Re: HW#3 question 2

Stephen Edwards (edwards@CS.VT.EDU)
Mon, 17 Sep 2001 09:28:50 -0400

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Message-ID:  <3BA5FA92.BD20EC14@cs.vt.edu>
Date:         Mon, 17 Sep 2001 09:28:50 -0400
From: Stephen Edwards <edwards@CS.VT.EDU>
Subject:      Re: HW#3 question 2

> Jonathan Berkowitz wrote:
>
> I don't understand what question 2 means by two lists having the same
> list structure and also possibly having different atoms. If someone
> could give an example of two lists that are structurally equal that
> would be help.

Consider these four lists:

A is (a b c (d (e f)) (g))

B is (h i j (k (l m)) (n))

C is (a b c d e f g)

D is (a b c (d e f) (g))

Here, A and B have the same "list structure", even though the atoms they
contain are different. A and C have the same atoms, but different
list structure. A is a list of 5 elements: three atoms followed by two
lists. C is a list of 7 atoms that has no sublists within it.

Note that A and D also have different structure. Even though they both
have the same number of elements, the 4th item in A is (d (e f)) and the
4th item in D is (d e f), and these two elements clearly have different
list structure.

                                -- Steve

--
Stephen Edwards            604 McBryde Hall          Dept. of Computer Science
e-mail      : edwards@cs.vt.edu           U.S. mail: Virginia Tech (VPI&SU)
office phone: (540)-231-5723                         Blacksburg, VA  24061-0106
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