    {-

    Copyright (c) 2002, members of the Haskell Internationalisation Working
    Group All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:

    * Redistributions of source code must retain the above copyright notice,
       this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright notice,
       this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.
    * Neither the name of the Haskell Internationalisation Working Group nor
       the names of its contributors may be used to endorse or promote products
       derived from this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.

    This module provides lazy stream encoding/decoding facilities for UTF-8,
    the Unicode Transformation Format with 8-bit words.

    2002-09-02  Sven Moritz Hallberg <pesco@gmx.de>

    -}

    {-

    2007-04-30 Henning Thielemann:
    Slight changes to make decode lazy.
    The calls of 'reverse' in the original version have broken laziness
    and thus had memory leaks.

    -}

    module Data.String.UTF8
      ( encode
      , decode
      , decodeEmbedErrors
      , encodeOne
      , decodeOne
      , Error
             -- Haddock does not want to document signatures with private types
             -- these functions should be moved to a utility module
      ) where

    import Data.Char (ord, chr)
    import Data.Word (Word8, Word16, Word32)
    import Data.Bits (shiftL, shiftR, (.&.), (.|.))

    import Data.List (unfoldr)

    -- - UTF-8 in General -

    -- Adapted from the Unicode standard, version 3.2,
    -- Table 3.1 "UTF-8 Bit Distribution" (excluded are UTF-16 encodings):

    --   Scalar                    1st Byte  2nd Byte  3rd Byte  4th Byte
    --           000000000xxxxxxx  0xxxxxxx
    --           00000yyyyyxxxxxx  110yyyyy  10xxxxxx
    --           zzzzyyyyyyxxxxxx  1110zzzz  10yyyyyy  10xxxxxx
    --   000uuuzzzzzzyyyyyyxxxxxx  11110uuu  10zzzzzz  10yyyyyy  10xxxxxx

    -- Also from the Unicode standard, version 3.2,
    -- Table 3.1B "Legal UTF-8 Byte Sequences":

    --   Code Points         1st Byte  2nd Byte  3rd Byte  4th Byte
    --     U+0000..U+007F    00..7F
    --     U+0080..U+07FF    C2..DF    80..BF
    --     U+0800..U+0FFF    E0        A0..BF    80..BF
    --     U+1000..U+CFFF    E1..EC    80..BF    80..BF
    --     U+D000..U+D7FF    ED        80..9F    80..BF
    --     U+D800..U+DFFF    ill-formed
    --     U+E000..U+FFFF    EE..EF    80..BF    80..BF
    --    U+10000..U+3FFFF   F0        90..BF    80..BF    80..BF
    --    U+40000..U+FFFFF   F1..F3    80..BF    80..BF    80..BF
    --   U+100000..U+10FFFF  F4        80..8F    80..BF    80..BF

    -- - Encoding Functions -

    -- Must the encoder ensure that no illegal byte sequences are output or
    -- can we trust the Haskell system to supply only legal values?
    -- For now I include error case for the surrogate values U+D800..U+DFFF and
    -- out-of-range scalars.

    -- The function is pretty much a transscript of table 3.1B with error checks.
    -- It dispatches the actual encoding to functions specific to the number of
    -- required bytes.

    encodeOne :: Char -> [Word8]
    encodeOne :: Char -> [Word8]
    encodeOne Char
    c
        -- The report guarantees in (6.1.2) that this won't happen:
        --   | n < 0       = error "encodeUTF8: ord returned a negative value"
        | Int
    n Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    0x0080  = Word8 -> [Word8]
    encodeOne_onebyte Word8
    n8
        | Int
    n Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    0x0800  = Word16 -> [Word8]
    encodeOne_twobyte Word16
    n16
        | Int
    n Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    0xD800  = Word16 -> [Word8]
    encodeOne_threebyte Word16
    n16
        | Int
    n Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    0xE000  = [Char] -> [Word8]
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "encodeUTF8: ord returned a surrogate value"
        | Int
    n Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    0x10000       = Word16 -> [Word8]
    encodeOne_threebyte Word16
    n16
        -- Haskell 98 only talks about 16 bit characters, but ghc handles 20.1.
        | Int
    n Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    0x10FFFF      = Word32 -> [Word8]
    encodeOne_fourbyte Word32
    n32
        | Bool
    otherwise  = [Char] -> [Word8]
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "encodeUTF8: ord returned a value above 0x10FFFF"
        where
        n :: Int
    n = Char -> Int
    ord Char
    c            :: Int
        n8 :: Word8
    n8 = Int -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral Int
    n  :: Word8
        n16 :: Word16
    n16 = Int -> Word16
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral Int
    n :: Word16
        n32 :: Word32
    n32 = Int -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral Int
    n :: Word32

