/ 
Regexp-Exhaustive-0.02
River stage one • 1 direct dependent • 1 total dependent
/ Regexp::Exhaustive

NAME

Regexp::Exhaustive - Find all possible matches, including backtracked and overlapping, of a pattern against a string

SYNOPSIS

use Regexp::Exhaustive qw/ exhaustive /;

print "Subsets:\n";
print "$_\n" for exhaustive('abc' => qr/.+/);

print "\n";

print "Overlapping matching:\n";
print "$_\n" for exhaustive('abc' => qr/(?>.+)/);

print "\n";

print "Heads and tails:\n";
print "@$_\n" for exhaustive('abcde' => qr/^(.+?)(.+)\z/);

print "\n";

print "Triplets:\n";
print "@$_\n" for exhaustive('abcde' => qr/(.)(.)(.)/);

print "\n";

print "Binary count:\n";
print map(length, @$_), "\n"
    for exhaustive('111', qr/^(.??)(.??)(.??)/);

__END__
Subsets:
abc
ab
a
bc
b
c

Overlapping matching:
abc
bc
c

Heads and tails:
a bcde
ab cde
abc de
abcd e

Triplets:
a b c
b c d
c d e

Binary count:
000
001
010
011
100
101
110
111

DESCRIPTION

This module does an exhaustive match of a pattern against a string. That means that it will match all ways possible, including all backtracked and overlapping matches.

It works a lot like the familiar m//g regarding return values.

Beware that exhaustive matching may generate a very large number of matches. If you only need overlapping matches that's easily achieved. Overlapping matching has a maximum number of matches being the length of the string plus one.

This is an initial release, and many things may change for the next version. If you feel something is missing or poorly designed, now is the time to voice your opinion.

EXPORTED FUNCTIONS

Nothing is exported by default. The :ALL tag exports everything that can be exported.

exhaustive(STRING => qr/PATTERN/)

Exhaustively generates and returns all matches in list context. Returns the number of matches in scalar context.

If the pattern doesn't contain any capturing subpatterns, the matched string ($&) is returned. If only one capturing subpattern is seen ($1), that is returned. Otherwise $1, $2, etc is returned grouped using array references.

This is like m//g in list context, except m//g returns all capturing subpatterns as a flat list.

This method does not effect pos($str).

exhaustive(STRING => qr/PATTERN/, $1, $2, $+, $^R, \@+, ...)

Optionally, you can specify which variables to return. If @- and/or @+ is used they must be passed as references, and will end up as array references in the return list.

If two or more variables are specified they will be grouped using array references.

Beware, not using any capturing group will make $& be used, with all the usual caveats.

overlapping(STRING => qr/PATTERN/)

If this function would exist, but it doesn't, it would be like global but try to match from every position of the string. It's like an exhaustive match that doesn't backtrack inside the pattern.

This function doesn't exist because it isn't needed. Instead use

exhaustive(STRING => qr/(?>PATTERN)/)

i.e. wrap the pattern with the (?>...) assertion. This will lock the match once the pattern has matched, forcing the regex engine to skip behind the pattern when backtracking, thus moving forward on string for the next match.

Using

STRING =~ /(?=PATTERN)/g

will be faster, but has three key differences: (1) assumes pos() is undefined, (2) undefines pos(), and (3) returns all captured groups as a flat list. Note that saving away pos() and then restoring it may cause certain global matches to loop infinitely.

$_ = 'foo';

while (/.??/g) {
    print pos();
    pos() = pos(); # Not really doing anything, or is it?
}

This will loop forever.

DIAGNOSTICS

The second argument to Regexp::Exhaustive::exhaustive must be a Regexp (qr//) object

(F) Self-explanatory.

EXAMPLES

See "SYNOPSIS" for more examples.

Finding all divisors

A commonly known snippet of regex can be used to find out if an integer is a prime number or not.

sub is_prime {
    my ($n) = @_;

    my $str = '.' x $n;

    return $str =~ /^(?:..+)\1+$/ ? 0 : 1;
}

print '9 is prime: ', is_prime(9), "\n";
print '11 is prime: ', is_prime(11), "\n";

__END__
9 is prime: 0
11 is prime: 1

Equally simple is it, with Regexp::Exhaustive, to find out not only if it's a prime number, but which its divisors are.

use Regexp::Exhaustive;

sub divisors {
    my ($i) = @_;

    return map length, exhaustive('.' x $i => qr/^(.+?)\1*$/);
}

print "$_\n" for divisors(12);

__END__
1
2
3
4
6
12

Finding the cross product

Set::CrossProduct gives you the cross product of a set, and that's the good way of doing just that. But as an example, here's how you can find all possible combinations of two four-sided dice using Regexp::Exhaustive. To illustrate the difference between greedy and non-greedy matches I let the second die be in reversed order.

use Regexp::Exhaustive;

my $sides = '1234';
my @sets = exhaustive(
    "$sides\n$sides"
    =>
    qr/^.*?(.).*\n.*(.)/)
);

print "@$_\n" for @sets;

__END__
14
13
12
11
24
23
22
21
34
33
32
31
44
43
42
41

N-ary count

Using Regexp::Exhaustive you can generate all values of a certain digit length using an n-ary count. This is demonstrated for binary numbers with a length of three.

sub all_values {
    my ($n, @base) = @_;
    my $str = (join('', @base) . "\n") x $n;
    my $re = ".*?(.).*\n" x $n;
    return map { join '', @$_ } exhaustive($str, qr/^$re/);
}

print "$_\n" for all_values(3, qw/ 0 1 /);

__END__
000
001
010
011
100
101
110
111

WARNING

This module uses the experimental (?{ ... }) assertion. Thus this module is as experimental as that assertion.

AUTHOR

Johan Lodin <lodin@cpan.org>

COPYRIGHT

Copyright 2005-2007 Johan Lodin. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

perlre for regular expressions.

perlvar for the special variables.