Implemented token splitting as a generator

src/token/List.go

@@ -30,9 +30,9 @@ func (list List) LastIndexKind(kind Kind) int {
 }
 
 // Split calls the callback function on each set of tokens in a comma separated list.
-func (list List) Split(call func(List) error) error {
+func (list List) Split(yield func(List) bool) {
 	if len(list) == 0 {
-		return nil
+		return
 	}
 
 	start := 0
@@ -52,18 +52,16 @@ func (list List) Split(call func(List) error) error {
 			}
 
 			parameter := list[start:i]
-			err := call(parameter)
 
-			if err != nil {
-				return err
+			if !yield(parameter) {
+				return
 			}
 
 			start = i + 1
 		}
 	}
 
-	parameter := list[start:]
-	return call(parameter)
+	yield(list[start:])
 }
 
 // Text returns the concatenated token text.