    -- With the above, a stream decoder is trivial:

    encode :: [Char] -> [Word8]
    encode :: [Char] -> [Word8]
    encode = (Char -> [Word8]) -> [Char] -> [Word8]
    forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
    concatMap Char -> [Word8]
    encodeOne

    -- Now follow the individual encoders for certain numbers of bytes...
    --           _
    --          / |  __  ___  __ __
    --         / ^| //  /__/ // //
    --        /.==| \\ //_  // //
    -- It's  //  || // \_/_//_//_  and it's here to stay!

    encodeOne_onebyte :: Word8 -> [Word8]
    encodeOne_onebyte :: Word8 -> [Word8]
    encodeOne_onebyte Word8
    cp = [Word8
    cp]

    -- 00000yyyyyxxxxxx -> 110yyyyy 10xxxxxx

    encodeOne_twobyte :: Word16 -> [Word8]
    encodeOne_twobyte :: Word16 -> [Word8]
    encodeOne_twobyte Word16
    cp = [(Word8
    0xC0Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    ys), (Word8
    0x80Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    xs)]
        where
        xs, ys :: Word8
        ys :: Word8
    ys = Word16 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word16 -> Int -> Word16
    forall a. Bits a => a -> Int -> a
    shiftR Word16
    cp Int
    6)
        xs :: Word8
    xs = (Word16 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral Word16
    cp) Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F

    -- zzzzyyyyyyxxxxxx -> 1110zzzz 10yyyyyy 10xxxxxx

    encodeOne_threebyte :: Word16 -> [Word8]
    encodeOne_threebyte :: Word16 -> [Word8]
    encodeOne_threebyte Word16
    cp = [(Word8
    0xE0Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    zs), (Word8
    0x80Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    ys), (Word8
    0x80Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    xs)]
        where
        xs, ys, zs :: Word8
        xs :: Word8
    xs = (Word16 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral Word16
    cp) Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F
        ys :: Word8
    ys = (Word16 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word16 -> Int -> Word16
    forall a. Bits a => a -> Int -> a
    shiftR Word16
    cp Int
    6)) Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F
        zs :: Word8
    zs = Word16 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word16 -> Int -> Word16
    forall a. Bits a => a -> Int -> a
    shiftR Word16
    cp Int
    12)

    -- 000uuuzzzzzzyyyyyyxxxxxx -> 11110uuu 10zzzzzz 10yyyyyy 10xxxxxx

    encodeOne_fourbyte :: Word32 -> [Word8]
    encodeOne_fourbyte :: Word32 -> [Word8]
    encodeOne_fourbyte Word32
    cp = [Word8
    0xF0Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    us, Word8
    0x80Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    zs, Word8
    0x80Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    ys, Word8
    0x80Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .|.Word8
    xs]
        where
        xs, ys, zs, us :: Word8
        xs :: Word8
    xs = (Word32 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral Word32
    cp) Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F
        ys :: Word8
    ys = (Word32 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftR Word32
    cp Int
    6)) Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F
        zs :: Word8
    zs = (Word32 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftR Word32
    cp Int
    12)) Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F
        us :: Word8
    us = Word32 -> Word8
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftR Word32
    cp Int
    18)

    -- - Decoding -

    -- The decoding is a bit more involved. The byte sequence could contain all
    -- sorts of corruptions. The user must be able to either notice or ignore these
    -- errors.

    -- I will first look at the decoding of a single character. The process
    -- consumes a certain number of bytes from the input. It returns the
    -- remaining input and either an error and the index of its occurance in the
    -- byte sequence or the decoded character.

    data Error

    -- The first byte in a sequence starts with either zero, two, three, or four
    -- ones and one zero to indicate the length of the sequence. If it doesn't,
    -- it is invalid. It is dropped and the next byte interpreted as the start
    -- of a new sequence.

