operator-post-inc.go: new post int decrement operator '--'

This feature is implemented by expansion, not by dedicated operators, e.g. a*=2+x is exapanded as a=a*(2+x)

ast.go

@@ -45,19 +45,19 @@ func (expr *ast) String() string {
 
 func (expr *ast) addTokens(tokens ...*Token) (err error) {
 	for _, tk := range tokens {
-		if err = expr.addToken(tk); err != nil {
+		if _, err = expr.addToken(tk); err != nil {
 			break
 		}
 	}
 	return
 }
 
-func (expr *ast) addToken(tk *Token) (err error) {
+// func (expr *ast) addToken(tk *Token) (err error) {
-	_, err = expr.addToken2(tk)
+// 	_, err = expr.addToken2(tk)
-	return
+// 	return
-}
+// }
 
-func (expr *ast) addToken2(tk *Token) (t *term, err error) {
+func (expr *ast) addToken(tk *Token) (t *term, err error) {
 	if t = newTerm(tk); t != nil {
 		err = expr.addTerm(t)
 	} else {

builtin-iterator.go

@@ -12,6 +12,7 @@ import (
 const (
 	iterParamOperator = "operator"
 	iterParamVars     = "vars"
+	iterVarStatus     = "status"
 )
 
 func parseRunArgs(localCtx ExprContext, args []any) (it Iterator, op Functor, err error) {
@@ -54,7 +55,7 @@ func runFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	var item any
 
 	localCtx := ctx.Clone()
-	localCtx.UnsafeSetVar("it_status", nil)
+	localCtx.UnsafeSetVar(iterVarStatus, nil)
 
 	if it, op, err = parseRunArgs(localCtx, args); err != nil {
 		return
@@ -84,7 +85,7 @@ func runFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 		err = nil
 	}
 	if err == nil {
-		result, _ = localCtx.GetVar("it_status")
+		result, _ = localCtx.GetVar(iterVarStatus)
 	}
 	return
 }

builtin-math-arith.go

@@ -34,8 +34,8 @@ func doAdd(ctx ExprContext, name string, it Iterator, count, level int) (result
 			if v, err = doAdd(ctx, name, subIter, count, level); err != nil {
 				break
 			}
-			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(cleanName) {
+			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(CleanName) {
-				if _, err = extIter.CallOperation(cleanName, nil); err != nil {
+				if _, err = extIter.CallOperation(CleanName, nil); err != nil {
 					return
 				}
 			}
@@ -107,8 +107,8 @@ func doMul(ctx ExprContext, name string, it Iterator, count, level int) (result
 			if v, err = doMul(ctx, name, subIter, count, level); err != nil {
 				break
 			}
-			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(cleanName) {
+			if extIter, ok := v.(ExtIterator); ok && extIter.HasOperation(CleanName) {
-				if _, err = extIter.CallOperation(cleanName, nil); err != nil {
+				if _, err = extIter.CallOperation(CleanName, nil); err != nil {
 					return
 				}
 			}

data-cursor.go

@@ -5,30 +5,45 @@
 package expr
 
 import (
-	"errors"
 	"io"
 )
 
 type dataCursor struct {
 	ds        map[string]Functor
 	ctx       ExprContext
+	initState bool // true if no item has prodiced yet (this replace di initial Next() call in the contructor)
 	index     int
+	count     int
+	current   any
+	lastErr   error
 	resource  any
 	nextFunc  Functor
 	cleanFunc Functor
 	resetFunc Functor
-	currentFunc Functor
 }
 
-func newDataCursor(ctx ExprContext, ds map[string]Functor) (dc *dataCursor) {
+func NewDataCursor(ctx ExprContext, ds map[string]Functor, resource any) (dc *dataCursor) {
 	dc = &dataCursor{
 		ds:        ds,
+		initState: true,
 		index:     -1,
+		count:     0,
+		current:   nil,
+		lastErr:   nil,
+		resource:  resource,
 		ctx:       ctx.Clone(),
+		nextFunc:  ds[NextName],
+		cleanFunc: ds[CleanName],
+		resetFunc: ds[ResetName],
 	}
+	//dc.Next()
 	return
 }
 
+func (dc *dataCursor) Context() ExprContext {
+	return dc.ctx
+}
+
 func (dc *dataCursor) TypeName() string {
 	return "DataCursor"
 }
@@ -62,7 +77,7 @@ func (dc *dataCursor) String() string {
 }
 
 func (dc *dataCursor) HasOperation(name string) (exists bool) {
-	exists = name == indexName
+	exists = name == IndexName
 	if !exists {
 		f, ok := dc.ds[name]
 		exists = ok && isFunctor(f)
@@ -71,7 +86,7 @@ func (dc *dataCursor) HasOperation(name string) (exists bool) {
 }
 
 func (dc *dataCursor) CallOperation(name string, args []any) (value any, err error) {
-	if name == indexName {
+	if name == IndexName {
 		value = int64(dc.Index())
 	} else if functor, ok := dc.ds[name]; ok && isFunctor(functor) {
 		if functor == dc.cleanFunc {
@@ -93,15 +108,19 @@ 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 {
+			_, err = dc.resetFunc.Invoke(ctx, ResetName, []any{dc.resource})
-				dc.index = -1
-			}
 			exportObjects(dc.ctx, ctx)
+			dc.index = -1
+			dc.count = 0
+			dc.initState = true
+			dc.current = nil
+			dc.lastErr = nil
+			//dc.Next()
 		} else {
 			err = errInvalidDataSource()
 		}
 	} else {
-		err = errNoOperation(resetName)
+		err = errNoOperation(ResetName)
 	}
 	success = err == nil
 	return
@@ -111,107 +130,104 @@ 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})
+			_, err = dc.cleanFunc.Invoke(ctx, CleanName, []any{dc.resource})
-			dc.resource = nil
+			//			dc.resource = nil
 			exportObjects(dc.ctx, ctx)
 		} else {
 			err = errInvalidDataSource()
 		}
 	} else {
-		err = errors.New("no 'clean' function defined in the data-source")
+		err = errNoOperation(CleanName)
 	}
 	success = err == nil
 	return
 }
 
 func (dc *dataCursor) Current() (item any, err error) { // must return io.EOF at the last item
-	ctx := cloneContext(dc.ctx)
+	dc.init()
-	if item, err = dc.currentFunc.Invoke(ctx, currentName, []any{}); err == nil && item == nil {
+
+	if dc.current != nil {
+		item = dc.current
+	} else {
 		err = io.EOF
 	}
-	exportObjects(dc.ctx, ctx)
 	return
 }
 
