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SERIES 60 (LEVEL.68)
MULTICS
EMACS EXTENSION WRITERS GUIDE
SUBJECT
Guide for Programmers Writing Extensions and 'Ibrminal Control Modules
(CTL) in the LISP Programming Language for the Emacs %xt Editor
SPECIAL INSTRUCTIONS
This manual presupposes thorough familiarity with the Emacs text editor,
which is described in the E m s lkzt Editor Users' Guide. Extensions and CTLs
can be written by those without programming experience, but familiarity with
some programming language is valuable. Experience with Lisp is useful, but
not necessary.
SOFTWARE SUPPORTED
.. Multics Software Release 8.0
ORDER NUMBER
CJ52-00 January 1980
Honeywell
I
PREFACE
i
T h i s manual d e s c r i b e s how t o w r i t e u s e r e x t e n s i o n s t o t h e
M u l t i c s Emacs e d i t o r . The r e a d e r should be t h o r o u g h l y f a m i l i a r
w i t h t h e Emacs e d i t o r , p r o f i c i e n t i n i t s u s e , and a c q u a i n t e d w i t h
i t s visible organization. The Emacs Text E d i t o r U s e r s 1 Guide,
Order No. CH27, p r o v i d e s t h i s n e c e s s a r y i n f o r m a t i o n . The
methods f o r w r i t i n g t e r m i n a l c-ontrol modules ( C T L s ) t o s u p p o r t
additional terminal types a r e a l s o described here.
Programming knowledge i s not n e c e s s a r y t o w r i t e e x t e n s i o n s
s u c c e s s f u l l y , although i t i s h e l p f u l . Section 1 is a s h o r t
introduction t o extension writing. Section 2 provides a s h o r t
c o u r s e i n L i s p , t h e programming language used f o r w r i t i n g
e x t e n s i o n s , and t h e language i n which t h e Emacs e d i t o r i t s e l f i s
written. B a s i c a l l y , t h e e x t e n s i o n w r i t e r o n l y needs t o l e a r n
enough about L i s p t o be a b l e t o i m i t a t e examples.
1
. S e c t i o n 3 shows, b y example, how t o w r i t e e x t e n s i o n s . It
i n c l u d e s t h e f u n c t i o n s and forms most l i k e l y t o be needed b y t h e
e x t e n s i o n w r i t e r . S e c t i o n 4 d e s c r i b e s LDEBUG.mode, t h e Emacs
mode f o r debugging t h e L i s p code used i n e x t e n s i o n s . F i n a l l y ,
S e c t i o n 5 d e m o n s t r a t e s how t o w r i t e a CTL t o s u p p o r t a new
t e r m i n a l t y p e . Again, t h e CTL w r i t e r u s e s e x i s t i n g C T L s t o l e a r n
t o w r i t e h i s own.
T h i s manual c o n t a i n s s u f f i c i e n t i n f o r m a t i o n t o e f f e c t i v e l y
w r i t e and debug M u l t i c s Emacs e x t e n s i o n s . However, i t i s not
i n t e n d e d t o be a r e f e r e n c e document f o r e i t h e r L i s p , i n g e n e r a l ,
o r M u l t i c s MacLisp. Reference documentation f o r MacLisp i s
a v a i l a b l e from: I
M I T I n f o r m a t i o n P r o c e s s i n g Center
Publications Office
60 Vassar S t r e e t
Cambridge, MA 02139
@ Honeywell I n f o r m a t i o n Systems I n c . , 1980 F i l e No.: 1L13
CONTENTS
Page
Section 1 Introduction . . . . . . . . . . . . . . . 1-1
Section 2 An Introduction to Lisp . . . . . . . . .
Predicates . . . . . . . . . . . . . .
Predicates for Numbers . . . . . . .
Predicates for Strings . . . . . . .
Predicates for Any Objects .....
Lisp Special Forms . . . . . . . . . .
The if Special Form . . . . . . . .
The setq special Form . . . . . . .
The do-forever and stop-doing
Special Forms ...........
The let Special Form . . . . . . . .
The prog and go Special Forms . . .
The or And and Special Forms. And
not ................
The progn and prog2 Special Forms .
Symbols ......... : . . . . . .
LispLists ..............
Section 3 Writing Emacs Extensions . . . . . . . . .
Using Emacs Requests in Extension
Coding . . . . . . . . . . . . . . . .
Marks and Their Management . . . . . .
The set.mark. release-mark and
wipe-point-mark Functions . . . . .
The with-mark Special Form . . . . .
The save-excursion Special Form . .
Cleanup Handlers . . . . . . . . . . .
The unwind-protect Special Form . .
Useful Predicates . . . . . . . . . . .
Whitespace Management . . . . . . . . .
Extracting Text From the Buffer . . . .
Talking to the User . . . . . . . . . .
Message Printing Functions . . . . .
Variables . . . . . . . . . . . . . . .
Example o f Local Variables . . .
Registered Variables . . . . . . . . ..
Large Scale Output . . . . . . . . . .
Manipulating Buffers . . . . . . . . .
Creating a Temporary Buffer . . . .
Variable for Buffer Manipulation . .
The save-excursion-buffer Special
iii
CONTENTS ( c o n t )
Page
Form. . . .. . . . . . . . . . .
C a l l i n g t h e Redisplay . . . . . . . . .
EISTables . . .. . . . . . . . . . .
F u n c t i o n s Using t h e C h a r s c a n T a b l e .
Options . . . . .. . . . . . . . . . .
Name Scope I s s u e s . . . . . . . . . . .
Modes . . . . . .. . . . . . . . . . .
Major Modes .. . . . . . . . . . .
Minor Modes .. . . .
. . . . . . .
Character Dispatching . .
. . . . . . .
Program Development . . .
. . . . . . .
Coding Problems . . .
. . . . . . .
Compilation . . . . . . .
. . . . . . .
Documenting R e q u e s t s . .
. . . . . .
Window Management . . . .
. . . . . . .
Writing Searches . . . .
. . . . . . .
. . . . . .
C a l l i n g M u l t i c s Commands .
Multics Error Table . . .
. . . . . . .
. . . .
D e f i n i n g R e q u e s t s w i t h defcom .
Section 4 Ldebug Mode . . . . . . . . . . . . . . .
LDEBUG B u f f e r s . . . . . . . . . . . .
Emacs and L i s p Debug Mode . . . . . . .
. . .
E r r o r T r a p E n t r i e s t o LDEBUG . .
Code B r e a k p o i n t s . . . . . . . . . . .
. . .
F u n c t i o n T r a c i n g w i t h LDEBUG . .
Section 5 W r i t i n g Emacs T e r m i n a l C o n t r o l Modules
(CTLs) . . . . . . . . . . . . . . . .
Index
SECTION 1
INTRODUCTION
An e d i t o r e x t e n s i o n i s a u s e r - p r o v i d e d c a p a b i l i t y , w h i c h i s
a d d e d t o t h e e d i t o r t o e x t e n d i t s Dower. I t i s d i f f e r e n t f r o m a
macro, which is s i m p l y ~ l e c t i o ' n o f e d i t o r r e q u e s t s g a t h e r e d
u p a n d ( p e r h a p s ) g i v e n a name. E x t e n s i o n s a r e p r o g r a m s ; t h e y a r e
w r i t t e n i n t h e l a n g u a g e o f t h e M u l t i c s Emacs e n v i r o n m e n t . An
- -
extension is a body o f c o d e t h a t augments t h e e d i t o r ' s
c a p a b i l i t y , b u t d o e s n o t embed o r r e q u i r e k n o w l e d g e o f how d a t a
i n t h e e d i t o r is s t o r e d o r manipulated. In t h i s sense, a l l of
t h e word, s e n t e n c e , p a r a g r a p h , and L i s p - l i s t r e q u e s t s , and t h e
v a r i o u s llmodesll ( e . g . , PL/I mode) a r e e x t e n s i o n s .
