Homework 1

Due Sept. 19, 2000

1. Which of the following S-expressions are atoms? Which of them are lists?

A, “this is foo”, (), T, (1 2 3), 25, (sqrt 36), NIL

(You may use CLISP to verify you answers if you are not sure.)

2. What will be returned when evaluating each of the following S-expressions?

a) (mapcar #’= L1 (reverse L1)), where L1 has been assigned value (1 2 3)

b) (set y x), where x has been assigned value 5 but y has not

c) (nth 1 ‘(a b c))

3. Using recursive definition to define a LISP function

(union L1 L2)

that returns the union of two sets represented as lists L1 and L2. Both L1 and L2 can be empty sets.

4. Write a function

(average L)

that iteratively computes the average of a list of real numbers in list L. You may assume that L is non-empty.