    {-# LANGUAGE BangPatterns, CPP, MagicHash #-}

    -- |
    -- Module      : Data.Text.Internal.Fusion
    -- Copyright   : (c) Tom Harper 2008-2009,
    --               (c) Bryan O'Sullivan 2009-2010,
    --               (c) Duncan Coutts 2009
    --
    -- License     : BSD-style
    -- Maintainer  : bos@serpentine.com
    -- Stability   : experimental
    -- Portability : GHC
    --
    -- /Warning/: this is an internal module, and does not have a stable
    -- API or name. Functions in this module may not check or enforce
    -- preconditions expected by public modules. Use at your own risk!
    --
    -- Text manipulation functions represented as fusible operations over
    -- streams.
    module Data.Text.Internal.Fusion
        (
        -- * Types
          Stream(..)
        , Step(..)

        -- * Creation and elimination
        , stream
        , unstream
        , reverseStream

        , length

        -- * Transformations
        , reverse

        -- * Construction
        -- ** Scans
        , reverseScanr

        -- ** Accumulating maps
        , mapAccumL

        -- ** Generation and unfolding
        , unfoldrN

        -- * Indexing
        , index
        , findIndex
        , countChar
        ) where

    import Prelude (Bool(..), Char, Maybe(..), Monad(..), Int,
                    Num(..), Ord(..), ($),
                    otherwise)
    import Data.Bits (shiftL, shiftR)
    import Data.Text.Internal (Text(..))
    import Data.Text.Internal.Private (runText)
    import Data.Text.Internal.Unsafe.Char (unsafeChr8, unsafeWrite)
    import qualified Data.Text.Array as A
    import qualified Data.Text.Internal.Fusion.Common as S
    import Data.Text.Internal.Fusion.Types
    import Data.Text.Internal.Fusion.Size
    import qualified Data.Text.Internal as I
    import qualified Data.Text.Internal.Encoding.Utf8 as U8
    import GHC.Stack (HasCallStack)

    default(Int)

    -- | /O(n)/ Convert 'Text' into a 'Stream' 'Char'.
    --
    -- __Properties__
    --
    -- @'unstream' . 'stream' = 'Data.Function.id'@
    --
    -- @'stream' . 'unstream' = 'Data.Function.id' @
    stream ::
    #if defined(ASSERTS)
      HasCallStack =>
    #endif
      Text -> Stream Char
    stream :: Text -> Stream Char
    stream (Text Array
    arr Int
    off Int
    len) = (Int -> Step Int Char) -> Int -> Size -> Stream Char
    forall a s. (s -> Step s a) -> s -> Size -> Stream a
    Stream Int -> Step Int Char
    next Int
    off (Int -> Int -> Size
    betweenSize (Int
    len Int -> Int -> Int
    forall a. Bits a => a -> Int -> a
    `shiftR` Int
    2) Int
    len)
        where
          !end :: Int
    end = Int
    offInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +Int
    len
          next :: Int -> Step Int Char
    next !Int
    i
              | Int
    i Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    >= Int
    end  = Step Int Char
    forall s a. Step s a
    Done
              | Bool
    otherwise = Char -> Int -> Step Int Char
    forall s a. a -> s -> Step s a
    Yield Char
    chr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    l)
              where
                n0 :: Word8
    n0 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr Int
    i
                n1 :: Word8
    n1 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    1)
                n2 :: Word8
    n2 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    2)
                n3 :: Word8
    n3 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    3)

                l :: Int
    l  = Word8 -> Int
    U8.utf8LengthByLeader Word8
    n0
                chr :: Char
    chr = case Int
    l of
                  Int
    1 -> Word8 -> Char
    unsafeChr8 Word8
    n0
                  Int
    2 -> Word8 -> Word8 -> Char
    U8.chr2 Word8
    n0 Word8
    n1
                  Int
    3 -> Word8 -> Word8 -> Word8 -> Char
    U8.chr3 Word8
    n0 Word8
    n1 Word8
    n2
                  Int
    _ -> Word8 -> Word8 -> Word8 -> Word8 -> Char
    U8.chr4 Word8
    n0 Word8
    n1 Word8
    n2 Word8
    n3
    {-# INLINE [0] stream #-}

