1 -- BNF Converter: Error Monad
2 -- Copyright (C) 2004 Author: Aarne Ranta
4 -- This file comes with NO WARRANTY and may be used FOR ANY PURPOSE.
7 -- the Error monad: like Maybe type with error msgs
9 data Err a = Ok a | Bad String
10 deriving (Read, Show, Eq)
12 instance Monad Err where