T h e p e r s o n who w i s h e s t o a d d t o h i s Emacs e n v i r o n m e n t a n y
powerful o r sophisticated c a p a b i l i t y must l e a r n t o write
extensions. The keyboard macro f a c i l i t y X , "X)) is n o t
intended f o r such usage. T h i s m a n u a l e x p l a i n s how t o w r i t e
extensions.
One o f t h e g u i d i n g d e s i g n p r i n c i p l e s i n t h e Emacs e d i t o r w a s
t h a t t h e c r e a t i o n o f e d i t o r e x t e n s i o n s , e i t h e r by t h e e d i t o r
implementors o r end u s e r s , s h o u l d be i n a programming l a n g u a g e o f
e s t a b l i s h e d e l e g a n c e and power. L i s p was t h e l a n g u a g e c h o s e n .
T h i s p r i m e r g i v e s you a s t a r t i n g p o i n t f o r w r i t i n g L i s p c o d e t o
r u n a s e d i t o r e x t e n s i o n s i n t h e Emacs e n v i r o n m e n t . If y o u h a v e
some knowledge o f L i s p a l r e a d y , i t w i l l b e o f v a l u e . However, i t
is assumed i n t h i s manual t h a t t h e r e a d e r h a s no f a m i l i a r i t y w i t h
L i s p , b u t d o e s , p e r h a p s , w i t h P L / I o r BASIC.
For examples o f e x t e n s i o n c o d i n g , t h e e x t e n s i o n writer's
u l t i m a t e r e f e r e n c e m a t e r i a l w i l l b e t h e Emacs s o u r c e . T h e Emacs
m a i l s y s t e m (RMAIL), FORTRAN a n d P L / I m o d e s , a n d t h e c o d e f o r t h e
word, s e n t e n c e , and paragraph r e q u e s t s ( a l o n g w i t h most o f t h e
o t h e r c o d e i n t h e Emacs m o d u l e e m a c o p s . l i s p ) a r e s t a n d a r d
examples o f e x t e n s i o n code. Techniques, s z y l e s , and s u b t l e t i e s
d i f f i c u l t t o c o n v e y i n p r i n t may b e g l e a n e d b y c a r e f u l s t u d y o f
(-. t h i s code.
SECTION 2
AN 1,NTRODUCTION TO L I S P
L i s p programs a r e b u i l t o f f u n c t i o n s , which a r e s i m i l a r t o
p r o c e d u r e s o r s u b r o u t i n e s i n o t h e r l a n g u a g e s , a l t h o u g h more a k i n
t o PL/I a n d ALGOL f u n c t i o n s . You w r i t e a L i s p p r o g r a m b y
c r e a t i n g a f i l e f u l l o f f u n c t i o n d e f i n i t i o n s . - A- f u n c t i o h
d e f i n i t i o n s p e c i f i e s t h e name o f a f u n c t i o n , a n d w h a t i t d o e s .
Here i s a s a m p l e f u n c t i o n d e f i n i t i o n :
(defun addandmult ( a b c ) ; T h i s i s a comment
(* (- a b)
(+ a b c ) ) )
T h i s d e f i n e s a f u n c t i o n named a d d a n d m u l t t h a t t a k e s t h r e e
a r g u m e n t s , c a l l e d a , b , a n d c . The a d d a n d m u l t f u n c t i o n c o m p u t e s
t h e r e s u l t o f m u l t i p l y i n g t h e d i f f e r e n c e o f a a n d b b y t h e sum o f
a , b , a n d c , a n d r e t u r n s t h a t number a s a r e s u l t , o r v a l u e . T h e
s e m i c o l o n on t h e f i r s t l i n e a b o v e b e g i n s a comment; comments
t h r o u g h o u t t h e e x a m p l e s p r o v i d e some a d d i t i o n a l i n f o r m a t i o n a b o u t
t h e code.
Here i s a n o t h e r f u n c t i o n d e f i n i t i o n :
(defun squareprint (arg)
( p r i n t "The s q u a r e o f w )
(print arg)
( p r i n t ltisU)
(print (* arg arg))
5
T h i s f u n c t i o n p r i n t s t h e message nThe s q u a r e o f 1 ? , p r i n t s t h e
v a l u e o f i t s a r g u m e n t , p r i n t s t h e word l l i s f l , a n d p r i n t s t h e v a l u e
o f t h e s q u a r e o f its argument. I n a d d i t i o n , it r e t u r n s t h e value
5. The f u n c t i o n l 1 s q u a r e p r i n t l 1 h a s s i d e e f f e c t s : it c a u s e s
o u t p u t on t h e t e r m i n a l . It a l s o r e t u r n s a v a l u e , t h e number 5 .
N o t e t h a t a l l L i s p f u n c t i o n s produ.ce a v a l u e ; o n l y some p r o d u c e
. side e f f e c t s . The f i r s t f u n c t i o n d e f i n e d r e t u r n s t h e p r o d u c t o f
(- t h o s e numbers a s a v a l u e ; t h e second r e t u r n s 5.
If y o u l o o k a t s q u a r e p r i n t , you see t h a t it c o n s i s t s o f
several statements, the "print statements" t h a t p r i n t things.
These s t a t e m e n t s a r e c a l l e d f o r m s , and t h e y a r e , i n f a c t , c a l l s
t o other functions, in t h i s case the builtin print function. In
t h e form:
( p r i n t "The s q u a r e o f n )
t h e s t r i n g "The s q u a r e o f r f i s b e i n g p a s s e d a s a n a r g u m e n t t o t h e
p r i n t f u n c t i o n . Like a l l f u n c t i o n s , p r i n t r e t u r n s a v a l u e , which
is n o t used i n t h i s c a s e . The s i d e effect o f p r i n t i n g s o m e t h i n g
d o e s o c c u r . I n t h e form:
y o u a r e i n v o k i n g t h e lf+" f u n c t i o n , w h i c h i s a l s o b u i l t i n . T h e
v a l u e s o f t h e p a r a m e t e r v a r i a b l e s a , b , and c a r e p a s s e d t o it a s
a r g u m e n t s . I t r e t u r n s a v a l u e , which i s t h e r e q u e s t e d sum, and
produces no s i d e effects.
There a r e five forms in the function-definition for
sauare~rint:
(print "The s q u a r e o f r f )
(print arg)
(print ffisff)
(print (* arg arg))
5
Forms i m m e d i a t e l y i n s i d e a f u n c t i o n d e f i n i t i o n a r e e x e c u t e d
s e q u e n t i a l l y , l i k e s t a t e m e n t s i n o t h e r programming l a n g u a g e s .
