boftx:
Latnam doesn't generate any negative numbers in his or her  @source array, but if all the numbers were negative, the results would be spurious. List::Util::max and min don't have this problem (although they don't produce any index information; maybe see List::MoreUtils::first_index for this).

>perl -wMstrict -le
"my @source = ( -1, -2, -33, -4 );
 ;;
 my $maxseen = 0;
 my $seen_at = 0;
 my $cntr = 0;
 for ( @source ) {
   if ( $_ > $maxseen ) {
     $maxseen = $_;
     $seen_at = $cntr;
     }
     ++$cntr;
   }
 ;;
 print qq{max $maxseen at index $seen_at};
"
max 0 at index 0
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