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Re: PEG Parser Updates/Questions

From: Michael Lucy
Subject: Re: PEG Parser Updates/Questions
Date: Mon, 16 Aug 2010 00:37:46 -0500

On Fri, Aug 6, 2010 at 1:40 AM, Michael Lucy <address@hidden> wrote:
> On Wed, Jul 28, 2010 at 12:13 AM, Michael Lucy <address@hidden> wrote:
>> I've officially eliminated the last define-macro expression.
>> However, I get the feeling that things may not be exactly as desired.
>> The original program made extensive use of functions in building the
>> macros, and I originally tried to replace these with macros.  This
>> turned out to be a little difficult to debug, however (read: I was
>> unable to make the code actually work).  I eventually abandoned this
>> and just made datum->syntax calls.
> I've left this alone since then; it would be nice to get some
> confirmation that this was the right choice though.  If it isn't, I
> think I still have time to change it before the GSOC deadline (and
> like I said, I'll hang around after it).

So, we're essentially at the GSOC deadline.  I pushed up the finished
form of what I have to the git repository, plus some benchmarks.  I
also added a variant on packrat parsing using a cache instead of a
hash (the hash performs poorly on flat text files).  This turned out
to be well worth it; on the relatively limited benchmarking suite it
was about a 50x performance boost.

Quick summary of files added (all in origin/mlucy):
Actual module: module/ice-9/peg.scm
Test suite: test-suite/tests/peg.test
Benchmarks: test-suite/tests/peg.bench (wasn't quite sure where to put this)
Documentation: doc/ref/api-peg.texi (also updated guile.texi to include it)

The macros haven't been touched (except I fixed up one define-macro
macro that had slipped past my radar).  I'll be hanging around after
the deadline tidying up a bit more (I'd like some more benchmarks); if
the macro situation isn't what you guys want I'll fix it.

> Anyway, I just pushed up everything I have to the git repository (I
> think; I may have screwed up the syntax).  I'm basically done except
> that the documentation/comments could use some more touching up, I
> don't have a set of benchmarks yet and I haven't really optimized
> things all that much.
>> On the one hand, this works.  I also find it easier to debug, and I
>> think it looks cleaner.
>> The downside is that one doesn't get all the same benefits of
>> referential transparency, so I still have gensyms in the functions
>> etc.  Is this a problem?
>> If so, I can definitely replace everything with macros, but I might
>> not be able to do that and get everything else done by the GSOC
>> project deadline.  I'd like to hang around after the project is
>> officially done from Google's point of view to polish things up, so I
>> could also do it then.
>> Another question about module namespaces:  I have some syntax that I'd
>> like to be available to code generated by macros in my module, but
>> which I'd rather not export to the user (to avoid clobbering their
>> functions).  Is there a standard way of doing this?  I can't seem to
>> find anything in the module documentation regarding giving namespaces
>> to things in modules except for :renamer, which has to be done by the
>> user--the only options appear to be not exporting it at all, or
>> exporting it straight into the user's namespace.  The best fix I can
>> think of is naming the syntax things the user is unlikely to ever take
>> (or maybe using gensyms to make sure it isn't a name they take).

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