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 some 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 (equivalent of $&) is returned. If only one capturing
        subpattern is seen then $1 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 interact with "pos($str)" and can be safely
        intermixed with other match operations against the string.

        Worthy to note is that it's much more efficient to use "qr/(.)/"
        than "qr/./", i.e. making direct use of $1 instead of having
        "exhaustive" calculate $&.

    "exhaustive(STRING => qr/PATTERN/, qw[ $1 $2 @- $^R ... ])"
        Optionally, you can specify which variables to return. Arrays and
        hashes will end up as references in the return list.

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

            my @matches = exhaustive('abc' => qr/(a)|(b)/, qw/ $1 $2 $+ /);

            for (@matches) {
                print join("\t", map { defined() ? $_ : 'undef' } @$_) . "\n";
            }

            __END__
            a       undef   a
            undef   b       b

        Supported variables:

            Punctuation:    English alias:
            $<*digits*>
            $`              $PREMATCH
            $&              $MATCH
            $'              $POSTMATCH
            $+              $LAST_PAREN_MATCH
            $^N
            @-              @LAST_MATCH_START
            @+              @LAST_MATCH_END
            %-
            %+
            $^R             $LAST_REGEXP_CODE_RESULT

        Using $`, $&, and $' with "exhaustive" doesn't impose the
        performance penalty that those variables otherwise impose. However,
        they're usually slower to use than rewriting the pattern to use
        capturing subpatterns. In particular, $& is often easy to avoid by
        just adding an outer capturing parenthesis and using $1 instead.

    "overlapping(STRING => qr/PATTERN/)"
        If this function would exist, but it doesn't, it would be like
        global match 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
        the 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
        subpatterns 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
    Use of uninitialized value in &Regexp::Exhaustive::exhaustive
        (W|uninitialized) The string given to "exhaustive" was not defined.

    The second argument to &Regexp::Exhaustive::exhaustive must be a Regexp
    object (qr//)
        (F) Self-explanatory.

    Uninitialized value passed to &Regexp::Exhaustive::exhaustive as
    variable name
        (F) An argument for a regex variable name was not defined.

    Bad variable name(s) to &Regexp::Exhaustive::exhaustive: %s
        (F) You supplied a string that didn't look like a known regex
        variable. See "exhaustive" for supported variables.

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 '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 'exhaustive';

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

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

        __END__
        1 4
        1 3
        1 2
        1 1
        2 4
        2 3
        2 2
        2 1
        3 4
        3 3
        3 2
        3 1
        4 4
        4 3
        4 2
        4 1

  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. (The length is assumed to be greater
    than one.)

        use Regexp::Exhaustive 'exhaustive';

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

ACKNOWLEDGEMENTS
    Thanks to Mike Rosulek for giving useful feedback and suggestions.

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.