I tested this in the yard and it seemed to work fine. You haul the halyard and it pulls the throat block up towards the masthead block. Eventually, the luff (front edge of the sail) becomes tight, and the throat block can't go any higher. If you keep pulling on the halyard, the peak (end of the yard) comes up until either the peak can't be raised any more or the leech (back edge of the sail) becomes tight.