
 					}
 				}
 			} else {
-				t.Errorf("%d: %q -> got = %v (value=%v [%T), want %v (value=%v [%T)", i+1,
+				t.Errorf("%d: %q -> got = %v (value=%v [%T]), want %v (value=%v [%T])", i+1,
 					input.source, tk.Sym, tk.Value, tk.Value, input.wantSym, input.wantValue, input.wantValue)
 			}
 		}

simple-func-store.go

@@ -1,7 +1,13 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // simple-func-store.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 type SimpleFuncStore struct {
 	SimpleVarStore
@@ -15,6 +21,29 @@ type funcInfo struct {
 	functor Functor
 }
 
+func (info *funcInfo) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	var i int
+	sb.WriteString("func(")
+	for i = 0; i < info.minArgs; i++ {
+		if i > 0 {
+			sb.WriteString(", ")
+		}
+		sb.WriteString(fmt.Sprintf("arg%d", i+1))
+	}
+	for ; i < info.maxArgs; i++ {
+		sb.WriteString(fmt.Sprintf("arg%d", i+1))
+	}
+	if info.maxArgs < 0 {
+		if info.minArgs > 0 {
+			sb.WriteString(", ")
+		}
+		sb.WriteString("...")
+	}
+	sb.WriteString(") {...}")
+	return sb.String()
+}
+
 func (info *funcInfo) Name() string {
 	return info.name
 }
@@ -32,21 +61,55 @@ func (info *funcInfo) Functor() Functor {
 }
 
 func NewSimpleFuncStore() *SimpleFuncStore {
-	return &SimpleFuncStore{
+	ctx := &SimpleFuncStore{
 		SimpleVarStore: SimpleVarStore{varStore: make(map[string]any)},
 		funcStore:      make(map[string]*funcInfo),
 	}
+	ImportBuiltinsFuncs(ctx)
+	return ctx
 }
 
 func (ctx *SimpleFuncStore) Clone() ExprContext {
+	svs := ctx.SimpleVarStore
 	return &SimpleFuncStore{
-		SimpleVarStore: SimpleVarStore{varStore: CloneMap(ctx.varStore)},
-		funcStore:      CloneMap(ctx.funcStore),
+		// SimpleVarStore: SimpleVarStore{varStore: CloneMap(ctx.varStore)},
+		SimpleVarStore: SimpleVarStore{varStore: svs.cloneVars()},
+		funcStore:      CloneFilteredMap(ctx.funcStore, func(name string) bool { return name[0] != '@' }),
 	}
 }
 
-func (ctx *SimpleFuncStore) GetFuncInfo(name string) (info ExprFunc) {
-	info, _ = ctx.funcStore[name]
+func funcsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
+	sb.WriteString("funcs: {\n")
+	first := true
+	for _, name := range ctx.EnumFuncs(func(name string) bool { return true }) {
+		if first {
+			first = false
+		} else {
+			sb.WriteByte(',')
+			sb.WriteByte('\n')
+		}
+		value, _ := ctx.GetFuncInfo(name)
+		sb.WriteString(strings.Repeat("\t", indent+1))
+		sb.WriteString(name)
+		sb.WriteString("=")
+		if formatter, ok := value.(Formatter); ok {
+			sb.WriteString(formatter.ToString(0))
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", value))
+		}
+	}
+	sb.WriteString("\n}\n")
+}
+
+func (ctx *SimpleFuncStore) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	sb.WriteString(ctx.SimpleVarStore.ToString(opt))
+	funcsCtxToBuilder(&sb, ctx, 0)
+	return sb.String()
+}
+
+func (ctx *SimpleFuncStore) GetFuncInfo(name string) (info ExprFunc, exists bool) {
+	info, exists = ctx.funcStore[name]
 	return
 }
 

simple-var-store.go

@@ -1,6 +1,14 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
 // simple-var-store.go
 package expr
 
+import (
+	"fmt"
+	"strings"
+)
+
 type SimpleVarStore struct {
 	varStore map[string]any
 }
@@ -11,9 +19,14 @@ func NewSimpleVarStore() *SimpleVarStore {
 	}
 }
 