-// func (dc *dataCursor) _Next() (item any, err error) { // must return io.EOF after the last item
-// 	if dc.resource != nil {
-// 		ctx := cloneContext(dc.ctx)
-// 		// fmt.Printf("Entering Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
-// 		if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{dc.resource}); err == nil {
-// 			if item == nil {
-// 				err = io.EOF
-// 			} else {
-// 				dc.index++
-// 			}
-// 		}
-// 		// fmt.Printf("Exiting Inner-Ctx [%p]: %s\n", ctx, CtxToString(ctx, 0))
-// 		exportObjects(dc.ctx, ctx)
-// 		// fmt.Printf("Outer-Ctx [%p]: %s\n", dc.ctx, CtxToString(dc.ctx, 0))
-// 	} else {
-// 		err = errInvalidDataSource()
-// 	}
-// 	return
-// }
-
-// func (dc *dataCursor) _filter(item any) (filterdItem any, err error) {
-// 	if filter, ok := dc.ds[filterName]; ok {
-// 		ctx := cloneContext(dc.ctx)
-// 		filterdItem, err = filter.Invoke(ctx, filterName, []any{item, dc.index})
-// 	} else {
-// 		filterdItem = item
-// 	}
-// 	return
-// }
-
 func (dc *dataCursor) checkFilter(filter Functor, item any) (accepted bool, err error) {
 	var v any
 	var ok bool
 	ctx := cloneContext(dc.ctx)
-	if v, err = filter.Invoke(ctx, filterName, []any{item, dc.index}); err == nil && v != nil {
+	if v, err = filter.Invoke(ctx, FilterName, []any{item, dc.index}); err == nil && v != nil {
 		if accepted, ok = v.(bool); !ok {
 			accepted = true // NOTE: A non-boolean value that is not nil means the item has been accepted
 		}
 	}
-	
 	return
 }
+
 func (dc *dataCursor) mapItem(mapper Functor, item any) (mappedItem any, err error) {
 	ctx := cloneContext(dc.ctx)
-	mappedItem, err = mapper.Invoke(ctx, mapName, []any{item, dc.index});
+	mappedItem, err = mapper.Invoke(ctx, MapName, []any{item, dc.index})
 	return
 }
 
-func (dc *dataCursor) Next() (item any, err error) { // must return io.EOF after the last item
+func (dc *dataCursor) init() {
-	var accepted bool
+	if dc.initState {
-	if dc.resource != nil {
+		dc.initState = false
-		filter := dc.ds[filterName]
+		dc.Next()
-		mapper := dc.ds[mapName]
+	}
+}
 
-		for item == nil && err == nil {
+func (dc *dataCursor) Next() (current any, err error) { // must return io.EOF after the last item
+	if dc.initState {
+		dc.init()
+	} else if err = dc.lastErr; err != nil {
+		return
+	}
+	current = dc.current
+	if dc.resource != nil {
+		filter := dc.ds[FilterName]
+		mapper := dc.ds[MapName]
+		var item any
+		for item == nil && dc.lastErr == nil {
 			ctx := cloneContext(dc.ctx)
-			if item, err = dc.nextFunc.Invoke(ctx, nextName, []any{dc.resource}); err == nil {
-				if item == nil {
-					err = io.EOF
-				} else {
 			dc.index++
+			if item, dc.lastErr = dc.nextFunc.Invoke(ctx, NextName, []any{dc.resource, dc.index}); dc.lastErr == nil {
+				if item == nil {
+					dc.lastErr = io.EOF
+				} else {
+					accepted := true
 					if filter != nil {
-						if accepted, err = dc.checkFilter(filter, item); err != nil || !accepted {
+						if accepted, dc.lastErr = dc.checkFilter(filter, item); dc.lastErr != nil || !accepted {
 							item = nil
 						}
 					}
+					if accepted {
+						dc.count++
+					}
 					if item != nil && mapper != nil {
-						item, err = dc.mapItem(mapper, item)
+						item, dc.lastErr = dc.mapItem(mapper, item)
 					}
 				}
 			}
 			exportObjects(dc.ctx, ctx)
 		}
+		dc.current = item
+		if dc.lastErr != nil {
+			dc.index--
+			dc.Clean()
+		}
 	} else {
-		err = errInvalidDataSource()
+		dc.lastErr = errInvalidDataSource()
 	}
 	return
 }
 
 func (dc *dataCursor) Index() int {
-	return dc.index
+	return dc.index - 1
+}
+
+func (dc *dataCursor) Count() int {
+	return dc.count
 }

dict-type.go

@@ -18,7 +18,22 @@ func MakeDict() (dict *DictType) {
 	return
 }
 
+func NewDict(dictAny map[any]any) (dict *DictType) {
+	var d DictType
+	if dictAny != nil {
+		d = make(DictType, len(dictAny))
+		for i, item := range dictAny {
+			d[i] = item
+		}
+	} else {
+		d = make(DictType)
+	}
+	dict = &d
+	return
+}
+
 func newDict(dictAny map[any]*term) (dict *DictType) {
+	// TODO Change wi a call to NewDict()
 	var d DictType
 	if dictAny != nil {
 		d = make(DictType, len(dictAny))

import-utils.go

@@ -75,7 +75,11 @@ func isFile(filePath string) bool {
 }
 
 func searchAmongPath(filename string, dirList []string) (filePath string) {
+	var err error
 	for _, dir := range dirList {
+		if dir, err = ExpandPath(dir); err != nil {
+			continue
+		}
 		if fullPath := path.Join(dir, filename); isFile(fullPath) {
 			filePath = fullPath
 			break
@@ -90,6 +94,10 @@ func isPathRelative(filePath string) bool {
 }
 
 func makeFilepath(filename string, dirList []string) (filePath string, err error) {
+	if filename, err = ExpandPath(filename); err != nil {
+		return
+	}
+
 	if path.IsAbs(filename) || isPathRelative(filename) {
 		if isFile(filename) {
 			filePath = filename

