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import Data.Pipe
import Data.Char
import System.IO
import "monads-tf" Control.Monad.Trans
main :: IO ()
main = do
_ <- runPipe $ readFileP "sample.txt"
=$= takeP 3
=$= convert (map toUpper)
=$= writeString
return ()
readFileP :: FilePath -> Pipe () String IO ()
readFileP fp = bracket (openFile fp ReadMode) hClose hRead
hRead :: Handle -> Pipe () String IO ()
hRead h = do
eof <- lift $ hIsEOF h
if eof then return () else do
l <- lift $ hGetLine h
yield l
hRead h
writeString :: Pipe String () IO ()
writeString = do
ms <- await
case ms of
Just s -> lift (putStrLn s) >> writeString
_ -> return ()
takeP :: Monad m => Int -> Pipe a a m ()
takeP 0 = return ()
takeP n = do
mx <- await
case mx of
Just x -> yield x >> takeP (n - 1)
_ -> return ()
