Re: Tweaking the Skip Parser, was RE: [Boost-users] Spirit 1.6 with VC6

From: Joel de Guzman (joel_at_[hidden])
Date: 2004-06-25 21:07:43

Mark Storer wrote:

     >>No chance of switching to 7.1? :-)
     >
     >
     > Things are looking up.  We just did a project-wide upgrade
     to... VC7.1.  Problem solved.  I'm now merrily writing rules for
     my JavaScript parser.  It doesn't have to support the whole
     language (not for a while, maybe never), I just need to be able
     to parse out the names and locations of all the functions in a
     file. It's for a JavaScript editor built into one of our
     products, and later we'll be adding auto-completion. That'll
     require a more thorough parser, but for now, I'm just after
     funciton locations.

Great! Nice to hear.

     > So far so good... though I'll undoubtedly be quite familiar
     with the BOOST_SPIRIT_DEBUG* macros before I'm done.
     >
     > I've got another Spirit question:  I've been adding "*comment"
     throughout the rules and it's getting tiresome:
     >
     >   rule<phrase_scanner_t> blockComment = comment_p( "/*", "*/" );
     >   rule<phrase_scanner_t> lineComment  = comment_p( "//" );
     >   rule<phrase_scanner_t> comment      = blockComment | lineComment;
     >
     > Spraying the "comment" rule liberally through my rules is an
     option...
     >
     >   rule<phrase_scanner_t> codeBlock    = ch_p('{') >>
     *(comment | codeBlock | ~ch_p('}')) >> ch_p('}');
     >
     > ... but not an appealing one.  This becomes particularly true
     once I start working on the auto- completion parser.

Certainly not appealing.

     >   It just occured to me that if the skip parser ate comments
     for me, it would greatly simplify my rules. I'd like to tweak the
     skip parser so it skips over my "comment" rule as well as white
     space.

That's the way to go. See the C-parser, for example:
http://tinyurl.com/29mcn

     I just took a stab at this, but didn't get very far.  I
     tried:
     >
     > parse(str, rules, space_p | comment)
     >
     > but that resulted in a compiler error.  7.1's errors are MUCH
     easier to read that 6's.  I'm going to like this new compiler. >
     [...]
     >
     > Pointing me to the relevant section of the docs is an
     acceptable answer, though I wouldn't mind a little more info than
     that. ;)

It's the no. 1 FAQ. See the Scanner Business:
http://tinyurl.com/3abgf

In general, put your "rules" in a grammar.

     > I'll keep plugging away.  If I come up with an answer, I'll
     post it to the list.  I'd expect this to be useful to other
     beginners at the very least.

Well, HTH... If you have further questions, please post them to
Spirit's mailing list where other Spirit folks can help:

Spirit-general mailing list
Spirit-general_at_[hidden]
https://lists.sourceforge.net/lists/listinfo/spirit-general

Cheers,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net