duck

var waves : Wave[];
static var spawn : boolean;

function Start()
{
    spawn = false;
    var pos = transform.position;
    var rot = transform.rotation;

    for (var wave in waves) {
        for (var enemy in wave.enemies) {

            // wait until ok to spawn next enemy:
            while (!spawn) {
                yield;
            }

            Instantiate(enemy, pos, rot);
            spawn = false;
        }
    }
}