a solution to an Anglican exercise

clojure_meetup_8_dec_2017.clj

;; To do this we've provided scaffolding
;; that can be modified to achieve
;; your objective:
(with-primitive-procedures
  [create-world simulate-world balls-in-box]
  (defquery arrange-bumpers []
    (let [;; *** TASK: REPLACE THE FOLLOWING LINE WITH 
          ;;     STOCHASTIC CODE TO SAMPLE POSSIBLE 
          ;; 	 BUMPER CONFIGURATIONS ***
          n-bumpers 4 ;; (sample (poisson 4)) ;; this is to let Anglican select the number of bumpers; maybe (poisson 2) is better 
          bumper-positions (repeatedly n-bumpers #(list 
                                            (sample (uniform-continuous -5 16))
                                            (sample (uniform-continuous -20 8))))

          ;; Code to simulate the world:
          world (create-world bumper-positions)
          end-world (simulate-world world)
          balls (:balls end-world)

          ;; How many balls entered the box?
          num-balls-in-box (balls-in-box end-world)]

      ;; *** ADD A LIKELIHOOD FUNCTION (observe) HERE ***
      ;;(observe (normal n-bumpers 1) 0) ;; to get as few bumpers as possible
      (observe (normal num-balls-in-box 1) 10)
      
      (predict :balls balls)
      (predict :num-balls-in-box num-balls-in-box)
      (predict :bumper-positions bumper-positions))))