Lesson Plan - 6.001 SP04 - recitation 2

More Scheme

Administrivia

* project due today 6pm
* tutorials next week - everyone scheduled?
* project 1 out

Lecture review

if

(if test cons alt)
test not false
why special form? 

lambda

(lambda params body)
favorite
makes a compound procedure
eval/apply

cond - variant of if table

Solutions:

1.

(if #t (+ 1 1) 17)
;Value: 2

(if #f #f 42)
;Value: 42

(if (> x 0) x (- x))
;Value: 3

(if 0 1 2)
;Value: 1

(if x 7 (7))
;Value: 7

2.

(lambda (x) x)
;Value: #[compound-procedure 2]

((lambda (x) x) 17)
;Value: 17

((lambda (x y) x) 42 17)
;Value: 42

((lambda (x y) y) (/ 1 0) 3)
;Hardware trap INT_DIVIDE_BY_ZERO

((lambda (x y) (x y 3)) (lambda (a b) (+ a b)) 14)
;Value: 17

3.

(define biggie-size
  (lambda (combo)
    (+ 4 combo)))

(define unbiggie-size
  (lambda (combo)
    (- combo 4)))

(define biggie-size?
  (lambda (combo)
    (> combo 4)))

(define combo-price
  (lambda (combo)
    (if (biggie-size? combo)
	(+ .5 (* 1.17 (unbiggie-size combo)))
	(* 1.17 combo))))

(define empty-order
  (lambda ()
    0))

(define add-to-order
  (lambda (order combo)
    (+ (* 10 order) combo)))

(define order-size
  (lambda (order)
    (if (= order 0)
	0
	(+ 1 (order-size (quotient order 10))))))

(define order-price
  (lambda (order)
    (if (= order 0)
	0
	(+ (combo-price (remainder order 10))
	   (order-price (quotient order 10))))))