funcs_test.go: added many new tests

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

ast.go

@@ -63,7 +63,7 @@ func (self *ast) addToken2(tk *Token) (t *term, err error) {
 	if t = newTerm(tk, nil); 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
 }

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 +1,37 @@
+// 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)
+}
+
+// --- 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

@@ -27,8 +27,10 @@ func exportFunc(ctx ExprContext, name string, info ExprFunc) {
 
 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)
 	}

data-cursor.go

@@ -5,34 +5,119 @@
 package expr
 
 import (
+	"errors"
 	"io"
 )
 
-const (
-	initName    = "init"
-	nextName    = "next"
-	currentName = "current"
-)
-
 type dataCursor struct {
-	ds          map[any]*term
+	ds          map[string]Functor
 	ctx         ExprContext
 	index       int
 	resource    any
 	nextFunc    Functor
+	cleanFunc   Functor
+	resetFunc   Functor
 	currentFunc Functor
 }
 
-func newDataCursor(ctx ExprContext) (dc *dataCursor) {
+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 "$(...)"
+	return "$()"
+	/*
+	   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
@@ -45,15 +130,22 @@ func (dc *dataCursor) Current() (item any, err error) { // must return io.EOF at
 }
 
 func (dc *dataCursor) Next() (item any, err error) { // must return io.EOF after the last item
+	if dc.resource != nil {
 		ctx := cloneContext(dc.ctx)
-	if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{}); err == nil {
+		// 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
 }
 

dict_test.go

@@ -0,0 +1,115 @@
+// 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},
+		// /*  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},
+	}
+
+	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

@@ -169,7 +169,7 @@ x = 1; y = 2*x
 == 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.
+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.
 
@@ -187,7 +187,7 @@ a=1; b=2; c=3; a+b+c    // returns 6
 [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 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
@@ -202,13 +202,22 @@ The _selector operator_ is very similar to the _switch/case/default_ statement a
 .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>}
+<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>}
 ----
 
-.Example
+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 find 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]
 ----
 1 ? {"a"} : {"b"}                           // returns "b"
@@ -224,33 +233,38 @@ The _selector operator_ is very similar to the _switch/case/default_ statement a
 The table below shows all supported operators by decreasing priorities.
 
 .Operators priorities
-[cols="^2,^2,^2,^5,<5"]
+[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+|*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_
 |===

expr_test.go

@@ -5,7 +5,6 @@
 package expr
 
 import (
-	"fmt"
 	"strings"
 	"testing"
 )
@@ -22,13 +21,8 @@ func TestExpr(t *testing.T) {
 		/*   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},
-	}
-
-	succeeded := 0
-	failed := 0
-
-	inputs1 := []inputType{
-		/*   1 */ {`
+		/*   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},
@@ -42,7 +36,10 @@ func TestExpr(t *testing.T) {
 `, int64(1), nil},
 	}
 
-	for i, input := range inputs1 {
+	succeeded := 0
+	failed := 0
+
+	for i, input := range inputs {
 		var expr Expr
 		var gotResult any
 		var gotErr error
@@ -53,7 +50,7 @@ func TestExpr(t *testing.T) {
 		ImportOsFuncs(ctx)
 		parser := NewParser(ctx)
 
-		logTest(t, i+1, input.source, input.wantResult, input.wantErr)
+		logTest(t, i+1, "Expr", input.source, input.wantResult, input.wantErr)
 
 		r := strings.NewReader(input.source)
 		scanner := NewScanner(r, DefaultTranslations())
@@ -81,5 +78,5 @@ func TestExpr(t *testing.T) {
 			failed++
 		}
 	}
-	t.Log(fmt.Sprintf("test count: %d, succeeded count: %d, failed count: %d", len(inputs), succeeded, 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 +1,16 @@
+// 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
+)
+
+type Formatter interface {
+	ToString(options FmtOpt) string
+}

func-base.go

@@ -55,5 +55,5 @@ func ImportBuiltinsFuncs(ctx ExprContext) {
 }
 
 func init() {
-	registerImport("builtins", ImportBuiltinsFuncs)
+	registerImport("base", ImportBuiltinsFuncs, "Base expression tools like isNil(), int(), etc.")
 }

func-common.go

@@ -1,17 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// func-common.go
-package expr
-
-import (
-	"fmt"
-)
-
-func errOneParam(funcName string) error {
-	return fmt.Errorf("%s() requires exactly one param", funcName)
-}
-
-func errCantConvert(funcName string, value any, kind string) error {
-	return fmt.Errorf("%s() can't convert %T to %s", funcName, value, kind)
-}

func-import.go

@@ -20,7 +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)
 }
@@ -30,7 +30,7 @@ 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
 }
 
@@ -138,9 +138,9 @@ func doImport(ctx ExprContext, name string, dirList []string, it Iterator) (resu
 