iterator.go

@@ -12,15 +12,15 @@ import (
 // Operator names
 
 const (
-	initName    = "init"
+	InitName    = "init"
-	cleanName   = "clean"
+	CleanName   = "clean"
-	resetName   = "reset"
+	ResetName   = "reset"
-	nextName    = "next"
+	NextName    = "next"
-	currentName = "current"
+	CurrentName = "current"
-	indexName   = "index"
+	IndexName   = "index"
-	countName   = "count"
+	CountName   = "count"
-	filterName  = "filter"
+	FilterName  = "filter"
-	mapName     = "map"
+	MapName     = "map"
 )
 
 type Iterator interface {
@@ -28,6 +28,7 @@ type Iterator interface {
 	Next() (item any, err error) // must return io.EOF after the last item
 	Current() (item any, err error)
 	Index() int
+	Count() int
 }
 
 type ExtIterator interface {

list-iterator.go

@@ -90,21 +90,21 @@ func (it *ListIterator) TypeName() string {
 }
 
 func (it *ListIterator) HasOperation(name string) bool {
-	yes := name == nextName || name == resetName || name == indexName || name == countName || name == currentName
+	yes := name == NextName || name == ResetName || name == IndexName || name == CountName || name == CurrentName
 	return yes
 }
 
 func (it *ListIterator) CallOperation(name string, args []any) (v any, err error) {
 	switch name {
-	case nextName:
+	case NextName:
 		v, err = it.Next()
-	case resetName:
+	case ResetName:
 		v, err = it.Reset()
-	case indexName:
+	case IndexName:
 		v = int64(it.Index())
-	case currentName:
+	case CurrentName:
 		v, err = it.Current()
-	case countName:
+	case CountName:
 		v = it.count
 	default:
 		err = errNoOperation(name)
@@ -143,7 +143,12 @@ func (it *ListIterator) Index() int {
 	return it.index
 }
 
+func (it *ListIterator) Count() int {
+	return it.count
+}
+
 func (it *ListIterator) Reset() (bool, error) {
 	it.index = it.start - it.step
+	it.count = 0
 	return true, nil
 }

operand-iterator.go

@@ -66,8 +66,8 @@ func evalFirstChild(ctx ExprContext, iteratorTerm *term) (value any, err error)
 
 func getDataSourceDict(iteratorTerm *term, firstChildValue any) (ds map[string]Functor, err error) {
 	if dictAny, ok := firstChildValue.(*DictType); ok {
-		requiredFields := []string{currentName, nextName}
+		requiredFields := []string{NextName}
-		fieldsMask := 0b11
+		fieldsMask := 0b1
 		foundFields := 0
 		ds = make(map[string]Functor)
 		for keyAny, item := range *dictAny {
@@ -88,7 +88,6 @@ func getDataSourceDict(iteratorTerm *term, firstChildValue any) (ds map[string]F
 					missingFields = append(missingFields, field)
 				}
 			}
-//			err = fmt.Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
 			err = iteratorTerm.children[0].Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
 		}
 	}
@@ -108,9 +107,10 @@ func evalIterator(ctx ExprContext, opTerm *term) (v any, err error) {
 	}
 
 	if ds != nil {
-		dc := newDataCursor(ctx, ds)
+		var dc *dataCursor
-		if initFunc, exists := ds[initName]; exists && initFunc != nil {
+		if initFunc, exists := ds[InitName]; exists && initFunc != nil {
 			var args []any
+			var resource any
 			if len(opTerm.children) > 1 {
 				if args, err = evalTermArray(ctx, opTerm.children[1:]); err != nil {
 					return
@@ -119,18 +119,15 @@ func evalIterator(ctx ExprContext, opTerm *term) (v any, err error) {
 				args = []any{}
 			}
 
-			initCtx := dc.ctx.Clone()
+			initCtx := ctx.Clone()
-			if dc.resource, err = initFunc.Invoke(initCtx, initName, args); err != nil {
+			if resource, err = initFunc.Invoke(initCtx, InitName, args); err != nil {
 				return
 			}
-			exportObjects(dc.ctx, initCtx)
+			dcCtx := ctx.Clone()
+			exportObjects(dcCtx, initCtx)
+			dc = NewDataCursor(dcCtx, ds, resource)
 		}
 
-		dc.nextFunc = ds[nextName]
-		dc.currentFunc = ds[currentName]
-		dc.cleanFunc = ds[cleanName]
-		dc.resetFunc = ds[resetName]
-
 		v = dc
 	} else if list, ok := firstChildValue.(*ListType); ok {
 		var args []any

operator-length.go

@@ -30,16 +30,16 @@ func evalLength(ctx ExprContext, opTerm *term) (v any, err error) {
 		s, _ := childValue.(string)
 		v = int64(len(s))
 	} else if IsDict(childValue) {
-		// m, _ := childValue.(map[any]any)
 		m, _ := childValue.(*DictType)
 		v = int64(len(*m))
 	} else if it, ok := childValue.(Iterator); ok {
-		if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(countName) {
+		v = int64(it.Count())
-			count, _ := extIt.CallOperation(countName, nil)
+		// if extIt, ok := childValue.(ExtIterator); ok && extIt.HasOperation(CountName) {
-			v, _ = ToGoInt(count, "")
+		// 	count, _ := extIt.CallOperation(CountName, nil)
-		} else {
+		// 	v, _ = ToGoInt(count, "")
-			v = int64(it.Index() + 1)
+		// } else {
-		}
+		// 	v = int64(it.Index() + 1)
+		// }
 	} else {
 		err = opTerm.errIncompatibleType(childValue)
 	}

operator-plugin.go

@@ -4,10 +4,6 @@
 // operator-plugin.go
 package expr
 
-import (
-	"io"
-)
-
 //-------- plugin term
 
 func newPluginTerm(tk *Token) (inst *term) {
@@ -22,31 +18,13 @@ func newPluginTerm(tk *Token) (inst *term) {
 
 func evalPlugin(ctx ExprContext, opTerm *term) (v any, err error) {
 	var childValue any
-	var moduleSpec any
+	var count int
 