T h e v a l u e p r o d u c e d by t h e l a s t f o r m i s t h e o n e t h e f u n c t i o n
i t s e l f r e t u r n s . What d o e s i t mean t o " e x e c u t e t ' a 5 ? E x e c u t e i s
n o t e x a c t l y t h e r i g h t term; w h a t r e a l l y h a p p e n s i s t h a t t h e s e
f o r m s a r e e v a l u a t e d . T h i s means t h a t a v a l u e i s produced from
t h e m . E v a l u a t i n g a 5 p r o d u c e s t h e number 5 ; e v a l u a t i n g t h e f o r m :
c a l l s t h e If+" f u n c t i o n w i t h . t h e a p p r o p r i a t e a r g u m e n t s , a n d
p r o d u c e s w h a t e v e r v a l u e t h e "+If f u n c t i o n r e t u r n s . The v a l u e
p r o d u c e d by t h e f f p r i n t t l f u n c t i o n i s s o m e t h i n g t h a t is n o t
i n t e r e s t i n g , b u t a value is produced.
Numbers, l i k e 5 , and s t r i n g s , l i k e "The s q u a r e o f t f , a r e s a i d
t o evaluate t o themselves. Things between p a r e n t h e s e s , l i k e :
(+ a b c)
( p r i n t "The s q u a r e o f f 1 )
a r e c a l l s t o f u n c t i o n s , w h i c h a r e e v a l u a t e d by c a l l i n g t h e
f u n c t i o n i n d i c a t e d , and producing t h e v a l u e it r e t u r n s .
Function c a l l s have t h e syntax:
(-- (FUNCTIONNAME ARGFORMl ARGFORM2 ARGFORM3 ... ARGFORMn)
w h e r e FUNCTIONNAME i s t h e name o f t h e f u n c t i o n t o c a l l and t h e
ARGFORMs a r e t h e m s e l v e s f o r m s , w h i c h a r e e v a l u a t e d t o p r o d u c e t h e
arguments t o g i v e t o t h e function. Thus, t o e v a l u a t e ( i . e . ,
t t e x e c u t e l l and f i n d t h e v a l u e r e t u r n e d ) a form l i k e :
e v a l u a t e t h e i n n e r form ( * a b ) t o produce a v a l u e
e v a l u a t e t h e 15 t o p r o d u c e 1 5 ( r e m e m b e r , numbers and
s t r i n g s evaluate t o themselves)
e v a l u a t e t h e v a r i a b l e c t o produce its value
p a s s t h e s e t h r e e y a l u e s on t o the function, and
r e t u r n what i t r e t u r n s .
The n e w l i n e s a r e i g n o r e d .
(1'' ,j T h u s , f o r m s a r e e i t h e r n u m b e r s l i k e 5 , s t r i n g s l i k e " i s t t,
variables l i k e b, or function c a l l s l i k e (* a b).
V a r i a b l e s a r e much l i k e v a r i a b l e s i n o t h e r l a n g u a g e s . A
v a r i a b l e h a s a v a l u e , which i s c a l l e d i t s b i n d i n g . At this
s t a g e , a s s u m e t h a t t h i s v a l u e m u s t b e a s t r i n g o r a number. When
a f u n c t i o n i s i n v o k e d , t h e p a r a m e t e r v a r i a b l e s ( l i k e a , b , and c
above) o f t h e function acquire t h e arguments of t h e function c a l l
a s bindings. Evaluating a v a r i a b l e produces its binding a s a
v a l u e . F o r i n s t a n c e , i f s o m e p l a c e i n a f u n c t i o n you e v a l u a t e t h e
form:
(addandmult 2 (+ 3 2) 6 )
a , b , and c w i l l h a v e t h e b i n d i n g s 2 , 5 , and 6 w h i l e t h e f o r m s i n
t h e d e f i n i t i o n o f addandmult a r e b e i n g e v a l u a t e d . This is not
u n l i k e t h e s u b r o u t i n e p a r a m e t e r mechanism i n o t h e r l a n g u a g e s . It
i s d i f f e r e n t i n s o f a r a s i t s p e c i f i e s what v a l u e a v a r i a b l e h a s
during "subroutinet1 execution. I n P L / I o r FORTRAN, a p a r a m e t e r
is a s s o c i a t e d with a v a r i a b l e i n t h e c a l l i n g program, n o t a
value, during subroutine execution.
There a r e parameter v a r i a b l e s , a s used above, temporary
( I v a r i a b l e s , d e s c r i b e d b e l o w , and g l o b a l v a r i a b l e s . Regardless of
t h e k i n d o f v a r i a b l e , t h e y a l l - have b i n d i n g s ( v a l u e s ) , and
evaluation of t h e v a r i a b l e produces t h a t value.
I
To summarize: 1
1. L i s p programs a r e b u i l t o f f u n c t i o n s . 1 1
-
2. F u n c t i o n d e f i n i t i o n s c o n s i s t o f t h e word n d e f u n n , t h e I
f u n c t i o n ' s name, a p a r a m e t e r l i s t , and a number o f I
f o r m s , which a r e t o be s e q u e n t i a l l y e v a l u a t e d a t
f u n c t i o n c a l l time, w i t h a p a i r of p a r e n t h e s e s around
t h e whole t h i n g . i
I
3. The v a l u e o f t h e l a s t form i n a function is t h e value . I
r e t u r n e d by t h a t f u n c t i o n . I
4. Forms can be s t r i n g s , numbers, v a r i a b l e s , o r c a l l s t o
functions. Forms a r e e v a l u a t e d t o p r o d u c e v a l u e s ,
which a r e p a s s e d between f u n c t i o n s a s a r g u m e n t s and
results.
5. S t r i n g s and numbers e v a l u a t e t o t h e m s e l v e s .
6. V a r i a b l e s e v a l u a t e t o t h e datum t o which t h e y a r e
bound, w h i c h , f o r a p a r a m e t e r , i s t h e c o r r e s p o n d i n g
argument t o t h e c o n t a i n i n g f u n c t i o n .
7. F u n c t i o n c a l l s c o n t a i n t h e name o f a f u n c t i o n t o c a l l I
and f o r m s t h a t a r e e v a l u a t e d t o p r o d u c e t h e a r g u m e n t s
t o the function. F u n c t i o n c a l l s may p r o d u c e s i d e
effects. L i k e any f o r m , when a f u n c t i o n c a l l i s
I
e v a l u a t e d , it produces a value.
i
PREDICATES
Programming l a n g u a g e s need c o n d i t i o n a l e x e c u t i o n . I n o r d e r
t o c o n t r o l c o n d i t i o n a l e x e c u t i o n , you need t h i n g s upon which t o
base a decision. Two d a t a o b j e c t s i n t h e L i s p world c o r r e s p o n d
t o t r u t h and f a l s i t y , f o r t h e p u r p o s e s of p a r t s o f t h e L i s p
s y s t e m t h a t d e a l w i t h c o n d i t i o n s . A s e t of f u n c t i o n s c a l l e d
predicates return these objects a s values. For i n s t a n c e , a
function called invoked a s :
r e t u r n s t h e i n d i c a t o r o f f a l s i t y , and when invoked a s :
r e t u r n s t h e i n d i c a t o r of t r u t h . P r e d i c a t e s work j u s t l i k e o t h e r
b u i l t i n and nonbuiltin functions, l i k e p r i n t , addandrnult,
s q u a r e p r i n t , and +. They t a k e a r g u m e n t s , and p r o d u c e a r e s u l t .
I n t h e c a s e o f p r e d i c a t e s . , however, t h e r e s u l t i s n o t a s t r i n g o r
a number, b u t an i n d i c a t i o n of t r u t h o r f a l s i t y . The r e s u l t o f a
p r e d i c a t e can be used b y t h e i f s p e c i a l form ( s e e below) t o ]
c o n t r o l t h e execution of a f u n c t i o n .
The f o l l o w i n g a r e some o f t h e m o s t u s e f u l L i s p p r e d i c a t e s .
