Hmmm.. I'm inclined to doubt that this is true for all cases. In principle, I'd agree, but saying that anything expecting a return list is too simple an assumtion.

I'm quite sure (although I'm too lazy now, to come up with some proof) that I'd find a map with a discarded return list that does something faster than an equivalent for/foreach.

BTW, has someone thought that a smart while() might be fastest anyway?

while is for...

> perl -MO=Deparse -e"for(;;){}"
for (;;) {
    ();
}
-e syntax OK

> perl -MO=Deparse -e"while(1){}"
for (;;) {
    ();
}
-e syntax OK

> perl -MO=Deparse -e"for(1){}"
foreach $_ (1) {
    ();
}
-e syntax OK

>
[download]

~Particle *accelerates*

> perl -MO=Deparse -e 'while($x++ < 10){}'
while ($x++ < 10) {
    ();
}
[download]

Now, why is that? Shouldn't that be

for(;$x++ < 10;){}
[download]

then? On the contrary actually:

> perl -MO=Deparse -e 'for(;();){}'
while (()) {
    ();
}
[download]

So, it seems that while is for only for the obvious endless loop, and in other cases for is while (as I had expected...)

However, I am intriqued by the fact that

> perl -MO=Deparse -e 'for($x;$y;$z){()}'
for ($x; $y; $z) {
    ();
}
[download]

and not

{
    $x; 
    while($y) {
        ();
    } 
    continue {
        $z;
    }
}
[download]

(at least not on the Perl level of things).

Cool stuff anyway! Thanks a million. I learned a lot from your reply. I flew over the optimizer and Deparse a few times (mostly when searching for other things), but using it that way looks powerful. Got any pointers to good information on it? Is there some "How to wrink the guts out of your script using -MO=Deparse/the Optimizer" somewhere?

So long,
Flexx

(I like the photo on your home node, BTW).

No, while isn't for. It is optimized to a for(;;) in the case where it is used as while(SOME_TRUE_CONSTANT). It is also optimized away in the case where it is used as while(SOME_FALSE_CONSTANT).

$ perl -MO=Deparse -e 'while (0) {}'
;
-e syntax OK

$ perl -MO=Deparse -e 'while (1) {}'
for (;;) {
    ();
}
-e syntax OK

$ perl -MO=Deparse -e 'while (@_) {}'
while (@_) {
    ();
}
-e syntax OK
[download]

For that matter, even though for and foreach are synonymous, what's in the parens determines how perl actually parses them:

$ perl -MO=Deparse -e 'for (;;) {}'
for (;;) {
    ();
}
-e syntax OK

$ perl -MO=Deparse -e 'foreach (;;) {}'
for (;;) {
    ();
}
-e syntax OK

$ perl -MO=Deparse -e 'for (@_) {}'
foreach $_ (@_) {
    ();
}
-e syntax OK

$ perl -MO=Deparse -e 'foreach (@_) {}'
foreach $_ (@_) {
    ();
}
-e syntax OK
[download]

-sauoq
"My two cents aren't worth a dime.";