+func (ctx *SimpleVarStore) cloneVars() (vars map[string]any) {
+	return CloneFilteredMap(ctx.varStore, func(name string) bool { return name[0] != '@' })
+}
+
 func (ctx *SimpleVarStore) Clone() (clone ExprContext) {
+	// fmt.Println("*** Cloning context ***")
 	clone = &SimpleVarStore{
-		varStore: CloneMap(ctx.varStore),
+		varStore: ctx.cloneVars(),
 	}
 	return clone
 }
@@ -23,10 +36,20 @@ func (ctx *SimpleVarStore) GetVar(varName string) (v any, exists bool) {
 	return
 }
 
-func (ctx *SimpleVarStore) SetVar(varName string, value any) {
+func (ctx *SimpleVarStore) setVar(varName string, value any) {
+	// fmt.Printf("[%p] setVar(%v, %v)\n", ctx, varName, value)
 	ctx.varStore[varName] = value
 }
 
+func (ctx *SimpleVarStore) SetVar(varName string, value any) {
+	// fmt.Printf("[%p] SetVar(%v, %v)\n", ctx, varName, value)
+	if allowedValue, ok := fromGenericAny(value); ok {
+		ctx.varStore[varName] = allowedValue
+	} else {
+		panic(fmt.Errorf("unsupported type %T of value %v", value, value))
+	}
+}
+
 func (ctx *SimpleVarStore) EnumVars(acceptor func(name string) (accept bool)) (varNames []string) {
 	varNames = make([]string, 0)
 	for name := range ctx.varStore {
@@ -41,7 +64,7 @@ func (ctx *SimpleVarStore) EnumVars(acceptor func(name string) (accept bool)) (v
 	return
 }
 
-func (ctx *SimpleVarStore) GetFuncInfo(name string) (f ExprFunc) {
+func (ctx *SimpleVarStore) GetFuncInfo(name string) (f ExprFunc, exists bool) {
 	return
 }
 
@@ -55,3 +78,44 @@ func (ctx *SimpleVarStore) RegisterFunc(name string, functor Functor, minArgs, m
 func (ctx *SimpleVarStore) EnumFuncs(acceptor func(name string) (accept bool)) (funcNames []string) {
 	return
 }
+
+func varsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
+	sb.WriteString("vars: {\n")
+	first := true
+	for _, name := range ctx.EnumVars(func(name string) bool { return name[0] != '_' }) {
+		if first {
+			first = false
+		} else {
+			sb.WriteByte(',')
+			sb.WriteByte('\n')
+		}
+
+		value, _ := ctx.GetVar(name)
+		sb.WriteString(strings.Repeat("\t", indent+1))
+		sb.WriteString(name)
+		sb.WriteString(": ")
+		if f, ok := value.(Formatter); ok {
+			sb.WriteString(f.ToString(0))
+		} else if _, ok = value.(Functor); ok {
+			sb.WriteString("func(){}")
+		} else if _, ok = value.(map[any]any); ok {
+			sb.WriteString("dict{}")
+		} else {
+			sb.WriteString(fmt.Sprintf("%v", value))
+		}
+	}
+	sb.WriteString(strings.Repeat("\t", indent))
+	sb.WriteString("\n}\n")
+}
+
+func varsCtxToString(ctx ExprContext, indent int) string {
+	var sb strings.Builder
+	varsCtxToBuilder(&sb, ctx, indent)
+	return sb.String()
+}
+
+func (ctx *SimpleVarStore) ToString(opt FmtOpt) string {
+	var sb strings.Builder
+	varsCtxToBuilder(&sb, ctx, 0)
+	return sb.String()
+}

strings_test.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// strings_test.go
+package expr
+
+import (
+	"testing"
+)
+
+func TestStringsParser(t *testing.T) {
+	inputs := []inputType{
+		/*  1 */ {`"uno" + "due"`, `unodue`, nil},
+		/*  2 */ {`"uno" + 2`, `uno2`, nil},
+		/*  3 */ {`"uno" + (2+1)`, `uno3`, nil},
+		/*  4 */ {`"uno" * (2+1)`, `unounouno`, nil},
+		/*  5 */ {`"abc".1`, `b`, nil},
+		/*  5 */ {`#"abc"`, int64(3), nil},
+	}
+	parserTest(t, "String", inputs)
+}

