Parsing XML

One of the targets for Perl 5.8 is to speed up XML parsing, but nobody really has any idea how to do that. The current XML::Parser uses an external library, which means that a lot of speed is lost in flapping around in XS. The idea was mentioned of a pure-Perl version, which we would then be able to ship in core. Jarkko says: Okay, I lied. I do have an opinion: relying on an external library to do XML parsing is weird. expat is nice and is a de facto standard, and reinventing the wheel that has already been extensively invented and debugged is silly in the extreme -- but we are, after all, supposed to be The Text Processing Language.

Matt Sergeant, as ever, had good XML suggestions:

If you do that, I suggest/recommend at least doing it the Python way - by letting XML experts (i.e. a SIG) discuss what would be the best way to do it. Note also that ActivePerl ships with XML::Parser, though in a few months it may not necessarily be the best option any more.

He also pointed out that:

The speed problem is that expat is basically a callback/event based parser, so you have a storm of events crossing the XS/Perl barrier, meaning that you're constantly building SV's. Orchard can get around this by doing the parsing to a tree structure in C. (Note that Orchard is also based on expat). Or it can also do SAX based event passing, but again that's about as slow as XML::Parser.

Doing it all in Perl is possible, but not entirely trivial to get exactly right. XML has a lot of annoying nuances that were left in from SGML, mostly to do with DTDs. And while I don't use most of the annoying features, I think I'd be upset if the core Perl started shipping an "XML" parser that wasn't fully XML compliant.

I wonder if the perl-xml mailing list could go chew on that and let us know the best way to proceed.

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Coyote