use B 'main_cv';
use B::Deparse;
$deparse = B::Deparse->new;

# This prints "{}\n" which doesn't seem right
print $deparse->deparse_sub(main_cv), $/;

$qr = qr|(?:.(?{print $deparse->deparse_sub(main_cv), $/}))+|;

for (0 .. 9) {
  print "$_\n";
  $text = ' ' x $_;
  $text =~ $qr;
}