Re: [Haskell-cafe] Stacked return

24 Nov 2013


      Antonio  writes:
...
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances,
  FlexibleContexts, OverlappingInstances, TypeFamilies #-}
class Monad m => Ret a m b where
    returnN :: a -> m b
instance (Monad m, a ~ b) => Ret a m b where
    returnN = return
instance (Monad m, Monad n, Ret a m b) => Ret a n (m b) where
    returnN = return . returnN
boo :: [[[Maybe [Either () [Int]]]]]
boo = returnN 0
Great! Now I know what I do not know. Thanks!
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