 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)
+	registerImport("import", ImportImportFuncs, "Functions import() and include()")
 }

func-math.go

@@ -9,41 +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 list, ok := v.(*ListType); ok {
+			v = NewListIterator(list, nil)
+		}
 		if subIter, ok := v.(Iterator); ok {
-			if v, err = doAdd(ctx, name, subIter); err != nil {
+			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 !sumAsFloat {
+			if isFloat(v) {
+				sumAsFloat = true
+				if sumAsFract {
+					floatSum = fractSum.toFloat()
 				} else {
-			if err = checkNumberParamExpected(name, v, it.Index()); err != nil {
-				break
-			}
-			if array, ok := v.([]any); ok {
-				if v, err = doAdd(ctx, name, NewFlatArrayIterator(array)); err != nil {
-					break
+					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
@@ -53,6 +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
 		}
@@ -61,33 +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 {
+		if list, ok := v.(*ListType); ok {
+			v = NewListIterator(list, nil)
+		}
+		if subIter, ok := v.(Iterator); ok {
+			if v, err = doMul(ctx, name, subIter, count, level); err != nil {
 				break
 			}
-
-		if array, ok := v.([]any); ok {
-			if v, err = doAdd(ctx, name, NewFlatArrayIterator(array)); err != nil {
+			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) {
+		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
@@ -97,6 +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
 		}
@@ -105,7 +162,7 @@ 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
 }
 
@@ -115,5 +172,5 @@ func ImportMathFuncs(ctx ExprContext) {
 }
 
 func init() {
-	registerImport("math.arith", ImportMathFuncs)
+	registerImport("math.arith", ImportMathFuncs, "Functions add() and mul()")
 }

func-os.go

@@ -126,7 +126,7 @@ func writeFileFunc(ctx ExprContext, name string, args []any) (result any, err er
 
 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)
 	}
@@ -141,13 +141,16 @@ func readFileFunc(ctx ExprContext, name string, args []any) (result any, err err
 						limit = s[0]
 					}
 				}
-				if v, err = r.reader.ReadString(limit); err == nil || err == io.EOF {
+				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
+				}
 			}
 		}
 	}
@@ -164,5 +167,5 @@ func ImportOsFuncs(ctx ExprContext) {
 }
 
 func init() {
-	registerImport("os", ImportOsFuncs)
+	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

@@ -6,18 +6,10 @@ package expr
 
 import (
 	"errors"
-	"fmt"
-	"strings"
 	"testing"
 )
 
 func TestFuncs(t *testing.T) {
-	type inputType struct {
-		source     string
-		wantResult any
-		wantErr    error
-	}
-
 	inputs := []inputType{
 		/*   1 */ {`isNil(nil)`, true, nil},
 		/*   2 */ {`v=nil; isNil(v)`, true, nil},
@@ -30,53 +22,45 @@ func TestFuncs(t *testing.T) {
 		/*   9 */ {`int("1.5")`, nil, errors.New(`strconv.Atoi: parsing "1.5": invalid syntax`)},
 		/*  10 */ {`int("432", 4)`, nil, errors.New(`int() requires exactly one param`)},
 		/*  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 */ {`["a", "b", "c"]`, newListA("a","b","c"), nil},
+		/*  46 */ {`["a", "b", "c"]`, newList([]any{"a","b","c"}), nil},
 	}
 
-	succeeded := 0
-	failed := 0
+	t.Setenv("EXPR_PATH", ".")
 
-	// inputs1 := []inputType{
-	// 	/*   1 */ {`0?{}`, nil, nil},
-	// }
-
-	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, 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.Log(fmt.Sprintf("test count: %d, succeeded count: %d, failed count: %d", len(inputs), succeeded, failed))
+	// parserTest(t, "Func", inputs[25:26])
+	parserTest(t, "Func", inputs)
 }

function-register.go

@@ -1,47 +0,0 @@
-// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
-// All rights reserved.
-
-// function-register.go
-package expr
-
-import (
-	"path/filepath"
-)
-
-var functionRegister map[string]func(ExprContext)
-
-func registerImport(name string, importFunc func(ExprContext)) {
-	if functionRegister == nil {
-		functionRegister = make(map[string]func(ExprContext))
-	}
-	functionRegister[name] = importFunc
-}
-
-func ImportInContext(ctx ExprContext, name string) (exists bool) {
-	var importFunc func(ExprContext)
-	if importFunc, exists = functionRegister[name]; exists {
-		importFunc(ctx)
-	}
-	return
-}
-
-func ImportInContextByGlobPattern(ctx ExprContext, pattern string) (count int, err error) {
-	var matched bool
-	for name, importFunc := range functionRegister {
-		if matched, err = filepath.Match(pattern, name); err == nil {
-			if matched {
-				count++
-				importFunc(ctx)
-			}
-		} else {
-			break
-		}
-	}
-	return
-}
-
-func init() {
-	if functionRegister == nil {
-		functionRegister = make(map[string]func(ExprContext))
-	}
-}

helpers.go

@@ -6,6 +6,8 @@ package expr
 
 import (
 	"fmt"
+	"io"
+	"os"
 	"strings"
 )
 