        = InvalidFirstByte

    -- All bytes in the sequence except the first match the bit pattern 10xxxxxx.
    -- If one doesn't, it is invalid. The sequence up to that point is dropped
    -- and the "invalid" byte interpreted as the start of a new sequence. The error
    -- includes the length of the partial sequence and the number of expected bytes.

        | InvalidLaterByte Int      -- the byte at relative index n was invalid

    -- If a sequence ends prematurely, it has been truncated. It dropped and
    -- decoding stops. The error reports the actual and expected lengths of the
    -- sequence.

        | Truncated Int Int         -- only n of m expected bytes were present

    -- Some sequences would represent code points which would be encoded as a
    -- shorter sequence by a conformant encoder. Such non-shortest sequences are
    -- considered erroneous and dropped. The error reports the actual and
    -- expected number of bytes used.

        | NonShortest Int Int       -- n instead of m bytes were used

    -- Unicode code points are in the range of [0..0x10FFFF]. Any values outside
    -- of those bounds are simply invalid.

        | ValueOutOfBounds

    -- There is no such thing as "surrogate pairs" any more in UTF-8. The
    -- corresponding code points now form illegal byte sequences.

        | Surrogate
          deriving (Int -> Error -> ShowS
    [Error] -> ShowS
    Error -> [Char]
    (Int -> Error -> ShowS)
    -> (Error -> [Char]) -> ([Error] -> ShowS) -> Show Error
    forall a.
    (Int -> a -> ShowS) -> (a -> [Char]) -> ([a] -> ShowS) -> Show a
    $cshowsPrec :: Int -> Error -> ShowS
    showsPrec :: Int -> Error -> ShowS
    $cshow :: Error -> [Char]
    show :: Error -> [Char]
    $cshowList :: [Error] -> ShowS
    showList :: [Error] -> ShowS
    Show, Error -> Error -> Bool
    (Error -> Error -> Bool) -> (Error -> Error -> Bool) -> Eq Error
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: Error -> Error -> Bool
    == :: Error -> Error -> Bool
    $c/= :: Error -> Error -> Bool
    /= :: Error -> Error -> Bool
    Eq)

    -- Second, third, and fourth bytes share the common requirement to start
    -- with the bit sequence 10. So, here's the function to check that property.

    first_bits_not_10 :: Word8 -> Bool
    first_bits_not_10 :: Word8 -> Bool
    first_bits_not_10 Word8
    b
        | (Word8
    bWord8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&.Word8
    0xC0) Word8 -> Word8 -> Bool
    forall a. Eq a => a -> a -> Bool
    /= Word8
    0x80  = Bool
    True
        | Bool
    otherwise           = Bool
    False

    -- Erm, OK, the single-character decoding function's return type is a bit
    -- longish. It is a tripel:

    --  - The first component contains the decoded character or an error
    --    if the byte sequence was erroneous.
    --  - The second component contains the number of bytes that were consumed
    --    from the input.
    --  - The third component contains the remaining bytes of input.

    decodeOne :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne bs :: [Word8]
    bs@(Word8
    b1:[Word8]
    rest)
        | Word8
    b1 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word8
    0x80   = [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_onebyte [Word8]
    bs
        | Word8
    b1 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word8
    0xC0   = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left Error
    InvalidFirstByte, Int
    1, [Word8]
    rest)
        | Word8
    b1 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word8
    0xE0   = [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_twobyte [Word8]
    bs
        | Word8
    b1 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word8
    0xF0   = [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_threebyte [Word8]
    bs
        | Word8
    b1 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word8
    0xF5   = [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_fourbyte [Word8]
    bs
        | Bool
    otherwise   = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left Error
    ValueOutOfBounds, Int
    1, [Word8]
    rest)
    decodeOne [] = [Char] -> (Either Error Char, Int, [Word8])
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "UTF8.decodeOne: No input"

    -- 0xxxxxxx -> 000000000xxxxxxx

    decodeOne_onebyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_onebyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_onebyte (Word8
    b:[Word8]
    bs) = (Char -> Either Error Char
    forall a b. b -> Either a b
    Right (Word8 -> Char
    forall a. Integral a => a -> Char
    cpToChar Word8
    b), Int
    1, [Word8]
    bs)
    decodeOne_onebyte[] = [Char] -> (Either Error Char, Int, [Word8])
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "UTF8.decodeOne_onebyte: No input (can't happen)"

    cpToChar :: Integral a => a -> Char
    cpToChar :: forall a. Integral a => a -> Char
    cpToChar = Int -> Char
    chr (Int -> Char) -> (a -> Int) -> a -> Char
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . a -> Int
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral

