sub nice_list {
   return ''    if @_ == 0;
   return shift if @_ == 1;
   
   my $last = pop;
   return join(', ', @_) . " and $last";
}

my %is_eaten_by = (
   apple  => [ qw( Tom David ) ],
   orange => [ qw( Tom       ) ],
   pear   => [ qw( Tom       ) ],
   mango  => [ qw(     David ) ],
);

foreach my $fruit (keys %is_eaten_by) {
   my $eaters = $is_eaten_by{$fruit};
   my $num_eaters = @$eaters;
   my $s = $num_eaters == 1 ? 's' : '';
   my $p = $num_eaters == 1 ? '' : 's';
   print("$num_eaters person$p eat$s ${fruit}s: ",
         nice_list(@$eaters), "\n");
}