@@ -59,3 +61,24 @@ func EvalStringV(source string, args []Arg) (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
+}

int.list

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

iter-list.go

@@ -4,39 +4,129 @@
 // iter-list.go
 package expr
 
-import "io"
+import (
+	"fmt"
+	"io"
+)
 
-type FlatArrayIterator struct {
-	a     []any
+type ListIterator struct {
+	a     *ListType
+	count int
 	index int
+	start int
+	stop  int
+	step  int
 }
 
-func NewFlatArrayIterator(array []any) *FlatArrayIterator {
-	return &FlatArrayIterator{a: array, index: 0}
+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 (it *FlatArrayIterator) Current() (item any, err error) {
-	if it.index >= 0 && it.index < len(it.a) {
-		item = it.a[it.index]
+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 *FlatArrayIterator) Next() (item any, err error) {
+func (it *ListIterator) Next() (item any, err error) {
+	it.index += it.step
 	if item, err = it.Current(); err != io.EOF {
-		it.index++
+		it.count++
 	}
-	// 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 (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

@@ -4,8 +4,39 @@
 // iterator.go
 package expr
 
+import (
+	"errors"
+	"fmt"
+)
+
+// Operator names
+
+const (
+	initName    = "init"
+	cleanName   = "clean"
+	resetName   = "reset"
+	nextName    = "next"
+	currentName = "current"
+	indexName   = "index"
+	countName   = "count"
+)
+
 type Iterator interface {
 	Next() (item any, err error) // must return io.EOF after the last item
 	Current() (item any, err error)
 	Index() int
 }
+
+type ExtIterator interface {
+	Iterator
+	HasOperation(name string) bool
+	CallOperation(name string, args []any) (value any, err error)
+}
+
+func errNoOperation(name string) error {
+	return fmt.Errorf("no %q function defined in the data-source", name)
+}
+
+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 +1,115 @@
+// 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},
+
+		// /*  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 +1,74 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// module-register.go
+package expr
+
+import (
+	"fmt"
+	"path/filepath"
+)
+
+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-func.go

@@ -6,6 +6,7 @@ package expr
 
 import (
 	"errors"
+	"fmt"
 )
 
 // -------- function call term
@@ -21,9 +22,28 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 }
 
 // -------- eval func call
+func checkFunctionCall(ctx ExprContext, name string, params []any) (err error) {
+	if info, exists := ctx.GetFuncInfo(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 info.MaxArgs() >= 0 && info.MaxArgs() < len(params) {
+			err = fmt.Errorf("too much params -- expected %d, got %d", info.MaxArgs(), len(params))
+		}
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}
+
 func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 	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
@@ -33,19 +53,21 @@ func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 		params[i] = param
 	}
 	if err == nil {
+		if err = checkFunctionCall(ctx, name, params); err == nil {
 			if v, err = ctx.Call(name, params); err == nil {
 				exportObjects(parentCtx, ctx)
 			}
 		}
+	}
 	return
 }
 
 // -------- 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,

operand-iterator.go

@@ -6,11 +6,13 @@ package expr
 
 import (
 	"fmt"
+	"slices"
+	"strings"
 )
 
 // -------- iterator term
 
-func newIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
+func newDsIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
 	tk.Sym = SymIterator
 
 	children := make([]*term, 0, 1+len(args))
@@ -26,6 +28,18 @@ func newIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
 	}
 }
 
+func newIteratorTerm(tk *Token, args []*term) *term {
+	tk.Sym = SymIterator
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: args,
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalIterator,
+	}
+}
+
 // -------- eval iterator
 
 func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
@@ -41,44 +55,60 @@ func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
 	return
 }
 
-func getDataSourceDict(ctx ExprContext, self *term) (ds map[string]Functor, err error) {
-	var value any
+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
 	}
 
-	if value, err = self.children[0].compute(ctx); err != nil {
+	value, err = self.children[0].compute(ctx)
 	return
-	}
+}
 
-	if dictAny, ok := value.(map[any]any); ok {
+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 _, k := range []string{initName, currentName, nextName} {
-			if item, exists := dictAny[k]; exists && item != nil {
+		for keyAny, item := range dictAny {
+			if key, ok := keyAny.(string); ok {
 				if functor, ok := item.(*funcDefFunctor); ok {
-					ds[k] = functor
-				}
-			} else if k != initName {
-				err = fmt.Errorf("the data-source must provide a non-nil %q operator", k)
-				break
+					ds[key] = functor
+					if index := slices.Index(requiredFields, key); index >= 0 {
+						foundFields |= 1 << index
 					}
 				}
-	} else {
-		err = self.Errorf("the first param (data-source) of an iterator must be a dict, not a %T", value)
+			}
+		}
+		// 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 ds, err = getDataSourceDict(ctx, self); err != nil {
+	if firstChildValue, err = evalFirstChild(ctx, self); err != nil {
 		return
 	}
 
