use strict;
use warnings;

sub action_1_to_999 {
    print "1 to 999\n";
}

my %dispatch = (
    0 => sub { print "Zero\n" },
    map { $_ => \&action_1_to_999 } ( 1 .. 999 ),
    1000 => sub { print "1e3\n" },
);

$dispatch{0}->();
$dispatch{23}->();