--- /dev/null
+-- BNF Converter: Error Monad
+-- Copyright (C) 2004 Author: Aarne Ranta
+
+-- This file comes with NO WARRANTY and may be used FOR ANY PURPOSE.
+module ErrM where
+
+-- the Error monad: like Maybe type with error msgs
+
+data Err a = Ok a | Bad String
+ deriving (Read, Show, Eq)
+
+instance Monad Err where
+ return = Ok
+ fail = Bad
+ Ok a >>= f = f a
+ Bad s >>= f = Bad s