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Blame information for rev 4

Line No.	Rev	Author	Line
1	1	paulosilva
2			{-# OPTIONS_GHC -Wall #-}
3
4			-------------------------------------------------------------------------------
5
6			{- |
7			Module      :  Control.MonadOr
8			Description :  MonadOr definition.
9			Copyright   :  (c) Paulo Silva
10			License     :  LGPL
11
12			Maintainer  :  paufil@di.uminho.pt
13			Stability   :  experimental
14			Portability :  portable
15
16			Monad definition satisfying the Monoid and Left Catch laws as refered in
17			<http://www.haskell.org/haskellwiki/MonadPlus_reform_proposal>
18
19			-}
20
21			-------------------------------------------------------------------------------
22
23			module Control.MonadOr (
24			MonadOr,
25	4	paulosilva	mzero,
26	1	paulosilva	morelse
27			) where
28
29	3	paulosilva	import Control.Monad.Error
30			import Control.Monad.State
31	1	paulosilva
32			-------------------------------------------------------------------------------
33
34			class MonadPlus m => MonadOr m where
35			morelse :: m a -> m a -> m a
36
37			-------------------------------------------------------------------------------
38
39			instance MonadOr [] where
40			morelse [] b = b
41			morelse a _ = a
42
43			-------------------------------------------------------------------------------
44
45			-- This instance is equal to mplus for maybe
46			instance MonadOr Maybe where
47			morelse = mplus
48
49			-------------------------------------------------------------------------------
50
51	3	paulosilva	instance (Monad m, Error e) => MonadOr (ErrorT e m) where
52			morelse = mplus
53
54			-------------------------------------------------------------------------------
55
56			instance MonadOr m => MonadOr (StateT s m) where
57			m `morelse` n = StateT $ \s -> runStateT m s `morelse` runStateT n s
58
59			-------------------------------------------------------------------------------