 	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
 		return
 	}
 
-	dirList := buildSearchDirList("plugin", ENV_EXPR_PLUGIN_PATH)
+	if count, err = importPluginFromSearchPath(childValue); err == nil {
-	count := 0
-	it := NewAnyIterator(childValue)
-	for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
-		if module, ok := moduleSpec.(string); ok {
-			if err = importPlugin(dirList, module); err != nil {
-				break
-			}
-			count++
-		} else {
-			err = opTerm.Errorf("expected string as item nr %d, got %s", it.Index()+1, TypeName(moduleSpec))
-			break
-		}
-	}
-	if err == io.EOF {
-		err = nil
-	}
-
-	if err == nil {
 		v = int64(count)
 	}
 	return

operator-post-inc.go

@@ -35,7 +35,39 @@ func evalPostInc(ctx ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
+// -------- post decrement term
+
+func newPostDecTerm(tk *Token) *term {
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: make([]*term, 0, 1),
+		position: posPostfix,
+		priority: priIncDec,
+		evalFunc: evalPostDec,
+	}
+}
+
+func evalPostDec(ctx ExprContext, opTerm *term) (v any, err error) {
+	var childValue any
+	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	/* if it, ok := childValue.(Iterator); ok {
+		v, err = it.Next()
+	} else  */if IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+		v = childValue
+		i, _ := childValue.(int64)
+		ctx.SetVar(opTerm.children[0].source(), i-1)
+	} else {
+		err = opTerm.errIncompatibleType(childValue)
+	}
+	return
+}
+
 // init
 func init() {
 	registerTermConstructor(SymDoublePlus, newPostIncTerm)
+	registerTermConstructor(SymDoubleMinus, newPostDecTerm)
 }

parser.go

@@ -18,6 +18,12 @@ func NewParser() (p *parser) {
 	return p
 }
 
+func (parser *parser) Next(scanner *scanner) (tk *Token) {
+	for tk = scanner.Next(); tk.IsSymbol(SymComment); tk = scanner.Next() {
+	}
+	return
+}
+
 func (parser *parser) parseFuncCall(scanner *scanner, allowVarRef bool, tk *Token) (tree *term, err error) {
 	args := make([]*term, 0, 10)
 	itemExpected := false
@@ -57,11 +63,11 @@ func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 	itemExpected := false
 	tk := scanner.Previous()
 	for lastSym != SymClosedRound && lastSym != SymEos {
-		tk = scanner.Next()
+		tk = parser.Next(scanner)
 		if tk.IsSymbol(SymIdentifier) {
 			param := newTerm(tk)
 			args = append(args, param)
-			tk = scanner.Next()
+			tk = parser.Next(scanner)
 			if tk.Sym == SymEqual {
 				var paramExpr *ast
 				defaultParamsStarted = true
@@ -86,7 +92,7 @@ func (parser *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 		err = tk.ErrorExpectedGot(")")
 	}
 	if err == nil {
-		tk = scanner.Next()
+		tk = parser.Next(scanner)
 		if tk.IsSymbol(SymOpenBrace) {
 			body, err = parser.parseGeneral(scanner, true, true, SymClosedBrace)
 		} else {
@@ -184,8 +190,8 @@ func (parser *parser) parseIterDef(scanner *scanner, allowVarRef bool) (subtree
 	return
 }
 
-func (parser *parser) parseDictKey(scanner *scanner, allowVarRef bool) (key any, err error) {
+func (parser *parser) parseDictKey(scanner *scanner) (key any, err error) {
-	tk := scanner.Next()
+	tk := parser.Next(scanner)
 	if tk.Sym == SymError {
 		err = tk.Error()
 		return
@@ -194,7 +200,7 @@ func (parser *parser) parseDictKey(scanner *scanner, allowVarRef bool) (key any,
 		return
 	}
 	if tk.Sym == SymInteger || tk.Sym == SymString {
-		tkSep := scanner.Next()
+		tkSep := parser.Next(scanner)
 		if tkSep.Sym != SymColon {
 			err = tkSep.ErrorExpectedGot(":")
 		} else {
@@ -213,7 +219,7 @@ func (parser *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtr
 	for lastSym != SymClosedBrace && lastSym != SymEos {
 		var subTree *ast
 		var key any
-		if key, err = parser.parseDictKey(scanner, allowVarRef); err != nil {
+		if key, err = parser.parseDictKey(scanner); err != nil {
 			break
 		} else if key == nil {
 			tk := scanner.Previous()
@@ -251,7 +257,7 @@ func (parser *parser) parseDictionary(scanner *scanner, allowVarRef bool) (subtr
 func (parser *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaultCase bool) (caseTerm *term, err error) {
 	var filterList *term
 	var caseExpr *ast
-	tk := scanner.Next()
+	tk := parser.Next(scanner)
 	startRow := tk.row
 	startCol := tk.col
 	if tk.Sym == SymOpenSquare {
@@ -262,7 +268,7 @@ func (parser *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defa
 		if filterList, err = parser.parseList(scanner, false, allowVarRef); err != nil {
 			return
 		}
-		tk = scanner.Next()
+		tk = parser.Next(scanner)
 		startRow = tk.row
 		startCol = tk.col
 	} else if !defaultCase {
@@ -299,7 +305,7 @@ func addSelectorCase(selectorTerm, caseTerm *term) {
 func (parser *parser) parseSelector(scanner *scanner, tree *ast, allowVarRef bool) (selectorTerm *term, err error) {
 	var caseTerm *term
 	tk := scanner.makeToken(SymSelector, '?')
-	if selectorTerm, err = tree.addToken2(tk); err != nil {
+	if selectorTerm, err = tree.addToken(tk); err != nil {
 		return
 	}
 
@@ -337,13 +343,14 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 	var selectorTerm *term = nil
 	var currentTerm *term = nil
 	var tk *Token
+
 	tree = NewAst()
 	firstToken := true
 	// lastSym := SymUnknown
-	for tk = scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); /*&& !areSymbolsOutOfCtx(tk, selectorTerm, SymColon, SymDoubleColon)*/ tk = scanner.Next() {
+	for tk = parser.Next(scanner); err == nil && tk != nil && !tk.IsTerm(termSymbols); /*&& !areSymbolsOutOfCtx(tk, selectorTerm, SymColon, SymDoubleColon)*/ tk = parser.Next(scanner) {
-		if tk.Sym == SymComment {
+		// if tk.Sym == SymComment {
-			continue
+		// 	continue
-		}
+		// }
 
