It has always seemed weird to me to write code like

  my $iold;
  for my $i ( 1 .. $foo ) {
    if( bar($i) ) {
      $iold = $i;
      last;
    }
  }

Doesn't it just seem like a waste of variables? You're clearly using $i and $iold for the same purpose.

No, you're using $i as a loop variable and $iold as the return value of the loop. Variables are cheap. Using them to buy clarity is a "good deal"™.

As for why it isn't a subroutine, perhaps because I like this code all in one place. Shrug.

This code is all in one place. It is just a loop with a return value. Read carefully.

my $iold = sub {
  for my $i ( 1 .. $foo ) {
    if( bar($i) ) {
      return($i);
    }
  }
}->();  # calls this anonymous sub (setting $iold)
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Note that it takes the same number of lines to set an external (to the loop) value and last; as it does to define your loop as an anonymous sub and return($i);

This also gets you the benefit that if the loop gets more complicated or needs to be reuse, refactoring just means yanking it verbatim and making it a named sub because nothing inside of it relies on lexical scope. (Yeah, you have to put any parameters in the ->($var1, $var2); part for this to scale.)