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#38235
string-foldcase bug for trailing sigma
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On Sat, Nov 16, 2019 at 3:42 PM Andy Wingo <wingo <at> pobox.com> wrote:
> The expected result is "μέλοσ"; see R6RS libraries section 1.2. However
> instead Guile's result is "μέλος". Note that although Σ usually
> downcases to σ, at the end of a string it's ς.
More precisely, it downcases to σ if a letter follows and to ς if not
(being at the end of a string is a particular case). However, this is not
actually always Greekly correct: the string "ΦΙΛΟΣ." with a period at the
end downcases to "φιλος." if it is the word φίλος 'friend' (without its
proper accent) at the end of a sentence, but as "φιλος." if it is an
abbreviation for φιλοσοφία 'philosophy'. For this reason, R7RS does not
require mapping to ς in this situation as R6RS does.
This test shows a
> limitation of defining string-foldcase as simply (string-downcase
> (string-upcase str)).
>
As explained in Unicode section 5.18, the foldcase mappings (in <
https://www.unicode.org/Public/UNIDATA/CaseFolding.txt>, the lines with
status C and F) actually create a set of equivalence classes that are
closed under {upper,lower,title}case mapping, and then choose a single
character to represent each class. This is usually the unique lowercase
character, but not always: in Cherokee it is the uppercase character, and
in the set {Σ, σ, ς} it is σ.
On Sun, Nov 17, 2019 at 6:20 AM <tomas <at> tuxteam.de> wrote:
Good catch. I think there's even a worse example: dotless
> and dotted I [1]. Here it seems even impossible to do
> up- and downcase correctly without knowing the language
> context.
>
Language-specific case mappings are explicitly out of Scheme's remit: they
have to be performed by specialized libraries. There is an additional
situation in Lithuanian dictionaries (but not running text): an "i" with a
tone accent is represented as "i" + dot above + accent, like this: "i̇́".
However, this dot above must be dropped when uppercasing, producing
ordinary "Í".
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This bug report was last modified 5 years and 209 days ago.
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