On Mon, Jul 21, 2008 at 09:39:26AM -0500, Ted Zlatanov wrote:
>  On Fri, 18 Jul 2008 16:40:34 -0700 Eric Wilhelm <scratchcomputing@[...].com> wrote: 
>  
>  EW> # from Ted Zlatanov
>  EW> # on Friday 18 July 2008 06:26:
>  
>  >> 2) there's a way to know not just the line, but also the character
>  >> position of a function call, so we can do
>  >> 
>  >> if (every(5) || every(6)) {}
>  >> 
>  >> without resorting to shenanigans like using \5 and \6 or passing a
>  >> special identifier in addition to the number.
>  
>  EW> It looks like the every(6) would miss a count whenever every(5) was 
>  EW> true -- would that be intentional?  Or did you mean '|' instead 
>  EW> of '||' ?
>  
>  The logic is screwy, but I was trying to draw attention to how every(6)
>  will have the same counter as every(5) based on the called line.  You're
>  right this is a bug waiting to bite though :)
>  
>  EW> In any case, how does the calling character position matter if you're 
>  EW> keying by divisor and caller()?  if(every(5) | every(5)) ?
>  
>  Probably a better example would be
>  
>  sub go { foreach (@_) { print if every(5); print if every(6); } }
>  
>  This should print every fifth and sixth member: 5, 6, 10, 12, etc.

And it will print every 30th member twice.

Considering that both

    print if every(5) || every(6);

and

    print if every(5);
    print if every(6);  # Ugly code duplication.

don't print every fifth and sixth member just once, I think that 
using:

    print if ++ $count % 5 == 0 ||
                $count % 6 == 0;

is preferably, as it doesn't surprise people.

I guess 

    print if every(5) + every(6);

would work, but that's not something I'd really like to use.


>  EW> Provide a closure for more advanced usages?
>  
>  EW>   my $fives = Every->new(5);
>  EW>   ... if($fives->());
>  
>  Yes, I thought about that too, but it can be called in tight loops so
>  I'm not sure using objects would be efficient.  I'd need to time it.
>  It's also more verbose and introduces yet another variable, both of
>  which I love to avoid :)


If it's done in a tight loop, tight enough that what you do in the loop
is significant, I'd go for '++ $count % 5 == 0', instead of calling an
extra subroutine.

Of course, if I just wanted to print every fifth member of an array,
I'd write:

    for (my $i = 4; $i < @_; $i += 5) {
        print $_ [$i];
    }


Abigail