TalkChess.com

[H.G.Muller]

I like the design with a referee engine. It means that only the author of the first engine for a certain game is burdoned with things like rule enforcement, result adjudication, (and optionally move highlighting). Any later engine could be 'light weight', and omit implementation of the parts of the protocol involved in these tasks. The GUI would use the heavy-weight engine as referee, consulting it to obtain the required rule knowledge.

I might convert WinBoard / XBoard to utilize this scheme. In fact these are already sort of using this method: the first engine is always following the currently displayed position, even in Edit Game mode, judging move legality. So the referee engine in fact is already there. But currently you cannot play against any other engine than the referee engine, and when two engines play, it is always the referee against another.

So what I would have to do is allow active use of the second engine (for analysis or human-engine play) where the first engine remains following the game in force mode silently (unless there are illegal moves, or it detects game end). It seems a good feature anyway to make it possible to analyze with two engines at once, which requires nearly the same code change (just refraining from silencing the referee). And for engine-engine games there would have to be a third engine. Although that would be less important, as the referee is mainly needed for implementing functions that involve humans. (Who make mistakes during move entry, want to see target squares highlighted, and one-click moving to be available.)