"12180" =~ m{
  (?{ local @n = () })
  (?: (\d) (?{ local @n = (@n, $1) }) )+
  \d
  (?{ @d = @n })
}x;

##</code><code>##

local @n;
/(.)(?{ ++$n[0] })^/;
@d = @n;

##</code><code>##

$p = '\w+-\d+';
/$p/;
/$p/;

##</code><code>##

$p = '\w+-\d+';
for $i (1,2) { /$p/ }

##</code><code>##

($x,$y) = ('a+', 'b');
for (1,2) {
  /$x$y/;
  ($x,$y) = ('a', '+b');
}