queens blog

def-subo.clj

(def subo
  (fn ([x y r]
        (conde
          [(== x 0) (== y 0) (== r 0)]
          [(== x 0) (== y 1) (== r -1)]
          [(== x 1) (== y 0) (== r 1)]
          [(== x 1) (== y 1) (== r 0)]))))

run-4q.clj

(run* [r]
      (fresh [x1 x2 x3 x4]
             (safeo [x1 0] [x2 1])
             (safeo [x1 0] [x3 2])
             (safeo [x1 0] [x4 3])
             (safeo [x2 1] [x3 2])
             (safeo [x2 1] [x4 3])
             (safeo [x3 2] [x4 3])
             (== r [[x1 0] [x2 1] [x3 2] [x4 3]]))))

safe.clj

(defn safe? [[x1 y1] [x2 y2]]
  (and
   (not= x1 x2)
   (not= y1 y2)
   (not= (- x2 x1) (- y2 y1))
   (not= (- x1 y2) (- x2 y1))))

safeo.clj

(defn safeo
  "Are 2 queens threatening each ohter?"
  [[x1 y1] [x2 y2]]
  (fresh [d1 d2 d3 d4]
         (subo x2 x1 d1)
         (subo y2 y1 d2)
         (subo x1 y2 d3)
         (subo x2 y1 d4)         
         (!= x1 x2)
         (!= y1 y2)
         (!= d1 d2)
         (!= d3 d4)))