genetic.clj

; A Field Guide to
; Genetic Programming
; http://www.lulu.com/items/volume_63/2167000/2167025/2/print/book.pdf
(defn f2-1
  "Figure 2.1 max(x+x, x+3*y)"
  [x y]
  (max (+ x x)
    (+ x
	  (* 3 y))))


(defn gen-rand-expr
  "My impl of algorithm 2.1 - Full and grow methods"
  [func-set term-set max-depth method]
  (if (or (= max-depth 0)
          (and (= method :grow)
               (< (rand)
                  (/ (count term-set)
                     (+ (count term-set) (count func-set))))))
    (nth term-set (rand-int (count term-set))) ; choose a terminal
    (let [func (nth func-set (rand-int (count func-set)))]
      (cons func (for [i [1 2]]
                  (gen-rand-expr func-set term-set (dec max-depth) method))))))

(gen-rand-expr [+ - /] [1 2 3] 2 :grow)

; (#<core$_PLUS___3332 clojure.core$_PLUS___3332@1f1f38e>
;  		       (#<core$___3358 clojure.core$___3358@1f5eb7f> 3 1) 1)
; (+ (- 3 1) 1)
; 3