 		if tk.Sym == SymSemiColon {
 			if allowForest {
@@ -409,7 +416,7 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 			}
 		case SymEqual:
 			// if err = checkPrevSymbol(lastSym, SymIdentifier, tk); err == nil {
-			currentTerm, err = tree.addToken2(tk)
+			currentTerm, err = tree.addToken(tk)
 			// }
 		case SymFuncDef:
 			var funcDefTerm *term
@@ -427,7 +434,7 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 			if tk.source[0] == '@' && !allowVarRef {
 				err = tk.Errorf("variable references are not allowed in top level expressions: %q", tk.source)
 			} else {
-				currentTerm, err = tree.addToken2(tk)
+				currentTerm, err = tree.addToken(tk)
 			}
 		case SymQuestion:
 			if selectorTerm, err = parser.parseSelector(scanner, tree, allowVarRef); err == nil {
@@ -444,14 +451,16 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 					}
 				}
 			} else {
-				currentTerm, err = tree.addToken2(tk)
+				currentTerm, err = tree.addToken(tk)
 			}
 			if tk.IsSymbol(SymColon) {
 				// Colon outside a selector term acts like a separator
 				firstToken = true
 			}
+		case SymPlusEqual, SymMinusEqual, SymStarEqual:
+			currentTerm, err = parser.expandOpAssign(scanner, tree, tk, allowVarRef)
 		default:
-			currentTerm, err = tree.addToken2(tk)
+			currentTerm, err = tree.addToken(tk)
 		}
 
 		if currentTerm != nil && currentTerm.tk.Sym != SymSelector && currentTerm.parent != nil && currentTerm.parent.tk.Sym != SymSelector {
@@ -460,6 +469,7 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 		}
 		// lastSym = tk.Sym
 	}
+
 	if err == nil {
 		err = tk.Error()
 	}
@@ -472,3 +482,49 @@ func (parser *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarR
 // 	}
 // 	return
 // }
+
+func (parser *parser) expandOpAssign(scanner * scanner, tree *ast, tk *Token, allowVarRef bool) (t *term, err error) {
+	var opSym Symbol
+	var opString string
+
+	if tree.root != nil {
+		switch tk.Sym {
+		case SymPlusEqual:
+			opString = "+"
+			opSym = SymPlus
+		case SymMinusEqual:
+			opString = "-"
+			opSym = SymMinus
+		case SymStarEqual:
+			opString = "*"
+			opSym = SymStar
+		default:
+			err = tk.Errorf("unsopported operator %q", tk.source)
+			return
+		}
+		leftExpr := tree.root.Clone()
+		leftExpr.setParent(nil)
+		if t, err = tree.addToken(NewToken(tk.row, tk.col, SymEqual, "=")); err == nil {
+			t = leftExpr
+			if err = tree.addTerm(leftExpr); err == nil {
+				if t, err = tree.addToken(NewToken(tk.row, tk.col, opSym, opString)); err == nil {
+
+					var subTree *ast
+					if subTree, err = parser.parseGeneral(scanner, false, allowVarRef, SymSemiColon, SymClosedRound, SymClosedBrace, SymClosedSquare); err == nil {
+						if scanner.Previous().IsOneOfA(SymSemiColon, SymClosedRound, SymClosedBrace, SymClosedSquare) {
+							if err = scanner.UnreadToken(); err != nil {
+								return
+							}
+						}
+						subTree.root.priority = priValue
+						err = tree.addTerm(newExprTerm(subTree.root))
+						t = subTree.root
+					}
+				}
+			}
+		}
+	} else {
+		err = tk.Errorf("left operand of %q must be a variable or a variable expression", tk)
+	}
+	return
+}

plugins.go

@@ -6,6 +6,7 @@ package expr
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"plugin"
 	"strings"
@@ -90,6 +91,29 @@ func importPlugin( /*ctx ExprContext,*/ dirList []string, name string) (err erro
 	return
 }
 
+func importPluginFromSearchPath(name any) (count int, err error) {
+	var moduleSpec any
+
+	dirList := buildSearchDirList("plugin", ENV_EXPR_PLUGIN_PATH)
+	count = 0
+	it := NewAnyIterator(name)
+	for moduleSpec, err = it.Next(); err == nil; moduleSpec, err = it.Next() {
+		if module, ok := moduleSpec.(string); ok {
+			if err = importPlugin(dirList, module); err != nil {
+				break
+			}
+			count++
+		} else {
+			err = fmt.Errorf("expected string as item nr %d, got %s", it.Index()+1, TypeName(moduleSpec))
+			break
+		}
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	return
+}
+
 func loadModules(dirList []string, moduleNames []string) (err error) {
 	for _, name := range moduleNames {
 		if err1 := importPlugin(dirList, name); err1 != nil {

scanner.go

@@ -16,6 +16,7 @@ import (
 type scanner struct {
 	current      *Token
 	prev         *Token
+	stage        *Token
 	stream       *bufio.Reader
 	row          int
 	column       int
@@ -74,6 +75,16 @@ func (scanner *scanner) unreadChar() (err error) {
 	return
 }
 
+func (scanner *scanner) UnreadToken() (err error) {
+	if scanner.stage == nil {
+		scanner.stage = scanner.current
+		scanner.current = scanner.prev
+	} else {
+		err = fmt.Errorf("staging already present, currently one level only of staging is allowed")
+	}
+	return
+}
+
 func (scanner *scanner) lastPos() (r, c int) {
 	if scanner.prev != nil {
 		r = scanner.prev.row
@@ -89,7 +100,12 @@ func (scanner *scanner) Previous() *Token {
 func (scanner *scanner) Next() (tk *Token) {
 	scanner.prev = scanner.current
 	tk = scanner.current
+	if scanner.stage != nil {
+		scanner.current = scanner.stage
+		scanner.stage = nil
+	} else {
 		scanner.current = scanner.fetchNextToken()
+	}
 	return tk
 }
 
