Re: Non-stub gettext API functions committed, ready for testing

[Rich Felker <dalias@libc.org>]

On Sun, Jul 27, 2014 at 07:23:09PM +0200, Szabolcs Nagy wrote:
> * Rich Felker <dalias@libc.org> [2014-07-27 12:49:21 -0400]:
> > On Sun, Jul 27, 2014 at 04:14:18PM +0200, Szabolcs Nagy wrote:
> > > it shows that a c arithmetic expression parser is needed to handle plurals
> > > (and the expression has to be evaluated every time dcngettext is invoked)
> > 
> > Not necessarily. You could cache results. Or (this is likely the more
> > reasonable implementation) just hard-code the expression strings that
> > are actually used for real languages and implement them in C when a
> > match is found.
> > 
> 
> hardcoding the strings will fail if .mo files are updated to
> use different expressions
> 
> with caching the expr has to be evaluated for every uncached n

Yes.

> > >   Plural-Forms: nplurals=2; plural=n == 1 ? 0 : 1;
> > > 
> > >   The nplurals value must be a decimal number which specifies how many
> > >   different plural forms exist for this language. The string following
> > >   plural is an expression which is using the C language syntax.
> > >   Exceptions are that no negative numbers are allowed, numbers must be
> > >   decimal, and the only variable allowed is n.
> > 
> > This is a very poor description. Does it allow casts? Compound
> > literals? Floating point? Function calls? ...?
> > 
> 
> the parser in gnu gettext:
> http://git.savannah.gnu.org/cgit/gettext.git/tree/gettext-runtime/intl/plural.y
> 
> so they implement
>  conditional (?:)
>  logic (&&, ||, !)
>  relational (==, !=, <, >, <=, >=)
>  and arithmetic (+, -, *, /, %)
> operators with unsigned long args only

And parentheses?

From what I can tell, that's not so bad. Anyone feel like writing an
expression evaluator for it? I think recursive descent is fine as long
as the length of the string being evaluated is capped at a sane length
(or just keep a depth counter and abort the evaluation if it exceeds
some reasonable limit).

Rich