stream-traversal-foldl.hs

import Control.Applicative
import Control.Foldl (FoldM(..))
import Control.Monad
import Data.Foldable
import Data.Sequence ((|>))


chunksOf :: (Applicative m) => ([a] -> m ()) -> Int -> FoldM m a ()
chunksOf yield n =
    FoldM go
          (pure mempty)
          (liftA2 when (not . null) (yield . toList))

    where
    go xs' x =
        let xs = xs' |> x in
        if length xs >= n
          then mempty <$ yield (toList xs)
          else pure xs