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|
{-#LANGUAGE RankNTypes#-}
module Pipes.Prelude.Text
(
-- * Simple line-based Text IO
-- $lineio
fromHandleLn
, toHandleLn
, stdinLn
, stdoutLn
, stdoutLn'
, readFileLn
, writeFileLn
) 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(..), runSafeT, runSafeP)
import Prelude hiding (readFile, writeFile)
{- $lineio
Line-based operations are marked with a final \-@Ln@, like 'stdinLn', 'readFileLn', etc.
They are drop-in 'Text' replacements for the corresponding 'String' operations in
@Pipes.Prelude@ and @Pipes.Safe.Prelude@ - a final \-@Ln@ being added where necessary.
In using them, one is producing and consuming semantically significant individual texts,
understood as lines, just as one would produce or pipe 'Int's or 'Char's or anything else.
Thus, the standard materials from @Pipes@ and @Pipes.Prelude@ and
@Data.Text@ are all you need to work with them, and
you can use these operations without using any of the other modules in this package.
Thus, to take a trivial case, here we upper-case three lines from standard input and write
them to a file.
>>> import Pipes
>>> import qualified Pipes.Prelude as P
>>> import qualified Pipes.Text.IO as Text
>>> import qualified Data.Text as T
>>> Text.runSafeT $ runEffect $ Text.stdinLn >-> P.take 3 >-> P.map T.toUpper >-> Text.writeFileLn "threelines.txt"
one<Enter>
two<Enter>
three<Enter>
>>> :! cat "threelines.txt"
ONE
TWO
THREE
The point of view is very much that of @Pipes.Prelude@. It would still be the same even if
we did something a bit more sophisticated, like run an ordinary attoparsec 'Text' parser on
each line, as is frequently desirable. Here we run
a minimal attoparsec number parser, @scientific@, on separate lines of standard input,
dropping bad parses with @P.concat@:
>>> import qualified Data.Attoparsec.Text as A
>>> P.toListM $ Text.stdinLn >-> P.map (A.parseOnly A.scientific) >-> P.concat >-> P.take 3
1<Enter>
2<Enter>
bad<Enter>
3<Enter>
[1.0,2.0,3.0]
The line-based operations are, however, subject to a number of caveats.
First, where they read from a handle, they will of course happily
accumulate indefinitely long lines. This is likely to be legitimate for input
typed in by a user, and for locally produced log files and other known material, but
otherwise not. See the post on
<http://www.haskellforall.com/2013/09/perfect-streaming-using-pipes-bytestring.html perfect streaming>
to see why @pipes-bytestring@ and this package take a different approach. Furthermore,
like those in @Data.Text.IO@, the operations use the system encoding (and @T.hGetLine@)
and thus are slower than the \'official\' route, which would use bytestring IO and
the encoding and decoding functions in @Pipes.Text.Encoding@. Finally, they will generate
text exceptions after the fashion of @Data.Text.Encoding@ rather than returning the
undigested bytes in the style of @Pipes.Text.Encoding@
-}
{-| Read separate lines of 'Text' from 'IO.stdin' using 'T.getLine'
This function will accumulate indefinitely long strict 'Text's. See the caveats above.
Terminates on end of input
-}
stdinLn :: MonadIO m => Producer' T.Text m ()
stdinLn = fromHandleLn IO.stdin
{-# INLINABLE stdinLn #-}
{-| Write 'Text' lines to 'IO.stdout' using 'putStrLn'
Unlike 'toHandle', 'stdoutLn' gracefully terminates on a broken output pipe
-}
stdoutLn :: MonadIO m => Consumer' T.Text m ()
stdoutLn = go
where
go = do
str <- await
x <- liftIO $ try (T.putStrLn str)
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 stdoutLn #-}
{-| Write lines of 'Text' to 'IO.stdout'.
This does not handle a broken output pipe, but has a polymorphic return
value.
-}
stdoutLn' :: MonadIO m => Consumer' T.Text m r
stdoutLn' = for cat (\str -> liftIO (T.putStrLn str))
{-# INLINABLE stdoutLn' #-}
{-# RULES
"p >-> stdoutLn'" forall p .
p >-> stdoutLn' = for p (\str -> liftIO (T.putStrLn str))
#-}
{-| Read separate lines of 'Text' from a 'IO.Handle' using 'T.hGetLine'.
This operation will accumulate indefinitely large strict texts. See the caveats above.
Terminates on end of input
-}
fromHandleLn :: MonadIO m => IO.Handle -> Producer' Text m ()
fromHandleLn h = go where
getLine :: IO (Either G.IOException Text)
getLine = try (T.hGetLine h)
go = do txt <- liftIO getLine
case txt of
Left e -> return ()
Right y -> do yield y
go
{-# INLINABLE fromHandleLn #-}
-- to do: investigate differences from the above:
-- fromHandleLn :: MonadIO m => IO.Handle -> Producer' T.Text m ()
-- fromHandleLn h = go
-- where
-- go = do
-- eof <- liftIO $ IO.hIsEOF h
-- unless eof $ do
-- str <- liftIO $ T.hGetLine h
-- yield str
-- go
-- {-# INLINABLE fromHandleLn #-}
-- | Write separate lines of 'Text' to a 'IO.Handle' using 'T.hPutStrLn'
toHandleLn :: MonadIO m => IO.Handle -> Consumer' T.Text m r
toHandleLn handle = for cat (\str -> liftIO (T.hPutStrLn handle str))
{-# INLINABLE toHandleLn #-}
{-# RULES
"p >-> toHandleLn handle" forall p handle .
p >-> toHandleLn handle = for p (\str -> liftIO (T.hPutStrLn handle str))
#-}
{-| Stream separate lines of text from a file. This operation will accumulate
indefinitely long strict text chunks. See the caveats above.
-}
readFileLn :: MonadSafe m => FilePath -> Producer Text m ()
readFileLn file = Safe.withFile file IO.ReadMode fromHandleLn
{-# INLINE readFileLn #-}
{-| Write lines to a file, automatically opening and closing the file as
necessary
-}
writeFileLn :: (MonadSafe m) => FilePath -> Consumer' Text m r
writeFileLn file = Safe.withFile file IO.WriteMode toHandleLn
{-# INLINABLE writeFileLn #-}
|
