at operator return -1 when fails in lists and arrays; insert operators (<< and >>) changes che container if it is a variable

operator-at.go

@@ -36,6 +36,7 @@ func evalAt(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		return
 	}
 
+	v = int64(-1) // default value if not found
 	if array.IsArray(rightValue) {
 		a, _ := rightValue.(*array.ArrayType)
 		if index := a.IndexDeepSameCmp(leftValue); index >= 0 {
@@ -45,14 +46,16 @@ func evalAt(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		dict, _ := rightValue.(*dict.DictType)
 		if k, exists := dict.FindKey(leftValue); exists {
 			v = k
+		} else {
+			v = nil
 		}
-
 	} else if list.IsLinkedList(rightValue) {
 		ls, _ := rightValue.(*list.LinkedList)
 		if index := ls.Index(leftValue); index >= 0 {
 			v = index
 		}
 	} else {
+		v = nil
 		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
 	}
 	return