There are two main contexts for evaluating the legality of potential moves. One is the normal context of evaluating whether a move from one space to another is legal. In this context, the destination should be the space the piece moves to. The other context is evaluating whether a piece is checking the King. For displacement captures, this simply involves evaluating whether a piece can move to the King's position. So, for non-displacement captures, you will have to simulate a move to the King's position.
The fairychess include file has a mechanism for dealing with these two types of moves. It's not well-documented, but it does come up in the breakdown of the White_Pawn function. If you go to the include file itself and compare the checked subroutine with the stalemated subroutine, you will see that each gives a different value to the variable movetype. The White_Pawn function uses this value to stop the function early when all it has to evaluate is whether it can check the King, since as a divergent piece, some of its powers of movement will not be relevant to this question. Although the Pawn can capture another Pawn by en passant, it cannot capture a King by en passant. So, its ability to capture by non-displacement has no effect on its ability to check a King.
But for a piece that normally captures by non-displacement, you will need to write its move function to account for two types of moves. For moves with the MOVE type, your function should evaluate whether the piece can move to the destination, and it should handle non-displacement captures with the remove built-in function, just as the Pawn functions do for en passant. For moves with the CHECK type, your function should evaluate whether it can capture a piece on the destination. Since this will be used only for telling whether it is checking a King, you may treat this as a move to the King's space without worrying about moving the piece to another space.
If you use the fairychess include file, you should be able to use its checked and stalemated subroutines without writing your own. The main thing you will need to do is write your piece functions to handle two different types of moves.
There are two main contexts for evaluating the legality of potential moves. One is the normal context of evaluating whether a move from one space to another is legal. In this context, the destination should be the space the piece moves to. The other context is evaluating whether a piece is checking the King. For displacement captures, this simply involves evaluating whether a piece can move to the King's position. So, for non-displacement captures, you will have to simulate a move to the King's position.
The fairychess include file has a mechanism for dealing with these two types of moves. It's not well-documented, but it does come up in the breakdown of the White_Pawn function. If you go to the include file itself and compare the
checkedsubroutine with thestalematedsubroutine, you will see that each gives a different value to the variablemovetype. The White_Pawn function uses this value to stop the function early when all it has to evaluate is whether it can check the King, since as a divergent piece, some of its powers of movement will not be relevant to this question. Although the Pawn can capture another Pawn by en passant, it cannot capture a King by en passant. So, its ability to capture by non-displacement has no effect on its ability to check a King.But for a piece that normally captures by non-displacement, you will need to write its move function to account for two types of moves. For moves with the MOVE type, your function should evaluate whether the piece can move to the destination, and it should handle non-displacement captures with the
removebuilt-in function, just as the Pawn functions do for en passant. For moves with the CHECK type, your function should evaluate whether it can capture a piece on the destination. Since this will be used only for telling whether it is checking a King, you may treat this as a move to the King's space without worrying about moving the piece to another space.If you use the fairychess include file, you should be able to use its
checkedandstalematedsubroutines without writing your own. The main thing you will need to do is write your piece functions to handle two different types of moves.