TalkChess.com

[H.G.Muller]

I think that a versatile protocol should allow the engine to be servant as well as master. I don't see why one should exclude the other. The difference is really only in what the GUI does with the info an engine sends it. In servant mode, refusing a move as illegal is a capital crime, forfeiting the engine. In master mode, the GUI would side with the engine, and take back the move. To run in master mode, the engine can offer the service of sending a list of legal moves, on GUI request. In servant mode the engine should have no say in the matter, and the GUI would just not use the command to request the list.

Note that a list of legal moves is not logically needed in a GUI, even if it wants to leave the engine in total control. It is just the awkward design of the UCI 'searchmoves' that makes this necessary. With separate commands for excluding and including moves, that also understand the qualifier 'all', the same job can be done entirely without knowledge of the full move list.

In the WinBoard 'Alien Edition' we even have extended WB protocol with commands to allow the engine to highlight squares (by sending a 'color FEN' to the GUI), in response to 'lift' and 'hover' commands sent by the GUI to inform the engine when the user grabs a piece with the mouse, or drags it over a square where it can make a capture. The engine can also send 'click' commands in response to a 'lift', to implement one-click moving. You really should try the Nebiyu engine once, for playing Ultima, to see how well this works!