I n a l l o f t h e s e e x a m p l e s , A l , A2, S 1 , 0 1 , e t c . , s t a n d f o r f o r m s ,
(.- w h i c h means t h e y c a n b e 1 2 , ( + 6 q ) , (myfun 33 ( - a b ) ) , e t c .
"A1 i s a n u m b e r , " b e l o w , means t h a t A1 i s some f o r m w h i c h
e v a l u a t e s t o a n u m b e r , s u c h a s 3 , ( + 6 2 1 , o r x 4 9 , i f ~ 4 9 ' sv a l u e
i s i n d e e d a number.
P r e d i c a t e s f o r Numbers
A 1 a n d A2 a r e n u m b e r s :
predicate Example R e t u r n s TRUTH i f ..., otherwise f a l s i t y .
-
- (= A1 A2) A1 and A2 a r e t h e same n u m b e r .
> (> A1 A2) A1 i s a b i g g e r number t h a n A2.
< (< A1 A2) A 1 i s a s m a l l e r number t h a n A2.
Predicates - Strings
for
S1 a n d S 2 a r e s t r i n g s :
samepnamep
(samepnamep S1 S 2 )
S1 and S2 a r e s t r i n g s of i d e n t i c a l c o n t e n t , i . e . , t h e
"same s t r i n g 1 ! . T h i s i s t h e s t a n d a r d way t o see i f t w o
s t r i n g s a r e t h e s a m e , a s i n (sarnepnamep t e s t " - h o l d f f )
alphalessp
( a l p h a l e s s p S1 S 2 )
$1 c o l l a t e s b e f o r e S 2 a l p h a b e t i c a l l y , e . g . ,
( a l p h a l e s s p "Ablef1 llBakerfl) r e t u r n s t r u t h , b u t
( a l p h a l e s s p I1Zekew I f J o e " ) d o e s n o t .
P r e d i c a t e s ' f o r Any O b j e c t s
0 1 i s some o b j e c t , o f perhaps; unknown t y p e (objects are
discussed l a t e r ) :
eq ( e q 01 0 2 ) 01 a n d 0 2 a r e t h e same s y m b o l
o r t h e same c o n s .
fixp ( f i x p 01) 01 i s a n u m b e r , a s o p p o s e d t o
some o t h e r k i n d o f o b j e c t .
stringp ( s t r i n g p 01) 0 1 i s a s t r i n g , a s op.posed t o
anythin,g else.
symbolp (symbolp 0 1 ) 01 i s a s y m b o l , a s o p p o s e d t o
anything else.
null ( n u l l 01) 01 is not only a symbol, but
t h e important and
c r i t i c a l s y m b o l named f f n i l u .
L I S P SPECIAL FORMS
A number o f s p e c i a l f o r m s i n L i s p d o n o t go by t h e s i m p l e
rules given above. You have already seen one. The
function-defining f o r m , which b e g i n s w i t h t h e word I1defunff, i s
not simply a function c a l l with forms t o produce t h e f u n c t i o n f s
a r g u m e n t s . By a l l r i g h t s , a f o r m l i k e :
(defun square (x)
(* x XI)
s h o u l d e v a l u a t e , i n o r d e r , t o produce arguments f o r I1defunff:
1. A v a r i a b l e named u s q u a r e f l .
2. The form, ( x ) , calling a f u n c t i o n named ffxtfw i t h no
arguments.
3. The form, ( * x x ) , m u l t i p l y i n g t h e v a l u e o f a v a r i a b l e
named " x W b y i t s e l f ,
T h i s form s h o u l d t h e n p a s s t h e s e t h r e e v a l u e s on t o t h e d e f u n I
function. T h i s , however, is not what a c t u a l l y happens. -1 1
E v a l u a t i n g t h e d e f u n f o r m c a u s e s a f u n c t i o n named s q u a r e t o b e
d e f i n e d , w h o s e p a r a m e t e r l i s t a n d "bodyIf a r e a s g i v e n . D e f u n i s I
I
a s p e c i a l f o r m , a n d when L i s p s e e s " d e f u n W a s t h e f u n c t i o n n a m e
i n a f o r m , i t a c t s i n a s p e c i a l way. I n t h i s case, L i s p d e f i n e s ~
a f u n c t i o n b u i l t o u t o f t h i s form itself. The a b o v e i s - a
not I
c a l l t o d e f u n w i t h a r g u m e n t s . I t may seem u n u s u a l , b u t y o u m u s t
have a t l e a s t one such s p e c i a l form i n o r d e r t o have an o p e r a t i v e
Lisp system.
I
The i f S p e c i a l Form ~
A s p e c i a l f o r m i n t h e M u l t i c s Emacs L i s p e n v i r o n m e n t , c a l l e d I
i f , controls conditional evaluation.
- An e x a m p l e o f i t s u s e :
(defun which-is-greater (first second)
( i f (> first second)
( p r i n t "The f i r s t o n e i s t h e g r e a t e r . " )
else
( i f (> second first)
( p r i n t !?The s e c o n d o n e i s g r e a t e r " )
else
( p r i n t " T h e y a r e e q u a l f f1 )
The s y n t a x o f - i s a s f o l l o w s :
if
( i f
...
else
.. .
)
Any n u m b e r , i n c l u d i n g n o n e , o f THEN-FORMS c a n b e s u p p l i e d .
S i m i l a r l y , a n y n u m b e r , i n c l u d i n g n o n e , o f t h e ELSE-FORMS c a n b e
given. I f t h e r e a r e n o ELSE-FORMS, t h e n t h e k e y w o r d " e l s e " may
be omitted, too.
Note t h a t a l l t h e forms i n t h e i f are n o t s e q u e n t i a l l y
e v a l u a t e d ; t h e word e l s e i s n o t e v e n i n t e n d e d t o b e a f o r m . If
a l l o f t h e f o r m s i n s i d e t h e i f were e v a l u a t e d , i t w o u l d b e
u s e l e s s , f o r e v a l u a t i o n w o u l d n o t b e c o n d i t i o n a l . T h a t i s why i f
i s a s p e c i a l f o r m ; t h e r e a r e s p e c i a l r u l e s a b o u t how f o r m s i n s i d e
it a r e t o b e e v a l u a t e d . The r u l e f o r a l l n o n s p e c i a l f o r m s i s t h e
same: y o u e v a l u a t e a l l t h e s u b f o r m s s e q u e n t i a l l y t o p r o d u c e t h e
(.. a r g u m e n t s t o t h e f u n c t i o n . E a c h s p e c i a l f o r m h a s i t s own r u l e s .
\
T h e i f s p e c i a l f o r m e v a l u a t e s t h e PREDICATE: i f it r e s u l t s
i n truth, t h e THEN-FORMS a r e s e q u e n t i a l l y e v a l u a t e d , a n d t h e
v a l u e o f t h e l a s t o n e i s r e t u r n e d a s t h e v a l u e of t h e i f .
O t h e r w i s e , t h e ELSE-FORMS a r e e v a l u a t e d s e q u e n t i a l l y , a n d t h e
v a l u e of t h e l a s t r e t u r n e d . If t h e r e a r e none, t h e symbol n i l
(see below) is r e t u r n e d , b u t is u s e l e s s i n t h e s e cases.
There are two g l o b a l v a r i a b l e s in Lisp, called n t ua n d
I!n i 1? t , whose b i n d i n g s a r e always the t r u t h and fal.sity
i n d i c a t o r s , r e s p e c t i v e l y . Thus:.
