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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
acaf905b | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2012 |
0cc8c85a | 4 | @c Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/objects |
b8d4c8d0 GM |
7 | @node Lisp Data Types, Numbers, Introduction, Top |
8 | @chapter Lisp Data Types | |
9 | @cindex object | |
10 | @cindex Lisp object | |
11 | @cindex type | |
12 | @cindex data type | |
13 | ||
14 | A Lisp @dfn{object} is a piece of data used and manipulated by Lisp | |
15 | programs. For our purposes, a @dfn{type} or @dfn{data type} is a set of | |
16 | possible objects. | |
17 | ||
18 | Every object belongs to at least one type. Objects of the same type | |
19 | have similar structures and may usually be used in the same contexts. | |
20 | Types can overlap, and objects can belong to two or more types. | |
21 | Consequently, we can ask whether an object belongs to a particular type, | |
22 | but not for ``the'' type of an object. | |
23 | ||
24 | @cindex primitive type | |
25 | A few fundamental object types are built into Emacs. These, from | |
26 | which all other types are constructed, are called @dfn{primitive types}. | |
27 | Each object belongs to one and only one primitive type. These types | |
28 | include @dfn{integer}, @dfn{float}, @dfn{cons}, @dfn{symbol}, | |
29 | @dfn{string}, @dfn{vector}, @dfn{hash-table}, @dfn{subr}, and | |
30 | @dfn{byte-code function}, plus several special types, such as | |
31 | @dfn{buffer}, that are related to editing. (@xref{Editing Types}.) | |
32 | ||
33 | Each primitive type has a corresponding Lisp function that checks | |
34 | whether an object is a member of that type. | |
35 | ||
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36 | Lisp is unlike many other languages in that its objects are |
37 | @dfn{self-typing}: the primitive type of each object is implicit in | |
38 | the object itself. For example, if an object is a vector, nothing can | |
39 | treat it as a number; Lisp knows it is a vector, not a number. | |
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40 | |
41 | In most languages, the programmer must declare the data type of each | |
42 | variable, and the type is known by the compiler but not represented in | |
43 | the data. Such type declarations do not exist in Emacs Lisp. A Lisp | |
44 | variable can have any type of value, and it remembers whatever value | |
45 | you store in it, type and all. (Actually, a small number of Emacs | |
46 | Lisp variables can only take on values of a certain type. | |
47 | @xref{Variables with Restricted Values}.) | |
48 | ||
49 | This chapter describes the purpose, printed representation, and read | |
50 | syntax of each of the standard types in GNU Emacs Lisp. Details on how | |
51 | to use these types can be found in later chapters. | |
52 | ||
53 | @menu | |
54 | * Printed Representation:: How Lisp objects are represented as text. | |
55 | * Comments:: Comments and their formatting conventions. | |
56 | * Programming Types:: Types found in all Lisp systems. | |
57 | * Editing Types:: Types specific to Emacs. | |
58 | * Circular Objects:: Read syntax for circular structure. | |
59 | * Type Predicates:: Tests related to types. | |
60 | * Equality Predicates:: Tests of equality between any two objects. | |
61 | @end menu | |
62 | ||
63 | @node Printed Representation | |
64 | @comment node-name, next, previous, up | |
65 | @section Printed Representation and Read Syntax | |
66 | @cindex printed representation | |
67 | @cindex read syntax | |
68 | ||
69 | The @dfn{printed representation} of an object is the format of the | |
70 | output generated by the Lisp printer (the function @code{prin1}) for | |
71 | that object. Every data type has a unique printed representation. | |
72 | The @dfn{read syntax} of an object is the format of the input accepted | |
73 | by the Lisp reader (the function @code{read}) for that object. This | |
74 | is not necessarily unique; many kinds of object have more than one | |
75 | syntax. @xref{Read and Print}. | |
76 | ||
77 | @cindex hash notation | |
78 | In most cases, an object's printed representation is also a read | |
79 | syntax for the object. However, some types have no read syntax, since | |
80 | it does not make sense to enter objects of these types as constants in | |
81 | a Lisp program. These objects are printed in @dfn{hash notation}, | |