    -- 110yyyyy 10xxxxxx -> 00000yyyyyxxxxxx

    decodeOne_twobyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_twobyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_twobyte (Word8
    _:[])
        = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    Truncated Int
    1 Int
    2), Int
    1, [])
    decodeOne_twobyte (Word8
    b1:Word8
    b2:[Word8]
    bs)
        | Word8
    b1 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word8
    0xC2            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    NonShortest Int
    2 Int
    1), Int
    2, [Word8]
    bs)
        | Word8 -> Bool
    first_bits_not_10 Word8
    b2 = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Error
    InvalidLaterByte Int
    1), Int
    1, (Word8
    b2Word8 -> [Word8] -> [Word8]
    forall a. a -> [a] -> [a]
    :[Word8]
    bs))
        | Bool
    otherwise            = (Char -> Either Error Char
    forall a b. b -> Either a b
    Right (Word32 -> Char
    forall a. Integral a => a -> Char
    cpToChar Word32
    result), Int
    2, [Word8]
    bs)
        where
        xs, ys, result :: Word32
        xs :: Word32
    xs = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b2Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&.Word8
    0x3F)
        ys :: Word32
    ys = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b1Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&.Word8
    0x1F)
        result :: Word32
    result = Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftL Word32
    ys Int
    6 Word32 -> Word32 -> Word32
    forall a. Bits a => a -> a -> a
    .|. Word32
    xs
    decodeOne_twobyte[] = [Char] -> (Either Error Char, Int, [Word8])
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "UTF8.decodeOne_twobyte: No input (can't happen)"

    -- 1110zzzz 10yyyyyy 10xxxxxx -> zzzzyyyyyyxxxxxx

    decodeOne_threebyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_threebyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_threebyte (Word8
    _:[])   = Int -> (Either Error Char, Int, [Word8])
    threebyte_truncated Int
    1
    decodeOne_threebyte (Word8
    _:Word8
    _:[]) = Int -> (Either Error Char, Int, [Word8])
    threebyte_truncated Int
    2
    decodeOne_threebyte bs :: [Word8]
    bs@(Word8
    b1:Word8
    b2:Word8
    b3:[Word8]
    rest)
        | Word8 -> Bool
    first_bits_not_10 Word8
    b2
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Error
    InvalidLaterByte Int
    1), Int
    1, Int -> [Word8] -> [Word8]
    forall a. Int -> [a] -> [a]
    drop Int
    1 [Word8]
    bs)
        | Word8 -> Bool
    first_bits_not_10 Word8
    b3
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Error
    InvalidLaterByte Int
    2), Int
    2, Int -> [Word8] -> [Word8]
    forall a. Int -> [a] -> [a]
    drop Int
    2 [Word8]
    bs)
        | Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word32
    0x0080
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    NonShortest Int
    3 Int
    1), Int
    3, [Word8]
    rest)
        | Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word32
    0x0800
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    NonShortest Int
    3 Int
    2), Int
    3, [Word8]
    rest)
        | Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    >= Word32
    0xD800 Bool -> Bool -> Bool
    && Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word32
    0xE000
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left Error
    Surrogate, Int
    3, [Word8]
    rest)
        | Bool
    otherwise
            = (Char -> Either Error Char
    forall a b. b -> Either a b
    Right (Word32 -> Char
    forall a. Integral a => a -> Char
    cpToChar Word32
    result), Int
    3, [Word8]
    rest)
        where
        xs, ys, zs, result :: Word32
        xs :: Word32
    xs = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b3Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&.Word8
    0x3F)
        ys :: Word32
    ys = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b2Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&.Word8
    0x3F)
        zs :: Word32
    zs = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b1Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&.Word8
    0x0F)
        result :: Word32
    result = Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftL Word32
    zs Int
    12 Word32 -> Word32 -> Word32
    forall a. Bits a => a -> a -> a
    .|. Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftL Word32
    ys Int
    6 Word32 -> Word32 -> Word32
    forall a. Bits a => a -> a -> a
    .|. Word32
    xs
    decodeOne_threebyte[]
     = [Char] -> (Either Error Char, Int, [Word8])
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "UTF8.decodeOne_threebyte: No input (can't happen)"

    threebyte_truncated :: Int -> (Either Error Char, Int, [Word8])
    threebyte_truncated :: Int -> (Either Error Char, Int, [Word8])
    threebyte_truncated Int
    n = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    Truncated Int
    n Int
    3), Int
    n, [])

