Regarding in_list I personally would prefer either:

sub in_list {my $target=shift; return 0+grep { $_ eq $target } @_}
[download]

if you really care about the count (and want to use grep) or if you want fast then:

sub in_list {my $target=shift; $_ eq $target and return 1 for @_; retu
+rn}
[download]

using the for modifier avoids creating and managing an extra scope (like grep,map and for statements) and avoiding the slice I think is more efficient. Afaik perl will have to create the sliced list first before iterating so you are really just copying the whole array which could get expensive for a large list.

Anyway heres an interesting/useful one :

sub find_first_index {
  my $target=shift;
  push @_,$target;
  my $i=0;
  $i++ while $_[$i] ne $target;
  return $i==$#_ ? undef : $i
}
[download]

Which is a nice trick to reduce the cost of the tight loop. Dunno if more modern perls have been optimised enough that these tricks are unnecessary though. Its been a while since I benchmarked this stuff last.