FWIW, at one time there was discussion that "<before>" and "<after>"
are actually keywords and not typical method calls that can be overridden,
precisely so optimizations can be made. They're that important to
efficient running of the regexes.
I'm not sure that a formal decision was ever made on this, however.
(I'd be okay with declaring them as keywords that cannot be overridden.)
Pm
On Tue, Aug 13, 2019 at 05:01:06PM +0200, Timo Paulssen wrote:
>
> > use v6;
> > 'abcd' ~~ / . <.before( /c/ )> . / # "bc"
> > 'abcd' ~~ / . <.before c > . / # "bc" # (exactly identical)
> >
> > A person could change the code in the `before` method to have it do
> > something different
>
>
> At least at the moment, that's not 100% accurate (only by virtue of
> leaving out a piece):
>
> timo@schmand ~> perl6 -e 'grammar test { regex before($re) { { say "yo"
> } }; regex TOP { <.before "hi"> } }; test.parse("hi")'
> yo
> Too few positionals passed; expected 2 arguments but got 1
> in regex before at -e line 1
> in regex TOP at -e line 1
> in block <unit> at -e line 1
>
> timo@schmand ~ [1]> perl6 -e 'grammar test { regex before($re) { { say
> "yo" } }; regex TOP { <before "hi"> } }; test.parse("hi")'
> yo
> Too few positionals passed; expected 2 arguments but got 1
> in regex before at -e line 1
> in regex TOP at -e line 1
> in block <unit> at -e line 1
>
> timo@schmand ~ [1]> perl6 -e 'grammar test { regex before($re) { { say
> "yo" } }; regex TOP { <?before "hi"> } }; test.parse("hi")'
>
> As you can see, using <?before> gives you the "real" lookahead assertion.
>
> I'm not sure if that's part of the language yet, but should probably
> made to be.
>
>
> This will allow more optimization efforts.
