merged with datasource-context

ast.go

@@ -5,7 +5,6 @@
 package expr
 
 import (
-	"errors"
 	"strings"
 )
 
@@ -84,8 +83,9 @@ func (self *ast) insert(tree, node *term) (root *term, err error) {
 		if tree.isComplete() {
 			var subRoot *term
 			last := tree.removeLastChild()
-			subRoot, err = self.insert(last, node)
-			subRoot.setParent(tree)
+			if subRoot, err = self.insert(last, node); err == nil {
+				subRoot.setParent(tree)
+			}
 		} else {
 			node.setParent(tree)
 		}
@@ -129,8 +129,8 @@ func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
 		if err == nil {
 			result, err = self.root.compute(ctx)
 		}
-	} else {
-		err = errors.New("empty expression")
+		// } else {
+		// 	err = errors.New("empty expression")
 	}
 	return
 }

context-helpers.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// context-helpers.go
+package expr
+
+func cloneContext(sourceCtx ExprContext) (clonedCtx ExprContext) {
+	if sourceCtx != nil {
+		clonedCtx = sourceCtx.Clone()
+	}
+	return
+}
+
+func exportVar(ctx ExprContext, name string, value any) {
+	if name[0] == '@' {
+		name = name[1:]
+	}
+	ctx.setVar(name, value)
+}
+
+func exportFunc(ctx ExprContext, name string, info ExprFunc) {
+	if name[0] == '@' {
+		name = name[1:]
+	}
+	ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
+}
+
+func exportObjects(destCtx, sourceCtx ExprContext) {
+	exportAll := isEnabled(sourceCtx, control_export_all)
+	// Export variables
+	for _, refName := range sourceCtx.EnumVars(func(name string) bool { return exportAll || name[0] == '@' }) {
+		refValue, _ := sourceCtx.GetVar(refName)
+		exportVar(destCtx, refName, refValue)
+	}
+	// Export functions
+	for _, refName := range sourceCtx.EnumFuncs(func(name string) bool { return exportAll || name[0] == '@' }) {
+		if info, _ := sourceCtx.GetFuncInfo(refName); info != nil {
+			exportFunc(destCtx, refName, info)
+		}
+	}
+}

context.go

@@ -36,7 +36,7 @@ type ExprContext interface {
 	setVar(varName string, value any)
 	EnumVars(func(name string) (accept bool)) (varNames []string)
 	EnumFuncs(func(name string) (accept bool)) (funcNames []string)
-	GetFuncInfo(name string) ExprFunc
+	GetFuncInfo(name string) (item ExprFunc, exists bool)
 	Call(name string, args []any) (result any, err error)
 	RegisterFunc(name string, f Functor, minArgs, maxArgs int)
 }

data-cursor.go

@@ -0,0 +1,62 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// data-cursors.go
+package expr
+
+import (
+	"io"
+)
+
+const (
+	initName    = "init"
+	nextName    = "next"
+	currentName = "current"
+)
+
+type dataCursor struct {
+	ds          map[any]*term
+	ctx         ExprContext
+	index       int
+	resource    any
+	nextFunc    Functor
+	currentFunc Functor
+}
+
+func newDataCursor(ctx ExprContext) (dc *dataCursor) {
+	dc = &dataCursor{
+		index: -1,
+		ctx:   ctx.Clone(),
+	}
+	return
+}
+
+func (dc *dataCursor) String() string {
+	return "$(...)"
+}
+
+func (dc *dataCursor) Current() (item any, err error) { // must return io.EOF at the last item
+	ctx := cloneContext(dc.ctx)
+	if item, err = dc.currentFunc.Invoke(ctx, currentName, []any{}); err == nil && item == nil {
+		err = io.EOF
+	}
+	exportObjects(dc.ctx, ctx)
+	return
+}
+
+func (dc *dataCursor) Next() (item any, err error) { // must return io.EOF after the last item
+	ctx := cloneContext(dc.ctx)
+	if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{}); err == nil {
+		if item == nil {
+			err = io.EOF
+		} else {
+			dc.index++
+		}
+	}
+	exportObjects(dc.ctx, ctx)
+	return
+}
+
+func (dc *dataCursor) Index() int {
+	return dc.index
+}

expr_test.go

@@ -18,15 +18,28 @@ func TestExpr(t *testing.T) {
 	}
 
 	inputs := []inputType{
-		/*   1 */ {`fact=func(n){(n)?{1}::{n*fact(n-1)}}; fact(5)`, int64(120), nil},
+		/*   1 */ {`0?{}`, nil, nil},
+		/*   2 */ {`fact=func(n){(n)?{1}::{n*fact(n-1)}}; fact(5)`, int64(120), nil},
+		/*   3 */ {`f=openFile("test-file.txt"); line=readFile(f); closeFile(f); line`, "uno", nil},
+		/*   4 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
 	}
 
 	succeeded := 0
 	failed := 0
 
 	inputs1 := []inputType{
-		{`f=openFile("/tmp/test2.txt"); line=readFile(f); closeFile(f); line`, "ciao", nil},
-		//{`f = func(op){op()}; f(func(){2})`, int64(2), nil},
+		/*   1 */ {`
+		ds={
+			"init":func(end){@end=end; @current=0 but true},
+			"current":func(){current},
+			"next":func(){
+				((next=current+1) <= end) ? [true] {@current=next but current} :: {nil}
+			}
+		};
+		it=$(ds,3);
+		it++;
+		it++
+`, int64(1), nil},
 	}
 
