{-# LANGUAGE CPP #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE Safe #-}


{- |
Module      :  Lens.Micro.Contra
Copyright   :  (C) 2013-2016 Edward Kmett, 2015-2016 Artyom Kazak, 2018 Monadfix
License     :  BSD-style (see the file LICENSE)

This module provides types and functions that require 'Contravariant'; they aren't included in the main microlens package because <http://hackage.haskell.org/package/contravariant contravariant> has a lot of dependencies.
-}
module Lens.Micro.Contra
(
  -- * Getter
  Getter,
  fromSimpleGetter,

  -- * Fold
  Fold,
  fromSimpleFold,
)
where


import Lens.Micro
import Lens.Micro.Extras (view)

import Data.Foldable (traverse_)
import Data.Functor.Contravariant (phantom, Contravariant)

#if __GLASGOW_HASKELL__ < 710
import Control.Applicative
#endif


{- |
This is the same thing as 'SimpleGetter' but more generalised (so that it would fully match the type used in lens).
-}
type Getter s a =
  forall f. (Contravariant f, Functor f) => (a -> f a) -> s -> f s

{- |
Turn a 'SimpleGetter' into a true 'Getter'.
-}
fromSimpleGetter :: SimpleGetter s a -> Getter s a
fromSimpleGetter :: forall s a. SimpleGetter s a -> Getter s a
fromSimpleGetter SimpleGetter s a
g a -> f a
f = f a -> f s
forall (f :: * -> *) a b.
(Functor f, Contravariant f) =>
f a -> f b
phantom (f a -> f s) -> (s -> f a) -> s -> f s
forall b c a. (b -> c) -> (a -> b) -> a -> c
. a -> f a
f (a -> f a) -> (s -> a) -> s -> f a
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Getting a s a -> s -> a
forall a s. Getting a s a -> s -> a
view Getting a s a
SimpleGetter s a
g
{-# INLINE fromSimpleGetter #-}

{- |
This is the same thing as 'SimpleFold' but more generalised (so that it would fully match the type used in lens). See documentation of 'SimpleFold' for the list of functions that work on 'Fold' but don't work on 'SimpleFold'.
-}
type Fold s a =
  forall f. (Contravariant f, Applicative f) => (a -> f a) -> s -> f s

{- |
Turn a 'SimpleFold' into a true 'Fold'.
-}
fromSimpleFold :: SimpleFold s a -> Fold s a
fromSimpleFold :: forall s a. SimpleFold s a -> Fold s a
fromSimpleFold SimpleFold s a
g a -> f a
f = f () -> f s
forall (f :: * -> *) a b.
(Functor f, Contravariant f) =>
f a -> f b
phantom (f () -> f s) -> (s -> f ()) -> s -> f s
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (a -> f a) -> [a] -> f ()
forall (t :: * -> *) (f :: * -> *) a b.
(Foldable t, Applicative f) =>
(a -> f b) -> t a -> f ()
traverse_ a -> f a
f ([a] -> f ()) -> (s -> [a]) -> s -> f ()
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Getting (Endo [a]) s a -> s -> [a]
forall a s. Getting (Endo [a]) s a -> s -> [a]
toListOf Getting (Endo [a]) s a
SimpleFold s a
g
{-# INLINE fromSimpleFold #-}