82 | which consists of the characters @samp{#<}, a descriptive string | |
83 | (typically the type name followed by the name of the object), and a | |
84 | closing @samp{>}. For example: | |
85 | ||
86 | @example | |
87 | (current-buffer) | |
88 | @result{} #<buffer objects.texi> | |
89 | @end example | |
90 | ||
91 | @noindent | |
92 | Hash notation cannot be read at all, so the Lisp reader signals the | |
93 | error @code{invalid-read-syntax} whenever it encounters @samp{#<}. | |
94 | @kindex invalid-read-syntax | |
95 | ||
96 | In other languages, an expression is text; it has no other form. In | |
97 | Lisp, an expression is primarily a Lisp object and only secondarily the | |
98 | text that is the object's read syntax. Often there is no need to | |
99 | emphasize this distinction, but you must keep it in the back of your | |
100 | mind, or you will occasionally be very confused. | |
101 | ||
102 | When you evaluate an expression interactively, the Lisp interpreter | |
103 | first reads the textual representation of it, producing a Lisp object, | |
104 | and then evaluates that object (@pxref{Evaluation}). However, | |
105 | evaluation and reading are separate activities. Reading returns the | |
106 | Lisp object represented by the text that is read; the object may or may | |
107 | not be evaluated later. @xref{Input Functions}, for a description of | |
108 | @code{read}, the basic function for reading objects. | |
109 | ||
110 | @node Comments | |
111 | @comment node-name, next, previous, up | |
112 | @section Comments | |
113 | @cindex comments | |
114 | @cindex @samp{;} in comment | |
115 | ||
116 | A @dfn{comment} is text that is written in a program only for the sake | |
117 | of humans that read the program, and that has no effect on the meaning | |
118 | of the program. In Lisp, a semicolon (@samp{;}) starts a comment if it | |
119 | is not within a string or character constant. The comment continues to | |
120 | the end of line. The Lisp reader discards comments; they do not become | |
121 | part of the Lisp objects which represent the program within the Lisp | |
122 | system. | |
123 | ||
124 | The @samp{#@@@var{count}} construct, which skips the next @var{count} | |
125 | characters, is useful for program-generated comments containing binary | |
126 | data. The Emacs Lisp byte compiler uses this in its output files | |
127 | (@pxref{Byte Compilation}). It isn't meant for source files, however. | |
128 | ||
129 | @xref{Comment Tips}, for conventions for formatting comments. | |
130 | ||
131 | @node Programming Types | |
132 | @section Programming Types | |
133 | @cindex programming types | |
134 | ||
135 | There are two general categories of types in Emacs Lisp: those having | |
136 | to do with Lisp programming, and those having to do with editing. The | |
137 | former exist in many Lisp implementations, in one form or another. The | |
138 | latter are unique to Emacs Lisp. | |
139 | ||
140 | @menu | |
141 | * Integer Type:: Numbers without fractional parts. | |
142 | * Floating Point Type:: Numbers with fractional parts and with a large range. | |
143 | * Character Type:: The representation of letters, numbers and | |
144 | control characters. | |
145 | * Symbol Type:: A multi-use object that refers to a function, | |
146 | variable, or property list, and has a unique identity. | |
147 | * Sequence Type:: Both lists and arrays are classified as sequences. | |
148 | * Cons Cell Type:: Cons cells, and lists (which are made from cons cells). | |
149 | * Array Type:: Arrays include strings and vectors. | |
150 | * String Type:: An (efficient) array of characters. | |
151 | * Vector Type:: One-dimensional arrays. | |
152 | * Char-Table Type:: One-dimensional sparse arrays indexed by characters. | |
153 | * Bool-Vector Type:: One-dimensional arrays of @code{t} or @code{nil}. | |
154 | * Hash Table Type:: Super-fast lookup tables. | |
155 | * Function Type:: A piece of executable code you can call from elsewhere. | |
156 | * Macro Type:: A method of expanding an expression into another | |
157 | expression, more fundamental but less pretty. | |
158 | * Primitive Function Type:: A function written in C, callable from Lisp. | |
159 | * Byte-Code Type:: A function written in Lisp, then compiled. | |
160 | * Autoload Type:: A type used for automatically loading seldom-used | |
161 | functions. | |
162 | @end menu | |