 	for i, input := range inputs1 {

func-builtins.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// func-builtins.go
+package expr
+
+import (
+	"math"
+	"strconv"
+)
+
+func isNilFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	if len(args) == 1 {
+		result = args[0] == nil
+	} else {
+		err = errOneParam(name)
+	}
+	return
+}
+
+func intFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	if len(args) == 1 {
+		switch v := args[0].(type) {
+		case int64:
+			result = v
+		case float64:
+			result = int64(math.Trunc(v))
+		case bool:
+			if v {
+				result = int64(1)
+			} else {
+				result = int64(0)
+			}
+		case string:
+			var i int
+			if i, err = strconv.Atoi(v); err == nil {
+				result = int64(i)
+			}
+		default:
+			err = errCantConvert(name, v, "int")
+		}
+	} else {
+		err = errOneParam(name)
+	}
+	return
+}
+
+func iteratorFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	return
+}
+
+func ImportBuiltinsFuncs(ctx ExprContext) {
+	ctx.RegisterFunc("isNil", &simpleFunctor{f: isNilFunc}, 1, -1)
+	ctx.RegisterFunc("int", &simpleFunctor{f: intFunc}, 1, -1)
+}
+
+func init() {
+	registerImport("builtins", ImportBuiltinsFuncs)
+}

func-common.go

@@ -0,0 +1,17 @@
+// 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

@@ -140,3 +140,7 @@ func ImportImportFuncs(ctx ExprContext) {
 	ctx.RegisterFunc("import", &simpleFunctor{f: importFunc}, 1, -1)
 	ctx.RegisterFunc("include", &simpleFunctor{f: includeFunc}, 1, -1)
 }
+
+func init() {
+	registerImport("import", ImportImportFuncs)
+}

func-math.go

@@ -23,14 +23,19 @@ func doAdd(ctx ExprContext, name string, it Iterator) (result any, err error) {
 	var v any
 
 	for v, err = it.Next(); err == nil; v, err = it.Next() {
-		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 {
+		if subIter, ok := v.(Iterator); ok {
+			if v, err = doAdd(ctx, name, subIter); err != nil {
 				break
 			}
+		} 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
+				}
+			}
 		}
 
 		if !sumAsFloat && isFloat(v) {

func-os.go

@@ -162,3 +162,7 @@ func ImportOsFuncs(ctx ExprContext) {
 	ctx.RegisterFunc("readFile", &simpleFunctor{f: readFileFunc}, 1, 2)
 	ctx.RegisterFunc("closeFile", &simpleFunctor{f: closeFileFunc}, 1, 1)
 }
+
+func init() {
+	registerImport("os", ImportOsFuncs)
+}

funcs_test.go

@@ -0,0 +1,82 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// funcs_test.go
+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},
+		/*   3 */ {`v=5; isNil(v)`, false, nil},
+		/*   4 */ {`int(true)`, int64(1), nil},
+		/*   5 */ {`int(false)`, int64(0), nil},
+		/*   6 */ {`int(3.1)`, int64(3), nil},
+		/*   7 */ {`int(3.9)`, int64(3), nil},
+		/*   8 */ {`int("432")`, int64(432), nil},
+		/*   9 */ {`int("1.5")`, nil, errors.New(`strconv.Atoi: parsing "1.5": invalid syntax`)},
+		/*  10 */ {`int("432", 4)`, nil, errors.New(`int() requires exactly one param`)},
+		/*  11 */ {`int(nil)`, nil, errors.New(`int() can't convert <nil> to int`)},
+	}
+
+	succeeded := 0
+	failed := 0
+
+	// 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))
+}

iter-list.go

@@ -0,0 +1,42 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// iter-list.go
+package expr
+
+import "io"
+
+type FlatArrayIterator struct {
+	a     []any
+	index int
+}
+
+func NewFlatArrayIterator(array []any) *FlatArrayIterator {
+	return &FlatArrayIterator{a: array, index: 0}
+}
+
+func (it *FlatArrayIterator) Current() (item any, err error) {
+	if it.index >= 0 && it.index < len(it.a) {
+		item = it.a[it.index]
+	} else {
+		err = io.EOF
+	}
+	return
+}
+
+func (it *FlatArrayIterator) Next() (item any, err error) {
+	if item, err = it.Current(); err != io.EOF {
+		it.index++
+	}
+	// 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
+}

iterator.go

@@ -4,37 +4,8 @@
 // iterator.go
 package expr
 
-import "io"
-
 type Iterator interface {
-	Reset()
 	Next() (item any, err error) // must return io.EOF after the last item
+	Current() (item any, err error)
 	Index() int
 }
-
-type FlatArrayIterator struct {
-	a     []any
-	index int
-}
-
-func NewFlatArrayIterator(array []any) *FlatArrayIterator {
-	return &FlatArrayIterator{a: array, index: 0}
-}
-
-func (it *FlatArrayIterator) Reset() {
-	it.index = 0
-}
-
-func (it *FlatArrayIterator) Next() (item any, err error) {
-	if it.index < len(it.a) {
-		item = it.a[it.index]
-		it.index++
-	} else {
-		err = io.EOF
-	}
-	return
-}
-
-func (it *FlatArrayIterator) Index() int {
-	return it.index - 1
-}

operand-const.go

@@ -4,22 +4,8 @@
 // operand-const.go
 package expr
 
-// -------- bool const term
-func newBoolTerm(tk *Token) *term {
-	return &term{
-		tk: *tk,
-		// class:    classConst,
-		// kind:     kindBool,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- integer const term
-func newIntegerTerm(tk *Token) *term {
+// -------- const term
+func newConstTerm(tk *Token) *term {
 	return &term{
 		tk:       *tk,
 		parent:   nil,
@@ -30,34 +16,6 @@ func newIntegerTerm(tk *Token) *term {
 	}
 }
 
-// -------- float const term
-func newFloatTerm(tk *Token) *term {
-	return &term{
-		tk: *tk,
-		// class:    classConst,
-		// kind:     kindFloat,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
-// -------- string const term
-func newStringTerm(tk *Token) *term {
-	return &term{
-		tk: *tk,
-		// class:    classConst,
-		// kind:     kindString,
-		parent:   nil,
-		children: nil,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalConst,
-	}
-}
-
 // -------- eval func
 func evalConst(ctx ExprContext, self *term) (v any, err error) {
 	v = self.tk.Value
@@ -66,8 +24,9 @@ func evalConst(ctx ExprContext, self *term) (v any, err error) {
 