@@ -124,6 +140,8 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 				tk = scanner.moveOn(SymDoubleStar, ch, next)
 				// } else if next == '/' {
 				// 	tk = self.moveOn(SymClosedComment, ch, next)
+			} else if next, _ = scanner.peek(); next == '=' {
+				tk = scanner.moveOn(SymStarEqual, ch, next)
 			} else {
 				tk = scanner.makeToken(SymStar, ch)
 			}
@@ -269,11 +287,11 @@ func (scanner *scanner) fetchNextToken() (tk *Token) {
 				tk = scanner.makeToken(SymDollar, ch)
 			}
 		case '(':
-//			if next, _ := scanner.peek(); next == ')' {
+			//			if next, _ := scanner.peek(); next == ')' {
-//				tk = scanner.moveOn(SymOpenClosedRound, ch, next)
+			//				tk = scanner.moveOn(SymOpenClosedRound, ch, next)
-//			} else {
+			//			} else {
 			tk = scanner.makeToken(SymOpenRound, ch)
-//			}
+			//			}
 		case ')':
 			tk = scanner.makeToken(SymClosedRound, ch)
 		case '[':

symbol.go

@@ -68,6 +68,7 @@ const (
 	SymDoubleDollar                      //  57: '$$'
 	SymDoubleDot                         //  58: '..'
 	SymTripleDot                         //  59: '...'
+	SymStarEqual                         //  60: '*='
 	SymChangeSign
 	SymUnchangeSign
 	SymIdentifier

t_ast_test.go

@@ -47,7 +47,7 @@ func TestAddUnknownTokens(t *testing.T) {
 	wantErr := errors.New(`unexpected token "%"`)
 
 	tree := NewAst()
-	if gotErr := tree.addToken(tk0); gotErr != nil && gotErr.Error() != wantErr.Error() {
+	if _, gotErr := tree.addToken(tk0); gotErr != nil && gotErr.Error() != wantErr.Error() {
 		t.Errorf("err: got <%v>, want <%v>", gotErr, wantErr)
 	}
 }

t_builtin-iterator_test.go

@@ -14,7 +14,7 @@ func TestFuncRun(t *testing.T) {
 	inputs := []inputType{
 		/*   1 */ {`builtin "iterator"; it=$(1,2,3); run(it)`, nil, nil},
 		/*   2 */ {`builtin "iterator"; run($(1,2,3), func(index,item){item+10})`, nil, nil},
-		/*   3 */ {`builtin "iterator"; run($(1,2,3), func(index,item){it_status=it_status+item; true}, {"it_status":0})`, int64(6), nil},
+		/*   3 */ {`builtin "iterator"; run($(1,2,3), func(index,item){status=status+item; true}, {"status":0})`, int64(6), nil},
 		/*   4 */ {`builtin ["iterator", "fmt"]; run($(1,2,3), func(index,item){println(item+10)})`, nil, nil},
 		/*   5 */ {`builtin "iterator"; run(nil)`, nil, `paramter "iterator" must be an iterator, passed <nil> [nil]`},
 		/*   6 */ {`builtin "iterator"; run($(1,2,3), nil)`, nil, `paramter "operator" must be a function, passed <nil> [nil]`},
@@ -26,25 +26,3 @@ func TestFuncRun(t *testing.T) {
 	//runTestSuiteSpec(t, section, inputs, 3)
 	runTestSuite(t, section, inputs)
 }
-
-// func TestFmt(t *testing.T) {
-// 	section := "Builtin-Fmt"
-
-// 	text := "ciao mondo"
-// 	inputs := []inputType{
-// 		/*   1 */ {fmt.Sprintf(`println("%s")`, text), int64(11), nil},
-// 	}
-
-// 	// t.Setenv("EXPR_PATH", ".")
-
-// 	var b bytes.Buffer
-// 	ctx := NewSimpleStore()
-// 	currentStdout := SetCtrl(ctx, ControlStdout, &b)
-
-// 	runCtxTestSuite(t, ctx, section, inputs)
-
-// 	SetCtrl(ctx, ControlStdout, currentStdout)
-// 	if b.String() != text+"\n" {
-// 		t.Errorf("println(): Got: %q, Want: %q", b.String(), text+"\n")
-// 	}
-// }

t_common_test.go

@@ -97,7 +97,7 @@ func doTest(t *testing.T, ctx ExprContext, section string, input *inputType, cou
 
 	if gotErr != wantErr {
 		if wantErr == nil || gotErr == nil || (gotErr.Error() != wantErr.Error()) {
-			t.Errorf("%d: %q -> got-err = <%v>, expected-err = <%v>", count, input.source, gotErr, wantErr)
+			t.Errorf("%d: %s -> got-err = <%v>, expected-err = <%v>", count, input.source, gotErr, wantErr)
 			good = false
 		}
 	}

t_dict_test.go

@@ -22,7 +22,7 @@ func TestDictParser(t *testing.T) {
 
 	inputs := []inputType{
 		/*  1 */ {`{}`, map[any]any{}, nil},
-		/*  2 */ {`{123}`, nil, errors.New(`[1:6] expected ":", got "}"`)},
+		/*  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"}[3]`, "three", nil},
 		/*  5 */ {`#{1:"one",2:"two",3:"three"}`, int64(3), nil},
@@ -32,6 +32,11 @@ func TestDictParser(t *testing.T) {
 		/*  9 */ {`D={"a":1, "b":2}; D["z"]=9; D`, map[any]any{"z": 9, "a": 1, "b": 2}, nil},
 		/* 10 */ {`D={"a":1, "b":2}; D[nil]=9`, nil, errors.New(`[1:21] index/key is nil`)},
 		/* 11 */ {`D={"a":1, "b":2}; D["a"]`, int64(1), nil},
+		/* 12 */ {`m={
+			"a":1,
+			//"b":2,
+			"c":3
+			}`, map[any]any{"a": 1, "c": 3}, nil},
 		}
 
 	succeeded := 0

t_expr_test.go

@@ -17,10 +17,21 @@ func TestExpr(t *testing.T) {
 		/*   3 */ {`builtin "os.file"; f=fileOpen("test-file.txt"); line=fileReadText(f); fileClose(f); line`, "uno", nil},
 		/*   4 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
 		/*   5 */ {`1 ? {1} : [1+0] {3*(1+1)}`, int64(6), nil},
-		/*   6 */ {`
+		/*   6 */ {`a=3; a+=1`, int64(4), nil},
+		/*   7 */ {`a=3; a-=1`, int64(2), nil},
+		/*   8 */ {`a=3; a*=2`, int64(6), nil},
+		/*   9 */ {`v=[10,20,30]; v[0]+=1; v[0]`, int64(11), nil},
+		/*  10 */ {`r={"a":10}; r["a"]+=1; r["a"]`, int64(11), nil},
+		/*  11 */ {`a=3; a/=2`, nil, `[1:8] left operand of "=" must be a variable or a collection's item`},
+		/*  12 */ {`*=2`, nil, `[1:2] left operand of "*=" must be a variable or a variable expression`},
+		/*  13 */ {`a=3; a*=2+1; a`, int64(9), nil},
+		/*  14 */ {`a=3; (a*=2)+1; a`, int64(6), nil},
+		/*  15 */ {`a=3; a*=2)+1; a`, nil, `[1:11] unexpected token ")"`},
+		/*  16 */ {`v=[2]; a=1; v[a-=1]=5; v[0]`, int64(5), nil},
+		/*  17 */ {`
 		ds={
-			"init":func(end){@end=end; @current=0 but true},
+			"init":func(@end){@current=0 but true},
-			"current":func(){current},
+			//"current":func(){current},
 			"next":func(){
 				((next=current+1) <= end) ? [true] {@current=next but current} :: {nil}
 			}
@@ -32,6 +43,6 @@ func TestExpr(t *testing.T) {
 	}
 	// t.Setenv("EXPR_PATH", ".")
 