    -- | /O(n)/ Converts 'Text' into a 'Stream' 'Char', but iterates
    -- backwards through the text.
    --
    -- __Properties__
    --
    -- @'unstream' . 'reverseStream' = 'Data.Text.reverse' @
    reverseStream :: Text -> Stream Char
    reverseStream :: Text -> Stream Char
    reverseStream (Text Array
    arr Int
    off Int
    len) = (Int -> Step Int Char) -> Int -> Size -> Stream Char
    forall a s. (s -> Step s a) -> s -> Size -> Stream a
    Stream Int -> Step Int Char
    next (Int
    offInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +Int
    lenInt -> Int -> Int
    forall a. Num a => a -> a -> a
    -Int
    1) (Int -> Int -> Size
    betweenSize (Int
    len Int -> Int -> Int
    forall a. Bits a => a -> Int -> a
    `shiftR` Int
    2) Int
    len)
        where
          {-# INLINE next #-}
          next :: Int -> Step Int Char
    next !Int
    i
              | Int
    i Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    off    = Step Int Char
    forall s a. Step s a
    Done
              | Word8
    n0 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    <  Word8
    0x80 = Char -> Int -> Step Int Char
    forall s a. a -> s -> Step s a
    Yield (Word8 -> Char
    unsafeChr8 Word8
    n0)       (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    1)
              | Word8
    n1 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    >= Word8
    0xC0 = Char -> Int -> Step Int Char
    forall s a. a -> s -> Step s a
    Yield (Word8 -> Word8 -> Char
    U8.chr2 Word8
    n1 Word8
    n0)       (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    2)
              | Word8
    n2 Word8 -> Word8 -> Bool
    forall a. Ord a => a -> a -> Bool
    >= Word8
    0xC0 = Char -> Int -> Step Int Char
    forall s a. a -> s -> Step s a
    Yield (Word8 -> Word8 -> Word8 -> Char
    U8.chr3 Word8
    n2 Word8
    n1 Word8
    n0)    (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    3)
              | Bool
    otherwise  = Char -> Int -> Step Int Char
    forall s a. a -> s -> Step s a
    Yield (Word8 -> Word8 -> Word8 -> Word8 -> Char
    U8.chr4 Word8
    n3 Word8
    n2 Word8
    n1 Word8
    n0) (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    4)
              where
                n0 :: Word8
    n0 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr Int
    i
                n1 :: Word8
    n1 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    1)
                n2 :: Word8
    n2 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    2)
                n3 :: Word8
    n3 = Array -> Int -> Word8
    A.unsafeIndex Array
    arr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    3)
    {-# INLINE [0] reverseStream #-}

    -- | /O(n)/ Convert 'Stream' 'Char' into a 'Text'.
    --
    -- __Properties__
    --
    -- @'unstream' . 'stream' = 'Data.Function.id'@
    --
    -- @'stream' . 'unstream' = 'Data.Function.id' @
    unstream :: Stream Char -> Text
    unstream :: Stream Char -> Text
    unstream (Stream s -> Step s Char
    next0 s
    s0 Size
    len) = (forall s. (MArray s -> Int -> ST s Text) -> ST s Text) -> Text
    runText ((forall s. (MArray s -> Int -> ST s Text) -> ST s Text) -> Text)
    -> (forall s. (MArray s -> Int -> ST s Text) -> ST s Text) -> Text
    forall a b. (a -> b) -> a -> b
    $ \MArray s -> Int -> ST s Text
    done -> do
      -- Before encoding each char we perform a buffer realloc check assuming
      -- worst case encoding size of four 8-bit units for the char. Just add an
      -- extra space to the buffer so that we do not end up reallocating even when
      -- all the chars are encoded as single unit.
      let mlen :: Int
    mlen = Int -> Size -> Int
    upperBound Int
    4 Size
    len Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    3
      arr0 <- Int -> ST s (MArray s)
    forall s. Int -> ST s (MArray s)
    A.new Int
    mlen
      let outer !MArray s
    arr !Int
    maxi = s -> Int -> ST s Text
    encode
           where
            -- keep the common case loop as small as possible
            encode :: s -> Int -> ST s Text
    encode !s
    si !Int
    di =
                case s -> Step s Char
    next0 s
    si of
                    Step s Char
    Done        -> MArray s -> Int -> ST s Text
    done MArray s
    arr Int
    di
                    Skip s
    si'    -> s -> Int -> ST s Text
    encode s
    si' Int
    di
                    Yield Char
    c s
    si'
                        -- simply check for the worst case
                        | Int
    maxi Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    di Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    3 -> s -> Int -> ST s Text
    realloc s
    si Int
    di
                        | Bool
    otherwise -> do
                                n <- MArray s -> Int -> Char -> ST s Int
    forall s. MArray s -> Int -> Char -> ST s Int
    unsafeWrite MArray s
    arr Int
    di Char
    c
                                encode si' (di + n)