 // init
 func init() {
-	registerTermConstructor(SymString, newStringTerm)
-	registerTermConstructor(SymInteger, newIntegerTerm)
-	registerTermConstructor(SymFloat, newFloatTerm)
-	registerTermConstructor(SymBool, newBoolTerm)
+	registerTermConstructor(SymString, newConstTerm)
+	registerTermConstructor(SymInteger, newConstTerm)
+	registerTermConstructor(SymFloat, newConstTerm)
+	registerTermConstructor(SymBool, newConstTerm)
+	registerTermConstructor(SymKwNil, newConstTerm)
 }

operand-dict.go

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

operand-expr.go

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

operand-func.go

@@ -11,9 +11,7 @@ import (
 // -------- function call term
 func newFuncCallTerm(tk *Token, args []*term) *term {
 	return &term{
-		tk: *tk,
-		// class:    classVar,
-		// kind:     kindUnknown,
+		tk:       *tk,
 		parent:   nil,
 		children: args,
 		position: posLeaf,
@@ -24,7 +22,7 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 
 // -------- eval func call
 func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
-	ctx := parentCtx.Clone()
+	ctx := cloneContext(parentCtx)
 	name, _ := self.tk.Value.(string)
 	params := make([]any, len(self.children))
 	for i, tree := range self.children {
@@ -36,37 +34,12 @@ func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 	}
 	if err == nil {
 		if v, err = ctx.Call(name, params); err == nil {
-			exportAll := isEnabled(ctx, control_export_all)
-			// Export variables
-			for _, refName := range ctx.EnumVars(func(name string) bool { return exportAll || name[0] == '@' }) {
-				refValue, _ := ctx.GetVar(refName)
-				exportVar(parentCtx, refName, refValue)
-			}
-			// Export functions
-			for _, refName := range ctx.EnumFuncs(func(name string) bool { return exportAll || name[0] == '@' }) {
-				if info := ctx.GetFuncInfo(refName); info != nil {
-					exportFunc(parentCtx, refName, info)
-				}
-			}
+			exportObjects(parentCtx, ctx)
 		}
 	}
 	return
 }
 
-func exportVar(ctx ExprContext, name string, value any) {
-	if name[0] == '@' {
-		name = name[1:]
-	}
-	ctx.setVar(name, value)
-}
-
-func exportFunc(ctx ExprContext, name string, info ExprFunc) {
-	if name[0] == '@' {
-		name = name[1:]
-	}
-	ctx.RegisterFunc(name, info.Functor(), info.MinArgs(), info.MaxArgs())
-}
-
 // -------- function definition term
 func newFuncDefTerm(tk *Token, args []*term) *term {
 	return &term{
@@ -109,12 +82,6 @@ func evalFuncDef(ctx ExprContext, self *term) (v any, err error) {
 		paramList := make([]string, 0, len(self.children))
 		for _, param := range self.children {
 			paramList = append(paramList, param.source())
-			// if paramName, ok := param.value().(string); ok {
-			// 	paramList = append(paramList, paramName)
-			// } else {
-			// 	err = fmt.Errorf("invalid function definition: formal param nr %d must be an identifier", i+1)
-			// 	break
-			// }
 		}
 		v = &funcDefFunctor{
 			params: paramList,

operand-iterator.go

@@ -0,0 +1,104 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operand-iterator.go
+package expr
+
+import (
+	"fmt"
+)
+
+// -------- iterator term
+
+func newIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
+	tk.Sym = SymIterator
+
+	children := make([]*term, 0, 1+len(args))
+	children = append(children, dsTerm)
+	children = append(children, args...)
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: children,
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalIterator,
+	}
+}
+
+// -------- eval iterator
+
+func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
+	values = make([]any, len(a))
+	for i, t := range a {
+		var value any
+		if value, err = t.compute(ctx); err == nil {
+			values[i] = value
+		} else {
+			break
+		}
+	}
+	return
+}
+
+func getDataSourceDict(ctx ExprContext, self *term) (ds map[string]Functor, err error) {
+	var value any
+	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 {
+		return
+	}
+
+	if dictAny, ok := value.(map[any]any); ok {
+		ds = make(map[string]Functor)
+		for _, k := range []string{initName, currentName, nextName} {
+			if item, exists := dictAny[k]; exists && item != nil {
+				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
+			}
+		}
+	} else {
+		err = self.Errorf("the first param (data-source) of an iterator must be a dict, not a %T", value)
+	}
+	return
+}
+
+func evalIterator(ctx ExprContext, self *term) (v any, err error) {
+	var ds map[string]Functor
+
+	if ds, err = getDataSourceDict(ctx, self); err != nil {
+		return
+	}
+
+	dc := newDataCursor(ctx)
+
+	if initFunc, exists := ds[initName]; exists && initFunc != nil {
+		var args []any
+		if len(self.children) > 1 {
+			if args, err = evalTermArray(ctx, self.children[1:]); err != nil {
+				return
+			}
+		} else {
+			args = []any{}
+		}
+
+		initCtx := dc.ctx.Clone()
+		if dc.resource, err = initFunc.Invoke(initCtx, initName, args); err != nil {
+			return
+		}
+		exportObjects(dc.ctx, initCtx)
+	}
+
+	dc.nextFunc, _ = ds[nextName]
+	dc.currentFunc, _ = ds[currentName]
+	v = dc
+
+	return
+}