-	dc := newDataCursor(ctx)
+	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 {
@@ -98,7 +128,57 @@ func evalIterator(ctx ExprContext, self *term) (v any, err error) {
 
 		dc.nextFunc, _ = ds[nextName]
 		dc.currentFunc, _ = ds[currentName]
-	v = dc
+		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

@@ -4,6 +4,64 @@
 // 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)
@@ -23,7 +81,7 @@ func newListTerm(args []*term) *term {
 // -------- list func
 func evalList(ctx ExprContext, self *term) (v any, err error) {
 	list, _ := self.value().([]*term)
-	items := make([]any, len(list))
+	items := make(ListType, len(list))
 	for i, tree := range list {
 		var param any
 		if param, err = tree.compute(ctx); err != nil {
@@ -32,35 +90,7 @@ func evalList(ctx ExprContext, self *term) (v any, err error) {
 		items[i] = param
 	}
 	if err == nil {
-		v = items
+		v = &items
 	}
 	return
 }
-
-// // -------- list term
-// func newListTerm(args []*term) *term {
-// 	return &term{
-// 		tk:       *NewToken(0, 0, SymList, "[]"),
-// 		parent:   nil,
-// 		children: args,
-// 		position: posLeaf,
-// 		priority: priValue,
-// 		evalFunc: evalList,
-// 	}
-// }
-
-// // -------- list func
-// func evalList(ctx ExprContext, self *term) (v any, err error) {
-// 	items := make([]any, len(self.children))
-// 	for i, tree := range self.children {
-// 		var param any
-// 		if param, err = tree.compute(ctx); err != nil {
-// 			break
-// 		}
-// 		items[i] = param
-// 	}
-// 	if err == nil {
-// 		v = items
-// 	}
-// 	return
-// }

operator-assign.go

@@ -29,7 +29,14 @@ func evalAssign(ctx ExprContext, self *term) (v any, err error) {
 
 	if v, err = self.children[1].compute(ctx); err == nil {
 		if functor, ok := v.(Functor); ok {
-			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
+			var minArgs, maxArgs int = 0, 0
+
+			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.source(), v)
 		}

operator-builtin.go

@@ -1,9 +1,11 @@
 // Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
 // All rights reserved.
 
-// operator-length.go
+// operator-builtin.go
 package expr
 
+import "io"
+
 //-------- builtin term
 
 func newBuiltinTerm(tk *Token) (inst *term) {
@@ -17,16 +19,20 @@ func newBuiltinTerm(tk *Token) (inst *term) {
 }
 
 func evalBuiltin(ctx ExprContext, self *term) (v any, err error) {
-	var rightValue any
+	var childValue any
 
-	if rightValue, err = self.evalPrefix(ctx); err != nil {
+	if childValue, err = self.evalPrefix(ctx); err != nil {
 		return
 	}
 
 	count := 0
-	if isList(rightValue) {
-		list, _ := rightValue.([]any)
-		for i, moduleSpec := range list {
+	if isString(childValue) {
+		module, _ := childValue.(string)
+		count, err = ImportInContextByGlobPattern(ctx, 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(ctx, module) {
 					count++
@@ -35,18 +41,16 @@ func evalBuiltin(ctx ExprContext, self *term) (v any, err error) {
 					break
 				}
 			} else {
-				err = self.Errorf("expected string at item nr %d, got %T", i+1, moduleSpec)
+				err = self.Errorf("expected string at item nr %d, got %T", it.Index()+1, moduleSpec)
 				break
 			}
 		}
-	} else if isString(rightValue) {
-		module, _ := rightValue.(string)
-		count, err = ImportInContextByGlobPattern(ctx, module)
-	} else {
-		err = self.errIncompatibleType(rightValue)
+		if err == io.EOF {
+			err = nil
+		}
 	}
 	if err == nil {
-		v = count
+		v = int64(count)
 	}
 	return
 }

operator-context.go

@@ -11,7 +11,7 @@ func newContextTerm(tk *Token) (inst *term) {
 		tk:       *tk,
 		children: make([]*term, 0, 1),
 		position: posPrefix,
-		priority: priPrePost,
+		priority: priIncDec,
 		evalFunc: evalContextValue,
 	}
 }
@@ -31,12 +31,20 @@ func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	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)
 	}

operator-dot.go

@@ -17,50 +17,78 @@ func newDotTerm(tk *Token) (inst *term) {
 	}
 }
 
+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 {
+				index = v
+			} else if index >= -maxValue {
+				index = maxValue + 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 leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+	if err = self.checkOperands(); err != nil {
+		return
+	}
+	if leftValue, err = self.children[0].compute(ctx); err != nil {
 		return
 	}
 
 	indexTerm := self.children[1]
 