(if t
( p r i n t ?lTruthff
else
( p r i n t "Not s o t r u t h n ) )
when e v a l u a t e d , a l w a y s p r i n t s ? ? T r u t h H .
The s e t q S p e c i a l Form
V a r i a b l e s a c q u i r e v a l u e s by b e i n g p a r a m e t e r s , and a c q u i r i n g
v a l u e s a t f u n c t i o n c a l l time. I n a d d i t i o n , v a r i a b l e v a l u e s c a n
1
b e c h a n g e d by t h e s p e c i a l f o r m s e t q :
(defun adder-of-one ( x )
( p r i n t "The v a l u e o f x i s t 1 )
(print x)
("And t h e v a l u e o f x p l u s o n e i s f 1 )
(setq x (+ x 1))
(printx)) "
A s e t q form h a s t h e word I 1 s e t q u , t h e name o f a v a r i a b l e , a n d a n
i n s i d e form. The i n s i d e f o r m i s e v a l u a t e d , and t h a t v a l u e
assigned t o the variable. I t is l i k e an a s s i g n m e n t s t a t e m e n t i n
other languages.
T h e d o - f o r e v e r and s t o p - d o i n g S p e c i a l Forms
The c o n s t r u c t f o r l o o p i n g i n t h e Emacs L i s p e n v i r o n m e n t i s
a l s o a s p e c i a l form, c a l l e d do-forever:
(do-forever
( p r i n t llYay M u l t i c s w )
( p r i n t " s c i t l u M yayf1)
When e v a l u a t e d , i t p r i n t s t h e s e t w o s a y i n g s f o r e v e r . The way you /
s t o p doing i n a do-forever is t o e v a l u a t e t h e stop-doing s p e c i a l
form:
(defun print-n-times (n)
(do-forever
( i f ( = n O)(stop-doing))
( p r i n t "foolt)
(setq n (- n 1))))
T h i s f u n c t i o n , g i v e n a number a s a n a r g u m e n t , p r i n t s I1foo1l t h a t
many t i m e s . The " = I t b u i l t i n f u n c t i o n / p r e d i c a t e compares i t s two
a r g u m e n t s , w h i c h m u s t b e n u m b e r s , and r e t u r n s t r u t h o r f a l s i t y
d e p e n d i n g on w h e t h e r o r n o t t h e y a r e n u m e r i c a l l y e q u a l . The
a r g u m e n t s t o = a r e - n and 0 , b u t r a t h e r , t h e n u m b e r s t h a t a r e
not
t h e b i n d i n g s o f n a n d 0 . The number w h i c h i s t h e b i n d i n g o f n i s
d i f f e r e n t e a c h time a r o u n d t h e l o o p ; t h a t i s t h e p o i n t o f t h e
program. I t i s s e t q t h a t c h a n g e s t h e v a l u e o f n e a c h time
around, a s do-forever executes t h e loop. A do-forever form
g e n e r a l l y r e t u r n s s o m e t h i n g . u s e l e s s ( n i l ) , u n l e s s you e x i t by
saying (return 5 ) o r (return n i l ) , or (return a ) . In the l a t t e r
c a s e , t h e value of t h e variable a is returned.
-- Special
The l e t Form
/
(..- You can acquire temporary variables via the -special
let
form:
(defun sumtimesdif. (x y)
( l e t ((sum (+ x y ) )
(dif (- x y ) ) )
( p r i n t Ifsum times d i f f e r e n c e i s " 1
( p r i n t ( * sum' d i f ) )
( p r i n t llSum s q u a r e d i s 1 ' )
( p r i n t ( * sum s u m ) ) ) )
T h i s f u n c t i o n h a s two t e m p o r a r y v a r i a b l e s , ' s u r n and d i f , which a r e
i n i t i a l i z e d t o t h e v a l u e s o f ( + x y ) a n d ( - x y ) . The g e n e r a l
s y n t a x o f l e t is:
( l e t ((VAR1 VAL11
(VAR2 VAL2)
( The t e m p o r a r y v a r i a b l e s VAR1. ..VARn e x i s t o n l y w i t h i n t h e
let. They g e t t h e i n i t i a l v a l u e s o f VAL1-VALn, which a r e f o r m s
mt w i l l b e e v a l u a t e d . A l l t h e V A L s a r e e v a l u a t e d b e f o r e a n y o f
t h e i r values a r e assigned t o the VARs. Then, w i t h a l l t h e s e
t e m p o r a r y v a r i a b l e s s e t u p and i n i t i a l i z e d , e a c h FORMi i s
e v a l u a t e d s e q u e n t i a l l y , a n d t h e v a l u e o f t h e l a s t FORMi i s
r e t u r n e d by -let.
- p r o g - go S p e c i a l Forms
The and
A n o t h e r , l e s s u s e f u l way o f a c q u i r i n g t e m p o r a r y v a r i a b l e s i s
v i a t h e s p e c i a l f o r m p r o g . Forms . i n s i d e a p r o g a r e e v a l u a t e d
s e q u e n t i a l l y , l i k e f o r m s i n a f u n c t i o n d e f i n i t i o n . However, t h e
f i r s t form i n a p r o g i s n o t r e a l l y a form a t a l l , b u t a l i s t o f
temporary v a r i a b l e s used i n t h e prog, such a s "(a b c ) " . That is
why p r o g i s a s p e c i a l f o r m . The v a l u e r e t u r n e d by p r o g i s
usually useless, unless (return ...I is used t o r e t u r n something
meaningful.
I n s i d e a p r o g , you c a n p u t l a b e l s , t o u s e f o r g o - t o ' s :
(defun bar2 (x y)
(prog 0 ; n o t e t h e empty v a r i a b l e l i s t
( i f (< x y)(go l a b l ) )
( p r i n t IfX i s n o t l e s s t h a n Y v )
(return n i l ) ; r e t u r n f f f a l s e f fi n d i c a t i o n
labl
( p r i n t lVso b e i t If)
(return t ) ) ) ;return "trueff indication
I n t h e s p e c i a l f o r m -g o i t s o p e r a n d ( n o t a r g u m e n t ) i s a l a b e l t o
9
which t o go, i . e . , c o n t i n u e s e q u e n t i a l e v a l u a t i o n o f forms i n t h e
prog. L a b e l s are r a r e l y needed, due t o t h e powerful - and if
do-forever constructs.
T h e o r And a n d S p e c i a l ' F o r m s , And n o t
There a r e s p e c i a l forms f o r or-ing and and-ing p r e d i c a t e
results: they a r e s p e c i a l because they s t o p evaluating t h e i r
o p e r a n d s ( f r o m w h i c h a r g u m e n t s a r e p r o d u c e d ) when t h e y " k n o w f f
t h e i r answer for c e r t a i n :
( i f (and (not ( = x 0 ) )
( > ( / / 10 x ) 5 ) )
(print ffQuotienttoo large."))
The - f u n c t i o n i n v e r t s t r u t h and f a l s i t y .
not The d o u b l e s l a s h
indicates d i v i s i o n , because s l a s h is t h e escape character i n
Lisp.
The and d o e s n o t a t t e m p t . t o e v a l u a t e t h e s e c o n d form w i t h i n
it i f t h e i r s t p r o d u c e s f a l s i t y . T h i s p r e v e n t s a n e r r o r t h a t
w o u l d r e s u l t i f a n a t t e m p t were made t o d i v i d e b y z e r o .