-	// parserTestSpec(t, section, inputs, 3)
+	//runTestSuiteSpec(t, section, inputs, 9)
 	runTestSuite(t, section, inputs)
 }

t_funcs_test.go

@@ -27,7 +27,7 @@ func TestFuncs(t *testing.T) {
 		/*  14 */ {`two=func(){2}; two(123)`, nil, `two(): too much params -- expected 0, got 1`},
 		/*  15 */ {`f=func(x,n=2){x+n}; f(3)`, int64(5), nil},
 		/*  16 */ {`f=func(x,n=2,y){x+n}`, nil, `[1:16] can't mix default and non-default parameters`},
-		/*  17 */ {`f=func(x,n){1}; f(3,4,)`, nil, `[1:24] expected "function-param-value", got ")"`},
+		/*  17 */ {`f=func(x,n){1}; f(3,4,)`, nil, "[1:24] expected `function-param-value`, got `)`"},
 		/*  18 */ {`factory=func(base){func(){@base=base+1}}; inc10=factory(10); inc5=factory(5); inc10(); inc5(); inc10()`, int64(12), nil},
 		/*  19 */ {`f=func(a,y=1,z="sos"){}; string(f)`, `f(a, y=1, z="sos"):any{}`, nil},
 //		/*  20 */ {`a=[func(){3}]; a[0]()`, int64(3), nil},

t_iter-list_test.go

@@ -15,7 +15,7 @@ func TestNewListIterator(t *testing.T) {
 	if item, err := it.Next(); err != nil {
 		t.Errorf("error: %v", err)
 	} else if item != "b" {
-		t.Errorf("expcted %q, got %q", "b", item)
+		t.Errorf("expected %q, got %q", "b", item)
 	} else {
 		t.Logf("Next: %v", item)
 	}
@@ -27,7 +27,7 @@ func TestNewListIterator2(t *testing.T) {
 	if item, err := it.Next(); err != nil {
 		t.Errorf("error: %v", err)
 	} else if item != "d" {
-		t.Errorf("expcted %q, got %q", "d", item)
+		t.Errorf("expected %q, got %q", "d", item)
 	} else {
 		t.Logf("Next: %v", item)
 	}
@@ -39,7 +39,7 @@ func TestNewListIterator3(t *testing.T) {
 	if item, err := it.Next(); err != nil {
 		t.Errorf("error: %v", err)
 	} else if item != "b" {
-		t.Errorf("expcted %q, got %q", "b", item)
+		t.Errorf("expected %q, got %q", "b", item)
 	} else {
 		t.Logf("Next: %v", item)
 	}
@@ -51,7 +51,7 @@ func TestNewIterList2(t *testing.T) {
 	if item, err := it.Next(); err != nil {
 		t.Errorf("error: %v", err)
 	} else if item != "a" {
-		t.Errorf("expcted %q, got %q", "a", item)
+		t.Errorf("expected %q, got %q", "a", item)
 	} else {
 		t.Logf("Next: %v", item)
 	}
@@ -63,7 +63,7 @@ func TestNewIterList3(t *testing.T) {
 	if item, err := it.Next(); err != nil {
 		t.Errorf("error: %v", err)
 	} else if item != "a" {
-		t.Errorf("expcted %q, got %q", "a", item)
+		t.Errorf("expected %q, got %q", "a", item)
 	} else {
 		t.Logf("Next: %v", item)
 	}
@@ -83,7 +83,7 @@ func TestNewIterList5(t *testing.T) {
 	if item, err := it.Next(); err != nil {
 		t.Errorf("error: %v", err)
 	} else if item != "123" {
-		t.Errorf("expcted %q, got %q", "123", item)
+		t.Errorf("expected %q, got %q", "123", item)
 	} else {
 		t.Logf("Next: %v", item)
 	}
@@ -96,7 +96,7 @@ func TestNewIterList6(t *testing.T) {
 	if item, err := it.Next(); err != nil {
 		t.Errorf("error: %v", err)
 	} else if item != "a" {
-		t.Errorf("expcted %q, got %q", "a", item)
+		t.Errorf("expected %q, got %q", "a", item)
 	} else {
 		t.Logf("Next: %v", item)
 	}

t_iterator_test.go

@@ -11,7 +11,7 @@ func TestIteratorParser(t *testing.T) {
 	inputs := []inputType{
 		/*   1 */ {`include "test-resources/iterator.expr"; it=$(ds,3); ^it`, int64(0), nil},
 		/*   2 */ {`include "test-resources/iterator.expr"; it=$(ds,3); it++; it++`, int64(1), nil},
-		/*   3 */ {`include "test-resources/iterator.expr"; it=$(ds,3); it++; it++; #it`, int64(2), nil},
+		/*   3 */ {`include "test-resources/iterator.expr"; it=$(ds,3); it++; it++; #it`, int64(3), nil},
 		/*   4 */ {`include "test-resources/iterator.expr"; it=$(ds,3); it++; it++; it.reset; ^it`, int64(0), nil},
 		/*   5 */ {`builtin "math.arith"; include "test-resources/iterator.expr"; it=$(ds,3); add(it)`, int64(6), nil},
 		/*   6 */ {`builtin "math.arith"; include "test-resources/iterator.expr"; it=$(ds,3); mul(it)`, int64(0), nil},
@@ -27,6 +27,6 @@ func TestIteratorParser(t *testing.T) {
 		/*  16 */ {`include "test-resources/filter.expr"; it=$(ds,10); it++`, int64(2), nil},
 	}
 