163 | ||
164 | @node Integer Type | |
165 | @subsection Integer Type | |
166 | ||
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167 | The range of values for integers in Emacs Lisp is @minus{}536870912 to |
168 | 536870911 (30 bits; i.e., | |
b8d4c8d0 | 169 | @ifnottex |
1ddd6622 | 170 | -2**29 |
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171 | @end ifnottex |
172 | @tex | |
1ddd6622 | 173 | @math{-2^{29}} |
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174 | @end tex |
175 | to | |
176 | @ifnottex | |
1ddd6622 | 177 | 2**29 - 1) |
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178 | @end ifnottex |
179 | @tex | |
1ddd6622 | 180 | @math{2^{29}-1}) |
b8d4c8d0 | 181 | @end tex |
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182 | on typical 32-bit machines. (Some machines provide a wider range.) |
183 | Emacs Lisp arithmetic functions do not check for overflow. Thus | |
184 | @code{(1+ 536870911)} is @minus{}536870912 if Emacs integers are 30 bits. | |
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185 | |
186 | The read syntax for integers is a sequence of (base ten) digits with an | |
187 | optional sign at the beginning and an optional period at the end. The | |
188 | printed representation produced by the Lisp interpreter never has a | |
189 | leading @samp{+} or a final @samp{.}. | |
190 | ||
191 | @example | |
192 | @group | |
193 | -1 ; @r{The integer -1.} | |
194 | 1 ; @r{The integer 1.} | |
195 | 1. ; @r{Also the integer 1.} | |
196 | +1 ; @r{Also the integer 1.} | |
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197 | @end group |
198 | @end example | |
199 | ||
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200 | @noindent |
201 | As a special exception, if a sequence of digits specifies an integer | |
202 | too large or too small to be a valid integer object, the Lisp reader | |
203 | reads it as a floating-point number (@pxref{Floating Point Type}). | |
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204 | For instance, if Emacs integers are 30 bits, @code{536870912} is read |
205 | as the floating-point number @code{536870912.0}. | |
eed5c93a | 206 | |
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207 | @xref{Numbers}, for more information. |
208 | ||
209 | @node Floating Point Type | |
210 | @subsection Floating Point Type | |
211 | ||
212 | Floating point numbers are the computer equivalent of scientific | |
213 | notation; you can think of a floating point number as a fraction | |
214 | together with a power of ten. The precise number of significant | |
215 | figures and the range of possible exponents is machine-specific; Emacs | |
216 | uses the C data type @code{double} to store the value, and internally | |
217 | this records a power of 2 rather than a power of 10. | |
218 | ||
219 | The printed representation for floating point numbers requires either | |
220 | a decimal point (with at least one digit following), an exponent, or | |
221 | both. For example, @samp{1500.0}, @samp{15e2}, @samp{15.0e2}, | |
222 | @samp{1.5e3}, and @samp{.15e4} are five ways of writing a floating point | |
223 | number whose value is 1500. They are all equivalent. | |
224 | ||
225 | @xref{Numbers}, for more information. | |
226 | ||
227 | @node Character Type | |
228 | @subsection Character Type | |
229 | @cindex @acronym{ASCII} character codes | |
230 | ||
231 | A @dfn{character} in Emacs Lisp is nothing more than an integer. In | |
232 | other words, characters are represented by their character codes. For | |
233 | example, the character @kbd{A} is represented as the @w{integer 65}. | |
234 | ||
235 | Individual characters are used occasionally in programs, but it is | |
236 | more common to work with @emph{strings}, which are sequences composed | |
237 | of characters. @xref{String Type}. | |
238 | ||
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239 | Characters in strings and buffers are currently limited to the range |
240 | of 0 to 4194303---twenty two bits (@pxref{Character Codes}). Codes 0 | |
241 | through 127 are @acronym{ASCII} codes; the rest are | |
242 | non-@acronym{ASCII} (@pxref{Non-ASCII Characters}). Characters that | |
243 | represent keyboard input have a much wider range, to encode modifier | |
244 | keys such as Control, Meta and Shift. | |
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245 | |
