{-# LANGUAGE CPP #-}
#if __GLASGOW_HASKELL__ >= 704
{-# LANGUAGE Safe #-}
#elif __GLASGOW_HASKELL__ >= 702
{-# LANGUAGE Trustworthy #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Copyright   :  (C) 2011-2015 Edward Kmett
-- License     :  BSD-style (see the file LICENSE)
--
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  provisional
-- Portability :  portable
--
----------------------------------------------------------------------------
module Data.Semigroup.Traversable
  ( Traversable1(..)
  -- * Defining Traversable1 instances
  -- $traversable1instances
  , traverse1Maybe
  -- * Default superclass instance helpers
  , foldMap1Default
  ) where

import Control.Applicative
#if !(MIN_VERSION_base(4,11,0))
import Data.Semigroup
#endif
import Data.Semigroup.Traversable.Class
import Data.Functor.Bind.Class

-- | Default implementation of 'foldMap1' given an implementation of 'Traversable1'.
foldMap1Default :: (Traversable1 f, Semigroup m) => (a -> m) -> f a -> m
foldMap1Default :: (a -> m) -> f a -> m
foldMap1Default a -> m
f = Const m (f Any) -> m
forall a k (b :: k). Const a b -> a
getConst (Const m (f Any) -> m) -> (f a -> Const m (f Any)) -> f a -> m
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (a -> Const m Any) -> f a -> Const m (f Any)
forall (t :: * -> *) (f :: * -> *) a b.
(Traversable1 t, Apply f) =>
(a -> f b) -> t a -> f (t b)
traverse1 (m -> Const m Any
forall k a (b :: k). a -> Const a b
Const (m -> Const m Any) -> (a -> m) -> a -> Const m Any
forall b c a. (b -> c) -> (a -> b) -> a -> c
. a -> m
f)

-- $traversable1instances
-- Defining 'Traversable1' instances for types with both 'Traversable1' and 'Traversable'
-- substructures can be done with 'traverse1Maybe', '(<*.>)', and '(<.*>)'.
--
-- > data Foo a = Foo (Maybe a) (Maybe a) a [a]
-- >   deriving (Functor, Traversable, Foldable)
-- > instance Traversable1 Foo where
-- >   traverse1 f (Foo ma ma' a as) = Foo <$> traverseMaybe ma <*> traverseMaybe ma' <*.> f a <.*> traverseMaybe as
-- > instance Foldable1 Foo where
-- >   foldMap1 = foldMap1Default