simple-pipe

simple pipeline library like conduit.

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 ()