Seeding a PRNG - Custom Setter
I would expect the generator to seed itself (using the current time) in its constructor.

Therefore, I would not use a default parameter in your set_seed method.

Also, in your current code, you treat all the negative values the same as zero. I wouldn't recommend that. Many random seeders can handle negative seeds as well, if you don't want to do that: Throw an Exception/Error!

Therefore, I would use this:

public function set_seed(s: Number): void
{
    if (s &lt; 0) {
        throw new Error("Seed must be positive");
    }
    seed = s;
}


For comparison and inspiration, check Java's java.util.Random class. Note that it has two constructors available, one for initializing to System's seed and one for initializing to a specific seed. That is an approach I would recommend.