add safe decodeASCII'

[raehik]

Useful function for serialization libs. Currently you have to do something like this, which is nasty and weird for something that isn't really inherently so.

I find the decoding setup to be a little messy and this makes no attempt to improve on that. I wouldn't mind assisting on that work too.

[raehik]

decodeAsciiPrefix in #448 would also resolve this, I doubt anyone minds about a little extra allocation for the fail case.

[Lysxia]

And the extra allocation in #448 would get optimized away if you just check the suffix for emptiness.

[raehik]

With #448 merged, I'll rebase this and see what's left -- perhaps nothing, or perhaps a convenience definition if it seems sensible.

[Lysxia]

Yeah, I think a Maybe or Either variant of decodeASCII makes sense even if it's a simple wrapper around decodeASCIIPrefix, because it has a more natural-looking type.

[raehik]

Thanks to @Lysxia 's fantastic work on decoding there's not much here now:

decodeASCII' :: ByteString -> Maybe Text
decodeASCII' bs =
  let (prefix, suffix) = decodeASCIIPrefix bs in
  if B.empty suffix then Just t else Nothing
{-# INLINE decodeASCII' #-}

What do people think? It's perhaps more convenient, but gives less information than decodeASCIIPrefix.

[raehik]

pushed fix B.empty -> B.null lol and re-squashed