An intersperse enumeratee

gistfile1.hs

import Control.Monad.Trans.Class (lift)
import Data.Enumerator (Enumeratee, Step(..), Stream(..), runIteratee)
import qualified Data.Enumerator.List as EL

intersperse :: (Monad m) => a -> Enumeratee a a m b
intersperse v = first 
  where
    first (Continue k) = do
      h <- EL.head
      case h of
        Nothing -> return $ Continue k
        Just e  -> do
          newStep <- lift $ runIteratee $ k $ Chunks [e]
          loop newStep
    first step = return step
    loop = EL.concatMap (\x -> [v, x])