Bifurcate io-streams example

bifurcate.hs

{-# LANGUAGE OverloadedStrings #-}

module Main where

import           Control.Monad         (when)

import           Data.Maybe            (isJust)
import           Data.ByteString.Char8 as C

import           System.IO.Streams     as Streams

infListStream :: IO (InputStream Int)
infListStream = Streams.fromList [1..10]

bifurcate :: InputStream a -> OutputStream a -> OutputStream a -> IO ()
bifurcate is os1 os2 = do
    x <- Streams.read is
    Streams.write x os1
    Streams.write x os2 
    when (isJust x) $ bifurcate is os1 os2
    
echo :: IO (OutputStream ByteString, InputStream ByteString)
echo = do
    (inp, outp, _, _) <- Streams.runInteractiveProcess "/usr/bin/cat" [ "/dev/stdin" ] Nothing Nothing
    return (inp, outp)
    
echo2 :: IO (OutputStream ByteString, InputStream ByteString)
echo2 = do
    (inp, outp, _, _) <- Streams.runInteractiveProcess "/usr/bin/cat" [ "/dev/stdin" ] Nothing Nothing
    inp2 <- Streams.intersperse " " inp
    return (inp2, outp)
    
main :: IO ()
main = do
    xs <- infListStream
    ys <- Streams.map (C.pack . show) xs
    
    (i1, o1) <- echo
    (i2, o2) <- echo2
    
    bifurcate ys i1 i2
    
    x <- Streams.read o1
    y <- Streams.read o2
    print (x, y)

---- Output
-- (Just "12345678910",Just "1 2 3 4 5 6 7 8 9 10")