symbol.go

@@ -33,7 +33,7 @@ const (
 	SymBackTick                          //  22: '`'
 	SymExclamation                       //  23: '!'
 	SymQuestion                          //  24: '?'
-	SymAmpersand                         //  25: '&&'
+	SymAmpersand                         //  25: '&'
 	SymDoubleAmpersand                   //  26: '&&'
 	SymPercent                           //  27: '%'
 	SymAt                                //  28: '@'
@@ -59,13 +59,23 @@ const (
 	SymQuestionEqual                     //  48: '?='
 	SymDoubleAt                          //  49: '@@'
 	SymDoubleColon                       //  50: '::'
+	SymInsert                            //  51: '>>'
+	SymAppend                            //  52: '<<'
+	SymCaret                             //  53: '^'
+	SymDollarRound                       //  54: '$('
+	SymOpenClosedRound                   //  55: '()'
+	SymDoubleDollar                      //  56: '$$'
+	SymDoubleDot                         //  57: '..'
+	SymTripleDot                         //  58: '...'
 	SymChangeSign
 	SymUnchangeSign
 	SymIdentifier
 	SymBool
 	SymInteger
 	SymFloat
+	SymFraction
 	SymString
+	SymIterator
 	SymOr
 	SymAnd
 	SymNot
@@ -73,6 +83,7 @@ const (
 	SymFuncCall
 	SymFuncDef
 	SymList
+	SymDict
 	SymExpression
 	SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
 	SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
@@ -87,6 +98,9 @@ const (
 	SymKwOr
 	SymKwBut
 	SymKwFunc
+	SymKwBuiltin
+	SymKwInclude
+	SymKwNil
 )
 
 var keywords map[string]Symbol
@@ -94,10 +108,13 @@ var keywords map[string]Symbol
 func init() {
 	//keywords = make(map[string]Symbol)
 	keywords = map[string]Symbol{
-		"AND":  SymKwAnd,
-		"BUT":  SymKwBut,
-		"FUNC": SymKwFunc,
-		"NOT":  SymKwNot,
-		"OR":   SymKwOr,
+		"AND":     SymKwAnd,
+		"BUILTIN": SymKwBuiltin,
+		"BUT":     SymKwBut,
+		"FUNC":    SymKwFunc,
+		"INCLUDE": SymKwInclude,
+		"NOT":     SymKwNot,
+		"OR":      SymKwOr,
+		"NIL":     SymKwNil,
 	}
 }

term-constuctor-registry.go

@@ -17,11 +17,10 @@ func registerTermConstructor(sym Symbol, constructor termContructor) {
 	constructorRegistry[sym] = constructor
 }
 
-func newTerm(tk *Token, parent *term) (inst *term) {
+func newTerm(tk *Token) (inst *term) {
 	if constructorRegistry != nil {
 		if construct, exists := constructorRegistry[tk.Sym]; exists {
 			inst = construct(tk)
-			inst.setParent(parent)
 		}
 	}
 	return

term.go

@@ -20,10 +20,14 @@ const (
 	priRelational
 	priSum
 	priProduct
+	priFraction
 	priSelector
 	priSign
 	priFact
+	priIterValue
 	priCoalesce
+	priIncDec
+	priDot
 	priValue
 )
 
@@ -126,6 +130,10 @@ func (self *term) setParent(parent *term) {
 	}
 }
 
+func (self *term) symbol() Symbol {
+	return self.tk.Sym
+}
+
 func (self *term) source() string {
 	return self.tk.source
 }
@@ -143,6 +151,15 @@ func (self *term) compute(ctx ExprContext) (v any, err error) {
 	return
 }
 