-	if isList(leftValue) {
+	switch unboxedValue := leftValue.(type) {
+	case *ListType:
 		var index int
-		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
-			return
+		array := ([]any)(*unboxedValue)
+		if index, err = verifyIndex(ctx, indexTerm, len(array)); err == nil {
+			v = array[index]
 		}
-
-		list, _ := leftValue.([]any)
-		if index >= 0 && index < len(list) {
-			v = list[index]
-		} else if index >= -len(list) {
-			v = list[len(list)+index]
-		} else {
-			err = indexTerm.Errorf("index %v out of bounds", index)
-		}
-	} else if isString(leftValue) {
+	case string:
 		var index int
-		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
-			return
+		if index, err = verifyIndex(ctx, indexTerm, len(unboxedValue)); err == nil {
+			v = unboxedValue[index]
 		}
-
-		s, _ := leftValue.(string)
-		if index >= 0 && index < len(s) {
-			v = string(s[index])
-		} else if index >= -len(s) {
-			v = string(s[len(s)+index])
-		} else {
-			err = indexTerm.Errorf("index %v out of bounds", index)
-		}
-	} else if isDict(leftValue) {
+	case map[any]any:
 		var ok bool
-		d, _ := leftValue.(map[any]any)
-		if v, ok = d[rightValue]; !ok {
+		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

operator-fraction.go

@@ -0,0 +1,282 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-fraction.go
+package expr
+
+import (
+	"errors"
+	"fmt"
+	"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 (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

@@ -34,8 +34,9 @@ func evalInsert(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	if isList(rightValue) {
-		list, _ := rightValue.([]any)
-		v = append([]any{leftValue}, list...)
+		list, _ := rightValue.(*ListType)
+		newList := append(ListType{leftValue}, *list...)
+		v = &newList
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -50,8 +51,9 @@ func evalAppend(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	if isList(leftValue) {
-		list, _ := leftValue.([]any)
-		v = append(list, rightValue)
+		list, _ := leftValue.(*ListType)
+		newList := append(*list, rightValue)
+		v = &newList
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}

operator-iter-value.go

@@ -4,7 +4,6 @@
 // operator-iter-value.go
 package expr
 
-
 //-------- iter value term
 
 func newIterValueTerm(tk *Token) (inst *term) {
@@ -18,16 +17,16 @@ func newIterValueTerm(tk *Token) (inst *term) {
 }
 
 func evalIterValue(ctx ExprContext, self *term) (v any, err error) {
-	var leftValue any
+	var childValue any
 
-	if leftValue, err = self.evalPrefix(ctx); err != nil {
+	if childValue, err = self.evalPrefix(ctx); err != nil {
 		return
 	}
 
-	if dc, ok := leftValue.(*dataCursor); ok {
-		v, err = dc.Current()
+	if it, ok := childValue.(Iterator); ok {
+		v, err = it.Current()
 	} else {
-		err = self.errIncompatibleType(leftValue)
+		err = self.errIncompatibleType(childValue)
 	}
 	return
 }

operator-length.go

@@ -17,22 +17,27 @@ func newLengthTerm(tk *Token) (inst *term) {
 }
 
 func evalLength(ctx ExprContext, self *term) (v any, err error) {
-	var rightValue any
+	var childValue any
 
-	if rightValue, err = self.evalPrefix(ctx); err != nil {
+	if childValue, err = self.evalPrefix(ctx); err != nil {
 		return
 	}
 
-	if isList(rightValue) {
-		list, _ := rightValue.([]any)
-		v = len(list)
-	} else if isString(rightValue) {
-		s, _ := rightValue.(string)
-		v = len(s)
-	} else if it, ok := rightValue.(Iterator); ok {
-		v = it.Index()
+	if isList(childValue) {
+		list, _ := childValue.([]any)
+		v = int64(len(list))
+	} else if isString(childValue) {
+		s, _ := childValue.(string)
+		v = int64(len(s))
+	} 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 {
-		err = self.errIncompatibleType(rightValue)
+			v = int64(it.Index() + 1)
+		}
+	} else {
+		err = self.errIncompatibleType(childValue)
 	}
 	return
 }

operator-post-inc.go

@@ -12,25 +12,25 @@ func newPostIncTerm(tk *Token) *term {
 		parent:   nil,
 		children: make([]*term, 0, 1),
 		position: posPostfix,
-		priority: priPrePost,
+		priority: priIncDec,
 		evalFunc: evalPostInc,
 	}
 }
 
 func evalPostInc(ctx ExprContext, self *term) (v any, err error) {
-	var leftValue any
-	if leftValue, err = self.evalPrefix(ctx); err != nil {
+	var childValue any
+	if childValue, err = self.evalPrefix(ctx); err != nil {
 		return
 	}
 
