[Haskell-cafe] Stacked return

[Dmitry Bogatov]

Antonio <me at lelf.lu> 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!


--
Best regards, Dmitry Bogatov <KAction at gnu.org>,
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