renamed fold foldChars and began updating documentation

2 files changed, 239 insertions, 43 deletions

diff --git a/Pipes/Text/Internal.hs b/Pipes/Text/Internal.hs
index 7e5b044..76c2f4f 100644
--- a/Pipes/Text/Internal.hs
+++ b/Pipes/Text/Internal.hs
@@ -1,5 +1,7 @@
-{-# LANGUAGE BangPatterns, CPP, ForeignFunctionInterface, GeneralizedNewtypeDeriving, MagicHash,
-    UnliftedFFITypes #-}
+{-# LANGUAGE BangPatterns, CPP, ForeignFunctionInterface #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving, MagicHash, UnliftedFFITypes #-}
+{-# LANGUAGE DeriveDataTypeable, RankNTypes #-}
+
 -- This module lifts assorted materials from Brian O'Sullivan's text package 
 -- especially Data.Text.Encoding in order to define a pipes-appropriate
 -- streamDecodeUtf8
@@ -7,13 +9,20 @@ module Pipes.Text.Internal
     ( Decoding(..)
     , streamDecodeUtf8
     , decodeSomeUtf8
+    , Codec(..)
+    , TextException(..)
+    , utf8
     ) where
 import Control.Monad.ST.Unsafe (unsafeIOToST, unsafeSTToIO)
 import Control.Monad.ST (ST, runST)
 import Data.Bits ((.&.))
 import Data.ByteString as B 
+import Data.ByteString (ByteString)
 import Data.ByteString.Internal as B 
-import qualified Data.Text as T (null)
+import Data.ByteString.Char8 as B8
+import Data.Text (Text)
+import qualified Data.Text as T 
+import qualified Data.Text.Encoding as TE 
 import Data.Text.Encoding.Error ()
 import Data.Text.Internal (Text, textP)
 import Foreign.C.Types (CSize)
@@ -24,9 +33,226 @@ import Foreign.Storable (Storable, peek, poke)
 import GHC.Base  (Char(..), Int(..), MutableByteArray#, ord#, iShiftRA#)
 import GHC.Word (Word8, Word32)
 import qualified Data.Text.Array as A
-    
+import Data.Word (Word8, Word16)
+import System.IO.Unsafe (unsafePerformIO)
+import qualified Control.Exception as Exc
+import Data.Bits ((.&.), (.|.), shiftL)
+import Data.Typeable
+import Control.Arrow (first)
+import Data.Maybe (catMaybes)
 #include "pipes_text_cbits.h"
 
