Collated.hs

module Collated where

data CQueue a = CQ [a] [a] deriving (Show)

interleave :: [a] -> [a] -> [a]
interleave [] _ = []
interleave (x:xs) ys = x : interleave ys xs

buildCQ :: [a] -> CQueue a
buildCQ l = CQ (interleave l1 (reverse l2)) []
  where n = length l `div` 2
        (l1, l2) = splitAt n l

process1 :: Functor f => (a -> f a) -> CQueue a -> f (CQueue a)
process1 f (CQ [] ys) = process1 f (CQ ys [])
process1 f (CQ (x:x':xs) ys) = fmap go (f x)
  where go y = CQ xs (x':y:ys)


exampleStep :: Int -> IO Int
exampleStep n = print n >> return (n + 10)

demo :: Int -> CQueue Int -> IO ()
demo 0 _ = return ()
demo n cq = do
  cq' <- process1 exampleStep cq
  demo (n - 1) cq'

main :: IO ()
main = demo 30 (buildCQ [0..9])