diff --git a/operand-iterator.go b/operand-iterator.go
index 533abba..bb9b883 100644
--- a/operand-iterator.go
+++ b/operand-iterator.go
@@ -5,28 +5,27 @@
 package expr
 
 import (
-	"fmt"
 	"slices"
 	"strings"
 )
 
 // -------- iterator term
 
-func newDsIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
-	tk.Sym = SymIterator
+// func newDsIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
+// 	tk.Sym = SymIterator
 
-	children := make([]*term, 0, 1+len(args))
-	children = append(children, dsTerm)
-	children = append(children, args...)
-	return &term{
-		tk:       *tk,
-		parent:   nil,
-		children: children,
-		position: posLeaf,
-		priority: priValue,
-		evalFunc: evalIterator,
-	}
-}
+// 	children := make([]*term, 0, 1+len(args))
+// 	children = append(children, dsTerm)
+// 	children = append(children, args...)
+// 	return &term{
+// 		tk:       *tk,
+// 		parent:   nil,
+// 		children: children,
+// 		position: posLeaf,
+// 		priority: priValue,
+// 		evalFunc: evalIterator,
+// 	}
+// }
 
 func newIteratorTerm(tk *Token, args []*term) *term {
 	tk.Sym = SymIterator
@@ -42,9 +41,9 @@ func newIteratorTerm(tk *Token, args []*term) *term {
 
 // -------- eval iterator
 
-func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
-	values = make([]any, len(a))
-	for i, t := range a {
+func evalTermArray(ctx ExprContext, terms []*term) (values []any, err error) {
+	values = make([]any, len(terms))
+	for i, t := range terms {
 		var value any
 		if value, err = t.compute(ctx); err == nil {
 			values[i] = value
@@ -55,18 +54,17 @@ func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
 	return
 }
 
-func evalFirstChild(ctx ExprContext, self *term) (value any, err error) {
-	if len(self.children) < 1 || self.children[0] == nil {
-		err = self.Errorf("missing the data-source parameter")
+func evalFirstChild(ctx ExprContext, iteratorTerm *term) (value any, err error) {
+	if len(iteratorTerm.children) < 1 || iteratorTerm.children[0] == nil {
+		err = iteratorTerm.Errorf("missing the data-source parameter")
 		return
 	}
 
-	value, err = self.children[0].compute(ctx)
+	value, err = iteratorTerm.children[0].compute(ctx)
 	return
 }
 
-func getDataSourceDict(ctx ExprContext, self *term, firstChildValue any) (ds map[string]Functor, err error) {
-	// if dictAny, ok := firstChildValue.(map[any]any); ok {
+func getDataSourceDict(iteratorTerm *term, firstChildValue any) (ds map[string]Functor, err error) {
 	if dictAny, ok := firstChildValue.(*DictType); ok {
 		requiredFields := []string{currentName, nextName}
 		fieldsMask := 0b11
@@ -74,7 +72,6 @@ func getDataSourceDict(ctx ExprContext, self *term, firstChildValue any) (ds map
 		ds = make(map[string]Functor)
 		for keyAny, item := range *dictAny {
 			if key, ok := keyAny.(string); ok {
-				//if functor, ok := item.(*funcDefFunctor); ok {
 				if functor, ok := item.(Functor); ok {
 					ds[key] = functor
 					if index := slices.Index(requiredFields, key); index >= 0 {
@@ -91,21 +88,22 @@ func getDataSourceDict(ctx ExprContext, self *term, firstChildValue any) (ds map
 					missingFields = append(missingFields, field)
 				}
 			}
-			err = fmt.Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
+//			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, ", "))
 		}
 	}
 	return
 }
 
-func evalIterator(ctx ExprContext, self *term) (v any, err error) {
+func evalIterator(ctx ExprContext, iteratorTerm *term) (v any, err error) {
 	var firstChildValue any
 	var ds map[string]Functor
 
-	if firstChildValue, err = evalFirstChild(ctx, self); err != nil {
+	if firstChildValue, err = evalFirstChild(ctx, iteratorTerm); err != nil {
 		return
 	}
 
-	if ds, err = getDataSourceDict(ctx, self, firstChildValue); err != nil {
+	if ds, err = getDataSourceDict(iteratorTerm, firstChildValue); err != nil {
 		return
 	}
 
@@ -113,8 +111,8 @@ func evalIterator(ctx ExprContext, self *term) (v any, err error) {
 		dc := newDataCursor(ctx, ds)
 		if initFunc, exists := ds[initName]; exists && initFunc != nil {
 			var args []any
-			if len(self.children) > 1 {
-				if args, err = evalTermArray(ctx, self.children[1:]); err != nil {
+			if len(iteratorTerm.children) > 1 {
+				if args, err = evalTermArray(ctx, iteratorTerm.children[1:]); err != nil {
 					return
 				}
 			} else {
@@ -128,20 +126,20 @@ func evalIterator(ctx ExprContext, self *term) (v any, err error) {
 			exportObjects(dc.ctx, initCtx)
 		}
 
-		dc.nextFunc, _ = ds[nextName]
-		dc.currentFunc, _ = ds[currentName]
-		dc.cleanFunc, _ = ds[cleanName]
-		dc.resetFunc, _ = ds[resetName]
+		dc.nextFunc = ds[nextName]
+		dc.currentFunc = ds[currentName]
+		dc.cleanFunc = ds[cleanName]
+		dc.resetFunc = ds[resetName]
 
 		v = dc
 	} else if list, ok := firstChildValue.(*ListType); ok {
 		var args []any
-		if args, err = evalSibling(ctx, self.children, nil); err == nil {
+		if args, err = evalSibling(ctx, iteratorTerm.children, nil); err == nil {
 			v = NewListIterator(list, args)
 		}
 	} else {
 		var list []any
-		if list, err = evalSibling(ctx, self.children, firstChildValue); err == nil {
+		if list, err = evalSibling(ctx, iteratorTerm.children, firstChildValue); err == nil {
 			v = NewArrayIterator(list)
 		}
 	}