operand-var.go

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

operator-assign.go

@@ -31,7 +31,7 @@ func evalAssign(ctx ExprContext, self *term) (v any, err error) {
 		if functor, ok := v.(Functor); ok {
 			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
 		} else {
-			ctx.setVar(leftTerm.tk.source, v)
+			ctx.setVar(leftTerm.source(), v)
 		}
 	}
 	return

operator-coalesce.go

@@ -34,11 +34,11 @@ func evalNullCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
 		v = leftValue
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if _, ok := rightValue.(Functor); ok {
-			err = errCoalesceNoFunc(self.children[1])
-		} else {
-			v = rightValue
-		}
+		// if _, ok := rightValue.(Functor); ok {
+		// 	err = errCoalesceNoFunc(self.children[1])
+		// } else {
+		v = rightValue
+		// }
 	}
 	return
 }
@@ -71,8 +71,8 @@ func evalAssignCoalesce(ctx ExprContext, self *term) (v any, err error) {
 	if leftValue, exists := ctx.GetVar(leftTerm.source()); exists {
 		v = leftValue
 	} else if rightValue, err = self.children[1].compute(ctx); err == nil {
-		if _, ok := rightValue.(Functor); ok {
-			err = errCoalesceNoFunc(self.children[1])
+		if functor, ok := rightValue.(Functor); ok {
+			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
 		} else {
 			v = rightValue
 			ctx.setVar(leftTerm.source(), rightValue)
@@ -82,9 +82,9 @@ func evalAssignCoalesce(ctx ExprContext, self *term) (v any, err error) {
 }
 
 // utils
-func errCoalesceNoFunc(t *term) error {
-	return t.Errorf("the right operand of a coalescing operation cannot be a function definition")
-}
+// func errCoalesceNoFunc(t *term) error {
+// 	return t.Errorf("the right operand of a coalescing operation cannot be a function definition")
+// }
 
 // init
 func init() {

operator-context.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-context-value.go
+package expr
+
+//-------- context term
+
+func newContextTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priPrePost,
+		evalFunc: evalContextValue,
+	}
+}
+
+func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
+	var childValue any
+
+	var sourceCtx ExprContext
+	if len(self.children) == 0 {
+		sourceCtx = ctx
+	} else if childValue, err = self.evalPrefix(ctx); err == nil {
+		if dc, ok := childValue.(*dataCursor); ok {
+			sourceCtx = dc.ctx
+		}
+	} else {
+		return
+	}
+
+	if sourceCtx != nil {
+		keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+		d := make(map[string]any)
+		for _, key := range keys {
+			d[key], _ = sourceCtx.GetVar(key)
+		}
+		v = d
+	} else {
+		err = self.errIncompatibleType(childValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymDoubleDollar, newContextTerm)
+}

operator-dot.go

@@ -4,6 +4,8 @@
 // operator-dot.go
 package expr
 
+import "fmt"
+
 // -------- dot term
 func newDotTerm(tk *Token) (inst *term) {
 	return &term{
@@ -23,15 +25,13 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	indexTerm := self.children[1]
-	if !isInteger(rightValue) {
-		err = indexTerm.Errorf("index expression must be integer, got %T", rightValue)
-		return
-	}
-
-	index64, _ := rightValue.(int64)
-	index := int(index64)
 
 	if isList(leftValue) {
+		var index int
+		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
+			return
+		}
+
 		list, _ := leftValue.([]any)
 		if index >= 0 && index < len(list) {
 			v = list[index]
@@ -41,6 +41,11 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 			err = indexTerm.Errorf("index %v out of bounds", index)
 		}
 	} else if isString(leftValue) {
+		var index int
+		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
+			return
+		}
+
 		s, _ := leftValue.(string)
 		if index >= 0 && index < len(s) {
 			v = string(s[index])
@@ -49,6 +54,12 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 		} else {
 			err = indexTerm.Errorf("index %v out of bounds", index)
 		}
+	} else if isDict(leftValue) {
+		var ok bool
+		d, _ := leftValue.(map[any]any)
+		if v, ok = d[rightValue]; !ok {
+			err = fmt.Errorf("key %v does not belong to the dictionary", rightValue)
+		}
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}

operator-iter-value.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-iter-value.go
+package expr
+
+
+//-------- iter value term
+
+func newIterValueTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priIterValue,
+		evalFunc: evalIterValue,
+	}
+}
+
+func evalIterValue(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue any
+
+	if leftValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	if dc, ok := leftValue.(*dataCursor); ok {
+		v, err = dc.Current()
+	} else {
+		err = self.errIncompatibleType(leftValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymOpenClosedRound, newIterValueTerm)
+}

operator-length.go

@@ -29,9 +29,8 @@ func evalLength(ctx ExprContext, self *term) (v any, err error) {
 	} else if isString(rightValue) {
 		s, _ := rightValue.(string)
 		v = len(s)
-		// } else {
-		// 	v = 1
-		// }
+	} else if it, ok := rightValue.(Iterator); ok {
+		v = it.Index()
 	} else {
 		err = self.errIncompatibleType(rightValue)
 	}

