Am 27.04.2010 06:31, schrieb Stéphane Payrard:
When doing an analyse of a sample parse tree, I note that it is
cluttered by the reduction of optional subrules
to generate a zero length parse subtree. That is, rules with a '?'
quantifier matching zero time.
Suppressing such matching rules from the parse tree would make it
easier to read.
Additionnally, the actions associated with such a quantified rule
matching once would not necessitate a trailing [0].
my $twigil := $<twigil> ?? ~$<twigil>[0] !! '';
would read
my $twigil := $<twigil> ?? ~$<twigil> !! '';
... end even
my $twigil = $<twigil> // '';
But it raises other questions that need answering.
Currently the ? quantifier is just syntactic sugar for the general
quantifier ** 0..1.
Would that behave the same?
Are you proposing that all quantifiers that match zero times should not
appear in the parse tree? Then <twigil>+ could either lead to no capture
at all, a single value or a list - not very nice.
Or rather special-casing the 0..1 quantifier?
There's also another problem with your approach: If you have
<twigil>?
in your regex, and it matches the empty string, it is still a successful
match - yet with your proposal, it's impossible to distinguis a
successful zero-width match from an unsuccessful match (which can happen
in alternations).
Cheers,
Moritz
