H. G. Muller wrote on Sat, Nov 16, 2019 05:18 PM UTC:
But then I am not so happy that this requires an alteration of the normal (full-turn) FENs, which would require w2 and b2 stm field in your proposal. I would much rather have it that the exceptional partial-turn FENs would require something special. As the full-move counter is actually completely useless, and in balanced Marseillais the first turn is special in that it only allows a single move, recognizing half-turn FENs by artificially setting their move count to 1 would be OK with me.
The WinBoard Alien Edition would not consider positions half-way a turn not as game positions; when you step through the game later it would always alternate player between two turns, and show the effect of the pair of moves (like it was dealing with castling). Animation of the move might tell you the order.
As to the legality issue: I took the pragmatic approach in my Shogi engines as well as WinBoard: I do not consider Pawn-drop mates illegal, just losing. If checkmate is detected, its scoring depends on whether the previous move was a Pawn drop or not. So even without engine WinBoard allows the user to enter the Pawn drop, which then will end the game for him as a loss. For Shogi this is of course entirely justifiable. But it would not disturb me if Marseillais was treated the same; if we thing it should not be allowed to stalemate yourself after the first turn, just detect the stalemate and declare it a loss if the user elects to play into it.
But then I am not so happy that this requires an alteration of the normal (full-turn) FENs, which would require w2 and b2 stm field in your proposal. I would much rather have it that the exceptional partial-turn FENs would require something special. As the full-move counter is actually completely useless, and in balanced Marseillais the first turn is special in that it only allows a single move, recognizing half-turn FENs by artificially setting their move count to 1 would be OK with me.
The WinBoard Alien Edition would not consider positions half-way a turn not as game positions; when you step through the game later it would always alternate player between two turns, and show the effect of the pair of moves (like it was dealing with castling). Animation of the move might tell you the order.
As to the legality issue: I took the pragmatic approach in my Shogi engines as well as WinBoard: I do not consider Pawn-drop mates illegal, just losing. If checkmate is detected, its scoring depends on whether the previous move was a Pawn drop or not. So even without engine WinBoard allows the user to enter the Pawn drop, which then will end the game for him as a loss. For Shogi this is of course entirely justifiable. But it would not disturb me if Marseillais was treated the same; if we thing it should not be allowed to stalemate yourself after the first turn, just detect the stalemate and declare it a loss if the user elects to play into it.