operator-post-inc.go

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

operator-selector.go

@@ -4,65 +4,7 @@
 // operator-selector.go
 package expr
 
-// //-------- export all term
-
-// func newSelectorTerm(tk *Token) (inst *term) {
-// 	return &term{
-// 		tk:       *tk,
-// 		children: make([]*term, 0, 3),
-// 		position: posMultifix,
-// 		priority: priSelector,
-// 		evalFunc: evalSelector,
-// 	}
-// }
-
-// func isSelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (selectedValue any, err error) {
-// 	caseData, _ := caseSel.(*selectorCase)
-// 	if caseData.filterList == nil {
-// 		selectedValue, err = caseData.caseExpr.eval(ctx, false)
-// 	} else {
-// 		filterList := caseData.filterList.children
-// 		if len(filterList) == 0 && exprValue == int64(caseIndex) {
-// 			selectedValue, err = caseData.caseExpr.eval(ctx, false)
-// 		} else {
-// 			var caseValue any
-// 			for _, caseTerm := range filterList {
-// 				if caseValue, err = caseTerm.compute(ctx); err != nil || caseValue == exprValue {
-// 					selectedValue, err = caseData.caseExpr.eval(ctx, false)
-// 					break
-// 				}
-// 			}
-// 		}
-// 	}
-// 	return
-// }
-
-// func evalSelector(ctx ExprContext, self *term) (v any, err error) {
-// 	var exprValue any
-// 	// var caseList []*term
-
-// 	if err = self.checkOperands(); err != nil {
-// 		return
-// 	}
-// 	exprTerm := self.children[0]
-// 	if exprValue, err = exprTerm.compute(ctx); err != nil {
-// 		return
-// 	}
-
-// 	caseList := self.children[1:]
-// 	for i, caseTerm := range caseList {
-// 		caseSel := caseTerm.value()
-// 		if v, err = isSelectorCase(ctx, exprValue, caseSel, i); err != nil || v != nil {
-// 			break
-// 		}
-// 	}
-// 	if err == nil && v == nil {
-// 		err = exprTerm.tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
-// 	}
-// 	return
-// }
-
-//-------- export all term
+//-------- selector term
 
 func newSelectorTerm(tk *Token) (inst *term) {
 	return &term{
@@ -74,18 +16,21 @@ func newSelectorTerm(tk *Token) (inst *term) {
 	}
 }
 
-func isSelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (selectedValue any, err error) {
+func trySelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (match bool, selectedValue any, err error) {
 	caseData, _ := caseSel.(*selectorCase)
 	if caseData.filterList == nil {
 		selectedValue, err = caseData.caseExpr.eval(ctx, false)
+		match = true
 	} else if filterList, ok := caseData.filterList.value().([]*term); ok {
 		if len(filterList) == 0 && exprValue == int64(caseIndex) {
 			selectedValue, err = caseData.caseExpr.eval(ctx, false)
+			match = true
 		} else {
 			var caseValue any
 			for _, caseTerm := range filterList {
 				if caseValue, err = caseTerm.compute(ctx); err != nil || caseValue == exprValue {
 					selectedValue, err = caseData.caseExpr.eval(ctx, false)
+					match = true
 					break
 				}
 			}
@@ -96,7 +41,7 @@ func isSelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (sel
 
 func evalSelector(ctx ExprContext, self *term) (v any, err error) {
 	var exprValue any
-	// var caseList []*term
+	var match bool
 
 	if err = self.checkOperands(); err != nil {
 		return
@@ -110,11 +55,11 @@ func evalSelector(ctx ExprContext, self *term) (v any, err error) {
 	caseList, _ := caseListTerm.value().([]*term)
 	for i, caseTerm := range caseList {
 		caseSel := caseTerm.value()
-		if v, err = isSelectorCase(ctx, exprValue, caseSel, i); err != nil || v != nil {
+		if match, v, err = trySelectorCase(ctx, exprValue, caseSel, i); err != nil || match {
 			break
 		}
 	}
-	if err == nil && v == nil {
+	if err == nil && !match {
 		err = exprTerm.tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
 	}
 	return

parser.go

@@ -58,23 +58,72 @@ func (self *parser) parseFuncCall(scanner *scanner, allowVarRef bool, tk *Token)
 	return
 }
 
+// func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
+// 	// Example: "add = func(x,y) {x+y}
+// 	var body *ast
+// 	args := make([]*term, 0)
+// 	tk := scanner.Next()
+// 	for tk.Sym != SymClosedRound && tk.Sym != SymEos {
+// 		if tk.Sym == SymIdentifier {
+// 			t := newTerm(tk, nil)
+// 			args = append(args, t)
+// 		} else {
+// 			err = tk.Errorf("invalid param %q, variable identifier expected", tk.source)
+// 			break
+// 		}
+// 		tk = scanner.Next()
+// 	}
+// 	if err == nil && tk.Sym != SymClosedRound {
+// 		err = tk.Errorf("unterminate function params list")
+// 	}
+// 	if err == nil {
+// 		tk = scanner.Next()
+// 		if tk.Sym == SymOpenBrace {
+// 			body, err = self.parseGeneral(scanner, true, true, SymClosedBrace)
+// 		}
+// 	}
+// 	if err == nil {
+// 		// TODO Check arguments
+// 		if scanner.Previous().Sym != SymClosedBrace {
+// 			err = scanner.Previous().Errorf("not properly terminated function body")
+// 		} else {
+// 			tk = scanner.makeValueToken(SymExpression, "", body)
+// 			tree = newFuncDefTerm(tk, args)
+// 		}
+// 	}
+// 	return
+// }
+
 func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	// Example: "add = func(x,y) {x+y}
 	var body *ast
 	args := make([]*term, 0)
-	tk := scanner.Next()
-	for tk.Sym != SymClosedRound && tk.Sym != SymEos {
-		if tk.Sym == SymIdentifier {
-			t := newTerm(tk, nil)
-			args = append(args, t)
+	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("exptected identifier, got %q", subTree.root)
+				}
+			} else if itemExpected {
+				prev := scanner.Previous()
+				err = prev.Errorf("expected function parameter, got %q", prev)
+				break
+			}
 		} else {
-			err = tk.Errorf("invalid param %q, variable identifier expected", tk.source)
 			break
 		}
-		tk = scanner.Next()
+		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
 	}
-	if err == nil && tk.Sym != SymClosedRound {
-		err = tk.Errorf("unterminate function params list")
+
+	if err == nil && lastSym != SymClosedRound {
+		err = tk.Errorf("unterminated function parameters list")
 	}
 	if err == nil {
 		tk = scanner.Next()
@@ -97,16 +146,22 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
 	args := make([]*term, 0)
 	lastSym := SymUnknown
+	itemExpected := false
 	for lastSym != SymClosedSquare && lastSym != SymEos {
 		var subTree *ast
 		if subTree, err = self.parseItem(scanner, allowVarRef, SymComma, SymClosedSquare); err == nil {
 			if subTree.root != nil {
 				args = append(args, subTree.root)
+			} else if itemExpected {
+				prev := scanner.Previous()
+				err = prev.Errorf("expected list item, got %q", prev)
+				break
 			}
 		} else {
 			break
 		}
 		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
 	}
 	if err == nil {
 		// TODO Check arguments
@@ -119,6 +174,115 @@ func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term
 	return
 }
 