+func (self *term) toInt(computedValue any, valueDescription string) (i int, err error) {
+	if index64, ok := computedValue.(int64); ok {
+		i = int(index64)
+	} else {
+		err = self.Errorf("%s, got %T (%v)", valueDescription, computedValue, computedValue)
+	}
+	return
+}
+
 func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
 	return self.tk.Errorf(
 		"left operand '%v' [%T] and right operand '%v' [%T] are not compatible with operator %q",
@@ -166,7 +183,7 @@ func (self *term) checkOperands() (err error) {
 	switch self.position {
 	case posInfix:
 		if self.children == nil || len(self.children) != 2 || self.anyChildrenNil() {
-			err = self.tk.Errorf("infix operator %q requires two not nil operands, got %d", self.source(), self.getChildrenCount())
+			err = self.tk.Errorf("infix operator %q requires two non-nil operands, got %d", self.source(), self.getChildrenCount())
 		}
 	case posPrefix:
 		if self.children == nil || len(self.children) != 1 || self.children[0] == nil {
@@ -201,9 +218,9 @@ func (self *term) evalInfix(ctx ExprContext) (leftValue, rightValue any, err err
 	return
 }
 
-func (self *term) evalPrefix(ctx ExprContext) (rightValue any, err error) {
+func (self *term) evalPrefix(ctx ExprContext) (childValue any, err error) {
 	if err = self.checkOperands(); err == nil {
-		rightValue, err = self.children[0].compute(ctx)
+		childValue, err = self.children[0].compute(ctx)
 	}
 	return
 }

term_test.go

@@ -5,7 +5,6 @@
 package expr
 
 import (
-	"fmt"
 	"testing"
 )
 
@@ -16,7 +15,7 @@ func TestString(t *testing.T) {
 
 	tree := NewAst()
 	if gotErr := tree.addTokens(tk1, tk2, tk3); gotErr == nil {
-		fmt.Println("Tree:", tree)
+		t.Log("Tree:", tree)
 	} else {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}
@@ -27,7 +26,7 @@ func TestGetRoom(t *testing.T) {
 
 	tree := NewAst()
 	if gotErr := tree.addTokens(tk1); gotErr == nil {
-		fmt.Println("Tree-root room:", tree.root.getRoom())
+		t.Log("Tree-root room:", tree.root.getRoom())
 	} else {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}
@@ -37,7 +36,7 @@ func TestGetChildrenCount(t *testing.T) {
 
 	tree := NewAst()
 	if gotErr := tree.addTokens(tk1); gotErr == nil {
-		fmt.Println("Tree-root children count:", tree.root.getChildrenCount())
+		t.Log("Tree-root children count:", tree.root.getChildrenCount())
 	} else {
 		t.Errorf("err: got <%v>, want <nil>", gotErr)
 	}

test-file.txt

@@ -0,0 +1,2 @@
+uno
+due

token.go

@@ -27,7 +27,11 @@ func (tk *Token) DevString() string {
 
 func (tk *Token) String() string {
 	if tk.Value != nil {
-		return fmt.Sprintf("%#v", tk.Value)
+		if s, ok := tk.Value.(string); ok {
+			return fmt.Sprintf("%q", s)
+		} else {
+			return fmt.Sprintf("%v", tk.Value)
+		}
 	}
 	return fmt.Sprintf("%s", tk.source)
 }
@@ -42,7 +46,7 @@ func NewValueToken(row, col int, sym Symbol, source string, value any) *Token {
 
 func NewErrorToken(row, col int, err error) *Token {
 	if err == io.EOF {
-		return NewToken(row, col, SymEos, "")
+		return NewToken(row, col, SymEos, "<EOF>")
 	}
 	return NewValueToken(row, col, SymError, fmt.Sprintf("[%d:%d]", row, col), err)
 }
@@ -59,7 +63,35 @@ func (tk *Token) IsTerm(termSymbols []Symbol) bool {
 	return tk.IsEos() || tk.IsError() || (termSymbols != nil && slices.Index(termSymbols, tk.Sym) >= 0)
 }
 
