diff --git a/dict_test.go b/dict_test.go
index bd93bab..f69d509 100644
--- a/dict_test.go
+++ b/dict_test.go
@@ -102,3 +102,49 @@ func TestDictParser(t *testing.T) {
 	}
 	t.Logf("%s -- test count: %d, succeeded: %d, failed: %d", section, len(inputs), succeeded, failed)
 }
+
+func TestDictToStringMultiLine(t *testing.T) {
+	var good bool
+	section := "dict-ToString-ML"
+	want := `{
+	"first": 1
+}`
+	args := map[any]*term{
+		"first": newLiteralTerm(NewValueToken(0, 0, SymInteger, "1", 1)),
+	}
+	dict := newDict(args)
+	got := dict.ToString(MultiLine)
+	// fmt.Printf("got=%q\n", got)
+
+	if good = got == want; !good {
+		t.Errorf("ToString(MultiLine): got = %q, want %q", got, want)
+	}
+
+	if good {
+		t.Logf("%s -- succeeded", section)
+	} else {
+		t.Logf("%s -- failed", section)
+	}
+}
+
+func TestDictToString(t *testing.T) {
+	var good bool
+	section := "dict-ToString-SL"
+	want := `{"first": 1}`
+	args := map[any]*term{
+		"first": newLiteralTerm(NewValueToken(0, 0, SymInteger, "1", 1)),
+	}
+	dict := newDict(args)
+	got := dict.ToString(0)
+	// fmt.Printf("got=%q\n", got)
+
+	if good = got == want; !good {
+		t.Errorf("ToString(0): got = %q, want %q", got, want)
+	}
+
+	if good {
+		t.Logf("%s -- succeeded", section)
+	} else {
+		t.Logf("%s -- failed", section)
+	}
+}
diff --git a/expr_test.go b/expr_test.go
index fee2133..84536a1 100644
--- a/expr_test.go
+++ b/expr_test.go
@@ -22,7 +22,7 @@ func TestExpr(t *testing.T) {
 		/*   3 */ {`f=openFile("test-file.txt"); line=readFile(f); closeFile(f); line`, "uno", nil},
 		/*   4 */ {`mynot=func(v){int(v)?{true}::{false}}; mynot(0)`, true, nil},
 		/*   5 */ {`1 ? {1} : [1+0] {3*(1+1)}`, int64(6), nil},
-		/*   10 */ {`
+		/*   6 */ {`
 		ds={
 			"init":func(end){@end=end; @current=0 but true},
 			"current":func(){current},
diff --git a/operand-dict.go b/operand-dict.go
index ba1f6f0..2ff04a4 100644
--- a/operand-dict.go
+++ b/operand-dict.go
@@ -12,18 +12,24 @@ import (
 
 type DictType map[any]any
 
-func newDict(dictAny []any) (dict *DictType) {
+func newDict(dictAny map[any]*term) (dict *DictType) {
+	var d DictType
 	if dictAny != nil {
-		d := make(DictType, len(dictAny))
+		d = make(DictType, len(dictAny))
 		for i, item := range dictAny {
 			d[i] = item
 		}
-		dict = &d
+	} else {
+		d = make(DictType)
 	}
+	dict = &d
 	return
 }
 
 func (dict *DictType) toMultiLine(sb *strings.Builder, indent int) {
+	sb.WriteString(strings.Repeat("\t", indent))
+	sb.WriteString("{\n")
+
 	first := true
 	for name, value := range *dict {
 		if first {
@@ -35,13 +41,13 @@ func (dict *DictType) toMultiLine(sb *strings.Builder, indent int) {
 
 		sb.WriteString(strings.Repeat("\t", indent+1))
 		if key, ok := name.(string); ok {
-			sb.WriteString(key)
+			sb.WriteString(string('"') + key + string('"'))
 		} else {
 			sb.WriteString(fmt.Sprintf("%v", name))
 		}
 		sb.WriteString(": ")
 		if f, ok := value.(Formatter); ok {
-			sb.WriteString(f.ToString(0))
+			sb.WriteString(f.ToString(MultiLine))
 		} else if _, ok = value.(Functor); ok {
 			sb.WriteString("func(){}")
 		} else {
@@ -49,18 +55,42 @@ func (dict *DictType) toMultiLine(sb *strings.Builder, indent int) {
 		}
 	}
 	sb.WriteString(strings.Repeat("\t", indent))
-	sb.WriteString("\n}\n")
+	sb.WriteString("\n}")
 }
 
