Iteratee example from slide 12 of "A Parsing Trifecta" (http://comonad.com/reader/wp-content/uploads/2009/08/A-Parsing-Trifecta.pdf)

gistfile1.hs

-- http://comonad.com/reader/wp-content/uploads/2009/08/A-Parsing-Trifecta.pdf
--
import Prelude hiding (null)
import Data.ByteString
data Input = Chunk ByteString | EOF

data Iteratee a
    = Return a Input
    | Cont (Input -> Iteratee a)

instance Monad Iteratee where
    return a = Return a (Chunk empty)
    Return a (Chunk e) >>= f | null e = k -- ??
    Return a i >>= f = case f a of
        Return b _ -> Return b i
        Cont k -> k i
    Cont k >>= f = Cont (k >=> f)
        where (>=>) a b x = a x >>= b