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Check out Janggi (Korean Chess), our featured variant for December, 2024.
Check out Janggi (Korean Chess), our featured variant for December, 2024.
What succession=N does is to generate moves that swap the King with a piece of the indicated successor type and search those, after the search of all other moves has left the score at minus 'infinity' (meaning no legal moves and no draw by stalemate). That it has to scan the board for that is of no importance, as this code is almost never reached.
What you want (if I understood it) is far more complex, as capture of the King should normally abort further search with a +infinity score (flagging the preceding move as illegal), unless the previous position was done in a checkmated position (which it would not know yet at that point).
Funny enough the Princess promotion would be easy to do with some custom scripting. The ID calls a custom function (if one is supplied) for every move it generates, which could then tinker with the generated move. This function could test for capture of a Queen, and in that case add promotion of the Princess to the move encoding. The parameter trackPieces should make location of the Princess available resonably cheaply, so that this doesn't cause too much of a slowdown.
The difference is that exposing the Queen to capture is allowed at any time. But exposing the King to capture is allowed only when checkmated. This latter requirement is the hard part.