;;; mylisp - Lisp Study Lab 2 - Examples of apply, lambda, assoc, mapcar
;;; Copy this file to your own directory.
;;; Follow the instructions on the course page for running
;;;  lisp while in the emacs editor.
;;; Try evaluating each of these expressions by placing the
;;;  cursor to the right of the expression and typing 
;;;  control-x control-e.  By the end of this course, you
;;;  should be able to figure out what each expression evaluates
;;;  to without running lisp!!

(defun cube (x)
  (* x x x))

(cube 2) ; 8

(defun sqr (x)
  (* x x))

(sqr 2) ; 4

;; a different way to call the cube function:
(apply 'cube '(2)) ; 8

;; passing functions as arguments:
(defun sum-power (f a b) ; f(a) + f(b)
  (+ (apply f (list a))
     (apply f (list b))))

(sum-power 'cube 2 1)  ; 9

(sum-power 'sqr 2 1)   ; 5

;; function call using an anonymous function:
((lambda (x) (* x x x)) 2)   ; 8

(setq groceries '((dairy milk) (fruit apple) (starch bread) (fruit pear)))

(assoc 'fruit groceries)
; (fruit apple)

(defun is-fruit (x) 
  (equal 'fruit (car x)))

(is-fruit (car groceries))         ; nil
(is-fruit (car (cdr groceries)))   ; t

; applying function is-fruit to each element of groceries:
(mapcar 'is-fruit groceries) ; (nil t nil t)

; applying anonymous function to groceries:
(mapcar #'(lambda (x) (equal 'fruit (car x))) groceries)
; (nil t nil t)

(defun fruit-points (x)
  (cond ((is-fruit x) 1)
        (t 0)))

(fruit-points (car groceries)) ; 0
(fruit-points (car (cdr groceries))) ; 1

(mapcar 'fruit-points groceries) ; (0 1 0 1)

(apply '+ (mapcar 'fruit-points groceries)) ; 2