Interop.hs

{-# OPTIONS_GHC -Wno-name-shadowing #-}
{-# OPTIONS_HADDOCK hide #-}
{-# LANGUAGE LinearTypes #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE QualifiedDo #-}
{-# LANGUAGE RecordWildCards #-}

-- | This module contains functions for interoperating with other
-- streaming libraries.
module Streaming.Internal.Interop
  ( -- * Interoperating with other streaming libraries
    reread
  ) where

import Streaming.Internal.Type
import Streaming.Internal.Produce
import Data.Unrestricted.Linear
import Prelude.Linear (($))
import Prelude (Maybe(..))
import qualified Control.Functor.Linear as Control

{-| Read an @IORef (Maybe a)@ or a similar device until it reads @Nothing@.
    @reread@ provides convenient exit from the @io-streams@ library

> reread readIORef    :: IORef (Maybe a) -> Stream (Of a) IO ()
> reread Streams.read :: System.IO.Streams.InputStream a -> Stream (Of a) IO ()
-}
reread :: Control.Monad m =>
  (s -> m (Ur (Maybe a))) -> s -> Stream (Of a) m ()
reread f s = reread' f s
  where
    reread' :: Control.Monad m =>
      (s -> m (Ur (Maybe a))) -> s -> Stream (Of a) m ()
    reread' f s = Effect $ Control.do
      Ur maybeA <- f s
      case maybeA of
        Nothing -> Control.return $ Return ()
        Just a -> Control.return $ (yield a Control.>> reread f s)
{-# INLINABLE reread #-}