And why, pray tell, would you ever need that information? The first parameter is the first parameter, the second parameter is the second parameter ... so on. If your subroutine is set up to accept a hash (or hash ref), then you can easily tell such things:

foo(bar => 'baz');

sub foo {
   my %arg = @_;
   print "These were the 'vars' passed to me:\n";
   print "\t$_\n" for keys %arg;
}
[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)