Re: case insensitive collation of Greek's sigma

Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com> writes:
> Running lower() like this is really the wrong thing to do. We should be
> doing "case folding" instead, which normalizes these differences for the
> purpose of case-insensitive comparisons.

That just begs the question: if tolower (or towlower) isn't the
appropriate API, what is? Perhaps ICU has something for a more
generalized notion of case-similarity, but I'm not aware of any such
thing in the POSIX API.

BTW, I think it's only accidental that the regex example shown upthread
gets the right answer. In that example, what's happening is that we
consider a letter in a case-insensitive regex to match itself, or
tolower() of itself, or toupper() of itself. Both σ and ς have Σ
as toupper() so they both work. But if you'd written Σ in the regex,
only one of σ and ς would match that as a data character. (Haven't
actually tested this, but given the way the code works I'm pretty
sure it's so.) Again, it's hard to see how to do better atop a POSIX
locale library.

regards, tom lane