{-| Module : Data.Conduit.Algorithms.Utils Copyright : 2013-2017 Luis Pedro Coelho License : MIT Maintainer : luis@luispedro.org A few miscellaneous conduit utils -} module Data.Conduit.Algorithms.Utils ( awaitJust , enumerateC , groupC ) where import qualified Data.Conduit as C import Data.Maybe (maybe) import Control.Monad (unless) -- | Act on the next input (do nothing if no input). @awaitJust f@ is equivalent to -- -- -- @ do -- next <- C.await -- case next of -- Just val -> f val -- Nothing -> return () -- @ -- -- This is a simple utility adapted from -- http://neilmitchell.blogspot.de/2015/07/thoughts-on-conduits.html awaitJust :: Monad m => (a -> C.ConduitT a b m ()) -> C.ConduitT a b m () awaitJust f = C.await >>= maybe (return ()) f {-# INLINE awaitJust #-} -- | Conduit analogue to Python's enumerate function enumerateC :: Monad m => C.ConduitT a (Int, a) m () enumerateC = enumerateC' 0 where enumerateC' !i = awaitJust \$ \v -> do C.yield (i, v) enumerateC' (i + 1) {-# INLINE enumerateC #-} -- | groupC yields the input as groups of 'n' elements. If the input is not a -- multiple of 'n', the last element will be incomplete -- -- Example: -- -- @ -- CC.yieldMany [0..10] .| groupC 3 .| CC.consumeList -- @ -- -- results in @[ [0,1,2], [3,4,5], [6,7,8], [9, 10] ]@ -- -- This function is deprecated; use 'Data.Conduit.List.chunksOf' groupC :: (Monad m) => Int -> C.ConduitT a [a] m () groupC n = loop n [] where loop 0 ps = C.yield (reverse ps) >> loop n [] loop c ps = C.await >>= \case Nothing -> unless (null ps) \$ C.yield (reverse ps) Just p -> loop (c-1) (p:ps)