            -- keep uncommon case separate from the common case code
            {-# NOINLINE realloc #-}
            realloc :: s -> Int -> ST s Text
    realloc !s
    si !Int
    di = do
                let newlen :: Int
    newlen = (Int
    maxi Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    1) Int -> Int -> Int
    forall a. Num a => a -> a -> a
    * Int
    2
                arr' <- MArray s -> Int -> ST s (MArray s)
    forall s. MArray s -> Int -> ST s (MArray s)
    A.resizeM MArray s
    arr Int
    newlen
                outer arr' (newlen - 1) si di

      outer arr0 (mlen - 1) s0 0
    {-# INLINE [0] unstream #-}
    {-# RULES "STREAM stream/unstream fusion" forall s. stream (unstream s) = s #-}

    -- ----------------------------------------------------------------------------
    -- * Basic stream functions

    -- | /O(n)/ Returns the number of characters in a 'Stream'.
    --
    -- __Properties__
    --
    -- @'length' . 'stream' = 'Data.Text.length' @
    length :: Stream Char -> Int
    length :: Stream Char -> Int
    length = Stream Char -> Int
    forall a. Integral a => Stream Char -> a
    S.lengthI
    {-# INLINE[0] length #-}

    -- | /O(n)/ Reverse the characters of a 'Stream' returning 'Text'.
    --
    -- __Properties__
    --
    -- @'reverse' . 'stream' = 'Data.Text.reverse' @
    reverse ::
    #if defined(ASSERTS)
      HasCallStack =>
    #endif
      Stream Char -> Text
    reverse :: Stream Char -> Text
    reverse (Stream s -> Step s Char
    next s
    s Size
    len0)
        | Size -> Bool
    isEmpty Size
    len0 = Text
    I.empty
        | Bool
    otherwise    = Array -> Int -> Int -> Text
    I.text Array
    arr Int
    off' Int
    len'
      where
        len0' :: Int
    len0' = Int -> Size -> Int
    upperBound Int
    4 (Size -> Size -> Size
    larger Size
    len0 Size
    4)
        (Array
    arr, (Int
    off', Int
    len')) = (forall s. ST s (MArray s, (Int, Int))) -> (Array, (Int, Int))
    forall a. (forall s. ST s (MArray s, a)) -> (Array, a)
    A.run2 (Int -> ST s (MArray s)
    forall s. Int -> ST s (MArray s)
    A.new Int
    len0' ST s (MArray s)
    -> (MArray s -> ST s (MArray s, (Int, Int)))
    -> ST s (MArray s, (Int, Int))
    forall a b. ST s a -> (a -> ST s b) -> ST s b
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= s -> Int -> Int -> MArray s -> ST s (MArray s, (Int, Int))
    forall {s}.
    s
    -> Int
    -> Int
    -> MutableByteArray s
    -> ST s (MutableByteArray s, (Int, Int))
    loop s
    s (Int
    len0'Int -> Int -> Int
    forall a. Num a => a -> a -> a
    -Int
    1) Int
    len0')
        loop :: s
    -> Int
    -> Int
    -> MutableByteArray s
    -> ST s (MutableByteArray s, (Int, Int))
    loop !s
    s0 !Int
    i !Int
    len MutableByteArray s
    marr =
            case s -> Step s Char
    next s
    s0 of
              Step s Char
    Done -> (MutableByteArray s, (Int, Int))
    -> ST s (MutableByteArray s, (Int, Int))
    forall a. a -> ST s a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (MutableByteArray s
    marr, (Int
    j, Int
    lenInt -> Int -> Int
    forall a. Num a => a -> a -> a
    -Int
    j))
                  where j :: Int
    j = Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    1
              Skip s
    s1    -> s
    -> Int
    -> Int
    -> MutableByteArray s
    -> ST s (MutableByteArray s, (Int, Int))
    loop s
    s1 Int
    i Int
    len MutableByteArray s
    marr
              Yield Char
    x s
    s1 | Int
    i Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    < Int
    least -> {-# SCC "reverse/resize" #-} do
                           let newLen :: Int
    newLen = Int
    len Int -> Int -> Int
    forall a. Bits a => a -> Int -> a
    `shiftL` Int
    1
                           marr' <- Int -> ST s (MutableByteArray s)
    forall s. Int -> ST s (MArray s)
    A.new Int
    newLen
                           A.copyM marr' (newLen-len) marr 0 len
                           _ <- unsafeWrite marr' (len + i - least) x
                           loop s1 (len + i - least - 1) newLen marr'
                         | Bool
    otherwise -> do
                           _ <- MutableByteArray s -> Int -> Char -> ST s Int
    forall s. MArray s -> Int -> Char -> ST s Int
    unsafeWrite MutableByteArray s
    marr (Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    least) Char
    x
                           loop s1 (i - least - 1) len marr
                where least :: Int
    least = Char -> Int
    U8.utf8Length Char
    x Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    1
    {-# INLINE [0] reverse #-}

