{-# LANGUAGE RankNTypes #-}

-- | Adapter module to work with the <https://hackage.haskell.org/package/foldl foldl> package.

--

-- @since 1.1.16

module Data.Conduit.Foldl where

import Data.Conduit

import Control.Monad.Trans.Class (lift)

import qualified Data.Conduit.List as CL

-- | Convert a left fold into a 'Consumer'. This function is intended

-- to be used with @purely@ from the

-- <https://hackage.haskell.org/package/foldl foldl> package.

--

-- @since 1.1.16

sinkFold :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Consumer a m b

sinkFold combine seed extract = fmap extract (CL.fold combine seed)

-- | Convert a monadic left fold into a 'Consumer'. This function is

-- intended to be used with @impurely@ from the

-- <https://hackage.haskell.org/package/foldl foldl> package.

--

-- @since 1.1.16

sinkFoldM :: Monad m => (x -> a -> m x) -> m x -> (x -> m b) -> Consumer a m b

sinkFoldM combine seed extract =

  lift . extract =<< CL.foldM combine =<< lift seed