-	if dc, ok := leftValue.(*dataCursor); ok {
-		v, err = dc.Next()
-	} else if isInteger(leftValue) && self.children[0].symbol() == SymIdentifier {
-		v = leftValue
-		i, _ := leftValue.(int64)
+	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 {
-		self.errIncompatibleType(leftValue)
+		err = self.errIncompatibleType(childValue)
 	}
 	return
 }

operator-prod.go

@@ -42,6 +42,8 @@ func evalMultiply(ctx ExprContext, self *term) (v any, err error) {
 			rightInt, _ := rightValue.(int64)
 			v = leftInt * rightInt
 		}
+	} else if isFraction(leftValue) || isFraction(rightValue) {
+		v, err = mulAnyFract(leftValue, rightValue)
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -85,6 +87,8 @@ func evalDivide(ctx ExprContext, self *term) (v any, err error) {
 				v = leftInt / rightInt
 			}
 		}
+	} else if isFraction(leftValue) || isFraction(rightValue) {
+		v, err = divAnyFract(leftValue, rightValue)
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}

operator-sum.go

@@ -39,22 +39,24 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 			v = leftInt + rightInt
 		}
 	} else if isList(leftValue) || isList(rightValue) {
-		var leftList, rightList []any
+		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) {
+		v, err = sumAnyFract(leftValue, rightValue)
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
@@ -89,15 +91,17 @@ func evalMinus(ctx ExprContext, self *term) (v any, err error) {
 			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 {
+		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 if isFraction(leftValue) || isFraction(rightValue) {
+		v, err = subAnyFract(leftValue, rightValue)
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}

parser.go

@@ -62,30 +62,45 @@ func (self *parser) parseFuncCall(scanner *scanner, allowVarRef bool, tk *Token)
 // 	// 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)
+// 	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.Errorf("invalid param %q, variable identifier expected", tk.source)
+// 					err = tk.ErrorExpectedGotString("param-name", subTree.root.String())
+// 				}
+// 			} else if itemExpected {
+// 				prev := scanner.Previous()
+// 				err = prev.ErrorExpectedGot("function-param")
 // 				break
 // 			}
-// 		tk = scanner.Next()
+// 		} else {
+// 			break
 // 		}
-// 	if err == nil && tk.Sym != SymClosedRound {
-// 		err = tk.Errorf("unterminate function params list")
+// 		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().Errorf("not properly terminated function body")
+// 			err = scanner.Previous().ErrorExpectedGot("}")
 // 		} else {
 // 			tk = scanner.makeValueToken(SymExpression, "", body)
 // 			tree = newFuncDefTerm(tk, args)
@@ -102,20 +117,14 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	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.Errorf("exptected identifier, got %q", subTree.root)
-				}
+		tk = scanner.Next()
+		if tk.IsSymbol(SymIdentifier) {
+			param := newTerm(tk, nil)
+			args = append(args, param)
+			tk = scanner.Next()
 		} else if itemExpected {
 			prev := scanner.Previous()
-				err = prev.Errorf("expected function parameter, got %q", prev)
-				break
-			}
-		} else {
+			err = prev.ErrorExpectedGot("function-param")
 			break
 		}
 		lastSym = scanner.Previous().Sym
@@ -123,18 +132,20 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	}
 
 	if err == nil && lastSym != SymClosedRound {
-		err = tk.Errorf("unterminated function parameters list")
+		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)
@@ -154,7 +165,7 @@ func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term
 				args = append(args, subTree.root)
 			} else if itemExpected {
 				prev := scanner.Previous()
-				err = prev.Errorf("expected list item, got %q", prev)
+				err = prev.ErrorExpectedGot("list-item")
 				break
 			}
 		} else {
@@ -166,7 +177,7 @@ func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term
 	if err == nil {
 		// TODO Check arguments
 		if lastSym != SymClosedSquare {
-			err = scanner.Previous().Errorf("unterminate items list")
+			err = scanner.Previous().ErrorExpectedGot("]")
 		} else {
 			subtree = newListTerm(args)
 		}
@@ -175,29 +186,18 @@ func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term
 }
 