+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)
+				break
+			}
+		} else {
+			break
+		}
+		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
+	}
+	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)
+		} else {
+			tk.Errorf("missing data-source param")
+		}
+	}
+	return
+}
+
+func (self *parser) parseDictKey(scanner *scanner, allowVarRef bool) (key any, err error) {
+	tk := scanner.Next()
+	if tk.Sym == SymError {
+		err = tk.Error()
+		return
+	}
+	if tk.Sym == SymClosedBrace || tk.Sym == SymEos {
+		return
+	}
+	if tk.Sym == SymInteger || tk.Sym == SymString {
+		tkSep := scanner.Next()
+		if tkSep.Sym != SymColon {
+			err = tkSep.Errorf("expected \":\", got %q", tkSep)
+		} else {
+			key = tk.Value
+		}
+	} else {
+		err = tk.Errorf("expected dictionary key or closed brace, got %q", tk)
+	}
+	return
+}
+
+func (self *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
+	args := make(map[any]*term, 0)
+	lastSym := SymUnknown
+	itemExpected := false
+	for lastSym != SymClosedBrace && lastSym != SymEos {
+		var subTree *ast
+		var key any
+		if key, err = self.parseDictKey(scanner, allowVarRef); err != nil {
+			break
+		} else if key == nil {
+			tk := scanner.Previous()
+			lastSym = tk.Sym
+			if itemExpected {
+				err = tk.Errorf("expected dictionary key, got %q", tk)
+			}
+			break
+		}
+		if subTree, err = self.parseItem(scanner, allowVarRef, SymComma, SymClosedBrace); err == nil {
+			if subTree.root != nil {
+				args[key] = subTree.root
+			} else if key != nil {
+				prev := scanner.Previous()
+				err = prev.Errorf("expected dictionary value, got %q", prev)
+				break
+			}
+		} else {
+			break
+		}
+		lastSym = scanner.Previous().Sym
+		itemExpected = lastSym == SymComma
+	}
+	if err == nil {
+		// TODO Check arguments
+		if lastSym != SymClosedBrace {
+			err = scanner.Previous().Errorf("unterminated dictionary")
+		} else {
+			subtree = newDictTerm(args)
+		}
+	}
+	return
+}
+
 func (self *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaultCase bool) (caseTerm *term, err error) {
 	var filterList *term
 	var caseExpr *ast
@@ -241,6 +405,12 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 				err = tree.addTerm(listTerm)
 				currentTerm = listTerm
 			}
+		case SymOpenBrace:
+			var mapTerm *term
+			if mapTerm, err = self.parseDictionary(scanner, allowVarRef); err == nil {
+				err = tree.addTerm(mapTerm)
+				currentTerm = mapTerm
+			}
 		case SymEqual:
 			if err = checkPrevSymbol(lastSym, SymIdentifier, tk); err == nil {
 				currentTerm, err = tree.addToken2(tk)
@@ -251,6 +421,12 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 				err = tree.addTerm(funcDefTerm)
 				currentTerm = funcDefTerm
 			}
+		case SymDollarRound:
+			var iterDefTerm *term
+			if iterDefTerm, err = self.parseIterDef(scanner, allowVarRef); err == nil {
+				err = tree.addTerm(iterDefTerm)
+				currentTerm = iterDefTerm
+			}
 		case SymIdentifier:
 			if tk.source[0] == '@' && !allowVarRef {
 				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.source)

