in reply to Re^4: Doing "it" only once
in thread Doing "it" only once

I think you want the match-only-once operator: 
for ( @some_array ) {
    if ( ?^foo$? ) {
        print "skipping foo\n";
        next;
    }
    if ( ?^bar$? ) {
        handle_bar($_);
        next;
    }
    handle_rest($_);
}

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Re^6: Doing "it" only once
by Limbic~Region (Chancellor) on Sep 21, 2005 at 17:37 UTC
    Roy Johnson,
    Wow - thanks! That's neat, but I am not sure if it fits the bill. If my understanding of this is correct, it basically ignores subsequent matches if a match has already been found. If that is technically accurate, it fails in that it still checks to see if there is a match before deciding to ignore it.

    This really is a meditation about being able to modify the optree (or the p6 equivalent) while the code is running and what you would do with it if you could. I provided the example of removing a conditional block once the condition has been met and the block ran once. This means not even the condition itself is checked, it would just be "gone". This, I am sure, is not the only application.

    Cheers - L~R

[reply]
      This code illustrates that the op only performs the match once: 
      my $type;
my $r = qr/(?{print "$type\n"})/;
for (1..3) {
  $type = 'Regular';
  /$r/;
  $type = 'Once only';
  ?$r?;
}

      [download]
      On the broader subject of modifying the optree...well, it hasn't really occurred to me very often. The most common reason to do it is to introduce new syntax, which I guess is what you're suggesting, after a fashion. If I were up to it, I would probably want to implement a new operator.

      (update: But there's more to adding syntax than modifying the optree. It's gotta parse, too.)

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In Section Meditations