 func (self *parser) parseIterDef(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
-	var ds *term
 	tk := scanner.Previous()
 	args := make([]*term, 0)
 	lastSym := SymUnknown
-	dsExpected := true
 	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 {
-				if dsExpected {
-					if sym := subTree.root.symbol(); sym == SymDict || sym == SymIdentifier {
-						ds = subTree.root
-					} else {
-						err = subTree.root.Errorf("data-source dictionary expected, got %q", subTree.root.source())
-					}
-					dsExpected = false
-				} else {
 				args = append(args, subTree.root)
-				}
 			} else if itemExpected {
 				prev := scanner.Previous()
-				err = prev.Errorf("expected iterator argument, got %q", prev)
+				err = prev.ErrorExpectedGot("iterator-param")
 				break
 			}
 		} else {
@@ -209,11 +209,9 @@ func (self *parser) parseIterDef(scanner *scanner, allowVarRef bool) (subtree *t
 	if err == nil {
 		// TODO Check arguments
 		if lastSym != SymClosedRound {
-			err = scanner.Previous().Errorf("unterminate iterator param list")
-		} else if ds != nil {
-			subtree = newIteratorTerm(tk, ds, args)
+			err = scanner.Previous().ErrorExpectedGot(")")
 		} else {
-			tk.Errorf("missing data-source param")
+			subtree = newIteratorTerm(tk, args)
 		}
 	}
 	return
@@ -231,12 +229,13 @@ func (self *parser) parseDictKey(scanner *scanner, allowVarRef bool) (key any, e
 	if tk.Sym == SymInteger || tk.Sym == SymString {
 		tkSep := scanner.Next()
 		if tkSep.Sym != SymColon {
-			err = tkSep.Errorf("expected \":\", got %q", tkSep)
+			err = tkSep.ErrorExpectedGot(":")
 		} else {
 			key = tk.Value
 		}
 	} else {
-		err = tk.Errorf("expected dictionary key or closed brace, got %q", tk)
+		// err = tk.Errorf("expected dictionary key or closed brace, got %q", tk)
+		err = tk.ErrorExpectedGot("dictionary-key or }")
 	}
 	return
 }
@@ -254,7 +253,7 @@ func (self *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtree
 			tk := scanner.Previous()
 			lastSym = tk.Sym
 			if itemExpected {
-				err = tk.Errorf("expected dictionary key, got %q", tk)
+				err = tk.ErrorExpectedGot("dictionary-key")
 			}
 			break
 		}
@@ -263,7 +262,7 @@ func (self *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtree
 				args[key] = subTree.root
 			} else if key != nil {
 				prev := scanner.Previous()
-				err = prev.Errorf("expected dictionary value, got %q", prev)
+				err = prev.ErrorExpectedGot("dictionary-value")
 				break
 			}
 		} else {
@@ -275,7 +274,7 @@ func (self *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtree
 	if err == nil {
 		// TODO Check arguments
 		if lastSym != SymClosedBrace {
-			err = scanner.Previous().Errorf("unterminated dictionary")
+			err = scanner.Previous().ErrorExpectedGot("}")
 		} else {
 			subtree = newDictTerm(args)
 		}
@@ -309,7 +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 {

parser_test.go

@@ -6,19 +6,18 @@ package expr
 
 import (
 	"errors"
-	"fmt"
 	"reflect"
 	"strings"
 	"testing"
 )
 
-func TestParser(t *testing.T) {
-	type inputType struct {
+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},
@@ -52,140 +51,132 @@ 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 non-nil operands, got 1`)},
-		/*  46 */ {"", nil, nil},
-		/*  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 non-nil operands, got 1`)},
-		/*  61 */ {"1.5 > ", nil, errors.New(`[1:6] infix operator ">" requires two non-nil operands, got 1`)},
-		/*  62 */ {"1.5 <= ", nil, errors.New(`[1:6] infix operator "<=" requires two non-nil operands, got 1`)},
-		/*  63 */ {"1.5 >= ", nil, errors.New(`[1:6] infix operator ">=" requires two non-nil operands, got 1`)},
-		/*  64 */ {"1.5 != ", nil, errors.New(`[1:6] infix operator "!=" requires two non-nil operands, got 1`)},
-		/*  65 */ {"1.5 == ", nil, errors.New(`[1:6] infix operator "==" requires two non-nil operands, got 1`)},
-		/*  66 */ {`"1.5" < `, nil, errors.New(`[1:8] infix operator "<" requires two non-nil operands, got 1`)},
-		/*  67 */ {`"1.5" > `, nil, errors.New(`[1:8] infix operator ">" requires two non-nil operands, got 1`)},
-		/*  68 */ {`"1.5" == `, nil, errors.New(`[1:8] infix operator "==" requires two non-nil operands, got 1`)},
-		/*  69 */ {`"1.5" != `, nil, errors.New(`[1:8] infix operator "!=" requires two non-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 or function "x"`)},
-		/* 100 */ {`false or true`, true, nil},
-		/* 101 */ {`false or (x==2)`, nil, errors.New(`undefined variable or function "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 */ {`y=x ?? func(){4}; y()`, int64(4), nil},
-		/* 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 or function "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},
-		/* 137 */ {`2 + 1 ? {"a"} : {"b"} * 3`, "2bbb", nil},
-		/* 138 */ {`nil`, nil, nil},
-		/* 139 */ {`null`, nil, errors.New(`undefined variable or function "null"`)},
-		/* 140 */ {`{"key"}`, nil, errors.New(`[1:8] expected ":", got "}"`)},
-		/* 141 */ {`{"key":}`, nil, errors.New(`[1:9] expected dictionary value, got "}"`)},
-		/* 142 */ {`{}`, map[any]any{}, nil},
-		/* 144 */ //{`3^2`, int64(9), 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},
 	}
-	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{
-	// 	/* 140 */ {`ds={}; $(ds)`, nil, 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)
-		ImportImportFuncs(ctx)
 		parser := NewParser(ctx)
 
