fromCharCode BMP

[jamesdbrock]

fromCharCode should return Nothing if the code is out of the Basic Multilingual Plane Char range, right?

purescript-strings/src/Data/Char.purs

Line 16 in 157e372

fromCharCode = toEnum

>>> show $ fromCharCode 65900

(Just 'Ŭ')

The Bounded instance for Char says that “Characters fall within the Unicode range,” but the Char says “guaranteed to contain one code unit.”

[MonoidMusician]

Oh interesting, it appears this is actually the line at fault:
https://github.com/purescript/purescript-enums/blob/170d959644eb99e0025f4ab2e38f5f132fd85fa4/src/Data/Enum.purs#L316-L318

It's using top and bottom for ints, not chars. I guess n >= toCharCode bottom && n <= toCharCode top might work?

String.fromCharCode just does (code) % 0x10000 on the code, so what you're seeing is 65900 % 0x10000 = 0x16C.

[JordanMartinez]

I've opened an issue in purescript-enum to track this. Should this issue be closed?

[thomashoneyman]

I think it’s reasonable it stays open until the upstream issue is addressed

[JordanMartinez]

Technically, we still need a release of that library and then a dependency update here.

[JordanMartinez]

PR ready for approval: #163.