Dan Sugalski wrote in perl.perl6.language :
>
> Don't forget, we already change parsing rules at compile time. Perl's
> got three (maybe four) different sets of rules as it is:
>
> *) Normal perl
> *) Regexes
> *) Double-quoted strings
> *) Single-quoted strings
>
> Adding another, or changing those, isn't a big deal.
Strictly speaking, the last three are handled by perl 5's tokenizer.
An insteresting case of compile-time parsing rules modification is given
by prototypes : the perl 5 statement
foo 1, 2
is parsed differently if foo() has ($) or (@) as prototype.
