Now that it seems that Parse::RecDescent and, ultimately,
Parse::FastDescent, will be subsumed into the Perl 6 regex/grammar system,
I've been thinking about how to implement P::RD directives such as
<autotree>, <score> and <leftop>; or features such as tracing.
I've really only thought about <leftop>, but am not sure if those thoughts
are even going in the right direction, so please correct anything that
looks like nonsense.
Suppose you want a <leftop> assertion that works like the <leftop>
directive in P::RD, so that
<leftop atom, and, atom>
becomes the same as
<atom> (and <atom>)*
There could be a two-arg version of <leftop> that assumes the rightop
is the same as the leftop:
<leftop atom, and>
I'm not sure of the syntax to invoke rules that take more than one
argument. Maybe it would be
<leftop(atom, and, atom)>
<leftop(atom, and)>
(I hope I'm right in assuming that arguments to rules aren't evaluated
but rather passed in literally like a kind of macro mechanism, otherwise
I don't understand how
rule not ($rx) { <!$rx> }
is supposed to work.)
Now, could you just do
rule leftop ($leftop, $op) {
<$leftop> [$op <$leftop>]*
}
rule leftop ($leftop, $op, $rightop) {
<$leftop> [$op <$rightop>]*
}
That is, if there are multimethods. If not, i suppose we could have
rule leftop is multimethod($leftop, $op) { ... }
rule leftop is multimethod($leftop, $op, $rightop) { ... }
Does that look like valid Perl 6 code (it's my first try to be honest)
or is it just nonsense?
Thanks
Marcel
--
We are Perl. Your table will be assimilated. Your waiter will adapt to
service us. Surrender your beer. Resistance is futile.
-- London.pm strategy aka "embrace and extend" aka "mark and sweep"
