src/Reflex/FunctorMaybe.hs · reflex

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reflex/src/Reflex/FunctorMaybe.hs

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1{-# LANGUAGE CPP #-}

2#if MIN_VERSION_base(4,9,0)

3{-# LANGUAGE GeneralizedNewtypeDeriving #-}

4{-# LANGUAGE StandaloneDeriving #-}

5#endif

7-- |

8-- Module:

9-- Reflex.FunctorMaybe

10-- Description:

11-- This module defines the FunctorMaybe class, which extends Functors with the

12-- ability to delete values.

13module Reflex.FunctorMaybe

14 ( FunctorMaybe (..)

15 ) where

17import Data.IntMap (IntMap)

18import Data.Map (Map)

19#if MIN_VERSION_base(4,9,0)

20import Data.Semigroup (Option(..))

21#endif

22import Data.Witherable

24--TODO: See if there's a better class in the standard libraries already

26-- | A class for values that combines filtering and mapping using 'Maybe'.

27-- Morally, @'FunctorMaybe' ~ KleisliFunctor 'Maybe'@.

28{-# DEPRECATED FunctorMaybe "Use 'Filterable' from Data.Witherable instead" #-}

29class FunctorMaybe f where

30 -- | Combined mapping and filtering function.

31 fmapMaybe :: (a -> Maybe b) -> f a -> f b

33instance FunctorMaybe Maybe where

34 fmapMaybe = mapMaybe

36#if MIN_VERSION_base(4,9,0)

37deriving instance FunctorMaybe Option

38#endif

40instance FunctorMaybe [] where

41 fmapMaybe = mapMaybe

43instance FunctorMaybe (Map k) where

44 fmapMaybe = mapMaybe

46instance FunctorMaybe IntMap where

47 fmapMaybe = mapMaybe