S e q u e n t i a l e x e c u t i o n and s t o p p i n g a t an i n t e r m e d i a t e r e s u l t a r e
d e f i n e d and u s e f u l f e a t u r e s h e r e , a s opposed t o t h e l o g i c a l
o p e r a t o r s o f , s a y , PL/I.
The p r o g n and p r o g 2 S p e c i a l Forms
Two m o r e s p e c i a l f o r m s a r e p r o g n a n d p r o g 2 . To f o r c e
s e q u e n t i a l e x e c u t i o n o f forms and r e t u r n t h e v a l u e o f t h e l a s t ,
use progn. For i n s t a n c e :
( i f (and ( > x 3)
( p r o g n ( p r i n t IfOh d e a r t h i s i s g e t t i n g s e r i o u s f f )
0 y 5))
( p r i n t " F a t a l d i f f i c u l t y f f )1 )
I n t h e above, progn r e t u r n s t h e v a l u e o f i t s l a g t form. Thus,
t h e - tests whether x i s g r e a t e r t h a n 3 , and y is g r e a t e r t h a n
and
5 , b e f o r e t h e " p r i n t w o f " F a t a l d i f f i c u l t y M i s e v a l u a t e d . The
p r i n t i n g o f "Oh d e a r . . . " occurs a s part of the evaluation of the
p r o g n , b u t t h e and s e e s o n l y t h e s e c o n d v a l u e i n t h e p r o g n . The
progn is used t o f o r c e e v a l u a t i o n o f t h e p r i n t form.
.-
'
A prog2 is ~ ~ l i k e t progn, except t h a t it r e t u r n s its
s
second argument, e v a l u a t e d , r a t h e r t h a n i t s l a s t . I t must have
a t l e a s t t w o a r g u m e n t s . I t i s u s e f u l f o r s a v i n g some v a l u e t h a t
i s s u b s e q u e n t l y g o i n g t o b e d e s t r o y e d . The f o l l o w i n g f o r m , when
e v a l u a t e d , i n t e r c h a n g e s t h e v a l u e s o f x and y :
( s e t q x (prog2 0 ; t h i s z e r o i s evaluated t o 0,
; and i t s v a l u e t h r o w n away.
Y ; t h e value o f y is obtained h e r e ,
; and reriiembered a s i t i s h e r e .
(setq y X I ) ) ; x i s e v a l u a t e d , and t h a t v a l u e
; a s s i g n e d t o y . The v a l u e o f
; s e t q form i s t h a t v a l u e .
I n t h e above, however, t h e value o f prog2 i s t h a t value o f y a s
i t was b e f o r e i t was a s s i g n e d i n t o y , a n d now t h e o u t e r s e t q
a s s i g n s t h a t t o x.
SYMBOLS
- Another t y p e o f d a t a o b j e c t i n L i s p is c a l l e d t h e symbol.
S y m b o l s a r e named d a t a o b j e c t s k e p t i n a r e g i s t r y o f s y m b o l s , by
( Lisp. For c u r r e n t p u r p o s e s , t h e r e i s o n l y one symbol o f any
name. S y m b o l s a r e u s e d i n Emacs t o r e p r e s e n t b u f f e r n a m e s , a n d
v a r i o u s q u a n t i t i e s a s s o c i a t e d w i t h b u f f e r s . L i s p uses s y m b o l s t o
k e e p t r a c k o f f u n c t i o n s , qnd i n t e r n a l l y t o k e e p t r a c k o f g l o b a l
variables.
To u s e a s y m b o l i n a p r o g r a m , g i v e t h e name o f t h e symbol
p r e c e d e d by t h e ASCII q u o t e c h a r a c t e r , .
For instance, the
form:
(setq x 'Brunhilde)
a s s i g n s t h e s y m b o l named Brunhilde t o x. Note t h a t this is
d i f f e r e n t from:
( s e t q x "Brunhilde")
w h i c h a s s i g n s t h e string B r u n h i l d e t o x , a n d f r o m :
(setq x Brunhilde)
which a s s i g n s t h e v a l u e o f t h e v a r i a b l e B r u n h i l d e t o x.
LISP LISTS
The f i n a l L i s p d a t a t y p e o f i m p o r t a n c e i n w r i t i n g e x t e n s i o n s
is t h e c o n s ( f o r c o n s t r u c t ) , and t h e l a r g e r d a t a t y p e b u i l t o u t
.>\
'
o f i t , t h e l i s t . A c o n s i s a b l o c k t h a t r e l a t e s t o two ( u s u a l l y
o t h e r ) o b j e c t s i n t h e e n v i r o n m e n t , known a s i t s - a n d i t s -
car cdr.
T h e f u n c t i o n c o n s , g i v e n t w o o b j e c t s , p r o d u c e s a new c o n s , w h o s e
c a r and c d r , r e s p e c t i v e l y , a r e t h e two o b j e c t s g i v e n . For
instance, if the variable x has a value of. the string
l f B r u n h i l d e f f, a s a b o v e , t h e n :
(cons 7 x) - I
p r o d u c e s a c o n s w h o s e c a r i s t h e number 7 a n d w h o s e c d r i s t h e
s t r i n g l l B r u n h i l d e t f , r e t u r n i n g it a s a v a l u e . The f u n c t i o n s c a r - 1
a n d c d r c a n b e u s e d t o o b t a i n t h e c a r a n d c d r o f a c o n s . If y o u I
set t h e v a r i a b l e c t o t h e r e s u l t o f t h e form (cons 7 x) above,
then : 1
(car c) I
p r o d u c e s t h e number 7 a s a v a l u e .
U s u a l l y , y o u make l a r g e r a n d l a r g e r s t r u c t u r e s o u t o f
c o n s e s , by s e t t i n g u p c o n s e s w h o s e c a r a n d c d r a r e m o r e c o n s e s ,
and s o f o r t h , u n t i l you h a v e a l a r g e enough s t r u c t u r e t o
r e p r e s e n t a l l t h e v a l u e s you n e e d . The r e s u l t i n g c o n s t r u c t i o n .)
s e r v e s t h e same p u r p o s e a s a PL/I s t r u c t u r e : its various p a r t s
h a v e meaning a s s i g n e d by t h e programmer.
T h e m o s t common c o n s t r u c t i o n o f c o n s e s i s t h e l i s t . A l i s t
i s d e f i n e d a s a c h a i n of c o n s e s , e a c h o f w h i c h h a s t h e n e x t o n e
i n t h e c h a i n a s its c d r , except t h e l a s t o n e , which h a s t h e
s y m b o l l f n i l f 1 a s i t s c d r . A l i s t b u i l t i n t h i s way o f n c o n s e s i s
c a l l e d a list of n elements, t h e elements being t h e n o b j e c t s
t h a t a r e t h e c a r s o f t h e c o n s e s . The c o n s a t t h e head o f t h e
list is i d e n t i f i e d a s being Ifthe listff: its c a r is t h e f i r s t
e l e m e n t i n t h e l i s t , i t s c d r i s t h e c o n s whose c a r i s t h e s e c o n d
e l e m e n t o f t h e l i s t , a n d s o f o r t h . To c o n s t r u c t a l i s t o f t h e
numbers 2 , 4 , 5 , and 7 , i n t h a t o r d e r , and set t h e v a r i a b l e b t o
i t , you would,need:
(setq b (cons 2 (cons 4 (cons 5 (cons 7 n i l ) ) ) ) ) * 1
I
(Note t h a t t h e v a r i a b l e lfniltf is p e c u l i a r i n s o f a r a s its value is
a l w a y s t h e symbol t f n i l l f , t h u s you n e e d n o t s a y ' n i l . )
1
A function t h a t *simplifies t h e writing of such forms, f o r
c o n s t r u c t i n g l i s t s , b u i l d s l i s t s d i r e c t l y and a c c e p t s a n y number
of arguments. I t produ,ces t h e same r e s u l t a s t h e t y p e o f
c o n s t r u c t i o n shown a b o v e . I t i s c a l l e d " l i s t f f :
(setq b (list 2 4 5 7 ) )
( I To g e t t h e t h i r d e l e m e n t o f t h e l i s t , once this form i s
e v a l u a t e d , you c o u l d e v a l u a t e t h e f o r m : .
