Perl 6 dice roller

rollin.pl6

use Crypt::Random;

class Roll {
  has Int:D $.dice = 1;
  has Int:D $.sides is required;
  has Int:D $.constant = 0;

  method parse(Str:D $str) {
    if $str ~~ /[$<d>=(\d+) d]? $<s>=(\d+) [\+ $<c>=(\d+)]?/ {
      self.new(dice => ($<d>:v || 1).Int, sides => ($<s>:v).Int, constant => ($<c>:v).Int);
    }
  }
}

sub USAGE() { say "Usage: {$*PROGRAM-NAME} [<dice>d]<sides>[+<constant>]" }
sub MAIN(Str $roll-str) {
  my $roll = Roll.parse($roll-str) // return USAGE();
  say $roll.constant + [+] (1 .. $roll.dice)».&{ crypt_random_uniform($roll.sides) + 1 };
}