What is difference between: -
    while( my($index, $value) = each @rocks )
and
    while((my $index,my $value) = each @rocks )

You can see what Perl thinks the difference is by using the O compiler backend interface to the B::Deparse module (invoked here with  -p full parenthesization):

>perl -wMstrict -MO=Deparse,-p -le
"my @rocks = qw(a b c);
 ;;
 while (my ($i, $v) = each @rocks) {
   print qq{$i: '$v'};
   }
 ;;
 while ((my $i, my $v) = each @rocks) {
   print qq{$i: '$v'};
   }
"
BEGIN { $^W = 1; }
BEGIN { $/ = "\n"; $\ = "\n"; }
use strict 'refs';
(my(@rocks) = ('a', 'b', 'c'));
while ((my($i, $v) = each(@rocks))) {
    do {
        print("${i}: '${v}'")
    };
}
while ((my($i, $v) = each(@rocks))) {
    do {
        print("${i}: '${v}'")
    };
}
-e syntax OK
[download]

Apparently, Perl doesn't think there is any difference at all. (Same results under Strawberries 5.12.3.0 and 5.14.2.1.)

See also Basic debugging checklist.