gistfile1.clj

(defstruct game :current-score :throws)

(def darts
     (concat
      (range 1 21)
      (map (partial * 2) (range 1 21))
      (map (partial * 3) (range 1 21))
      '(25 50)))
      
(def finishes
     (set (concat (map (partial * 2) (range 1 21)) '(25 50))))

(defn next-throw
  "Given a value return the next valid darts"
  [n]
  (filter
   (partial not= 1)
   (filter 
    (partial <= 0)
    (map (fn [x] 
	   (let [result (- n x)]
	     (if (not= result 0)
	       result
	       (if (finishes x) 0 -1))))
	 darts))))

(defn next-dart
  "Given a value, return the next darts and record the state"
  [d]
  (map (fn [new-score]
	 (struct game 
		 new-score
		 (conj (:throws d) new-score)))
       (next-throw (:current-score d))))

(defn finished? [d] (zero? (:current-score d)))