    -- | /O(n)/ Perform the equivalent of 'scanr' over a list, only with
    -- the input and result reversed.
    --
    -- __Properties__
    --
    -- @'reverse' . 'reverseScanr' f c . 'reverseStream' = 'Data.Text.scanr' f c @
    reverseScanr :: (Char -> Char -> Char) -> Char -> Stream Char -> Stream Char
    reverseScanr :: (Char -> Char -> Char) -> Char -> Stream Char -> Stream Char
    reverseScanr Char -> Char -> Char
    f Char
    z0 (Stream s -> Step s Char
    next0 s
    s0 Size
    len) = (Scan s -> Step (Scan s) Char) -> Scan s -> Size -> Stream Char
    forall a s. (s -> Step s a) -> s -> Size -> Stream a
    Stream Scan s -> Step (Scan s) Char
    next (Char -> s -> Scan s
    forall s. Char -> s -> Scan s
    Scan1 Char
    z0 s
    s0) (Size
    lenSize -> Size -> Size
    forall a. Num a => a -> a -> a
    +Size
    1) -- HINT maybe too low
      where
        {-# INLINE next #-}
        next :: Scan s -> Step (Scan s) Char
    next (Scan1 Char
    z s
    s) = Char -> Scan s -> Step (Scan s) Char
    forall s a. a -> s -> Step s a
    Yield Char
    z (Char -> s -> Scan s
    forall s. Char -> s -> Scan s
    Scan2 Char
    z s
    s)
        next (Scan2 Char
    z s
    s) = case s -> Step s Char
    next0 s
    s of
                             Yield Char
    x s
    s' -> let !x' :: Char
    x' = Char -> Char -> Char
    f Char
    x Char
    z
                                           in Char -> Scan s -> Step (Scan s) Char
    forall s a. a -> s -> Step s a
    Yield Char
    x' (Char -> s -> Scan s
    forall s. Char -> s -> Scan s
    Scan2 Char
    x' s
    s')
                             Skip s
    s'    -> Scan s -> Step (Scan s) Char
    forall s a. s -> Step s a
    Skip (Char -> s -> Scan s
    forall s. Char -> s -> Scan s
    Scan2 Char
    z s
    s')
                             Step s Char
    Done       -> Step (Scan s) Char
    forall s a. Step s a
    Done
    {-# INLINE reverseScanr #-}

    -- | /O(n)/ Like 'unfoldr', 'unfoldrN' builds a stream from a seed
    -- value. However, the length of the result is limited by the
    -- first argument to 'unfoldrN'. This function is more efficient than
    -- 'unfoldr' when the length of the result is known.
    --
    -- __Properties__
    --
    -- @'unstream' ('unfoldrN' n f a) = 'Data.Text.unfoldrN' n f a @
    unfoldrN :: Int -> (a -> Maybe (Char,a)) -> a -> Stream Char
    unfoldrN :: forall a. Int -> (a -> Maybe (Char, a)) -> a -> Stream Char
    unfoldrN Int
    n = Int -> (a -> Maybe (Char, a)) -> a -> Stream Char
    forall a b.
    Integral a =>
    a -> (b -> Maybe (Char, b)) -> b -> Stream Char
    S.unfoldrNI Int
    n
    {-# INLINE [0] unfoldrN #-}

    -------------------------------------------------------------------------------
    -- ** Indexing streams

    -- | /O(n)/ stream index (subscript) operator, starting from 0.
    --
    -- __Properties__
    --
    -- @'index' ('stream' t) n  = 'Data.Text.index' t n @
    index :: HasCallStack => Stream Char -> Int -> Char
    index :: HasCallStack => Stream Char -> Int -> Char
    index = Stream Char -> Int -> Char
    forall a. (HasCallStack, Integral a) => Stream Char -> a -> Char
    S.indexI
    {-# INLINE [0] index #-}

    -- | The 'findIndex' function takes a predicate and a stream and
    -- returns the index of the first element in the stream
    -- satisfying the predicate.
    --
    -- __Properties__
    --
    -- @'findIndex' p . 'stream'  = 'Data.Text.findIndex' p @
    findIndex :: (Char -> Bool) -> Stream Char -> Maybe Int
    findIndex :: (Char -> Bool) -> Stream Char -> Maybe Int
    findIndex = (Char -> Bool) -> Stream Char -> Maybe Int
    forall a. Integral a => (Char -> Bool) -> Stream Char -> Maybe a
    S.findIndexI
    {-# INLINE [0] findIndex #-}

