Missing Block error on line 20

stack.p6

#!perl6

class Stack {
  has Int @!store;

  method push(Int:D $elem --> Nil) {
    push @!store, $elem;
  }

  method pop(--> Int) {
    die "UNDERFLOW" if self.is-empty();

    pop @!store;
  }

  method peek(--> Int) {
    @!store[* - 1];
  }

  method is-empty(-> Bool) { # Missing block
    @!store.elems == 0;
  }
}

my $s = Stack.new();