parser_test.go

@@ -7,6 +7,7 @@ package expr
 import (
 	"errors"
 	"fmt"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -63,8 +64,8 @@ func TestParser(t *testing.T) {
 		/*  42 */ {`"s" + true`, nil, errors.New(`[1:6] left operand 's' [string] and right operand 'true' [bool] are not compatible with operator "+"`)},
 		/*  43 */ {`+false`, nil, errors.New(`[1:2] prefix/postfix operator "+" do not support operand 'false' [bool]`)},
 		/*  44 */ {`false // very simple expression`, false, nil},
-		/*  45 */ {`1 + // Missing right operator`, nil, errors.New(`[1:4] infix operator "+" requires two not nil operands, got 1`)},
-		/*  46 */ {"", nil, errors.New(`empty expression`)},
+		/*  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},
@@ -78,16 +79,16 @@ func TestParser(t *testing.T) {
 		/*  57 */ {`"1.5" > "7"`, false, nil},
 		/*  58 */ {`"1.5" == "7"`, false, nil},
 		/*  59 */ {`"1.5" != "7"`, true, nil},
-		/*  60 */ {"1.5 < ", nil, errors.New(`[1:6] infix operator "<" requires two not nil operands, got 1`)},
-		/*  61 */ {"1.5 > ", nil, errors.New(`[1:6] infix operator ">" requires two not nil operands, got 1`)},
-		/*  62 */ {"1.5 <= ", nil, errors.New(`[1:6] infix operator "<=" requires two not nil operands, got 1`)},
-		/*  63 */ {"1.5 >= ", nil, errors.New(`[1:6] infix operator ">=" requires two not nil operands, got 1`)},
-		/*  64 */ {"1.5 != ", nil, errors.New(`[1:6] infix operator "!=" requires two not nil operands, got 1`)},
-		/*  65 */ {"1.5 == ", nil, errors.New(`[1:6] infix operator "==" requires two not nil operands, got 1`)},
-		/*  66 */ {`"1.5" < `, nil, errors.New(`[1:8] infix operator "<" requires two not nil operands, got 1`)},
-		/*  67 */ {`"1.5" > `, nil, errors.New(`[1:8] infix operator ">" requires two not nil operands, got 1`)},
-		/*  68 */ {`"1.5" == `, nil, errors.New(`[1:8] infix operator "==" requires two not nil operands, got 1`)},
-		/*  69 */ {`"1.5" != `, nil, errors.New(`[1:8] infix operator "!=" requires two not nil operands, got 1`)},
+		/*  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`)},
@@ -117,9 +118,9 @@ func TestParser(t *testing.T) {
 		/*  96 */ {`x=2 but x*10`, int64(20), nil},
 		/*  97 */ {`false and true`, false, nil},
 		/*  98 */ {`false and (x==2)`, false, nil},
-		/*  99 */ {`false and (x=2 but x==2) or x==2`, nil, errors.New(`undefined variable "x"`)},
+		/*  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 "x"`)},
+		/* 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`)},
@@ -134,13 +135,13 @@ func TestParser(t *testing.T) {
 		/* 113 */ {`import("test-funcs.expr"); (double(3+a) + 1) * two()`, int64(34), nil},
 		/* 114 */ {`x ?? "default"`, "default", nil},
 		/* 115 */ {`x="hello"; x ?? "default"`, "hello", nil},
-		/* 116 */ {`x ?? func(){}"`, nil, errors.New(`[1:15] the right operand of a coalescing operation cannot be a function definition`)},
+		/* 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 "x"`)},
+		/* 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},
@@ -156,6 +157,12 @@ func TestParser(t *testing.T) {
 		/* 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},
 	}
 	check_env_expr_path := 113
 
@@ -163,7 +170,7 @@ func TestParser(t *testing.T) {
 	failed := 0
 
 	// inputs1 := []inputType{
-	// 	{`10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}`, "b", nil},
+	// 	/* 140 */ {`ds={}; $(ds)`, nil, nil},
 	// }
 
 	for i, input := range inputs {
@@ -188,7 +195,9 @@ func TestParser(t *testing.T) {
 			gotResult, gotErr = expr.Eval(ctx)
 		}
 
-		if gotResult != input.wantResult {
+		eq := reflect.DeepEqual(gotResult, input.wantResult)
+
+		if !eq /*gotResult != input.wantResult*/ {
 			t.Errorf("%d: %q -> result = %v [%T], want %v [%T]", i+1, input.source, gotResult, gotResult, input.wantResult, input.wantResult)
 			good = false
 		}
@@ -219,10 +228,6 @@ func TestListParser(t *testing.T) {
 		wantErr    error
 	}
 
-	// inputs1 := []inputType{
-	// 	{`add(1,2,3)`, int64(6), nil},
-	// }
-
 	inputs := []inputType{
 		/*  1 */ {`[]`, []any{}, nil},
 		/*  2 */ {`[1,2,3]`, []any{int64(1), int64(2), int64(3)}, nil},
@@ -242,6 +247,10 @@ func TestListParser(t *testing.T) {
 	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

scanner.go

@@ -86,13 +86,14 @@ func (self *scanner) Next() (tk *Token) {
 }
 
 func (self *scanner) fetchNextToken() (tk *Token) {
+	var ch byte
 	if err := self.skipBlanks(); err != nil {
 		return self.makeErrorToken(err)
 	}
 
 	escape := false
 	for {
-		ch, _ := self.readChar()
+		ch, _ = self.readChar()
 		switch ch {
 		case '+':
 			if next, _ := self.peek(); next == '+' {
@@ -143,6 +144,8 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 			}
 		case ',':
 			tk = self.makeToken(SymComma, ch)
+		case '^':
+			tk = self.makeToken(SymCaret, ch)
 		case ':':
 			if next, _ := self.peek(); next == ':' {
 				tk = self.moveOn(SymDoubleColon, ch, next)
@@ -236,9 +239,20 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 				tk = self.makeToken(SymGreater, ch)
 			}
 		case '$':
-			tk = self.makeToken(SymDollar, ch)
+			if next, _ := self.peek(); next == '(' {
+				tk = self.moveOn(SymDollarRound, ch, next)
+				tk.source += ")"
+			} else if next == '$' {
+				tk = self.moveOn(SymDoubleDollar, ch, next)
+			} else {
+				tk = self.makeToken(SymDollar, ch)
+			}
 		case '(':
-			tk = self.makeToken(SymOpenRound, ch)
+			if next, _ := self.peek(); next == ')' {
+				tk = self.moveOn(SymOpenClosedRound, ch, next)
+			} else {
+				tk = self.makeToken(SymOpenRound, ch)
+			}
 		case ')':
 			tk = self.makeToken(SymClosedRound, ch)
 		case '[':
@@ -271,6 +285,9 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 			break
 		}
 	}
+	if tk == nil {
+		tk = NewErrorToken(self.row, self.column, fmt.Errorf("unknown symbol '%c'", ch))
+	}
 	return
 }
 

scanner_test.go

@@ -36,7 +36,7 @@ func TestScanner(t *testing.T) {
 		/* 14 */ {`:`, SymColon, nil, nil},
 		/* 15 */ {`;`, SymSemiColon, nil, nil},
 		/* 16 */ {`.`, SymDot, nil, nil},
-		/* 17 */ {`.5`, SymFloat, float64(0.5), nil},
+		/* 17 */ {`0.5`, SymFloat, float64(0.5), nil},
 		/* 18 */ {`\\`, SymBackSlash, nil, nil},
 		/* 19 */ {"`", SymBackTick, nil, nil},
 		/* 20 */ {"?", SymQuestion, nil, nil},
@@ -74,7 +74,7 @@ func TestScanner(t *testing.T) {
 		scanner := NewScanner(r, nil)
 
