H. G. Muller wrote on Fri, Mar 13, 2020 08:08 AM UTC:
Just an idea: some chess GUIs allow 'reverse' entry of moves, by first clicking the destination square, and then the piece that should go there. (Usually in combination with some 'auto-complete' mode, where the move is executed immediately if only a single piece could reach the clicked empty square, and pieces that you click move immediately if there is only one place they could go.)
If you would in general allow the origin and destination of a move to be swapped, the difference could in exceptional cases (such as fast castling) be given a special meaning. Such as the reverse order (empty square x King) would indicate the castling, and move the Rook as a side effect.
Just an idea: some chess GUIs allow 'reverse' entry of moves, by first clicking the destination square, and then the piece that should go there. (Usually in combination with some 'auto-complete' mode, where the move is executed immediately if only a single piece could reach the clicked empty square, and pieces that you click move immediately if there is only one place they could go.)
If you would in general allow the origin and destination of a move to be swapped, the difference could in exceptional cases (such as fast castling) be given a special meaning. Such as the reverse order (empty square x King) would indicate the castling, and move the Rook as a side effect.