I have a move procedure that applies a legal move to a chess piece on the board by passing a pair: (cons source dest) so (cons 1 2) takes a piece on position 1 from the board and moves it to position 2.
I'm trying to make a procedure that applies the same move it made before. I tried to do
(move (reverse move)) which would pass in (cons 2 1) thereby moving the piece back.
unfortunately, reverse doesnt work for pairs. I can't convert it to a list because that would have to change a lot of the code to accommodate for the null at the end.
Can anyone think of anything? I'm using MIT Scheme by the way.
You need to implement your own reverse-pair procedure for this, it can be as simple as this:
(define (reverse-pair p)
(cons (cdr p) (car p)))
Or this, a bit fancier but less readable:
(define (reverse-pair p)
`(,(cdr p) . ,(car p)))
Either way it works as intended:
(reverse-pair '(1 . 2))
=> '(2 . 1)