Could you give an example of such code?

BTW, what you are asking for is a special case of "loop enlightment", and cog's solution is the standard way of solving this. It belongs in Programming 102.

Anonymous Monk,
No, what I am asking for is not a special case of "loop enlightment". What I am asking for is for people to consider what they would do if they had the ability to modify the optree (or the p6 equivalent) while the code is running.

To answer you code question - consider the following trivial example:

for ( @some_array ) {
    if ( $_ eq 'foo' ) {
        print "skipping foo\n";
        next;
    }
    if ( $_ eq 'bar' ) {
        handle_bar($_);
        next;
    }
    handle_rest($_);
}
[download]

To re-write this we need to first change

for ( @some_array ) { ... }
# to
my $index = -1;
while ( ++$index <= $#some_array ) { ... }
[download]

So that when we break out of the first loop to enter the second, we can remember where we left off. Unfortunately, the order that we will encounter 'foo' and 'bar' is unknown so we also have to create a flag variable and end up with 4 while loops instead of the original 1:
Read more... (997 Bytes)
This was a translation of a very simple example. I do not if there is any case where it would be impossible to do, but it certainly isn't easy. Again, the point of the medidation is to just take the functionality as a given for a second and think about what you would do with it.

Cheers - L~R

I think you want the match-only-once operator:

for ( @some_array ) {
    if ( ?^foo$? ) {
        print "skipping foo\n";
        next;
    }
    if ( ?^bar$? ) {
        handle_bar($_);
        next;
    }
    handle_rest($_);
}
[download]

---

Caution: Contents may have been coded under pressure.

my %things = (foo => sub {print "skipping foo\n"; next},
              bar => sub {handle_bar($_); next},
);
for (@some_array) {
    (delete $things{$_})->() if exists $things{$_};
    handle_rest($_);
}
[download]