I'm trying to write the first basic GP example in this free book:
http://www.lulu.com/items/volume_63/2167000/2167025/2/print/book.pdf
I've gotten a lot of the suppor methods working correctly (like
fitness) but I'm having problem convering the pseudocode on page 14
for generating random expressions to make up my initial population.
Here's what I have so far:
(defn gen-rand-expr [functions terminals max-depth arity method]
(if (or (= max-depth 0) (and (= method :grow) (< (rand) (/ (count
terminals) (+ (count terminals) (count functions))))))
(rand-element terminals)
(let [arg1 (gen-rand-expr functions terminals (- max-depth 1) arity
method)
arg2 (gen-rand-expr functions terminals (- max-depth 1) arity
method)
func (rand-element functions)]
(func arg1 arg2))))
First, how can I print out the definition of a function in clojure?
For example, if I do (defn add [x y] (+ x y)) how can inspect this
definition, like (show-def add) -> (defn add [x y] (+ x y)). This
would help a lot in debugging the random programs I'm trying to
generate.
Second, I believe the last line is the problem in my code. Let's
assume the function randomly selected was +, it will run (+ 1 2) and
the entire function returns 3 instead of a randomly generated syntax
tree like I need. I then tried '(func arg1 arg2) hoping it would
prevent evaluation, but then it will always just return (func arg1
arg2) which isn't what I need either. I need it to actually return a
syntax tree made up of expressions like (+ 1 2) but unevaluated.
I am guessing I need to start reading and using macros at this point?
Rob
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