CS 380: Optional Lisp Assignment
Fall 2006
1. Describe what happens when the following expressions are evaluated:
(a) (+ (- 5 1) (+ 3 7))
(b) (list 1 (+ 2 3))
(c) (if (listp 1) (+ 1 2) (+ 3 4))
(d) (list (and (listp 3) t) (+ 1 2))
2. Give three distinct cons expressions that return (a b c).
3. Using car and cdr, define a function to return the fourth element of a list.
4. Define a function that takes two arguments and returns the greater of the two.
5. What do the following functions do?
(a) (defun enigma(x)
(and (not (null x))
(or (null (car x))
(enigma (cdr x)))))
(b) (defun mystery (x y)
(if (null y)
nil
(if (eql (car y) x)
0
(let ((z (mystery x (cdr y))))
(and z (+ z 1))))))
6. Show the following lists in box notation1:
(a) (a b (c d))
(b) (a (b (c (d))))
(c) (((a b) c) d)
(d) (a (b . c) . d)
7. Write a version of union that preserves the order of the elements in the original lists. For example:
[1]> (new-union ’(a b c) ’(b a d))
(A B C D)
8. Write a recursive function that takes an integer as input and returns the “reverse” of that integer. The function should
not need to call any supplementary functions (i.e., those that are not built into common lisp). Your function may use
conversion to strings/lists, although it must return an integer. There is a way of doing this without using strings (Hint:
think logarithms, exponentiation, and modulus). Here’s an example of like what the output should look:
[1]> (reverse-integer 12345)
54321
Many of these problems were adapted from ANSI Common Lisp by Paul Graham (ISBN 0-13-370875-6): the book that
used to be required for this class.
1Since you don’t necessarily own a book on Lisp (one such book used to be used for this class), you will only be responsible for knowing box
notation if we cover it in class.
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