@hackage simple-pipe0.0.0.29

examples/upperFile.hs

• read file (sample.txt)

• take 3 lines

• to upper all lines

• write to stdout

extensions

• PackageImports

 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 ()