-		logTest(t, i+1, input.source, input.wantResult, input.wantErr)
+		logTest(t, i+1, "Iterator", input.source, input.wantResult, input.wantErr)
 
 		r := strings.NewReader(input.source)
 		scanner := NewScanner(r, DefaultTranslations())
@@ -213,114 +204,15 @@ func TestParser(t *testing.T) {
 			succeeded++
 		} else {
 			failed++
-			if i+1 == check_env_expr_path {
-				t.Logf(`NOTICE: Test nr %d requires EXPR_PATH="."`, 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
-	}
-
-	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
-
-	// 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, 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

@@ -160,6 +160,12 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 			//} 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)
 			}

simple-func-store.go

@@ -4,7 +4,10 @@
 // simple-func-store.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 type SimpleFuncStore struct {
 	SimpleVarStore
@@ -18,6 +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
 }
@@ -44,12 +70,44 @@ func NewSimpleFuncStore() *SimpleFuncStore {
 }
 
 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 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

@@ -4,7 +4,10 @@
 // simple-var-store.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 type SimpleVarStore struct {
 	varStore map[string]any
@@ -16,9 +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
 }
@@ -29,10 +37,12 @@ func (ctx *SimpleVarStore) GetVar(varName string) (v any, exists bool) {
 }
 
 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 {
@@ -68,3 +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()
+}

symbol.go

@@ -33,7 +33,7 @@ const (
 	SymBackTick                          //  22: '`'
 	SymExclamation                       //  23: '!'
 	SymQuestion                          //  24: '?'
-	SymAmpersand                         //  25: '&&'
+	SymAmpersand                         //  25: '&'
 	SymDoubleAmpersand                   //  26: '&&'
 	SymPercent                           //  27: '%'
 	SymAt                                //  28: '@'
@@ -64,7 +64,9 @@ const (
 	SymCaret                             //  53: '^'
 	SymDollarRound                       //  54: '$('
 	SymOpenClosedRound                   //  55: '()'
-	SymDoubleDollar                      //  56: '$$
+	SymDoubleDollar                      //  56: '$$'
+	SymDoubleDot                         //  57: '..'
+	SymTripleDot                         //  58: '...'
 	SymChangeSign
 	SymUnchangeSign
 	SymIdentifier
@@ -96,6 +98,7 @@ const (
 	SymKwBut
 	SymKwFunc
 	SymKwBuiltin
+	SymKwInclude
 	SymKwNil
 )
 
@@ -108,6 +111,7 @@ func init() {
 		"BUILTIN": SymKwBuiltin,
 		"BUT":     SymKwBut,
 		"FUNC":    SymKwFunc,
+		"INCLUDE": SymKwInclude,
 		"NOT":     SymKwNot,
 		"OR":      SymKwOr,
 		"NIL":     SymKwNil,

term.go

@@ -20,12 +20,13 @@ const (
 	priRelational
 	priSum
 	priProduct
+	priFraction
 	priSelector
 	priSign
 	priFact
 	priIterValue
 	priCoalesce
-	priPrePost
+	priIncDec
 	priDot
 	priValue
 )
@@ -154,7 +155,7 @@ func (self *term) toInt(computedValue any, valueDescription string) (i int, err
 	if index64, ok := computedValue.(int64); ok {
 		i = int(index64)
 	} else {
-		err = self.Errorf("%s, got %T", valueDescription, computedValue)
+		err = self.Errorf("%s, got %T (%v)", valueDescription, computedValue, computedValue)
 	}
 	return
 }
@@ -217,9 +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
 }

token.go

@@ -46,7 +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)
 }
@@ -63,6 +63,10 @@ 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
@@ -81,3 +85,13 @@ 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
+}

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

@@ -4,7 +4,10 @@
 // utils.go
 package expr
 
-import "reflect"
+import (
+	"fmt"
+	"reflect"
+)
 
 func isString(v any) (ok bool) {
 	_, ok = v.(string)
@@ -22,7 +25,7 @@ func isFloat(v any) (ok bool) {
 }
 
 func isList(v any) (ok bool) {
-	_, ok = v.([]any)
+	_, ok = v.(*ListType)
 	return ok
 }
 
@@ -39,12 +42,26 @@ func isNumberString(v any) (ok bool) {
 	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 {
+		if fract, ok := v.(*fraction); ok {
+			f = fract.toFloat()
+		} else {
 			i, _ := v.(int64)
 			f = float64(i)
 		}
+	}
 	return
 }
 
@@ -136,3 +153,32 @@ 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
+}