+
+-- | A specific character encoding.
+--
+-- Since 0.3.0
+data Codec = Codec
+  { codecName :: Text
+  , codecEncode :: Text -> (ByteString, Maybe (TextException, Text))
+  , codecDecode :: ByteString -> Decoding -- (Text, Either (TextException, ByteString) ByteString)
+  }
+
+instance Show Codec where
+    showsPrec d c = showParen (d > 10) $ showString "Codec " . shows (codecName c)
+
+-- Since 0.3.0
+data TextException = DecodeException Codec Word8
+                   | EncodeException Codec Char
+                   | LengthExceeded Int
+                   | TextException Exc.SomeException
+    deriving (Show, Typeable)
+instance Exc.Exception TextException
+
+toDecoding :: (ByteString -> (Text, Either (TextException, ByteString) ByteString))
+           -> (ByteString -> Decoding)
+toDecoding op = loop B.empty where
+  loop extra bs0 = case op (B.append extra bs0) of
+                    (txt, Right bs) -> Some txt bs (loop bs)
+                    (txt, Left (_,bs)) -> Other txt bs
+
+
+splitSlowly :: (ByteString -> Text)
+            -> ByteString 
+            -> (Text, Either (TextException, ByteString) ByteString)
+splitSlowly dec bytes = valid where
+    valid:_ = catMaybes $ Prelude.map decFirst $ splits (B.length bytes)
+    splits 0 = [(B.empty, bytes)]
+    splits n = B.splitAt n bytes : splits (n - 1)
+    decFirst (a, b) = case tryEvaluate (dec a) of
+        Left _ -> Nothing
+        Right text -> let trouble = case tryEvaluate (dec b) of
+                            Left exc -> Left (TextException exc, b)
+                            Right _  -> Right B.empty 
+                      in Just (text, trouble)
+                                      -- this case shouldn't occur, 
+                                      -- since splitSlowly is only called
+                                      -- when parsing failed somewhere
+
+utf8 :: Codec
+utf8 = Codec name enc (toDecoding dec) where
+    name = T.pack "UTF-8"
+    enc text = (TE.encodeUtf8 text, Nothing)
+    dec bytes = case decodeSomeUtf8 bytes of 
+      (t,b) -> (t, Right b)
+
+--     -- Whether the given byte is a continuation byte.
+--     isContinuation byte = byte .&. 0xC0 == 0x80
+-- 
+--     -- The number of continuation bytes needed by the given
+--     -- non-continuation byte. Returns -1 for an illegal UTF-8
+--     -- non-continuation byte and the whole split quickly must fail so
+--     -- as the input is passed to TE.decodeUtf8, which will issue a
+--     -- suitable error.
+--     required x0
+--         | x0 .&. 0x80 == 0x00 = 0
+--         | x0 .&. 0xE0 == 0xC0 = 1
+--         | x0 .&. 0xF0 == 0xE0 = 2
+--         | x0 .&. 0xF8 == 0xF0 = 3
+--         | otherwise           = -1
+-- 
+--     splitQuickly bytes
+--         | B.null l || req == -1 = Nothing
+--         | req == B.length r = Just (TE.decodeUtf8 bytes, B.empty)
+--         | otherwise = Just (TE.decodeUtf8 l', r')
+--       where
+--         (l, r) = B.spanEnd isContinuation bytes
+--         req = required (B.last l)
+--         l' = B.init l
+--         r' = B.cons (B.last l) r
+
+-- |
+-- Since 0.3.0
+utf16_le :: Codec
+utf16_le = Codec name enc (toDecoding dec) where
+    name = T.pack "UTF-16-LE"
+    enc text = (TE.encodeUtf16LE text, Nothing)
+    dec bytes = case splitQuickly bytes of
+        Just (text, extra) -> (text, Right extra)
+        Nothing -> splitSlowly TE.decodeUtf16LE bytes
+
+    splitQuickly bytes = maybeDecode (loop 0) where
+        maxN = B.length bytes
+
+        loop n |  n      == maxN = decodeAll
+               | (n + 1) == maxN = decodeTo n
+        loop n = let
+            req = utf16Required
+                (B.index bytes n)
+                (B.index bytes (n + 1))
+            decodeMore = loop $! n + req
+            in if n + req > maxN
+                then decodeTo n
+                else decodeMore
+
+        decodeTo n = first TE.decodeUtf16LE (B.splitAt n bytes)
+        decodeAll = (TE.decodeUtf16LE bytes, B.empty)
+
+-- |
+-- Since 0.3.0
+utf16_be :: Codec
+utf16_be = Codec name enc (toDecoding dec) where
+    name = T.pack "UTF-16-BE"
+    enc text = (TE.encodeUtf16BE text, Nothing)
+    dec bytes = case splitQuickly bytes of
+        Just (text, extra) -> (text, Right extra)
+        Nothing -> splitSlowly TE.decodeUtf16BE bytes
+
+    splitQuickly bytes = maybeDecode (loop 0) where
+        maxN = B.length bytes
+
+        loop n |  n      == maxN = decodeAll
+               | (n + 1) == maxN = decodeTo n
+        loop n = let
+            req = utf16Required
+                (B.index bytes (n + 1))
+                (B.index bytes n)
+            decodeMore = loop $! n + req
+            in if n + req > maxN
+                then decodeTo n
+                else decodeMore
+
+        decodeTo n = first TE.decodeUtf16BE (B.splitAt n bytes)
+        decodeAll = (TE.decodeUtf16BE bytes, B.empty)
+
+utf16Required :: Word8 -> Word8 -> Int
+utf16Required x0 x1 = if x >= 0xD800 && x <= 0xDBFF then 4 else 2 where
+    x :: Word16
+    x = (fromIntegral x1 `shiftL` 8) .|. fromIntegral x0
+
+-- |
+-- Since 0.3.0
+utf32_le :: Codec
+utf32_le = Codec name enc (toDecoding dec) where
+    name = T.pack "UTF-32-LE"
+    enc text = (TE.encodeUtf32LE text, Nothing)
+    dec bs = case utf32SplitBytes TE.decodeUtf32LE bs of
+        Just (text, extra) -> (text, Right extra)
+        Nothing -> splitSlowly TE.decodeUtf32LE bs
+
+-- |
+-- Since 0.3.0
+utf32_be :: Codec
+utf32_be = Codec name enc (toDecoding dec) where
+    name = T.pack "UTF-32-BE"
+    enc text = (TE.encodeUtf32BE text, Nothing)
+    dec bs = case utf32SplitBytes TE.decodeUtf32BE bs of
+        Just (text, extra) -> (text, Right extra)
+        Nothing -> splitSlowly TE.decodeUtf32BE bs
+
+utf32SplitBytes :: (ByteString -> Text)
+                -> ByteString
+                -> Maybe (Text, ByteString)
+utf32SplitBytes dec bytes = split where
+    split = maybeDecode (dec toDecode, extra)
+    len = B.length bytes
+    lenExtra = mod len 4
+
+    lenToDecode = len - lenExtra
+    (toDecode, extra) = if lenExtra == 0
+        then (bytes, B.empty)
+        else B.splitAt lenToDecode bytes
+
+-- |
+-- Since 0.3.0
+ascii :: Codec
+ascii = Codec name enc (toDecoding dec) where
+    name = T.pack "ASCII"
+    enc text = (bytes, extra) where
+        (safe, unsafe) = T.span (\c -> ord c <= 0x7F) text
+        bytes = B8.pack (T.unpack safe)
+        extra = if T.null unsafe
+            then Nothing
+            else Just (EncodeException ascii (T.head unsafe), unsafe)
+
+    dec bytes = (text, extra) where
+        (safe, unsafe) = B.span (<= 0x7F) bytes
+        text = T.pack (B8.unpack safe)
+        extra = if B.null unsafe
+            then Right B.empty
+            else Left (DecodeException ascii (B.head unsafe), unsafe)
+
+-- |
+-- Since 0.3.0
+iso8859_1 :: Codec
+iso8859_1 = Codec name enc (toDecoding dec) where
+    name = T.pack "ISO-8859-1"
+    enc text = (bytes, extra) where
+        (safe, unsafe) = T.span (\c -> ord c <= 0xFF) text
+        bytes = B8.pack (T.unpack safe)
+        extra = if T.null unsafe
+            then Nothing
+            else Just (EncodeException iso8859_1 (T.head unsafe), unsafe)
+
+    dec bytes = (T.pack (B8.unpack bytes), Right B.empty)
+
+tryEvaluate :: a -> Either Exc.SomeException a
+tryEvaluate = unsafePerformIO . Exc.try . Exc.evaluate
+
+maybeDecode :: (a, b) -> Maybe (a, b)
+maybeDecode (a, b) = case tryEvaluate a of
+    Left _ -> Nothing
+    Right _ -> Just (a, b)
+
 -- | A stream oriented decoding result.
 data Decoding = Some Text ByteString (ByteString -> Decoding)
               | Other Text ByteString
@@ -103,36 +329,6 @@ decodeSomeUtf8 bs@(PS fp off len) = runST $ do
           return $! (chunkText, remaining)
 {-# INLINE decodeSomeUtf8 #-}
 
