separated line-based material

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diff --git a/Pipes/Prelude/Text.hs b/Pipes/Prelude/Text.hs
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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'. 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 #-}
+