Pipes/Text/IO.hs

   1 {-#LANGUAGE RankNTypes#-}
   2
   3
   4 module Pipes.Text.IO
   5    (
   6    -- * Text IO
   7    -- $textio
   8
   9    -- * Caveats
  10    -- $caveats
  11
  12    -- * Producers
  13    fromHandle
  14    , stdin
  15    , readFile
  16    -- * Consumers
  17    , toHandle
  18    , stdout
  19    , writeFile
  20    ) where
  21
  22 import qualified System.IO as IO
  23 import Control.Exception (throwIO, try)
  24 import Foreign.C.Error (Errno(Errno), ePIPE)
  25 import qualified GHC.IO.Exception as G
  26 import Data.Text (Text)
  27 import qualified Data.Text as T
  28 import qualified Data.Text.IO as T
  29 import Pipes
  30 import qualified Pipes.Safe.Prelude as Safe
  31 import qualified Pipes.Safe as Safe
  32 import Pipes.Safe (MonadSafe(..), Base(..))
  33 import Prelude hiding (readFile, writeFile)
  34
  35 {- $textio
  36     Where pipes IO replaces lazy IO, @Producer Text m r@ replaces lazy 'Text'.
  37     This module exports some convenient functions for producing and consuming
  38     pipes 'Text' in IO, namely, 'readFile', 'writeFile', 'fromHandle', 'toHandle',
  39     'stdin' and 'stdout'.  Some caveats described below.
  40
  41     The main points are as in
  42     <https://hackage.haskell.org/package/pipes-bytestring-1.0.0/docs/Pipes-ByteString.html Pipes.ByteString>
  43
  44     An 'IO.Handle' can be associated with a 'Producer' or 'Consumer' according
  45     as it is read or written to.
  46
  47 > import Pipes
  48 > import qualified Pipes.Text as Text
  49 > import qualified Pipes.Text.IO as Text
  50 > import System.IO
  51 >
  52 > main =
  53 >     withFile "inFile.txt"  ReadMode  $ \hIn  ->
  54 >     withFile "outFile.txt" WriteMode $ \hOut ->
  55 >     runEffect $ Text.fromHandle hIn >-> Text.toHandle hOut
  56
  57 To stream from files, the following is perhaps more Prelude-like (note that it uses Pipes.Safe):
  58
  59 > import Pipes
  60 > import qualified Pipes.Text as Text
  61 > import qualified Pipes.Text.IO as Text
  62 > import Pipes.Safe
  63 >
  64 > main = runSafeT $ runEffect $ Text.readFile "inFile.txt" >-> Text.writeFile "outFile.txt"
  65
  66     Finally, you can stream to and from 'stdin' and 'stdout' using the predefined 'stdin'
  67     and 'stdout' pipes, as with the following \"echo\" program:
  68
  69 > main = runEffect $ Text.stdin >-> Text.stdout
  70
  71
  72 -}
  73
  74
  75 {- $caveats
  76
  77     The operations exported here are a convenience, like the similar operations in
  78     @Data.Text.IO@  (or rather, @Data.Text.Lazy.IO@, since, again, @Producer Text m r@ is
  79     'effectful text' and something like the pipes equivalent of lazy Text.)
  80
  81     * Like the functions in @Data.Text.IO@, they attempt to work with the system encoding.
  82
  83     * Like the functions in @Data.Text.IO@, they significantly slower than ByteString operations. Where
  84        you know what encoding you are working with, use @Pipes.ByteString@ and @Pipes.Text.Encoding@ instead,
  85        e.g. @view utf8 Bytes.stdin@ instead of @Text.stdin@
  86
  87     * Like the functions in  @Data.Text.IO@ , they use Text exceptions, not the standard Pipes protocols.
  88
  89    Something like
  90
  91 >  view utf8 . Bytes.fromHandle :: Handle -> Producer Text IO (Producer ByteString m ())
  92
  93    yields a stream of Text, and follows
  94    standard pipes protocols by reverting to (i.e. returning) the underlying byte stream
  95    upon reaching any decoding error. (See especially the pipes-binary package.)
  96
  97   By contrast, something like
  98
  99 > Text.fromHandle :: Handle -> Producer Text IO ()
 100
 101   supplies a stream of text returning '()', which is convenient for many tasks,
 102   but violates the pipes @pipes-binary@ approach to decoding errors and
 103   throws an exception of the kind characteristic of the @text@ library instead.
 104
 105
 106 -}
 107
 108 {-| Convert a 'IO.Handle' into a text stream using a text size
 109     determined by the good sense of the text library. Note with the remarks
 110     at the head of this module that this
 111     is  slower than @view utf8 (Pipes.ByteString.fromHandle h)@
 112     but uses the system encoding and has other nice @Data.Text.IO@ features
 113 -}
 114
 115 fromHandle :: MonadIO m => IO.Handle -> Producer Text m ()
 116 fromHandle h =  go where
 117       go = do txt <- liftIO (T.hGetChunk h)
 118               if T.null txt then return ()
 119                             else do yield txt
 120                                     go
 121 {-# INLINABLE fromHandle#-}
 122
 123 -- | Stream text from 'stdin'
 124 stdin :: MonadIO m => Producer Text m ()
 125 stdin = fromHandle IO.stdin
 126 {-# INLINE stdin #-}
 127
 128
 129 {-| Stream text from a file in the simple fashion of @Data.Text.IO@
 130
 131 >>> runSafeT $ runEffect $ Text.readFile "hello.hs" >-> Text.map toUpper >-> hoist lift Text.stdout
 132 MAIN = PUTSTRLN "HELLO WORLD"
 133 -}
 134
 135 readFile :: MonadSafe m => FilePath -> Producer Text m ()
 136 readFile file = Safe.withFile file IO.ReadMode fromHandle
 137 {-# INLINE readFile #-}
 138
 139
 140 {-| Stream text to 'stdout'
 141
 142     Unlike 'toHandle', 'stdout' gracefully terminates on a broken output pipe.
 143
 144     Note: For best performance, it might be best just to use @(for source (liftIO . putStr))@
 145     instead of @(source >-> stdout)@ .
 146 -}
 147 stdout :: MonadIO m => Consumer' Text m ()
 148 stdout = go
 149   where
 150     go = do
 151         txt <- await
 152         x  <- liftIO $ try (T.putStr txt)
 153         case x of
 154             Left (G.IOError { G.ioe_type  = G.ResourceVanished
 155                             , G.ioe_errno = Just ioe })
 156                  | Errno ioe == ePIPE
 157                      -> return ()
 158             Left  e  -> liftIO (throwIO e)
 159             Right () -> go
 160 {-# INLINABLE stdout #-}
 161
 162
 163 {-| Convert a text stream into a 'Handle'
 164
 165     Note: again, for best performance, where possible use
 166     @(for source (liftIO . hPutStr handle))@ instead of @(source >-> toHandle handle)@.
 167 -}
 168 toHandle :: MonadIO m => IO.Handle -> Consumer' Text m r
 169 toHandle h = for cat (liftIO . T.hPutStr h)
 170 {-# INLINABLE toHandle #-}
 171
 172 {-# RULES "p >-> toHandle h" forall p h .
 173         p >-> toHandle h = for p (\txt -> liftIO (T.hPutStr h txt))
 174   #-}
 175
 176
 177 -- | Stream text into a file. Uses @pipes-safe@.
 178 writeFile :: (MonadSafe m) => FilePath -> Consumer' Text m ()
 179 writeFile file = Safe.withFile file IO.WriteMode toHandle
 180 {-# INLINE writeFile #-}