nqueens-ckanren

queens.clj

(defn diago [qi qj d rng]
  (fresh [qid qjd]
         (infd qid qjd rng)
         (+fd qi d qid)
         (!=fd qid qj)
         (+fd qj d qjd)
         (!=fd qjd qi)))

(defn diagonalso [n r]
  ((fn dloop [r i s j]
     (cond
       (or (empty? r) (empty? (rest r))) s#
       (empty? s) (dloop (rest r) (inc i) (rest (rest r)) (+ i 2))
       :else (let [qi (first r), qj (first s)]
               (all
                (diago qi qj (- j i) (interval 0 (* 2 n)))
                (dloop r i (rest s) (inc j))))))
   r 0 (rest r) 1))

(defn n-queenso [q n]
  ((fn qloop [i l]
     (if (zero? i)
       (all
        (distinctfd l)
        (diagonalso n l)
        (== q l))
       (fresh [x]
              (infd x (interval 1 n))
              (qloop (dec i) (cons x l)))))
   n '()))

(count 
  (run* [q]
        (n-queenso q 8)))