(car (cdr (cdr b ) ) )
( i . e . , t h e c a r of t h e cons t h a t is t h e c d r of t h e c o n s t h a t is
t h e c d r o f t h e cons t h a t is t h e value of b ) . Again, t h e r e a r e
L i s p f u n c t i o n s t o s i m p l i f y s u c h c o n s t r u c t i o n s . The a b o v e f o r m i s
equivalent to:
(caddr b)
I n g e n e r a l , f o r up t o 4 c a r s a n d c d r s d e e p , t o t a l , f u n c t i o n s l i k e
c a d r , c d a r , c a d d r , c a d a r , and s o f o r t h , a r e p r o v i d e d ( u p t h r o u g h
c a a a a r and c d d d d r ) . The f i r s t f o u r e l e m e n t s o f a l i s t a r e g o t t e n
by c a r , c a d r , c a d d r , a n d c a d d d r ( i t i s a good e x e r c i s e t o work
t h a t t h r o u g h a n d v e r i f y why t h i s i s t h e c a s e ) .
When l i s t s a r e p r i n t e d o u t by L i s p , t h e y a r e r e p r e s e n t e d a s
a p a i r of parentheses around t h e p r i n t e d r e p r e s e n t a t i o n s o f a l l
o f t h e e l e m e n t s , i n s e q u e n c e , s e p a r a t e d by s p a c e s . T h u s , i f L i s p
p r i n t e d o u t t h e l i s t t h a t was b f s v a l u e a b o v e , i t would a p p e a r :
(2 4 5 7)
A c o n s whose c d r i s t h e s y m b o l n i l c a n a l w a y s b e v i e w e d a s a l i s t
o f o n e i t e m , a n d i s s o p r i n t e d o u t by L i s p , u n l e s s . i t i s i n t h e
p r o c e s s of p r i n t i n g a l a r g e r l i s t o f which t h e c o n s a t i s s u e i s a
chain-link. A c o n s whose c d r i s n e i t h e r n i l n o r a n o t h e r c o n s i s
p r i n t e d w i t h a d o t p r e c e d i n g t h e c d r . Thus:
(cons 'a ' b ) => ( a . b)
(cons 'a n i l ) => ( a ) ; a l i s t of one element
(cons 'a ( c o n s Ib ' c ) ) => ( a b c) .
(cons 'a ( c o n s ' b n i l ) ) => ( a b) ; l i s t o f two e l e m e n t s
(cons 'a (cons (cons ' b ' c ) ( c o n s 'd n i l ) ) )
=> ( a ( b . c ) d ) ;list of t h r e e elements
Lists c a n b e p u t i n t o p r o g r a m s , by q u o t i n g t h e m , a s s y m b o l s
a r e quoted:
(setq bl ' ( t h i s is ( a l i s t ) ( o f l i s t s ) ) )
Two f u n c t i o n s a r e p r o v i d e d t o r e d e f i n e t h e c a r o r c d r o f a n
e x i s t i n g c o n s . They c a n b e v e r y d a n g e r o u s i f m i s u s e d , e s p e c i a l l y ;1)
i f t h e y a l t e r a l i s t a s i n t h e form above, which is w r i t t e n i n t o
. a p r o g r a m a s a c o n s t a n t . The r p l a c a f u n c t i o n ( r e p l a c e c a r ) a n d
t h e r p l a c d f u n c t i o n ( r e p l a c e c d r ) e a c h t a k e two a r g u m e n t s . The
f i r s t i s t h e c o n 3 t h a t i s t o be a l t e r e d , and t h e s e c o n d i s t h e
new c a r o r new c d r , r e s p e c t i v e l y . The r e t u r n e d v a l u e i s t h e c o n s
itself.
SECTION 3
WRITING EMACS EXTENSIONS
The starting point for writing extensions is building
functions out of those.provided in the Emacs Lisp environment,
and hooking them up to keys. The Emacs set-key and
set-permanent-key extended requests can connect keys to Lisp
functions that you provide, as well as to the standard requests
and keyboard macros.
Many simple and useful extensions are just groups o f Emacs
requests strung together. For instance, to go to the beginning
o f a line, delete all whitespace there, go to the end of the
line, do the same, and then return to the beginning of the line,
( ... you could type:
"A ESC \ "E ESC \ "A
Alternatively, you could write a function, called shave-line
here, to do the same:
(defun shave-line 0 ;keystroke functions take no args.
(go-to-beginning-of-line)
(delete-white-sides)
(go-to-end-of-line)
(delete-white-sides)
(go-to-beginning-of-line))
Write this function into a file. When in Emacs, type ESC X
loadfile PATHNAME CR, to load it in as code. Then hook it up,
perhaps by typing:
ESC X set-key "XA shave-line CR
Thereafter, hitting "XA causes the chosen sequence o f actions to
happen.
T o use conditionals and variables, you might, for example,
(+. want a function that goes to the beginning of a line and deletes
all words that start with nfoow from the beginning of the line.
( % i n c l u d e e-macros)
(defun foodeleter (1
(go-'to-beginning-of-line)
(do-forever
( i f ( l o o k i n g - a t "fool1)
(delete-word)
(delete-white-sides)
else ( s t o p - d o i n g ) ) ) )
The ( % i n c l u d e e-macros) must b e a t t h e b e g i n n i n g of any f i l e t h a t
u s e s t h e Ernacs e n v i r o n m e n t L i s p m a c r o s . T h e e - m a c r o s . i n c l . l i s p
f i l e should be i n your lltranslatorll search path i n .order t o do
a n y Emacs e x t e n s i o n d e v e l o p m e n t work.
What t h i s f u n c t i o n d o e s i n e s s e n c e i s t y p e " A , a n d a s l o n g
a s t h e f i r s t t h r e e c h a r a c t e r s o n t h e l i n e a r e ! ' f ~ o ~ o e, s a n ESC
d~
D, f o l l o w e d b y ESC \ t o r e m o v e t h e w h i t e s p a c e a f t e r t h e w o r d .
When t h e f i r s t t h r e e c h a r a c t e r s a r e n o l o n g e r l l f o o l l , i t r e t u r n s .
The " l o o k i n g - a t " i s a n Emacs p r e d i c a t e ( t o b e d e s c r i b e d i n d e t a i l
below) t h a t tests whether a given s t r i n g is t o t h e r i g h t o f t h e
c u r r e n t llcursorll. For t h i s f u n c t i o n and any o t h e r s t h a t you
write, you c o u l d set a key a s d e s c r i b e d a b o v e ("XA for
shave-line).
The c o d e f o r t h e f o o d e l e t e r makes no mention o f p r i n t i n g ,
o u t p u t , o r d i s p l a y s b e c a u s e it d o e s n o t need t o . The s c r e e n o r
printing terminal is managed a u t o m a t i c a l l y b y t h e Emacs
redisplay. The d i s p l a y need n e v e r be t h o u g h t a b o u t i n c o d i n g
Emacs e x t e n s i o n s .
