-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Foldable
-- Copyright   :  (c) 2020-2021 EMQ Technologies Co., Ltd.
-- License     :  BSD-style (see the LICENSE file)
--
-- Maintainer  :  Feng Lee, feng@emqx.io
--                Yang M, yangm@emqx.io
-- Stability   :  experimental
-- Portability :  portable
--
-- The Foldable typeclass.
--
-----------------------------------------------------------------------------
module Data.Foldable
  ( class Foldable
  , foldl, foldr, foldMap
  , module Data.Monoid
  ) where

import Data.Monoid (class Monoid, mempty)
import Data.Semigroup ((<>))

class Foldable f where
  foldl :: forall a b. (b -> a -> b) -> b -> f a -> b
  foldr :: forall a b. (a -> b -> b) -> b -> f a -> b
  foldMap :: forall a m. Monoid m => (a -> m) -> f a -> m

instance Foldable List where
  foldl = foldlListImpl
  foldr = foldrListImpl
  foldMap = foldMapDefaultR

foreign import foldlListImpl :: forall a b. (b -> a -> b) -> b -> [a] -> b
foreign import foldrListImpl :: forall a b. (a -> b -> b) -> b -> [a] -> b

foldMapDefaultR
  :: forall f a m
   . Foldable f
  => Monoid m
  => (a -> m)
  -> f a
  -> m
foldMapDefaultR f = foldr (\x acc -> f x <> acc) mempty