2018-07-11 06:59:37 UTC
So to convert cases of a `String`, Haskell intends `fmap toUpper`, etc. But this has some bugs.
Case 1. German Ã (Eszett)
'Ã' (U+00DF), Latin Small Letter Sharp S, is a lowercase letter itself, but Unicode doesn't specify its 'simple' uppercase counterpart.
It's because its uppercase counterpart is not a single character, but two characters, "SS".
Case 2. Turkish Ä° and Ä±
Rather than the common 'I' and 'i' case pair, Turkish language has the 'Ä°' (U+0130) and ï»¿'i' pair and the 'I' and 'Ä±' (U+0131) pair. Those are, dotted I pair and dotless I pair, respectively.
Case 3. Greek Î£ (Sigma)
Greek 'Î£' (U+03A3) must be lowercase mapped to 'Ï' (U+03C2) if followed by a whitespace, rather than normal 'Ï' (U+03C3).
Case 4. Greek iota subscript (Ypogegrammeni)
Greek 'Capital' letters with iota subscripts (for example, 'áŸ' (U+1F88)), though they are the 'simple' uppercase counterpart of their lowercase counterpart, they themselves are actually treated as titlecase characters. For example, the actual uppercase counterpart of 'áŸ' (U+1F80) is "áŒÎ" (U+1F08 U+0399). That is, an actual capital iota instead of the iota subscript.
Case 5. Precomposed letters without upper/lowercase counterpart
For example, Î (U+03B0) doesn't have precomposed uppercase counterpart. It must be effectively mapped to "ÎªÌ" (U+03AA U+0301).
In Summary, we need more elaborated casing functions which are `String`-to-`String`.
The Unicode Standard Version 11.0 â Core Specification, Section 5.18.