2016/01/12

# SICP 問題 4.44

eight-queenをamb評価器を用いて解く．

ただし，まだamb評価器は実装していないのでコードだけ．

```
(define (eight-queen)
(define (cross? a b)
(= (/ (/ (car a) (car b))
(abs (- (cdr a) (cdr b))))
1))
(let ((chess (iota 8 1)))
(let ((one (cons 1 (amb chess))))
(let ((two (cons 2 (amb chess))))
(require (distinct (list one two)))
(require (not (cross? two one)))
(let ((three (cons 3 (amb chess))))
(require (distince (list one two three)))
(require (fold (lambda (x y) (and (not (cross? three x)) y)) #t (list one two)))
(let ((four (cons 4 (amb chess))))
(require (distinct? (list one two three four)))
(require (fold (lambda (x y) (and (not (cross? four x)) y)) #t (list one two three)))
(let ((five (cons 5 (amb chess))))
(require (distinct? (list one two three four five)))
(require (fold (lambda (x y) (and (not (cross? five x)) y)) #t (list one two three four)))
(let ((six (cons 6 (amb chess))))
(require (distinct? (list one two three four five six)))
(require (fold (lambda (x y) (and (not (cross? six x)) y)) #t (list one two three four five)))
(let ((seven (cons 7 (amb chess))))
(require (distinct? (list one two three four five six seven)))
(require (fold (lambda (x y) (and (not (cross? seven x)) y)) #t (list one two three four five six)))
(let ((eight (cons 8 (amb chess))))
(require (distinct? (lsit one two three four five six seven eight)))
(require (fold (lambda (x y) (and (not (cross? eight x)) y)) #t (list one two three four five six seven)))
(list one two three four five six seven eight)))))))))))
```