+
+ fun is_digit : Bool
+ do
+ return self >= '0' and self <= '9'
+ end
+
+ fun is_lower : Bool
+ do
+ return self >= 'a' and self <= 'z'
+ end
+
+ fun is_upper : Bool
+ do
+ return self >= 'A' and self <= 'Z'
+ end
+
+ fun is_letter : Bool
+ do
+ return is_lower or is_upper
+ end