impls/lib/memoize.mal

   1 ;; Memoize any function.
   2
   3 ;; Implement `memoize` using an atom (`mem`) which holds the memoized results
   4 ;; (hash-map from the arguments to the result). When the function is called,
   5 ;; the hash-map is checked to see if the result for the given argument was already
   6 ;; calculated and stored. If this is the case, it is returned immediately;
   7 ;; otherwise, it is calculated and stored in `mem`.
   8
   9 ;; For recursive functions, take care to store the wrapper under the
  10 ;; same name than the original computation with an assignment like
  11 ;; `(def! f (memoize f))`, so that intermediate results are memorized.
  12
  13 ;; Adapted from http://clojure.org/atoms
  14
  15 (def! memoize
  16   (fn* [f]
  17     (let* [mem (atom {})]
  18       (fn* [& args]
  19         (let* [key (str args)]
  20           (if (contains? @mem key)
  21             (get @mem key)
  22             (let* [ret (apply f args)]
  23               (do
  24                 (swap! mem assoc key ret)
  25                 ret))))))))