Homework 1 Answers

Part I

1.
a) 10
b) (10 1 2 3)
c) (44 a b c)
d) (10 44)
e) (10 (1 2 3))
f) (x y)
g) a
h) (b c)
i) 54

2.
a) 10
b) 5
c) 3
d) 66
e) 15

Part II

1.
(define pi 3.14159)
(define (square x) (* x x))
(define (circle-area r) (* pi (square r)))

2.
(define (fact n)
  (cond ((< n 0)  error "Cannot find factorial of a negative number")
        ((<= n 1) 1)
        (else (* n (fact (- n 1))))
  )
)

3.
(define (make-point x y) (list x y))
(define (x-point p) (car p))
(define (y-point p) (cadr p))

4.
(define (positive-only lst)
  (if (null? lst) '()
      (let ((head (car lst))
            (rest (positive-only (cdr lst))))
           (if (> head 0) (cons head rest)
                rest
           )
      )
  )
)