#!/usr/bin/perl --
use strict; use warnings;

print qr{yo}usim, "\n";
$::yo++;
print qr{yo}usim, "\n";
$::yo--;
use YAML::XS;
print YAML::XS::Dump( [ qr{yo}usim ] ), "\n";


package Regexp;
use Data::Dump;
sub ixsm { #~ (?s-xim:s)
    my( $i )=@_;
    my %onoff = ( qw/ s 0 i 0 m 0 x 0 / );
    
    $onoff{$1}++ while $i =~ /(.)/g;;
    
    delete $onoff{$_} for qw/ o a l u d /;
    
    my @off;
    my @on;
    while( my($k,$v) = each %onoff ){
        push @on, $k if $v;
        push @off, $k if not $v;
    }
    my $on = join'',@on;
    my $off = join'',@off;
    my $ret = "(?$on";
    $ret .="-$off" if length $off;
    $ret;
}
use overload '""' => sub {
    my( $self_operand_overloaded, $other_operand, $other_operand_was_on_the_left_side ) = @_;
    my( $patt, $mods ) = re::regexp_pattern( $self_operand_overloaded );
    $::yo and return ixsm($mods).':'.$patt.')';    ## oldstyle
    return $self_operand_overloaded; ## modern
};
__END__
(?^umsi:yo)
(?msi-x:yo)
---
- !!perl/regexp (?^umsi:yo)