oneShot + Sink

Sink.hs

module Main (main) where

import System.IO.Error

import GHC.Magic
data Sink = Await (Maybe Char -> Sink) | Done Int

countFrom :: Int -> Sink
countFrom n = let k = countFrom $! n + 1
              -- in Await $ \mi -> case mi of   
              in Await $ oneShot $ \mi -> case mi of
                  Nothing ->  Done n
                  Just _  -> k

feedFrom :: Int -> Sink -> IO ()
feedFrom _ (Done n)  = print n
feedFrom 0 (Await f) = feedFrom 0       (case f $ Nothing of  a -> a)
feedFrom n (Await f) = feedFrom (n - 1) (case f $ Just 'A' of a -> a)

main :: IO ()
main = let a = feedFrom 10000000 (countFrom 0) in a >> a