which version of perl? I can't seem to reproduce it... Mine is 5.6.1 on a solaris

  me@myhost> perl -MO=Deparse -e 'for( my $x = 0; $x < 10; $x++ ) { pr
+int "foo\n" }'
  for (my $x = 0; $x < 10; ++$x) {
      print "foo\n";
  }
  -e syntax OK
  me@myhost>
[download]

5.6.0 on OS X. Same result on 5.005_03. Presumably either Deparse or the peephole optimizer were thumped in 5.6.1 giving the different result.

B::Deparse is your friend here.

Ah. Well. Coming from you I'll take your word for it. But frankly I tend not to trust B::Deparse too much. :-)

D:\Development>perl -MO=Deparse  -e "for ($x = 0; $x < 10; $x++) {}"
for ($x = 0; $x < 10; ++$x) {
    ();
}
-e syntax OK

D:\Development>perl -MO=Deparse,-x3  -e "for ($x = 0; $x < 10; $x++) {
+}"
$x = 0;
while ($x < 10) {
    ();
}
continue {
    ++$x
}
-e syntax OK
[download]

This is on 5.6.1 AS631. Btw from the documentation for the -x switch

---

Expand conventional syntax constructions into equivalent ones that expose their internal operation. LEVEL should be a digit, with higher values meaning more expansion. As with -q, this actually involves turning off special cases in B::Deparse's normal operations.

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Which suggests to me that im right. (But which is also why I asked a Guru like yourself. I was hoping for a definitive answer that did not depend on Deparse.)

Nevertheless, thanks.

Older versions of deparse are accurate, as far as it goes. The problems in the node you referenced aren't Deparse's fault--it's not currently possible to turn an optree back into the source it came from. There's a not insignificant amount of stuff that's thrown away during the compile or peephole optimization phase, which makes things a bit tough.

Hey, at least I didn't recommend you rebuild perl with -DDEBUGGING and dig through the output of perl -Dt... :)

rebuild perl with -DDEBUGGING

Remarkably, the only reason im able to write this post (im at work) is because I decided to compile Perl with -DDEBGGING (but to add a debug switch to see whats happening with parsing and creating arguments in win32.c, yes i know -Dp does it, the yydebug was getting on my nerves...) and in a fit of stupidity deleted the win32/include directory :(

So maybe once I've finished Ill take a look...

Incidentally (re)learning c from perls source code is proving to be an interesting exercise. ;-)

Yves / DeMerphq
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Writing a good benchmark isnt as easy as it might look.