Re: [Haskell-cafe] MRP, 3-year-support-window, and the non-requirement of CPP

10 Oct 2015


      On Wed, Oct 7, 2015 at 3:35 AM, Herbert Valerio Riedel  wrote:
...
--8<---------------cut here---------------start------------->8---
import Control.Applicative as A (Applicative(..))
data Maybe' a = Nothing' | Just' a
instance Functor Maybe' where
    fmap f (Just' v) = Just' (f v)
    fmap _ Nothing'  = Nothing'
instance A.Applicative Maybe' where
    pure = Just'
    f1 <*> f2   = f1 >>= \v1 -> f2 >>= (pure . v1)
instance Monad Maybe' where
    Nothing' >>= _  = Nothing'
    Just' x  >>= f  = f x
return = pure -- "deprecated" since GHC 7.10
--8<---------------cut here---------------end--------------->8---
Alternately,

import Control.Applicative
import Prelude

data Maybe' a = Nothing' | Just' a

instance Functor Maybe' where
    fmap f (Just' v) = Just' (f v)
    fmap _ Nothing'  = Nothing'

instance Applicative Maybe' where
...
-- hvr
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Re: [Haskell-cafe] MRP, 3-year-support-window, and the non-requirement of CPP

Edward Kmett