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{-# LANGUAGE TypeFamilies, FlexibleContexts #-}
-- Trac #3590: a bug in typechecking of sections
module T3590 where
newtype ListT m a =
ListT { runListT :: m (Maybe (a, ListT m a)) }
class Monad (ItemM l) => List l where
type ItemM l :: * -> *
joinL :: [ItemM l (l a) -> l a]
instance Monad m => List (ListT m) where
type ItemM (ListT m) = m
joinL = [ ListT . (>>= runListT) -- Right section
, ListT . (runListT <<=) -- Left section
]
(<<=) :: Monad m => (a -> m b) -> m a -> m b
(<<=) k m = m >>= k
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