On Wed, 6 Dec 2006 21:56:09 +0000, Andy Armstrong wrote:
> That pretty much satisfies what I originally asked but doesn't help  
> in the case where the iterator isn't implemented as a single loop.  
> I'd really like to have the kind of loop exit communicated back to  
> the iterator so it can handle it in whatever way is appropriate. For  
> example the iterator might actually be recursively walking some data  
> structure without even containing an explicit loop
> 
> sub iter {
>      my $node = shift;
>      my $sub  = shift;
> 
>      iter($node->{left}, $sub) if exists $node->{left};
>      $sub->($node);
>      # Should redo $sub call if redo thrown
>      #        carry on       if next thrown
>      #        throw 'last' up the call stack
>      #                       if last thrown
>      iter($node->{right}, $sub) if exists $node->{right};
> }

Every block is a loop, so something like this might work (untested):

sub iter{
  my($node,$sub)=shift;
  my @args=whatever();

  my $continue;
  eval qq{
    $node:{
      if(defined \$continue){
        # $sub exited via redo
      }
      \$continue=0;
      \$sub->(\@args);
    }continue{
      ++\$continue;
    }
  };

  if($@){
    # $sub exited via die
  }elsif(!$continue){
    # $sub exited via last
  }else{
    # $sub exited normally or via next
  }
}

You can get rid of the warning with C<no warnings 'exiting';>,
but that has to be in the callback sub, unfortunately.

-- 
	Peter Haworth	pmh@edison.ioppublishing.com
"f y cn rd ths y mst hv bn sng nx"