    -- 11110uuu 10zzzzzz 10yyyyyy 10xxxxxx -> 000uuuzzzzzzyyyyyyxxxxxx

    decodeOne_fourbyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_fourbyte :: [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne_fourbyte (Word8
    _:[])     = Int -> (Either Error Char, Int, [Word8])
    fourbyte_truncated Int
    1
    decodeOne_fourbyte (Word8
    _:Word8
    _:[])   = Int -> (Either Error Char, Int, [Word8])
    fourbyte_truncated Int
    2
    decodeOne_fourbyte (Word8
    _:Word8
    _:Word8
    _:[]) = Int -> (Either Error Char, Int, [Word8])
    fourbyte_truncated Int
    3
    decodeOne_fourbyte bs :: [Word8]
    bs@(Word8
    b1:Word8
    b2:Word8
    b3:Word8
    b4:[Word8]
    rest)
        | Word8 -> Bool
    first_bits_not_10 Word8
    b2
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Error
    InvalidLaterByte Int
    1), Int
    1, Int -> [Word8] -> [Word8]
    forall a. Int -> [a] -> [a]
    drop Int
    1 [Word8]
    bs)
        | Word8 -> Bool
    first_bits_not_10 Word8
    b3
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Error
    InvalidLaterByte Int
    2), Int
    2, Int -> [Word8] -> [Word8]
    forall a. Int -> [a] -> [a]
    drop Int
    2 [Word8]
    bs)
        | Word8 -> Bool
    first_bits_not_10 Word8
    b4
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Error
    InvalidLaterByte Int
    3), Int
    3, Int -> [Word8] -> [Word8]
    forall a. Int -> [a] -> [a]
    drop Int
    3 [Word8]
    bs)
        | Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word32
    0x0080
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    NonShortest Int
    4 Int
    1), Int
    4, [Word8]
    rest)
        | Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word32
    0x0800
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    NonShortest Int
    4 Int
    2), Int
    4, [Word8]
    rest)
        | Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    < Word32
    0x10000
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    NonShortest Int
    4 Int
    3), Int
    4, [Word8]
    rest)
        | Word32
    result Word32 -> Word32 -> Bool
    forall a. Ord a => a -> a -> Bool
    > Word32
    0x10FFFF
            = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left Error
    ValueOutOfBounds, Int
    4, [Word8]
    rest)
        | Bool
    otherwise
            = (Char -> Either Error Char
    forall a b. b -> Either a b
    Right (Word32 -> Char
    forall a. Integral a => a -> Char
    cpToChar Word32
    result), Int
    4, [Word8]
    rest)
        where
        xs, ys, zs, us, result :: Word32
        xs :: Word32
    xs = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b4 Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F)
        ys :: Word32
    ys = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b3 Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F)
        zs :: Word32
    zs = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b2 Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x3F)
        us :: Word32
    us = Word8 -> Word32
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (Word8
    b1 Word8 -> Word8 -> Word8
    forall a. Bits a => a -> a -> a
    .&. Word8
    0x07)
        result :: Word32
    result = Word32
    xs Word32 -> Word32 -> Word32
    forall a. Bits a => a -> a -> a
    .|. Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftL Word32
    ys Int
    6 Word32 -> Word32 -> Word32
    forall a. Bits a => a -> a -> a
    .|. Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftL Word32
    zs Int
    12 Word32 -> Word32 -> Word32
    forall a. Bits a => a -> a -> a
    .|. Word32 -> Int -> Word32
    forall a. Bits a => a -> Int -> a
    shiftL Word32
    us Int
    18
    decodeOne_fourbyte[]
     = [Char] -> (Either Error Char, Int, [Word8])
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "UTF8.decodeOne_fourbyte: No input (can't happen)"

    fourbyte_truncated :: Int -> (Either Error Char, Int, [Word8])
    fourbyte_truncated :: Int -> (Either Error Char, Int, [Word8])
    fourbyte_truncated Int
    n = (Error -> Either Error Char
    forall a b. a -> Either a b
    Left (Int -> Int -> Error
    Truncated Int
    n Int
    4), Int
    n, [])

    -- The decoder examines all input, recording decoded characters as well as
    -- error-index pairs along the way.