--- decodeSomeUtf8 :: ByteString -> (Text, ByteString)
--- decodeSomeUtf8 bs@(PS fp off len) = 
---                   runST $ do marray <- A.new (len+1) 
---                              unsafeIOToST (decodeChunkToBuffer marray)
---   
---      where
---      decodeChunkToBuffer :: A.MArray s -> IO (Text, ByteString)
---      decodeChunkToBuffer dest = withForeignPtr fp $ \ptr ->
---        with (0::CSize)        $ \destOffPtr ->
---        with (0::CodePoint)    $ \codepointPtr ->
---        with (0::DecoderState) $ \statePtr ->
---        with nullPtr           $ \curPtrPtr ->
---          do let end = ptr `plusPtr` (off + len)
---                 curPtr = ptr `plusPtr` off
---             poke curPtrPtr curPtr
---             c_decode_utf8_with_state (A.maBA dest) destOffPtr curPtrPtr end codepointPtr statePtr
---             state <- peek statePtr
---             lastPtr <- peek curPtrPtr
---             codepoint <- peek codepointPtr
---             n <- peek destOffPtr
---             chunkText <- unsafeSTToIO $ do arr <- A.unsafeFreeze dest
---                                            return $! textP arr 0 (fromIntegral n)
---             let left      = lastPtr `minusPtr` curPtr
---                 remaining = B.drop left bs
---             return $! (chunkText, remaining)
---      {-# INLINE decodeChunkToBuffer #-}
--- {-# INLINE decodeSomeUtf8 #-}
-
-
-
 mkText :: A.MArray s -> CSize -> IO Text
 mkText dest n =  unsafeSTToIO $ do arr <- A.unsafeFreeze dest
                                    return $! textP arr 0 (fromIntegral n)
diff --git a/Pipes/Text/Parse.hs b/Pipes/Text/Parse.hs
index ed0afa1..9cabaa6 100644
--- a/Pipes/Text/Parse.hs
+++ b/Pipes/Text/Parse.hs
@@ -44,16 +44,16 @@ nextChar = go
 {-| Draw one 'Char' from the underlying 'Producer', returning 'Left' if the
     'Producer' is empty
 -}
-drawChar :: (Monad m) => StateT (Producer Text m r) m (Either r Char)
+drawChar :: (Monad m) => StateT (Producer Text m r) m (Maybe Char)
 drawChar = do
     x <- PP.draw
     case x of
-        Left  r  -> return (Left r)
-        Right txt -> case (T.uncons txt) of
+        Nothing  -> return Nothing
+        Just txt -> case (T.uncons txt) of
             Nothing        -> drawChar
             Just (c, txt') -> do
                 PP.unDraw txt'
-                return (Right c)
+                return (Just c)
 {-# INLINABLE drawChar #-}
 
 -- | Push back a 'Char' onto the underlying 'Producer'
@@ -71,12 +71,12 @@ unDrawChar c = modify (yield (T.singleton c) >>)
 >         Right c -> unDrawChar c
 >     return x
 -}
-peekChar :: (Monad m) => StateT (Producer Text m r) m (Either r Char)
+peekChar :: (Monad m) => StateT (Producer Text m r) m (Maybe Char)
 peekChar = do
     x <- drawChar
     case x of
-        Left  _  -> return ()
-        Right c -> unDrawChar c
+        Nothing  -> return ()
+        Just c -> unDrawChar c
     return x
 {-# INLINABLE peekChar #-}
 
@@ -91,8 +91,8 @@ isEndOfChars :: (Monad m) => StateT (Producer Text m r) m Bool
 isEndOfChars = do
     x <- peekChar
     return (case x of
-        Left  _ -> True
-        Right _ -> False )
+        Nothing -> True
+        Just _-> False )
 {-# INLINABLE isEndOfChars #-}
 
 {-| @(take n)@ only allows @n@ characters to pass