+func (tk *Token) IsSymbol(sym Symbol) bool {
+	return tk.Sym == sym
+}
+
 func (self *Token) Errorf(template string, args ...any) (err error) {
 	err = fmt.Errorf(fmt.Sprintf("[%d:%d] ", self.row, self.col)+template, args...)
 	return
 }
+
+func (self *Token) Error() (err error) {
+	if self.Sym == SymError {
+		if msg, ok := self.Value.(error); ok {
+			err = fmt.Errorf("[%d:%d] %v", self.row, self.col, msg)
+		}
+	}
+	return
+}
+
+func (self *Token) Errors(msg string) (err error) {
+	err = fmt.Errorf("[%d:%d] %v", self.row, self.col, msg)
+	return
+}
+
+func (self *Token) ErrorExpectedGot(symbol string) (err error) {
+	err = fmt.Errorf("[%d:%d] expected %q, got %q", self.row, self.col, symbol, self)
+	return
+}
+
+func (self *Token) ErrorExpectedGotString(symbol, got string) (err error) {
+	err = fmt.Errorf("[%d:%d] expected %q, got %q", self.row, self.col, symbol, got)
+	return
+}

token_test.go

@@ -10,9 +10,30 @@ import (
 )
 
 func TestDevString(t *testing.T) {
-	tk1 := NewValueToken(0, 0, SymInteger, "100", 100)
-	tk2 := NewToken(0, 0, SymPlus, "+")
+	type inputType struct {
+		source     string
+		sym        Symbol
+		value      any
+		wantResult string
+	}
 
-	fmt.Println("Token '100':", tk1.DevString())
-	fmt.Println("Token '+':", tk2.DevString())
+	inputs := []inputType{
+		/*   1 */ {"100", SymInteger, 100, fmt.Sprintf(`[%d]"100"{100}`, SymInteger)},
+		/*   2 */ {"+", SymPlus, nil, fmt.Sprintf(`[%d]"+"{}`, SymPlus)},
+	}
+
+	for i, input := range inputs {
+		var tk *Token
+		if input.value == nil {
+			tk = NewToken(0, 0, input.sym, input.source)
+		} else {
+			tk = NewValueToken(0, 0, input.sym, input.source, input.value)
+		}
+
+		t.Logf("Test nr %2d: %q --> %q", i+1, input.source, input.wantResult)
+
+		if s := tk.DevString(); s != input.wantResult {
+			t.Errorf("wrong token from symbol '+': expected %q, got %q", input.wantResult, s)
+		}
+	}
 }

tools/func-bolerplate.bash

@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+
+if [ $# -lt 2 ]; then
+	echo >&2 "Usage: $(basename "${0}") <module-name> <func-name>..."
+	exit 1
+fi
+
+MODULE_NAME=${1,,}
+GO_FILE="func-${MODULE_NAME//[-.]/_}.go"
+
+shift
+FUNC_LIST=
+i=0
+for name; do
+	if [ ${i} -gt 0 ]; then
+		if [ $((i+1)) -eq $# ]; then
+			FUNC_LIST+=" and "
+		else
+			FUNC_LIST+=", "
+		fi
+	fi
+	FUNC_LIST+="${name}()"
+	((i++))
+done
+
+cat > "${GO_FILE}" <<EOF
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-${MODULE_NAME}.go
+package expr
+
+import (
+)
+
+
+// --- Start of function definitions
+
+$(
+for name; do
+	cat <<IEOF
+func ${name}Func(ctx ExprContext, name string, args []any) (result any, err error) {
+        return
+}
+
+IEOF
+
+done
+)
+
+// --- End of function definitions
+
+// Import above functions in the context
+func Import${MODULE_NAME^}Funcs(ctx ExprContext) {
+$(
+for name; do
+        cat <<IEOF
+        ctx.RegisterFunc("${name}", &simpleFunctor{f: ${name}Func}, 1, -1)
+IEOF
+
+done
+)
+}
+
+// Register the import function in the import-register.
+// That will allow to import all function of this module by the "builtin" operator."
+func init() {
+	registerImport("${MODULE_NAME}", Import${name}Funcs, "The \"${MODULE_NAME}\" module implements the ${FUNC_LIST} function(s)")
+}
+EOF
+

utils.go

@@ -4,41 +4,84 @@
 // utils.go
 package expr
 
-import "reflect"
+import (
+	"fmt"
+	"reflect"
+)
 
-func isString(v any) (ok bool) {
+func IsString(v any) (ok bool) {
 	_, ok = v.(string)
 	return ok
 }
 
