use strict; use warnings; use feature 'say';

my @x = ( -2, 2, 3, 8, 10 );
my %y = map { $_ => 1 } @x;

say "missing: $_" for grep { not exists $y{ $_ } } ( -2 .. 10 );

##</code><code>##

perl 1186862.pl
missing: -1
missing: 0
missing: 1
missing: 4
missing: 5
missing: 6
missing: 7
missing: 9