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-- BNF Converter: Error Monad
-- Copyright (C) 2004 Author: Aarne Ranta
-- This file comes with NO WARRANTY and may be used FOR ANY PURPOSE.
module GF.JavaScript.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
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