    -- | /O(n)/ The 'count' function returns the number of times the query
    -- element appears in the given stream.
    --
    -- __Properties__
    --
    -- @'countChar' c . 'stream'  = 'Data.Text.countChar' c @
    countChar :: Char -> Stream Char -> Int
    countChar :: Char -> Stream Char -> Int
    countChar = Char -> Stream Char -> Int
    forall a. Integral a => Char -> Stream Char -> a
    S.countCharI
    {-# INLINE [0] countChar #-}

    -- | /O(n)/ Like a combination of 'map' and 'foldl''. Applies a
    -- function to each element of a 'Text', passing an accumulating
    -- parameter from left to right, and returns a final 'Text'.
    --
    -- __Properties__
    --
    -- @'mapAccumL' g z0 . 'stream' = 'Data.Text.mapAccumL' g z0@
    mapAccumL ::
    #if defined(ASSERTS)
      HasCallStack =>
    #endif
      (a -> Char -> (a,Char)) -> a -> Stream Char -> (a, Text)
    mapAccumL :: forall a. (a -> Char -> (a, Char)) -> a -> Stream Char -> (a, Text)
    mapAccumL a -> Char -> (a, Char)
    f a
    z0 (Stream s -> Step s Char
    next0 s
    s0 Size
    len) = (a
    nz, Array -> Int -> Int -> Text
    I.text Array
    na Int
    0 Int
    nl)
      where
        (Array
    na,(a
    nz,Int
    nl)) = (forall s. ST s (MArray s, (a, Int))) -> (Array, (a, Int))
    forall a. (forall s. ST s (MArray s, a)) -> (Array, a)
    A.run2 (Int -> ST s (MArray s)
    forall s. Int -> ST s (MArray s)
    A.new Int
    mlen ST s (MArray s)
    -> (MArray s -> ST s (MArray s, (a, Int)))
    -> ST s (MArray s, (a, Int))
    forall a b. ST s a -> (a -> ST s b) -> ST s b
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= \MArray s
    arr -> MArray s -> Int -> a -> s -> Int -> ST s (MArray s, (a, Int))
    forall {s}.
    MArray s -> Int -> a -> s -> Int -> ST s (MArray s, (a, Int))
    outer MArray s
    arr Int
    mlen a
    z0 s
    s0 Int
    0)
          where mlen :: Int
    mlen = Int -> Size -> Int
    upperBound Int
    4 Size
    len
        outer :: MArray s -> Int -> a -> s -> Int -> ST s (MArray s, (a, Int))
    outer MArray s
    arr Int
    top = a -> s -> Int -> ST s (MArray s, (a, Int))
    loop
          where
            loop :: a -> s -> Int -> ST s (MArray s, (a, Int))
    loop !a
    z !s
    s !Int
    i =
                case s -> Step s Char
    next0 s
    s of
                  Step s Char
    Done          -> (MArray s, (a, Int)) -> ST s (MArray s, (a, Int))
    forall a. a -> ST s a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (MArray s
    arr, (a
    z,Int
    i))
                  Skip s
    s'       -> a -> s -> Int -> ST s (MArray s, (a, Int))
    loop a
    z s
    s' Int
    i
                  Yield Char
    x s
    s'
                    | Int
    j Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    >= Int
    top  -> {-# SCC "mapAccumL/resize" #-} do
                                   let top' :: Int
    top' = (Int
    top Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Int
    1) Int -> Int -> Int
    forall a. Bits a => a -> Int -> a
    `shiftL` Int
    1
                                   arr' <- MArray s -> Int -> ST s (MArray s)
    forall s. MArray s -> Int -> ST s (MArray s)
    A.resizeM MArray s
    arr Int
    top'
                                   outer arr' top' z s i
                    | Bool
    otherwise -> do d <- MArray s -> Int -> Char -> ST s Int
    forall s. MArray s -> Int -> Char -> ST s Int
    unsafeWrite MArray s
    arr Int
    i Char
    c
                                      loop z' s' (i+d)
                    where (a
    z',Char
    c) = a -> Char -> (a, Char)
    f a
    z Char
    x
                          j :: Int
    j = Int
    i Int -> Int -> Int
    forall a. Num a => a -> a -> a
    + Char -> Int
    U8.utf8Length Char
    c Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    1
    {-# INLINE [0] mapAccumL #-}