further line-based functions

1 files changed, 177 insertions, 43 deletions

diff --git a/Pipes/Text/IO.hs b/Pipes/Text/IO.hs
index 51c6926..d30f13c 100644
--- a/Pipes/Text/IO.hs
+++ b/Pipes/Text/IO.hs
@@ -3,22 +3,39 @@
 
 module Pipes.Text.IO 
    ( 
-   -- * Text IO
+   -- * Simple line-based Text IO
+   -- $lineio
+   
+   fromHandleLn
+   , toHandleLn
+   , stdinLn
+   , stdoutLn
+   , stdoutLn'
+   , readFileLn
+   , writeFileLn
+  
+
+   -- * Simple streaming text IO
    -- $textio
    
    -- * Caveats
    -- $caveats
    
    -- * Producers
-   fromHandle
-   , fromHandleLn
+   , fromHandle
    , stdin
    , readFile
-   , readFileLn
+   
    -- * Consumers
    , toHandle
    , stdout
    , writeFile
+   
+   -- * Re-exports
+   , MonadSafe(..)
+   , runSafeT
+   , runSafeP
+   , Safe.withFile
    ) where
 
 import qualified System.IO as IO
@@ -30,14 +47,164 @@ 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 Pipes.Safe (MonadSafe(..), runSafeT, runSafeP)
 import Prelude hiding (readFile, writeFile)
 
+{- $lineio
+   Line-based operations are marked with a final \-@Ln@, like 'stdinLn', 'readFileLn'. They are
+   drop-in replacements for the line-based operations in @Pipes.Prelude@ and
+   @Pipes.Safe.Prelude@ - the final \-@Ln@ being added where necessary. 
+   With them, one is producing, piping and consuming semantically significant individual texts, 
+   understood as lines, just as one would pipe 'Int's. The standard materials from @Pipes@ and @Pipes.Prelude@ and
+   @Data.Text@ are all you need to interact with these lines as you read or write them.
+   You can use these operations without using any of the other material 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@ and the user who needs no more
+   can use them ignoring the rest of this package.
+
+   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 'String's 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's 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 #-}
+
+
+
 {- $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 official IO of this package and the pipes ecosystem generally would use the
+    IO functions in @Pipes.ByteString@ and the encoding and decoding material in 
+    @Pipes.Text.Encoding@.
+
+    The streaming functions exported here, namely, 'readFile', 'writeFile', 'fromHandle', 'toHandle', 
+    'stdin' and 'stdout' simplify this and use the system encoding on the model of @Data.Text.IO@ 
+    and @Data.Text.Lazy.IO@  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>:
@@ -69,6 +236,8 @@ To stream from files, the following is perhaps more Prelude-like (note that it u
 
 > main = runEffect $ Text.stdin >-> Text.stdout
 
+    These programs, unlike the corresponding programs written with the line-based functions,
+    will pass along a 1 terabyte line without affecting memory use. 
 
 -}
 
@@ -87,23 +256,6 @@ To stream from files, the following is perhaps more Prelude-like (note that it u
   
     * 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 
@@ -122,18 +274,6 @@ fromHandle h =  go where
 {-# INLINABLE fromHandle#-}
 
 
-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 #-}
-
 -- | Stream text from 'stdin'
 stdin :: MonadIO m => Producer Text m ()
 stdin = fromHandle IO.stdin
@@ -151,12 +291,6 @@ readFile file = Safe.withFile file IO.ReadMode fromHandle
 {-# INLINE readFile #-}
 
 
-{-| Stream lines of text from a file
--}
-readFileLn :: MonadSafe m => FilePath -> Producer Text m ()
-readFileLn file = Safe.withFile file IO.ReadMode fromHandleLn
-{-# INLINE readFileLn #-}
-
 
 {-| Stream text to 'stdout'