 func (dict *DictType) ToString(opt FmtOpt) string {
 	var sb strings.Builder
 	if opt&MultiLine != 0 {
 		dict.toMultiLine(&sb, 0)
+	} else {
+		sb.WriteByte('{')
+		first := true
+		for key, value := range *dict {
+			if first {
+				first = false
+			} else {
+				sb.WriteString(", ")
+			}
+			if s, ok := key.(string); ok {
+				sb.WriteString(string('"') + s + string('"'))
+			} else {
+				sb.WriteString(fmt.Sprintf("%v", key))
+			}
+			sb.WriteString(": ")
+			if formatter, ok := value.(Formatter); ok {
+				sb.WriteString(formatter.ToString(opt))
+			} else if t, ok := value.(*term); ok {
+				sb.WriteString(t.String())
+			} else {
+				sb.WriteString(fmt.Sprintf("%#v", value))
+			}
+		}
+		sb.WriteByte('}')
 	}
 	return sb.String()
 }
 
-func (dict *DictType) hasKey(d map[any]any, target any) (ok bool) {
+func (dict *DictType) hasKey(target any) (ok bool) {
 	for key := range *dict {
 		if ok = reflect.DeepEqual(key, target); ok {
 			break
@@ -69,6 +99,22 @@ func (dict *DictType) hasKey(d map[any]any, target any) (ok bool) {
 	return
 }
 
+func (dict *DictType) clone() (c *DictType) {
+	c = newDict(nil)
+	for k, v := range *dict {
+		(*c)[k] = v
+	}
+	return
+}
+
+func (dict *DictType) merge(second *DictType) {
+	if second != nil {
+		for k, v := range *second {
+			(*dict)[k] = v
+		}
+	}
+}
+
 // -------- dict term
 func newDictTerm(args map[any]*term) *term {
 	return &term{
@@ -84,7 +130,7 @@ func newDictTerm(args map[any]*term) *term {
 // -------- 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))
+	items := make(DictType, len(dict))
 	for key, tree := range dict {
 		var param any
 		if param, err = tree.compute(ctx); err != nil {
@@ -93,7 +139,7 @@ func evalDict(ctx ExprContext, self *term) (v any, err error) {
 		items[key] = param
 	}
 	if err == nil {
-		v = items
+		v = &items
 	}
 	return
 }
diff --git a/operator-dot.go b/operator-dot.go
index a13114f..48cbfa1 100644
--- a/operator-dot.go
+++ b/operator-dot.go
@@ -59,11 +59,11 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 		if index, err = verifyIndex(ctx, indexTerm, len(unboxedValue)); err == nil {
 			v = string(unboxedValue[index])
 		}
-	case map[any]any:
+	case *DictType:
 		var ok bool
 		var indexValue any
 		if indexValue, err = indexTerm.compute(ctx); err == nil {
-			if v, ok = unboxedValue[indexValue]; !ok {
+			if v, ok = (*unboxedValue)[indexValue]; !ok {
 				err = fmt.Errorf("key %v does not belong to the dictionary", rightValue)
 			}
 		}
diff --git a/operator-length.go b/operator-length.go
index 28bea6f..928e16f 100644
--- a/operator-length.go
+++ b/operator-length.go
@@ -30,8 +30,9 @@ func evalLength(ctx ExprContext, self *term) (v any, err error) {
 		s, _ := childValue.(string)
 		v = int64(len(s))
 	} else if IsDict(childValue) {
-		m, _ := childValue.(map[any]any)
-		v = int64(len(m))
+		// 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) {
 			count, _ := extIt.CallOperation(countName, nil)
diff --git a/operator-sum.go b/operator-sum.go
index 643fe38..85abace 100644
--- a/operator-sum.go
+++ b/operator-sum.go
@@ -62,12 +62,10 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 			v, err = sumAnyFract(leftValue, rightValue)
 		}
 	} else if IsDict(leftValue) && IsDict(rightValue) {
-		leftDict, _ := leftValue.(map[any]any)
-		rightDict, _ := rightValue.(map[any]any)
-		c := CloneMap(leftDict)
-		for key, value := range rightDict {
-			c[key] = value
-		}
+		leftDict, _ := leftValue.(*DictType)
+		rightDict, _ := rightValue.(*DictType)
+		c := leftDict.clone()
+		c.merge(rightDict)
 		v = c
 	} else {
 		err = self.errIncompatibleTypes(leftValue, rightValue)