Lazy.hs

{-# LANGUAGE FlexibleContexts #-}
-- | Use lazy I\/O for consuming the contents of a source. Warning: All normal
-- warnings of lazy I\/O apply. However, if you consume the content within the
-- ResourceT, you should be safe.
module Data.Conduit.Lazy
    ( lazyConsume
    ) where

import Data.Conduit
import System.IO.Unsafe (unsafeInterleaveIO)
import Control.Monad.Trans.Control (MonadBaseControl, liftBaseOp_)
import Control.Monad.Trans.Resource (resourceActive)

-- | Use lazy I\/O to consume all elements from a @Source@.
--
-- Since 0.2.0
lazyConsume :: (Resource m, MonadBaseControl IO m) => Source m a -> ResourceT m [a]
lazyConsume src0 = do
    go src0
  where

    go src = liftBaseOp_ unsafeInterleaveIO $ do
        ra <- resourceActive
        if ra
            then do
                res <- sourcePull src
                case res of
                    Closed -> return []
                    Open src' x -> do
                        y <- go src'
                        return $ x : y
            else return []