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Preface
Part I
Chap 1
Chap 2
Chap 3
XEmacs
Chap 4
Chap 5
Chap 6
Chap 7
Chap 8
Chap 9
Part II
Chap 10
Chap 11
Chap 12
Chap 13
Chap 14
Chap 15
Chap 16
Chap 17
Chap 18
Chap 19
Chap 20
Chap 21
Chap 22
Chap 23
Part III
Chap 24
Chap 25
Chap 26
Chap 27
Chap 28
Chap 29
Chap 30
Chap 31
Chap 32
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CHAPTER 8: BASIC LIST PROCESSING
- Notes
- Read Chapter 8.
- An easier way to build long lists is with the Common Lisp function
list, which takes an arbitrary number of arguments, and
returns a list of them. For example
USER(1): (list 'a 1 'b)
(A 1 B)
USER(2): (list 'a 'b 'c '(d e) 'f 'g)
(A B C (D E) F G)
USER(3): (list 'a)
(A)
USER(4): (list)
NIL
Note carefully the difference between cons and
list, illustrated by the following:
USER(5): (cons 'a '(b c))
(A B C)
USER(6): (list 'a '(b c))
(A (B C))
USER(7): (cons 'a '())
(A)
USER(8): (list 'a '())
(A NIL)
cons adds its first argument as a new first element of
the list which is its second argument. list makes a list
whose elements are all its arguments.
- Create a file named
ch8.cl into which you will
put answers to just those selected exercises, I tell you to
below.
- Do Exercises 8.1 and 8.2, and paste these interactions into
ch8.cl Notice how easy it is to miss the dot in dotted
pairs and dotted lists, but remember, if you ever generate a dotted
pair or a dotted list as an answer for an exercise before we get to
Chapter 18, it will be wrong!
- As Exercise 8.3, try for yourself those interactions of
Chapter 8 (including those above) that you find particularly
interesting or surprising. You needn't submit these.
- For Exercise 8.4, following the instructions, type forms to
the Lisp listener that evaluate to the following lists:
(1 2 "three")
((A B) C)
(A (B C))
(A (B) C)
Make sure the values you get are exactly as shown. Paste these 4
interactions into ch8.cl As an example, here is an
interaction that shows a form evaluating to ((1) "two" C)
USER(9): (cons (cons 1 '()) (cons "two" (cons 'c '())))
((1) "two" C)
Now do 8.4 again, but using list instead of
cons. For example,
USER(10): (list (list 1) "two" 'c)
((1) "two" C)
Notice carefully that you are not to include quoted non-empty lists in any
of the 8 forms you submit for this exercise. For example, the example
immediately above is NOT
USER(10): (list '(1) "two" 'c)
((1) "two" C)
even though that gives the same result. If you have quoted
non-empty lists in your answer, I will ask you to redo these exercises!
- Exercise 8.6: Don't do this exercise. It describes a
technique you won't need as long as you are running acl within XEmacs.
Instead, try out the following techniques:
- With your cursor after the Lisp prompt, type
C-c C-p
several times slowly. Each time, your previous input will be copied
to the line where you are. You can then edit it or have Lisp evaluate
it.
- With your cursor after the Lisp prompt, roll your mouse cursor
over the text in the *acl* buffer slowly. If you copied my
.emacs file, as I suggested, you should notice that Lisp
objects are highlighted as you roll the mouse over them. Leaving the
cursor where it is, and the mouse highlighting some Lisp list, type
M-middle. (Hold the Meta key while clicking the middle mouse button.)
The object your mouse is highlighting should be copied to the place
your cursor is. This is a very fast way to copy text.
- Exercise 8.7: Using one of the techniques above (just so you
don't have to retype that long list over and over), rather than
the technique of the book's Exercise 8.6, enter forms that take the
list given in the book, and evaluate to each of the following symbols:
A,
G, and
I
For example, here is such an interaction that evaluates to
H:
USER(6): (first (first (rest (rest '(((a b) (c d) e) (f g) (h) i)))))
H
Notice that each of your 3 answers will be a form that involves nested
calls to first and rest, and has that
long quoted list inside. Don't expect to come up with the three
correct answers directly from your head---try something, then edit it,
then edit it again, until it works correctly. Then paste the correct
interaction into ch8.cl
Make sure that your three forms evaluate to the symbols
A, G, and I, rather than the
lists (A), (G), and (I). I
have gotten many such incorrect answers in the past.
- When you have all 14 interactions (1 for 8.1, 2 for 8.2, 8 for
8.4, and 3 for 8.7) pasted into
ch8.cl, submit that file,
and go on to Chapter 9.
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