Stop recursion in Clojure

Question

I have created this rank-boards function. It takes a board, ranks it, makes the next move on the board and recurs. How can I stop the recur from happening when the board is full? The make-move-on-board function breaks when there are no moves left, and I get a Key must be integer error.

 (defn rank-boards [board max-mark min-mark depth]
  (cond
    (r/game-in-progress? board max-mark min-mark) in-progress-score
    (r/tie? board max-mark min-mark) tie-score
    (r/winner? board max-mark min-mark)       highest-score)
  (recur 
    (b/make-move-on board (next-space board max-mark min-mark depth) max-mark) 
       min-mark 
       max-mark
       (inc depth)))

Charles Duffy · Accepted Answer · 2014-10-22 20:15:10Z

2

Assuming a function called is-full? that returns a truthy value when it's time to stop recursing, and that your desired return value is the score:

(defn rank-boards [board max-mark min-mark depth]
 (if (r/is-full? board)

   ;; board is full, so we return the score
   (cond
     (r/game-in-progress? board max-mark min-mark) in-progress-score
     (r/tie? board max-mark min-mark)              tie-score
     (r/winner? board max-mark min-mark)           highest-score)

   ;; board is not yet full, so we recurse
   (recur
     (b/make-move-on board (next-space board max-mark min-mark depth) max-mark) 
        min-mark 
        max-mark
        (inc depth)))

The code originally threw away the results of the cond -- not a particularly sensible operation.

answered Oct 22, 2014 at 20:15

Charles Duffy

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