Short_new.hs

foldr' :: (Word8 -> a -> a) -> a -> ShortByteString -> a
foldr' k v = Foldable.foldr' k v . unpack

----

unpack :: ShortByteString -> [Word8]
unpack = unpackBytes
{-# INLINE unpack #-}

unpackBytes :: ShortByteString -> [Word8]
unpackBytes sbs = let ix = length sbs - 1
                  in List.map (unsafeIndex sbs) [0..ix]
{-# INLINE unpackBytes #-}

Short_old.hs

foldr' :: (Word8 -> a -> a) -> a -> ShortByteString -> a
foldr' k v = Foldable.foldr' k v . unpack

----

unpack :: ShortByteString -> [Word8]
unpack = unpackBytes

unpackBytes :: ShortByteString -> [Word8]
unpackBytes sbs = unpackAppendBytesLazy sbs []

unpackAppendBytesLazy :: ShortByteString -> [Word8] -> [Word8]
unpackAppendBytesLazy sbs = go 0 (length sbs)
  where
    sz = 100

    go off len ws
      | len <= sz = unpackAppendBytesStrict sbs off len ws
      | otherwise = unpackAppendBytesStrict sbs off sz  remainder
                      where remainder = go (off+sz) (len-sz) ws

unpackAppendBytesStrict :: ShortByteString -> Int -> Int -> [Word8] -> [Word8]
unpackAppendBytesStrict !sbs off len = go (off-1) (off-1 + len)
  where
    go !sentinal !i !acc
      | i == sentinal = acc
      | otherwise     = let !w = indexWord8Array (asBA sbs) i
                         in go sentinal (i-1) (w:acc)