-func isInteger(v any) (ok bool) {
+func IsInteger(v any) (ok bool) {
 	_, ok = v.(int64)
 	return ok
 }
 
-func isFloat(v any) (ok bool) {
+func IsFloat(v any) (ok bool) {
 	_, ok = v.(float64)
 	return ok
 }
 
-func isList(v any) (ok bool) {
-	_, ok = v.([]any)
+func IsBool(v any) (ok bool) {
+	_, ok = v.(bool)
 	return ok
 }
 
-func isNumber(v any) (ok bool) {
-	return isFloat(v) || isInteger(v)
+func IsList(v any) (ok bool) {
+	_, ok = v.(*ListType)
+	return ok
+}
+
+func IsDict(v any) (ok bool) {
+	_, ok = v.(map[any]any)
+	return ok
+}
+
+func IsFract(v any) (ok bool) {
+	_, ok = v.(*fraction)
+	return ok
+}
+
+func IsRational(v any) (ok bool) {
+	if _, ok = v.(*fraction); !ok {
+		_, ok = v.(int64)
+	}
+	return ok
+}
+
+func IsNumber(v any) (ok bool) {
+	return IsFloat(v) || IsInteger(v)
+}
+
+func isNumOrFract(v any) (ok bool) {
+	return IsFloat(v) || IsInteger(v) || isFraction(v)
 }
 
 func isNumberString(v any) (ok bool) {
-	return isString(v) || isNumber(v)
+	return IsString(v) || IsNumber(v)
+}
+
+func isFunctor(v any) (ok bool) {
+	_, ok = v.(Functor)
+	return
+}
+
+func isIterator(v any) (ok bool) {
+	_, ok = v.(Iterator)
+	return
 }
 
 func numAsFloat(v any) (f float64) {
 	var ok bool
 	if f, ok = v.(float64); !ok {
-		i, _ := v.(int64)
-		f = float64(i)
+		if fract, ok := v.(*fraction); ok {
+			f = fract.toFloat()
+		} else {
+			i, _ := v.(int64)
+			f = float64(i)
+		}
 	}
 	return
 }
@@ -73,6 +116,8 @@ func anyInteger(v any) (i int64, ok bool) {
 		i = int64(intval)
 	case uint16:
 		i = int64(intval)
+	case uint64:
+		i = int64(intval)
 	case uint32:
 		i = int64(intval)
 	case int8:
@@ -89,6 +134,22 @@ func anyInteger(v any) (i int64, ok bool) {
 	return
 }
 
+func fromGenericAny(v any) (exprAny any, ok bool) {
+	if exprAny, ok = v.(bool); ok {
+		return
+	}
+	if exprAny, ok = v.(string); ok {
+		return
+	}
+	if exprAny, ok = anyInteger(v); ok {
+		return
+	}
+	if exprAny, ok = anyFloat(v); ok {
+		return
+	}
+	return
+}
+
 func anyFloat(v any) (float float64, ok bool) {
 	ok = true
 	switch floatval := v.(type) {
@@ -113,3 +174,32 @@ func CloneMap[K comparable, V any](source map[K]V) map[K]V {
 	dest := make(map[K]V, len(source))
 	return CopyMap(dest, source)
 }
+
+func CopyFilteredMap[K comparable, V any](dest, source map[K]V, filter func(key K) (accept bool)) map[K]V {
+	// fmt.Printf("--- Clone with filter %p\n", filter)
+	if filter == nil {
+		return CopyMap(dest, source)
+	} else {
+		for k, v := range source {
+			if filter(k) {
+				// fmt.Printf("\tClone var %q\n", k)
+				dest[k] = v
+			}
+		}
+	}
+	return dest
+}
+
+func CloneFilteredMap[K comparable, V any](source map[K]V, filter func(key K) (accept bool)) map[K]V {
+	dest := make(map[K]V, len(source))
+	return CopyFilteredMap(dest, source, filter)
+}
+
+func toInt(value any, description string) (i int, err error) {
+	if valueInt64, ok := value.(int64); ok {
+		i = int(valueInt64)
+	} else {
+		err = fmt.Errorf("%s expected integer, got %T (%v)", description, value, value)
+	}
+	return
+}