anchor.diff:          (= (car cell) (- (car dimensions) 1))
           (= (cdr cell) (- (cadr dimensions) 1)))))
   
  +;; Check if in a single evaluation the cell has not already been visited.
   (defun new-cell-p (hashset cell)
     (not (gethash (write-to-string cell) hashset)))
   
  +;; FItness predicate function that checks if a fitness has 'succeeded'.
   (defun fitness-p (fitness)
     (let* ((dimensions dims)
            (wall-cells (+ (* 2 (car dimensions)) (* 2 (- (cadr dimensions) 2)))))
       (>= fitness (* wall-cells (length current-cell)))))
   
  +;; Fitness function helper that takes results and checks them for the fitness.
   (defun fitness-helper (results)
     (if (typep results 'list)
       (let ((hashset (make-hash-table :test 'equal)))
  
positive.code:             current-cell))))
  
  (defun s (grid-world current-cell)
    (let ((new-x (+ (car current-cell) 1)))
      (list grid-world
            (if (<= new-x (- (car (array-dimensions grid-world)) 1))
  
negative.code:                          (current-cell 3 1)
                           (current-cell 0 3)))
  
  ;; Assoc list of primitives and their arity.
  (setf primitives '((if 3) (and 2) (or 2) (not 1)))
  
  ;; Args for the lambda function that generates the program.
  (setf args '(grid-world current-cell))
  
  ;; Value of args for the generated program.
  (setf fargs (mapcar #'(lambda (x) (list grid-world x)) current-cell))
  
  ;; Set of actions.
  (setf actions '((n grid-world current-cell)
                  (w grid-world current-cell)
                  (e grid-world current-cell)
  