Improved error handling

src/build/token/Token.go

@@ -11,6 +11,11 @@ type Token struct {
 	Bytes    []byte
 }
 
+// After returns the position after the token.
+func (t Token) After() int {
+	return t.Position + len(t.Bytes)
+}
+
 // String creates a human readable representation for debugging purposes.
 func (t Token) String() string {
 	return fmt.Sprintf("%s %s", t.Kind, t.Text())