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module Main where
import Control.Concurrent
-- simple handshaking using two MVars,
-- must context switch twice for each character.
main = do
ready <- newEmptyMVar
datum <- newEmptyMVar
let
reader = do
putMVar ready ()
char <- takeMVar datum
if (char == '\n')
then return ()
else do putChar char; reader
writer "" = do
takeMVar ready
putMVar datum '\n'
writer (c:cs) = do
takeMVar ready
putMVar datum c
writer cs
forkIO reader
writer "Hello World"
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