does not compile, since the do does not know anything about the while.

~/perl$ cat x
do {
    charlie;
    last if bob;
    david;
} while (alice);
~/perl$ perl -c x
x syntax OK
~/perl$ perl -v

This is perl, v5.6.1 built for i386-linux
[download]

What is not working, though, is the last. This is because the block introduced with do is neither a loop nor a bare block. Your statement is basically equivalent in structure to print foo while bar.

What you can do instead is a bare block, because you can use next, last, redo on a bare block:

LOOP: {
  charlie;
  last LOOP if bob;
  david;
  redo LOOP if alice;
}
[download]

LOOP: {
  charlie;
  last LOOP if bob;
  david;
  redo LOOP if alice;
}
[download]

A more concise syntax:

for (;;) {
  charlie;
  last if bob;
  david;
  last if !alice;
}
[download]

It's my understanding that for (;;) { ... } can be replaced simply with loop { ... } in Perl6.

I'd prefer while (1) { ... } to for (;;) { ... }. Looks easier to understand to me.

Jenda


Support Denmark! Defend the free world!

See the section on statement modifiers in perlsyn.

Note also that the loop control statements described later will NOT work in this construct, because modifiers don't take loop labels. Sorry. You can always put another block inside of it (for next) or around it (for last) to do that sort of thing. For next, just double the braces:

do {{
    next if $x == $y;
    # do something here
}} until $x++ > $z;
[download]

For last, you have to be more elaborate:

LOOP: { 
        do {
            last if $x = $y**2;
            # do something here
        } while $x++ <= $z;
}
[download]

Mmhh, I know this is just copy and pasted code, but it makes me wonder anyway - is it just me or is the code for the last example slightly strange?

LOOP: {
        do {
            last if $x = $y**2;
            # do something here
        } while $x++ <= $z;
}
[download]

• if $x = $y**2; why choose a confusing assignment instead of a normal comparison?
• Why not the explicit last LOOP? I know that it works here without it all right but I don't see the benefit of labelling the block without using the label afterwards

-- Hofmator

Code written by Hofmator and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

I was thinking exactly the same things as I was writing the post. I foresee a couple of patches being sent to the maintainers.

--
<http://dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg