bug#24186: setlocale can't be localised

[Zefram]

Ludovic Courtes wrote:
>That wouldn't help with the "setlocale" issue you describe per se, but
>this would address such use cases in a different way.
>
>WDYT?

Yes, explicit locale objects and locale parameters to relevant functions
are a good thing.  In general, the model of a global locale state is
broken, at least by threading, so some advance beyond the setlocale system
is necessary.  Note the new(er) "uselocale" system in libc, which gives
a per-thread locale state, fixing the biggest problem with setlocale.
Some form of that could also be mapped into Guile; it would be reasonable
to have a fluid that determines the locale to use where not overridden
by an explicit parameter.

All of that is welcome, but, as you say, doesn't deal with the actual
problem I identified with setlocale.  One can expect that setlocale will
continue to be used for the foreseeable future, and it needs to be shorn
of its unwanted side effects.

-zefram