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{-# OPTIONS -XRecursiveDo #-}
-- OLD: mdo requires MonadFix instance, even
-- if no recursion is present
-- Dec 2010: Small change of behaviour
-- MonadFix is only required if recursion is present
module Main (main) where
import Control.Monad.Fix
import Control.Applicative (Applicative(..))
import Control.Monad (liftM, ap)
data X a = X a deriving Show
instance Functor X where
fmap = liftM
instance Applicative X where
pure = X
(<*>) = ap
instance Monad X where
(X a) >>= f = f a
z :: X [Int]
z = mdo { a <- return 1; return [a] }
main = print z
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