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{-# LANGUAGE RebindableSyntax, FlexibleInstances,
MultiParamTypeClasses, FunctionalDependencies #-}
-- Trac #1537
module Foo where
import qualified Prelude
import Prelude hiding (Monad(..))
newtype Identity a = Identity { runIdentity :: a }
instance Prelude.Monad Identity where
return a = Identity a
m >>= k = k (runIdentity m)
class Bind m1 m2 m3 | m1 m2 -> m3 where
(>>=) :: m1 a -> (a -> m2 b) -> m3 b
class Return m where
returnM :: a -> m a
fail :: String -> m a
instance Bind Maybe [] [] where
Just x >>= f = f x
Nothing >>= f = []
instance Functor a => Bind Identity a a where m >>= f = f (runIdentity m)
instance Functor a => Bind a Identity a where m >>= f = fmap (runIdentity . f) m
instance Prelude.Monad m => Bind m m m where (>>=) = (Prelude.>>=)
instance Return [] where
returnM x = [x]
fail _ = []
return :: a -> Identity a
return = Prelude.return
should_compile :: [Int]
should_compile = do
a <- Just 1
b <- [a*1,a*2]
return (b+1)
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