    decode :: [Word8] -> ([Char], [(Error,Int)])
    decode :: [Word8] -> ([Char], [(Error, Int)])
    decode = ([(Error, Int)], [Char]) -> ([Char], [(Error, Int)])
    forall a b. (a, b) -> (b, a)
    swap (([(Error, Int)], [Char]) -> ([Char], [(Error, Int)]))
    -> ([Word8] -> ([(Error, Int)], [Char]))
    -> [Word8]
    -> ([Char], [(Error, Int)])
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . [Either (Error, Int) Char] -> ([(Error, Int)], [Char])
    forall a b. [Either a b] -> ([a], [b])
    partitionEither ([Either (Error, Int) Char] -> ([(Error, Int)], [Char]))
    -> ([Word8] -> [Either (Error, Int) Char])
    -> [Word8]
    -> ([(Error, Int)], [Char])
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . [Word8] -> [Either (Error, Int) Char]
    decodeEmbedErrors

    decodeEmbedErrors :: [Word8] -> [Either (Error,Int) Char]
    decodeEmbedErrors :: [Word8] -> [Either (Error, Int) Char]
    decodeEmbedErrors =
       ((Int, [Word8])
     -> Maybe (Either (Error, Int) Char, (Int, [Word8])))
    -> (Int, [Word8]) -> [Either (Error, Int) Char]
    forall b a. (b -> Maybe (a, b)) -> b -> [a]
    unfoldr (\(Int
    pos,[Word8]
    xs) ->
           Bool
    -> (Either (Error, Int) Char, (Int, [Word8]))
    -> Maybe (Either (Error, Int) Char, (Int, [Word8]))
    forall a. Bool -> a -> Maybe a
    toMaybe
              (Bool -> Bool
    not (Bool -> Bool) -> Bool -> Bool
    forall a b. (a -> b) -> a -> b
    $ [Word8] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Word8]
    xs)
              (let (Either Error Char
    c,Int
    n,[Word8]
    rest) = [Word8] -> (Either Error Char, Int, [Word8])
    decodeOne [Word8]
    xs
               in  ((Error -> Either (Error, Int) Char)
    -> (Char -> Either (Error, Int) Char)
    -> Either Error Char
    -> Either (Error, Int) Char
    forall a c b. (a -> c) -> (b -> c) -> Either a b -> c
    either (\Error
    err -> (Error, Int) -> Either (Error, Int) Char
    forall a b. a -> Either a b
    Left (Error
    err,Int
    pos)) Char -> Either (Error, Int) Char
    forall a b. b -> Either a b
    Right Either Error Char
    c,
                    (Int
    posInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +Int
    n,[Word8]
    rest)))) ((Int, [Word8]) -> [Either (Error, Int) Char])
    -> ([Word8] -> (Int, [Word8]))
    -> [Word8]
    -> [Either (Error, Int) Char]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    .
       (,) Int
    0

    swap :: (a,b) -> (b,a)
    swap :: forall a b. (a, b) -> (b, a)
    swap (a
    x,b
    y) = (b
    y,a
    x)
    {-# INLINE swap #-}

    partitionEither :: [Either a b] -> ([a], [b])
    partitionEither :: forall a b. [Either a b] -> ([a], [b])
    partitionEither =
       (Either a b -> ([a], [b]) -> ([a], [b]))
    -> ([a], [b]) -> [Either a b] -> ([a], [b])
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (\Either a b
    x ~([a]
    ls,[b]
    rs) -> (a -> ([a], [b])) -> (b -> ([a], [b])) -> Either a b -> ([a], [b])
    forall a c b. (a -> c) -> (b -> c) -> Either a b -> c
    either (\a
    l -> (a
    la -> [a] -> [a]
    forall a. a -> [a] -> [a]
    :[a]
    ls,[b]
    rs)) (\b
    r -> ([a]
    ls,b
    rb -> [b] -> [b]
    forall a. a -> [a] -> [a]
    :[b]
    rs)) Either a b
    x) ([],[])
    {-# INLINE partitionEither #-}

    toMaybe :: Bool -> a -> Maybe a
    toMaybe :: forall a. Bool -> a -> Maybe a
    toMaybe Bool
    False a
    _ = Maybe a
    forall a. Maybe a
    Nothing
    toMaybe Bool
    True  a
    x = a -> Maybe a
    forall a. a -> Maybe a
    Just a
    x
    {-# INLINE toMaybe #-}

    -- ------------------------------------------------------------