blob: 1f3c566fd167197dc13c24280bb9a797b72f1ffe (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
|
-- BNF Converter: Error Monad
-- Copyright (C) 2004 Author: Aarne Ranta
-- This file comes with NO WARRANTY and may be used FOR ANY PURPOSE.
module Transfer.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
|