U S I N G EMACS REQUESTS - EXTENSION C O D I N G
.
IN
Many o f t h e E m a c s r e q u e s t s c a n a n d s h o u l d b e u s e d i n c o d i n g
extensions, for example, go-to-end-of-line, forward-char,
go-to-beginning-of-buffer, delete-word and skip-over-indentation.
Some r e q u e s t s , h o w e v e r , s h o u l d n o t b e u s e d i n e x t e n s i o n c o d e .
F o r e x a m p l e , i f you want t o s e a r c h f o r some s t r i n g , you d o n o t
want t o invoke string-search ( ^ S ) , s i n c e t h a t prompts t h e u s e r i n
t h e m i n i b u f f e r f o r a s e a r c h s t r i n g . The f o l l o w i n g t a b l e l i s t s
s o m e i m p o r t a n t k e y s t r o k e r e q u e s t s w h o s e command n a m e s y o u s h o u l d
n o t u s e and g i v e s a l t e r n a t i v e f u n c t i o n s t o use.
KEY DO NOT USE USE INSTEAD
^N next-line-command next-line
The next-line-c.ommand function is unnecessarily
e x p e n s i v e i n c o n s i d e r i n g s c r e e n p o s i t i o n , and h a n d l e s
n u m e r i c a r g u m e n t s . The n e x t - l i n e f u n c t i o n a l w a y s g o e s
t o t h e beginning of the next l i n e .
"P prev-line-command prev-line
Same reasons as above. The prev-line function always
goes to the previous line.
^K kill-lines kill-to-end-of-line
delete-char (at eol)
The kill-lines function is complex, has many cases, and
handles numeric arguments.
AS string-search forward-search
The forward-search function takes a string as a Lisp
argument, does not prompt, moves the cursor if the
search succeeds, and returns truth or falsity t o
indicate result.
A R reverse-string-search reverse-search
Same as ^S.
^XAR read-file read-in-file
The read-in-file function takes a Lisp argument for
pathname, does not prompt.
"X*W write-file write-out-file
Same as "XAR.
A W wipe-region wipe-point-mark
Use local marks, see below.
ESC / regexp-search-command regexp-search
Same issues as "S. Takes a Lisp argument, no slashes.
Returns falsity if not found or moves cursor t o after,
and returns mark to before, matched string. Be careful
to release this mark (see below).
^XB select-buffer go-to-or-create-buffer
Takes an a r g u m e n t , d o e s not prompt.
^XAF find-file find-file-subr
Takes an argument, does not prompt.
.Requests that accept a positive numeric argument as meaning
repeat that number o f times, e.g., "B, "D, "F, ESC B, ESC D , ESC
F , !I, ESC # , etc., are acceptable in extensions; they do not
inspect their arguments. They are invoked multiple times by the
Emacs listener if appropriate. Requests whose names include the
word "commandn (other than " G , command-quit) are usually not
intended to be used in code.
T h e v a l u e o f a n u m e r i c a r g u m e n t , e . g . , 5 i n ESC 5 ^ B , i s
a v a i l a b l e a s t h e b i n d i n g o f t h e g l o b a l v a r i a b l e llnumargfl; i f no
numeric argument is g i v e n , t h i s v a r i a b l e is set t o t h e symbol
11 n i 1II ( n o t t o b e confused w i t h t h e g l o b a l v a r i a b l e n i l , whose
b i n d i n g is t h e symbol n i l ) , which i s t h e r e p r e s e n t a t i o n o f
falsity. The defcom f a c i l i t y , d i s c u s s e d l a t e r , can b e used t o
a d v a n t a g e a s well.
The n o r m a l p r i n t i n g c h a r a c t e r s a r e bound t o t h e s e l f - i n s e r t
f u n c t i o n , which i n s e r t s t h e l a s t p h y s i c a l c h a r a c t e r typed a t t h e
current point in the buffer. T h i s is c l e a r l y unusable from code,
if your d e s i r e is t o i n s e r t text i n t o t h e b u f f e r . For t h i s
purpose, t h e Emacs e n v i r o n m e n t p r o v i d e s the insert-string
f u n c t i o n , whose argument i s a s t r i n g t o b e i n s e r t e d i n t o t h e
buffer a t t h e cursor. A s i n typing i n t e x t manually, t h e cursor
is l e f t a f t e r t h e i n s e r t e d t e x t :
( d e f u n make-a-point 0
(go-to-beginning-of-line)
( i n s e r t - s t r i n g IICASE I N POINT: ">>
T h i s make-a-point f u n c t i o n , when i n v o k e d , g o e s t o t h e
b e g i n n i n g o f t h e l i n e , a n d i n s e r t s t h e s t r i n g "CASE I POINT:
N
in the buffer. The c u r s o r is l e f t a f t e r t h e i n s e r t e d s t r i n g .
A s used here, phrases l i k e , " t h e c u r s o r i s moved a r o u n d w o r
"a s t r i n g is i , n s e r t e d u i n a f u n c t i o n , d o n o t imply t h a t t h e u s e r
w a t c h i n g t h e s c r e e n c a n see a l l t h e s e t h i n g s h a p p e n . No a c t i o n
on t h e s c r e e n o c c u r s u n t i l t h e e n t i r e f u n c t i o n h a s f i n i s h e d
r u n n i n g , a t w h i c h time t h e s c r e e n i s u p d a t e d a l l a t o n c e , s h o w i n g
t h e c u m u l a t i v e e f f e c t o f w h a t h a s h a p p e n e d , r e g a r d l e s s o f how i t
happened.
M A R K S - THEIR MANAGEMENT
AND
L i k e t h e c u r s o r , a mark i s a c o n c e p t u a l p o i n t e r t o t h e
p o s i t i o n b e t w e e n t.wo c h a r a c t e r s i n t h e c u r r e n t b u f f e r . Marks
remain between. t h e s e two c h a r a c t e r s regardless of other
i n s e r t i o n s o r d e l e t i o n s i n t h e same b u f f e r , e v e n o n t h e same l i n e
as t h e mark. Marks a r e v a l u a b l e beca.use r e g i o n s o f . t e x t i n t h e
b u f f e r a r e s p e c i f i e d a s t h e e x t e n t between t h e c u r r e n t c o n c e p t u a l
c u r s o r , ( t h e p o i n t ) , and a g i v e n mark. Marks a r e a t y p e o f d a t a
o b j e c t i n t h e Emacs L i s p e n v i r o n m e n t , l i k e s t r i n g s , n u m b e r s , a n d
s y m b o l s . T h e v a l u e o f a n y v a r i a b l e c a n b e made t o b e a m a r k .
T h e v a l u e o f s e v e r a l v a r i a b l e s m i g h t e v e n b e t h e same m a r k . The
w o r d s " t h e - m a r k n u s e d i n Emacs d e s c r i p t i o n s d e s i g n a t e o n e mark
t h a t i s t h e v a l u e o f a g l o b a l v a r i a b l e t h a t many s u p p l i e d
f u n c t i o n s know a b o u t . E m a c s f u n c t i o n s u s e many t e m p o r a r y m a r k s .
- set-mark,
The release-mark and wipe-point-mark Functions
The set-mark function creates a new mark, which points to
the current point in the current buffer. It stays around, and is
updated by the editor, any time text is inserted or deleted in
this buffer. This is expensive, so you must take care, to
discard, or release marks when you are done using them. This is
done by giving them to the release-mark function. A