# This is perl, v5.8.6 built for i386-linux-thread-multi
use Data::Dumper;

$rx = qr{ (.) (?{ print Dumper $1 }) }x;
"japhy" =~ m{    (??{ $rx }) }x;
## $VAR1 = undef;

$rx = qr{ (.) (?{ print Dumper $1 }) }x;
"japhy" =~ m{ () (??{ $rx }) }x;
## $VAR1 = 'j';