 		if tk := scanner.Next(); tk == nil {
-			t.Errorf("%d: %q -> got = (nil), want %v (value %v [%T)", i+1, input.source, input.wantSym, input.wantValue, input.wantValue)
+			t.Errorf("%d: %q -> got = (nil), want %v (value %v [%T])", i+1, input.source, input.wantSym, input.wantValue, input.wantValue)
 		} else if tk.Sym != input.wantSym || tk.Value != input.wantValue {
 			if tk.Sym == SymError && input.wantSym == tk.Sym {
 				if tkErr, tkOk := tk.Value.(error); tkOk {

simple-func-store.go

@@ -35,10 +35,12 @@ func (info *funcInfo) Functor() Functor {
 }
 
 func NewSimpleFuncStore() *SimpleFuncStore {
-	return &SimpleFuncStore{
+	ctx := &SimpleFuncStore{
 		SimpleVarStore: SimpleVarStore{varStore: make(map[string]any)},
 		funcStore:      make(map[string]*funcInfo),
 	}
+	ImportBuiltinsFuncs(ctx)
+	return ctx
 }
 
 func (ctx *SimpleFuncStore) Clone() ExprContext {
@@ -48,8 +50,8 @@ func (ctx *SimpleFuncStore) Clone() ExprContext {
 	}
 }
 
-func (ctx *SimpleFuncStore) GetFuncInfo(name string) (info ExprFunc) {
-	info, _ = ctx.funcStore[name]
+func (ctx *SimpleFuncStore) GetFuncInfo(name string) (info ExprFunc, exists bool) {
+	info, exists = ctx.funcStore[name]
 	return
 }
 

simple-var-store.go

@@ -54,7 +54,7 @@ func (ctx *SimpleVarStore) EnumVars(acceptor func(name string) (accept bool)) (v
 	return
 }
 
-func (ctx *SimpleVarStore) GetFuncInfo(name string) (f ExprFunc) {
+func (ctx *SimpleVarStore) GetFuncInfo(name string) (f ExprFunc, exists bool) {
 	return
 }
 

symbol.go

@@ -61,6 +61,10 @@ const (
 	SymDoubleColon                       //  50: '::'
 	SymInsert                            //  51: '>>'
 	SymAppend                            //  52: '<<'
+	SymCaret                             //  53: '^'
+	SymDollarRound                       //  54: '$('
+	SymOpenClosedRound                   //  55: '()'
+	SymDoubleDollar                      //  56: '$$
 	SymChangeSign
 	SymUnchangeSign
 	SymIdentifier
@@ -68,6 +72,7 @@ const (
 	SymInteger
 	SymFloat
 	SymString
+	SymIterator
 	SymOr
 	SymAnd
 	SymNot
@@ -75,6 +80,7 @@ const (
 	SymFuncCall
 	SymFuncDef
 	SymList
+	SymDict
 	SymExpression
 	SymSelector     // <selector> ::= <expr> "?" <selector-case> {":" <selector-case>} ["::" <default-selector-case>]
 	SymSelectorCase // <selector-case> ::= [<list>] "{" <multi-expr> "}"
@@ -90,6 +96,7 @@ const (
 	SymKwBut
 	SymKwFunc
 	SymKwBuiltin
+	SymKwNil
 )
 
 var keywords map[string]Symbol
@@ -103,5 +110,6 @@ func init() {
 		"FUNC":    SymKwFunc,
 		"NOT":     SymKwNot,
 		"OR":      SymKwOr,
+		"NIL":     SymKwNil,
 	}
 }

term.go

@@ -23,7 +23,9 @@ const (
 	priSelector
 	priSign
 	priFact
+	priIterValue
 	priCoalesce
+	priPrePost
 	priDot
 	priValue
 )
@@ -127,6 +129,10 @@ func (self *term) setParent(parent *term) {
 	}
 }
 
+func (self *term) symbol() Symbol {
+	return self.tk.Sym
+}
+
 func (self *term) source() string {
 	return self.tk.source
 }
@@ -144,6 +150,15 @@ func (self *term) compute(ctx ExprContext) (v any, err error) {
 	return
 }
 
+func (self *term) toInt(computedValue any, valueDescription string) (i int, err error) {
+	if index64, ok := computedValue.(int64); ok {
+		i = int(index64)
+	} else {
+		err = self.Errorf("%s, got %T", valueDescription, computedValue)
+	}
+	return
+}
+
 func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
 	return self.tk.Errorf(
 		"left operand '%v' [%T] and right operand '%v' [%T] are not compatible with operator %q",

test-file.txt

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

token_test.go

@@ -5,6 +5,7 @@
 package expr
 
 import (
+	"fmt"
 	"testing"
 )
 
@@ -17,8 +18,8 @@ func TestDevString(t *testing.T) {
 	}
 
 	inputs := []inputType{
-		/*   1 */ {"100", SymInteger, 100, `[55]"100"{100}`},
-		/*   2 */ {"+", SymPlus, nil, `[6]"+"{}`},
+		/*   1 */ {"100", SymInteger, 100, fmt.Sprintf(`[%d]"100"{100}`, SymInteger)},
+		/*   2 */ {"+", SymPlus, nil, fmt.Sprintf(`[%d]"+"{}`, SymPlus)},
 	}
 
 	for i, input := range inputs {

utils.go

@@ -26,6 +26,11 @@ func isList(v any) (ok bool) {
 	return ok
 }
 
+func isDict(v any) (ok bool) {
+	_, ok = v.(map[any]any)
+	return ok
+}
+
 func isNumber(v any) (ok bool) {
 	return isFloat(v) || isInteger(v)
 }