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Re: GSOC PEG project

From: Michael Lucy
Subject: Re: GSOC PEG project
Date: Fri, 9 Jul 2010 02:58:05 -0500

On Thu, Jul 8, 2010 at 5:29 AM, Andy Wingo <address@hidden> wrote:
> Hi Michael,
> I am travelling currently, so a bit of asynchronicity in the reply :)
> On Mon 05 Jul 2010 07:05, Michael Lucy <address@hidden> writes:
>> I finally got things into a usable state, so I pushed out what I have
>> to origin/mlucy.
> Great news!
>> Files I've added so far:
>> guile/modules/ice-9/peg.scm (I assume this is the right place to put this?)
> Probably, yes, for parts of PEG to be available as macros and
> procedures. You would probably want a language implementation as well,
> for string-based PEGs.
>> PEG compiler: Works for all the grammars I've tested, no known bugs.
>> Currently compiles to Scheme code rather than Tree-IL for debugging.
> That is the right thing to do. Most of PEG should be available through
> macros and procedures.
>> Comments: Pretty good I think, but I could stand to have more.
> Yes, it readable at a quick glance.
>> External documentation: None so far.
> A .texi file will be good, alongside the LALR(1) parser.

Working on this now; should be done soon.

>> Syntactic Sugar: Canonical string-based PEGs can be parsed just fine.
> Cool!
>> Testing: Small test suite.  Needs to be standardized with the other .test 
>> files.
> Great.
>> Benchmarks: None so far, but I haven't really done any optimization so
>> I'd bet it performs poorly.
> Well, it's good to have work left to do :)
>> Problems:
>> 1. PEG compiler compiles to scheme code rather than TREE-IL, and uses
>> some custom pieces of syntax that I then have to export.  I've been
>> meaning to ask, how big a deal is this?  I originally had it compile
>> to Scheme while I was debugging things, but the Scheme gets compiled
>> down to TREE-IL form, right?  Should I fix it to compile straight to
>> TREE-IL anyway rather than just finding a way to get around having to
>> export all that syntax?
> No it should compile to Scheme. However the biggest problem with your
> code is that it is implemented with define-macro. You should change it
> to be implemented with syntax-case. Please let me know if you need help.
> Syntax-case is a bit trickier in some ways than define-macro, but it's
> simpler in others (e.g., no need for your `safe-bind' macro). Check out
> "Macros" in the manual (from git) and tell me what's confusing there; it
> was only fleshed out with info on syntax-case recently.

The documentation looks pretty straightforward.  This will probably
take me a bit; some of the translations look a little complicated.
This will also solve my current problem of having to export a bunch of
macros for the compiled PEGs to work.

I've been thinking it might be good to work on the benchmarks
first--once I understand where the speed bottlenecks are I'll have to
rewrite some of the macros anyway, and it would probably be easier to
rewrite them as syntax-case macros then instead of doing it twice.  If
you'd rather I translate them first, though, I'm happy to.

Sorry I didn't do it this way in the first place.

>> 2. Tests aren't standardized (peg.test looks nothing like the other
>> .test files).
> This isn't a big deal
>> 3. This:
>> scheme@(guile-user)> (use-modules (ice-9 peg))
>> ;;; note: source file /home/zededarian/guile/module/ice-9/peg.scm
>> ;;;       newer than compiled
>> /home/zededarian/guile/cache/guile/ccache/2.0-0.R-LE-4/home/zededarian/guile/module/ice-9/peg.scm.go
>> ;;; note: autocompilation is enabled, set GUILE_AUTO_COMPILE=0
>> ;;;       or pass the --no-autocompile argument to disable.
>> ;;; compiling /home/zededarian/guile/module/ice-9/peg.scm
>> ;;; WARNING: compilation of /home/zededarian/guile/module/ice-9/peg.scm 
>> failed:
>> ;;; key wrong-type-arg, throw args ("vm-debug-engine" "Wrong type to
>> apply: ~S" (#f) (#f))
>> Somehow it works fine despite the warnings.  Can anybody shed light on
>> what this means?
> Dunno! We'll look at it after getting the macro situation sorted
> out. You can try:
>  (use-modules (system base compile))
>  (compile-file "module/ice-9/peg.scm")
> and see where the debugger leaves you.

Turns out I can fix this by wrapping my entire file in an (eval-when
(compile load eval) ...) form.  Is this one of those fixes that's
going to haunt me down the line?

>> 5. The pretty-print module doesn't get loaded when peg does, and some
>> of my functions use it.  I have:
>> :use-module (ice-9 pretty-print)
>> in my define-module form at the top of peg.scm; shouldn't that take
>> care of it?
> Yep, that should work.
>> Any thoughts or comments?  I'm sorry I didn't get this into a branch earlier.
> Heh, no problem. I'm looking forward to a lean mean PEG parsing machine!
> Andy
> --

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