Single Comment

I wonder if it would be worth it to support mandatory capture in the Interactive Diagram. Removing all non-captures from the move list if there is a capture in it would not be that difficult. If that doesn't leave any move (which normally would indicate the side to move is mated), it could undo that, so the search can use non-captures. I have no feeling what this would do for the piece values, though. And it would only work if the rule applies to pseudo-legal captures. (Which would be fine for games like Suicide Chess, which do not have royalty in the first place.)

If non-captures would be allowed when pseudo-legal captures are possible, but all illegal, it would be a bit harder. Whether a move is legal would only become clear after searching it deep enough to see the replies. I guess it could start the same way, though, suppressing all non-captures in the first few depth iterations it does for each position. If at the depth where illegality of captures can be seen no legal moves remain, it should get a second chance to re-enable the non-captures.

Of course we could try to generalize the rule and refine it, by allowing type specifity. E.g. a new symbol in the captureMatrix could indicate which captures are mandatory. Then you could define f.e. pieces that must be captured whenever the opportunity arises ('Sirenes'?), or pieces than must capture whenever they can ('Maniacs'?).