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|
{-#LANGUAGE RankNTypes#-}
module Pipes.Text.IO
(
-- * Text IO
-- $textio
-- * Caveats
-- $caveats
-- * Producers
fromHandle
, stdin
, readFile
-- * Consumers
, toHandle
, stdout
, writeFile
) where
import qualified System.IO as IO
import Control.Exception (throwIO, try)
import Foreign.C.Error (Errno(Errno), ePIPE)
import qualified GHC.IO.Exception as G
import Data.Text (Text)
import qualified Data.Text as T
import qualified Data.Text.IO as T
import Pipes
import qualified Pipes.Safe.Prelude as Safe
import Pipes.Safe (MonadSafe(..))
import Prelude hiding (readFile, writeFile)
{- $textio
Where pipes @IO@ replaces lazy @IO@, @Producer Text IO r@ replaces lazy 'Text'.
This module exports some convenient functions for producing and consuming
pipes 'Text' in @IO@, namely, 'readFile', 'writeFile', 'fromHandle', 'toHandle',
'stdin' and 'stdout'. Some caveats described below.
The main points are as in
<https://hackage.haskell.org/package/pipes-bytestring-1.0.0/docs/Pipes-ByteString.html Pipes.ByteString>:
A 'Handle' can be associated with a 'Producer' or 'Consumer' according
as it is read or written to.
> import Pipes
> import qualified Pipes.Text as Text
> import qualified Pipes.Text.IO as Text
> import System.IO
>
> main =
> withFile "inFile.txt" ReadMode $ \hIn ->
> withFile "outFile.txt" WriteMode $ \hOut ->
> runEffect $ Text.fromHandle hIn >-> Text.toHandle hOut
To stream from files, the following is perhaps more Prelude-like (note that it uses Pipes.Safe):
> import Pipes
> import qualified Pipes.Text as Text
> import qualified Pipes.Text.IO as Text
> import Pipes.Safe
>
> main = runSafeT $ runEffect $ Text.readFile "inFile.txt" >-> Text.writeFile "outFile.txt"
Finally, you can stream to and from 'stdin' and 'stdout' using the predefined 'stdin'
and 'stdout' pipes, as with the following \"echo\" program:
> main = runEffect $ Text.stdin >-> Text.stdout
-}
{- $caveats
The operations exported here are a convenience, like the similar operations in
@Data.Text.IO@ (or rather, @Data.Text.Lazy.IO@, since, again, @Producer Text m r@ is
'effectful text' and something like the pipes equivalent of lazy Text.)
* Like the functions in @Data.Text.IO@, they attempt to work with the system encoding.
* Like the functions in @Data.Text.IO@, they significantly slower than ByteString operations. Where
you know what encoding you are working with, use @Pipes.ByteString@ and @Pipes.Text.Encoding@ instead,
e.g. @view utf8 Bytes.stdin@ instead of @Text.stdin@
* Like the functions in @Data.Text.IO@ , they use Text exceptions, not the standard Pipes protocols.
Something like
> view utf8 . Bytes.fromHandle :: Handle -> Producer Text IO (Producer ByteString m ())
yields a stream of Text, and follows
standard pipes protocols by reverting to (i.e. returning) the underlying byte stream
upon reaching any decoding error. (See especially the pipes-binary package.)
By contrast, something like
> Text.fromHandle :: Handle -> Producer Text IO ()
supplies a stream of text returning '()', which is convenient for many tasks,
but violates the pipes @pipes-binary@ approach to decoding errors and
throws an exception of the kind characteristic of the @text@ library instead.
-}
{-| Convert a 'IO.Handle' into a text stream using a text size
determined by the good sense of the text library. Note with the remarks
at the head of this module that this
is slower than @view utf8 (Pipes.ByteString.fromHandle h)@
but uses the system encoding and has other nice @Data.Text.IO@ features
-}
fromHandle :: MonadIO m => IO.Handle -> Producer Text m ()
fromHandle h = go where
go = do txt <- liftIO (T.hGetChunk h)
if T.null txt then return ()
else do yield txt
go
{-# INLINABLE fromHandle#-}
-- | Stream text from 'stdin'
stdin :: MonadIO m => Producer Text m ()
stdin = fromHandle IO.stdin
{-# INLINE stdin #-}
{-| Stream text from a file in the simple fashion of @Data.Text.IO@
>>> runSafeT $ runEffect $ Text.readFile "hello.hs" >-> Text.map toUpper >-> hoist lift Text.stdout
MAIN = PUTSTRLN "HELLO WORLD"
-}
readFile :: MonadSafe m => FilePath -> Producer Text m ()
readFile file = Safe.withFile file IO.ReadMode fromHandle
{-# INLINE readFile #-}
{-| Stream text to 'stdout'
Unlike 'toHandle', 'stdout' gracefully terminates on a broken output pipe.
Note: For best performance, it might be best just to use @(for source (liftIO . putStr))@
instead of @(source >-> stdout)@ .
-}
stdout :: MonadIO m => Consumer' Text m ()
stdout = go
where
go = do
txt <- await
x <- liftIO $ try (T.putStr txt)
case x of
Left (G.IOError { G.ioe_type = G.ResourceVanished
, G.ioe_errno = Just ioe })
| Errno ioe == ePIPE
-> return ()
Left e -> liftIO (throwIO e)
Right () -> go
{-# INLINABLE stdout #-}
{-| Convert a text stream into a 'Handle'
Note: again, for best performance, where possible use
@(for source (liftIO . hPutStr handle))@ instead of @(source >-> toHandle handle)@.
-}
toHandle :: MonadIO m => IO.Handle -> Consumer' Text m r
toHandle h = for cat (liftIO . T.hPutStr h)
{-# INLINABLE toHandle #-}
-- | Stream text into a file. Uses @pipes-safe@.
writeFile :: (MonadSafe m) => FilePath -> Consumer' Text m ()
writeFile file = Safe.withFile file IO.WriteMode toHandle
{-# INLINE writeFile #-}
|