-	//runTestSuiteSpec(t, section, inputs, 4)
+	//runTestSuiteSpec(t, section, inputs, 3)
 	runTestSuite(t, section, inputs)
 }

t_parser_test.go

@@ -128,8 +128,8 @@ func TestGeneralParser(t *testing.T) {
 		/* 114 */ {`2 + 1 ? {"a"} : {"b"} * 3`, "2bbb", nil},
 		/* 115 */ {`nil`, nil, nil},
 		/* 116 */ {`null`, nil, `undefined variable or function "null"`},
-		/* 117 */ {`{"key"}`, nil, `[1:8] expected ":", got "}"`},
+		/* 117 */ {`{"key"}`, nil, "[1:8] expected `:`, got `}`"},
-		/* 118 */ {`{"key":}`, nil, `[1:9] expected "dictionary-value", got "}"`},
+		/* 118 */ {`{"key":}`, nil, "[1:9] expected `dictionary-value`, got `}`"},
 		/* 119 */ {`{}`, &DictType{}, nil},
 		/* 120 */ {`v=10; v++; v`, int64(11), nil},
 		/* 121 */ {`1+1|2+0.5`, float64(2), nil},
@@ -144,6 +144,6 @@ func TestGeneralParser(t *testing.T) {
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
-	// parserTestSpec(t, section, inputs, 102)
+	//runTestSuiteSpec(t, section, inputs, 130)
 	runTestSuite(t, section, inputs)
 }

t_plugin_test.go

@@ -9,8 +9,15 @@ import (
 )
 
 func _TestImportPlugin(t *testing.T) {
-	if err := importPlugin([]string{"test-resources"}, "json"); err != nil {
+	t.Setenv("PLUGINS", "${HOME}/go/src/git.portale-stac.it/go")
-		t.Errorf("importPlugin() failed: %v", err)
+	t.Setenv("EXPR_PLUGIN_PATH","${PLUGINS}/expr-json-plugin:${PLUGINS}/expr-csv-plugin")
+
+	gotCount, gotErr := importPluginFromSearchPath("json")
+	if gotCount != 1 {
+		t.Errorf("Import count: got=%d, want=1", gotCount)
+	}
+	if gotErr != nil {
+		t.Errorf("importPlugin() failed: %v", gotErr)
 	}
 }
 

term.go

@@ -53,6 +53,25 @@ type term struct {
 	evalFunc evalFuncType
 }
 
+func (s *term) Clone() (d *term) {
+	var children []*term
+	if s.children != nil {
+		children = make([]*term, len(s.children))
+		for i, c := range s.children {
+			children[i] = c.Clone()
+		}
+	}
+	d = &term{
+		tk: *s.tk.Clone(),
+		parent: s.parent,
+		children: children,
+		position: s.position,
+		priority: s.priority,
+		evalFunc: s.evalFunc,
+	}
+	return
+}
+
 func (term *term) String() string {
 	var sb strings.Builder
 	term.toString(&sb)

token.go

@@ -28,7 +28,7 @@ func (tk *Token) DevString() string {
 func (tk *Token) String() string {
 	if tk.Value != nil {
 		if s, ok := tk.Value.(string); ok {
-			return fmt.Sprintf("%q", s)
+			return s //fmt.Sprintf("%q", s)
 		} else {
 			return fmt.Sprintf("%v", tk.Value)
 		}
@@ -51,6 +51,10 @@ func NewErrorToken(row, col int, err error) *Token {
 	return NewValueToken(row, col, SymError, fmt.Sprintf("[%d:%d]", row, col), err)
 }
 
+func (tk *Token) Clone() (c *Token) {
+	return NewValueToken(tk.row, tk.col, tk.Sym, tk.source, tk.Value)
+}
+
 func (tk *Token) IsEos() bool {
 	return tk.Sym == SymEos
 }
@@ -67,6 +71,10 @@ func (tk *Token) IsOneOf(termSymbols []Symbol) bool {
 	return termSymbols != nil && slices.Index(termSymbols, tk.Sym) >= 0
 }
 
+func (tk *Token) IsOneOfA(termSymbols ...Symbol) bool {
+	return slices.Index(termSymbols, tk.Sym) >= 0
+}
+
 func (tk *Token) IsSymbol(sym Symbol) bool {
 	return tk.Sym == sym
 }
@@ -91,11 +99,11 @@ func (tk *Token) Errors(msg string) (err error) {
 }
 
 func (tk *Token) ErrorExpectedGot(symbol string) (err error) {
-	err = fmt.Errorf("[%d:%d] expected %q, got %q", tk.row, tk.col, symbol, tk)
+	err = fmt.Errorf("[%d:%d] expected `%s`, got `%s`", tk.row, tk.col, symbol, tk)
 	return
 }
 
 func (tk *Token) ErrorExpectedGotString(symbol, got string) (err error) {
-	err = fmt.Errorf("[%d:%d] expected %q, got %q", tk.row, tk.col, symbol, got)
+	err = fmt.Errorf("[%d:%d] expected `%s`, got `%s`", tk.row, tk.col, symbol, got)
 	return
 }

utils.go

@@ -6,7 +6,11 @@ package expr
 
 import (
 	"fmt"
+	"os"
+	"os/user"
+	"path"
 	"reflect"
+	"strings"
 )
 
 func IsString(v any) (ok bool) {
@@ -221,3 +225,37 @@ func ForAll[T, V any](ts []T, fn func(T) V) []V {
 	}
 	return result
 }
+
+func ExpandPath(sourcePath string) (expandedPath string, err error) {
+	for expandedPath = os.ExpandEnv(sourcePath); expandedPath != sourcePath; expandedPath = os.ExpandEnv(sourcePath) {
+		sourcePath = expandedPath
+	}
+
+	if strings.HasPrefix(sourcePath, "~") {
+		var home, userName, remainder string
+
+		slashPos := strings.IndexRune(sourcePath, '/')
+		if slashPos > 0 {
+			userName = sourcePath[1:slashPos]
+			remainder = sourcePath[slashPos:]
+		} else {
+			userName = sourcePath[1:]
+		}
+
+		if len(userName) == 0 {
+			home, err = os.UserHomeDir()
+			if err != nil {
+				return
+			}
+		} else {
+			var userInfo *user.User
+			userInfo, err = user.Lookup(userName)
+			if err != nil {
+				return
+			}
+			home = userInfo.HomeDir
+		}
+		expandedPath = path.Join(home, remainder)
+	}
+	return
+}