;; This program is a flexible, functionally designed program
;; that finds all of the objects that satisfy a given
;; test (given as parameter OBJ-TEST, a function binding)
;; and returns a list of them according to OBJ-ORDER
;; (another parameter that is also a function binding)

(defun mycollect (l obj-test obj-order)
  (cond ((null l) nil)
	((atom l) (and (funcall obj-test l) (list l)))
	(t (sort (nconc (mycollect (car l) obj-test obj-order)
			(mycollect (cdr l) obj-test obj-order))
		 obj-order))))

(defun mycollect-all (l)
  "Uses mycollect to return all objects in l in order -- basically just FLATTEN-LIST"
  (mycollect l #'(lambda(x) t) #'(lambda(x y) nil)))

(defun mycollect-posint (l)
  "Uses mycollect to return all positive integers -- just like POSINT"
  (mycollect l #'(lambda(x) (and (integerp x) (> x 0))) #'(lambda(x y) nil)))

(defun mycollect-posint-sorted (l)
  "Uses mycollect to return all positive integers in sorted order"
  (mycollect l #'(lambda(x) (and (integerp x) (> x 0))) 
	     #'(lambda(x y) (< x y))))

(defun mycollect-posint-reverse (l)
  "Uses mycollect to return all positive integers in reverse sorted order"
  (mycollect l #'(lambda(x) (and (integerp x) (> x 0))) 
	     #'>))