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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 10: DEFINING YOUR OWN FUNCTIONS
- Notes
-
- Read Chapter 10 along with the following
- p. 64
- Defining
list3 is still a good example for the
discussion in the text, but I decided not to put off telling you about
the function list till Exercise 10.12, and told you about
it, instead, in the notes to Chapter 8.
So now you should realize that (list o1 o2 o3) is a much
easier way of expressing (cons o1 (cons o2 (cons o3 '()))).
- p. 65-66
- Similarly, you don't really need to define
list2
since list is available. Study this material in the text
anyway for what it tells you about programming in Common Lisp.
- Do Exercise 10.1, but instead of
list3, use
average3 as given here
(defun average3 (x y z)
"Returns the average of the three numbers X, Y, and Z."
(/ (+ x y z) 3.0))
Notice:
- XEmacs indents nicely whenever you type a newline in the
middle of your function definition;
- since you are typing into an
editor, you can edit the function definition at any time before
completing it;
- if you complete the function definition, but made a mistake,
you can use
C-c C-p to yank it back and edit it (The
definition that is in effect is the last one you entered.);
- if you type a newline from anywhere inside a completed
S-expression, Lisp will evaluate it.
- Explore the "ACLHelp" menu. With your curser on or just after
any occurrence of the symbol
average3 in your
*acl* buffer, try each of the items in the "ACLHelp"
menu. Notice the keyboard shortcuts for these 4 menu items. (You
needn't use the shift key for
C-c a, C-c d, or C-c f.) Try
these 4 menu items with previously defined Lisp functions such as
cons. Try them with symbols that don't name functions.
- Do Exercise 10.2, but check the values of
x
y and z both before and after a call to
average3.
- You are to do Exercise 10.3, but instead of using
switch and list2, use median4
as shown here
(defun median4 (list)
"Returns the median of the numbers in the LIST,
assuming that LIST contains 4 numbers in order."
(average2 (second list) (third list)))
and average2.
Define median4 and try it out before defining
average2 in the same way that the Exercise tells you to
try switch before defining list2. You
should get an error message and be in the debugger.
The text asks you to find out how to determine the value the lambda
variable is bound to while in the debugger. The technique for acl in
XEmacs is:
- Under the "ACLDebug" menu, choose the "Debug process" item, or
type
C-c s. Accept the suggestion to debug the "Initial
Lisp Listener" by typing a carriage return in the minibuffer. -
Notice that you get information in a
"*debugger:Initial-Lisp-Listener*" window, and an arrow
(
->) points to the form you evaluated that caused the
error. - Put your cursor on that arrow and type the letter
l. - You will get a temporary window in which you
will see the binding of your lambda variable.
- Get rid of the
temporary window by typing
C-space as it suggests.
- Back in the debugger window, type a
q to return
to the *acl* window. - Back in the
*acl* window, you may enter C-c C-d to
return to the top-level listener.
- Replacement Exercise 10.4: Now define
average2
as a modification of my average3 above, and test
median4 again.
- Do Exercise 10.5, but trace the functions
median4, second, third, and
average2 while evaluating (median4 '(1 2 3
4)). Note you can also turn tracing on and off by putting your
cursor on or just after a function name, and choosing the "Toggle
trace" item under the "ACLDebug" menu or typing C-c t
(trace) with no arguments shows you all the functions
being traced. With one or more arguments, it add those functions to
the ones being traced.
(untrace) turns tracing off on
all functions being traced. With one or more arguments, it turns off
tracing on just those functions.
- Do Exercises 10.6, but use
median4 instead of
switch.
- Do Exercises 10.12 and 10.15 if you feel you need to.
- Do Exercises 10.14.
- Do Exercises 10.16 and 10.17.
- Create a file named
ch10.cl Paste the following
into it:
----------------------- cut here -----------------------
;;; Answers to Chapter 10 Exercises
;;;
;;; 10.4 The definition of average2 is
???
;;; 10.14 The definition of sqr is
???
;;; 10.16 The definition of reverse3 is
???
;;; 10.17
;;; Common Lisp has the functions first, second, third, up through and
including ???
----------------------- cut here -----------------------
Replace the question marks in ch10.cl with the function
definitions you wrote for the given Exercises 10.4, 10.14, and
10.16.
Replace the question marks for Exercise 10.17 with the name of
the last function in the series. Use these functions whenever they're
useful.
Submit ch10.cl, and go on to Chapter 11.
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