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Postings from April 2003
Yary Hluchan wrote:
>>making *productions* of strings/sounds/whatever that could possibly
>>match the regular expression?
>>
>>
>>>Correct me if I am wrong, but isn't this the :any switch of apoc 5?
>>>http://www.perl.com/pub/a/2002/06/26/synopsis5.html
>>>
>
>Not really, unless the input string is infinite!
>
Well, thats just in the general purpose case, right? That's because
a regex like /a*/ matches:
'w'
'qsdf'
'i bet you didn't wnt this to mtch'
So, you're going to need some sort of controlled input to a regex match
with the :any for it to work right.
Here's my approach to the problem: generate a possible string that
could match every atom in the regex individually, and then generate
matches for the whole regex off of that. I liked Luke's approach
of stapling methods onto the Rx classes, so I used an approach that
made use of that idea. I completed each of the needed rules, since
the methods in my example are pretty simple (they probably would be
in Luke's example too, but I just wanted to be sure I wasn't missing
anything).
use List::Permutations <<permutations>>; # Perl 5's name.
sub generate (rx $spec, Int $limit) {
my $string = $spec.generate_match (&propagate, $limit);
$string =~ m:any/ (<$spec>) { yield $1 } /;
my sub propagate ($atom) {
given ($atom) {
when Perl::sv_literal {
$string ~= $_.literal()
}
when Perl::Rx {
$string ~= .generate_match (&propagate, $limit)
if .isa(generate_match)
}
}
}
}
Perl::Rx::Atom::generate_match (&p, $limit) {
return &p.($.atom)
}
Perl::Rx::Zerowidth::generate_match (&p, $limit) {
return &p.($.atom)
}
Perl::Rx::Meta::generate_match (&p, $limit) {
return join '', $.possible
}
Perl::Rx::Oneof::generate_match (&p, $limit) {
return join '', $.possible
}
Perl::Rx::Charclass::generate_match (&p, $limit) {
return join '', $.possible
}
Perl::Rx::Sequence::generate_match (&p, $limit) {
my $string;
$string ~= &p.($_) for $.atoms;
return $string;
}
Perl::Rx::Alternation::generate_match (&p, $limit) {
my $string;
$string ~= &p.($_) for $.branches;
return $string;
}
Perl::Rx::Modifier::generate_match (&p, $limit) {
my $string;
$string ~= &p.($_) for $.atoms;
# is $self ($.) still the topic here? or is the last
# member of $.atoms?
return $self.mod.transform($string);
}
Perl::Rx::Modifier::repeat (&p, $limit) {
$string := join '', map { join '', $_ }
permutations (split //, &p.($.atom)) xx ($.max // $limit);
return $string;
}
So, given a call like:
generate (/(A*B*(C*|Z+))/, 4);
The C<$string> variable in the 2nd line of C<generate> would become:
AAAABBBBCCCCZZZZ
And the :any switch takes care of the rest. (-:
Joseph F. Ryan
ryan.311@osu.edu
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