[P5P] Checking if regex matches from XS

It is tricky and risky - trying to use perl's regex engine
to subsitute for Tcl's is one of the recurring porting issues
with perl/Tk.

The main snag (as I recall) is that in perl you need an "OP" in order
to call some of regex engine.
Unless you _really_ need this I strongly recommend writing the
"leaf" functions for this in perl and perl_call_sv()-ing them from your
XS code.

Unless Hugo wants to give us a clean interface?

Sigh ...

I was afraid someone would say something like that.
Well, the main reason Ilya and I are working on this XS code (for
Params::Validate) is to speed it up. Calling back and forth to Perl
unnecessarily somewhat defeats the purpose.
That'd be cool for the future.

One thing I'd say in general about XS is that it just doesn't expose
enough of Perl's functionality, at least not in what's documented. And I
include the Jenness/Cozens book in that documentation (good book, but it
doesn't cover everthing I _want_ to do with XS).

For example, in the Params::Validate XS code we need to find out what
package the caller is in. Now, obviously Perl can do this, because we
have the caller() function. Ilya somehow found the CopSTASHPV macro, and
then I found an equivalent way to do this for Perl 5.00503, but it's all a
nasty hack since this isn't a documented interface.

It seems to me that ideally you could call any Perl function from XS. I
realize that's extremely difficult, but there must be some subset of
Perl's functionality easily available from XS that isn't documented (like
CopSTASHPV).


-dave

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It does not have to be an OP that is linked anywhere - tkGlue.c
does do that, and it worked fine till UTF-8 stuff came along.
Now something is not-quite-right :-(
Depends what you consider documented :-)
XS pods document what "we" are reasonably happy maintaining as an
interface.

If you want to you can get at _anything_ via an XS hook.
I agree caller() is one of several things that are easy in perl, but
code that implements them is "inline" in some pp_xxxx() and not
easy to re-use from C/XS.
You can get at anything - but calling pp_caller() for example effectively
calls back into perl with associated stack twiddling.

Nick Ing-Simmons wrote:
:Dave Rolsky <autarch@urth.org> writes:
:>I've read the Jenness/Cozens book and the various perldocs on XS, but I
:>can find no hint of how to use the regex engine from XS.
[...]
:Unless you _really_ need this I strongly recommend writing the
:"leaf" functions for this in perl and perl_call_sv()-ing them from your
:XS code.
:
:Unless Hugo wants to give us a clean interface?

I'd love to, but it isn't likely to happen soon.

Hugo