Re: Stacks, registers, and bytecode. (Oh, my!)

[Simon Cozens]

On Mon, Jun 04, 2001 at 03:43:43PM -0400, Dan Sugalski wrote:
> I think he's looking for something that turns a regex into perl that 
> doesn't involve regexes.

Oh, well, if we follow Larry's suggestion and have regexp matching ops,
then we could claim that the regex *is* Perl, it's just written in a
slightly different language. :)

OK, here's how you do it. Run perl -Mre=debug -e '/your regexp/',
and use Perl to parse the bit in the middle. That's a state machine,
so we can emulate it with subroutines.

So, for instance: perl -Mre=debug -e '/fo+bar/'
...
   1: EXACT <f>(3)
   3: PLUS(6)
   4:   EXACT <o>(0)
   6: EXACT <bar>(8)
   8: END(0)
...

Now we translate that to something like this:
    sub node_1 { 
        $state = shift; 
        while ($_ = substr($state->{string},0,1,"")) {
            if ($_ eq "f") {
                return success if $state->node_3;
            }
        }
        return failure; 
    }
    ... and so on ...

In keeping with tradition, implementation is left as an exercise for
the reader. :)

> (Which isn't to say that I'm not interested in run time for something 
> like that if it's to be used in perl 6, but that's a separate issue)

Oh, I see, I see. Sorry, was confusing "implemention of thing for Perl 6"
and "implementation of this handy tool for exploration purposes".

Simon

-- 
        "The elder gods went to Suggoth and all I got was this lousy T-shirt."