246 | There are special functions for producing a human-readable textual | |
247 | description of a character for the sake of messages. @xref{Describing | |
248 | Characters}. | |
249 | ||
250 | @menu | |
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251 | * Basic Char Syntax:: Syntax for regular characters. |
252 | * General Escape Syntax:: How to specify characters by their codes. | |
253 | * Ctl-Char Syntax:: Syntax for control characters. | |
254 | * Meta-Char Syntax:: Syntax for meta-characters. | |
255 | * Other Char Bits:: Syntax for hyper-, super-, and alt-characters. | |
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256 | @end menu |
257 | ||
258 | @node Basic Char Syntax | |
259 | @subsubsection Basic Char Syntax | |
260 | @cindex read syntax for characters | |
261 | @cindex printed representation for characters | |
262 | @cindex syntax for characters | |
263 | @cindex @samp{?} in character constant | |
264 | @cindex question mark in character constant | |
265 | ||
266 | Since characters are really integers, the printed representation of | |
267 | a character is a decimal number. This is also a possible read syntax | |
268 | for a character, but writing characters that way in Lisp programs is | |
269 | not clear programming. You should @emph{always} use the special read | |
270 | syntax formats that Emacs Lisp provides for characters. These syntax | |
271 | formats start with a question mark. | |
272 | ||
273 | The usual read syntax for alphanumeric characters is a question mark | |
274 | followed by the character; thus, @samp{?A} for the character | |
275 | @kbd{A}, @samp{?B} for the character @kbd{B}, and @samp{?a} for the | |
276 | character @kbd{a}. | |
277 | ||
278 | For example: | |
279 | ||
280 | @example | |
281 | ?Q @result{} 81 ?q @result{} 113 | |
282 | @end example | |
283 | ||
284 | You can use the same syntax for punctuation characters, but it is | |
285 | often a good idea to add a @samp{\} so that the Emacs commands for | |
286 | editing Lisp code don't get confused. For example, @samp{?\(} is the | |
287 | way to write the open-paren character. If the character is @samp{\}, | |
288 | you @emph{must} use a second @samp{\} to quote it: @samp{?\\}. | |
289 | ||
290 | @cindex whitespace | |
291 | @cindex bell character | |
292 | @cindex @samp{\a} | |
293 | @cindex backspace | |
294 | @cindex @samp{\b} | |
295 | @cindex tab (ASCII character) | |
296 | @cindex @samp{\t} | |
297 | @cindex vertical tab | |
298 | @cindex @samp{\v} | |
299 | @cindex formfeed | |
300 | @cindex @samp{\f} | |
301 | @cindex newline | |
302 | @cindex @samp{\n} | |
303 | @cindex return (ASCII character) | |
304 | @cindex @samp{\r} | |
305 | @cindex escape (ASCII character) | |
306 | @cindex @samp{\e} | |
307 | @cindex space (ASCII character) | |
308 | @cindex @samp{\s} | |
309 | You can express the characters control-g, backspace, tab, newline, | |
310 | vertical tab, formfeed, space, return, del, and escape as @samp{?\a}, | |
311 | @samp{?\b}, @samp{?\t}, @samp{?\n}, @samp{?\v}, @samp{?\f}, | |
312 | @samp{?\s}, @samp{?\r}, @samp{?\d}, and @samp{?\e}, respectively. | |
313 | (@samp{?\s} followed by a dash has a different meaning---it applies | |
314 | the ``super'' modifier to the following character.) Thus, | |
315 | ||
316 | @example | |
317 | ?\a @result{} 7 ; @r{control-g, @kbd{C-g}} | |
318 | ?\b @result{} 8 ; @r{backspace, @key{BS}, @kbd{C-h}} | |
319 | ?\t @result{} 9 ; @r{tab, @key{TAB}, @kbd{C-i}} | |
320 | ?\n @result{} 10 ; @r{newline, @kbd{C-j}} | |
321 | ?\v @result{} 11 ; @r{vertical tab, @kbd{C-k}} | |
322 | ?\f @result{} 12 ; @r{formfeed character, @kbd{C-l}} | |
323 | ?\r @result{} 13 ; @r{carriage return, @key{RET}, @kbd{C-m}} | |
324 | ?\e @result{} 27 ; @r{escape character, @key{ESC}, @kbd{C-[}} | |
325 | ?\s @result{} 32 ; @r{space character, @key{SPC}} | |
326 | ?\\ @result{} 92 ; @r{backslash character, @kbd{\}} | |
327 | ?\d @result{} 127 ; @r{delete character, @key{DEL}} | |
328 | @end example | |
329 | ||
330 | @cindex escape sequence | |
331 | These sequences which start with backslash are also known as | |
332 | @dfn{escape sequences}, because backslash plays the role of an | |
333 | ``escape character''; this terminology has nothing to do with the | |
334 | character @key{ESC}. @samp{\s} is meant for use in character | |
335 | constants; in string constants, just write the space. | |
336 | ||
337 | A backslash is allowed, and harmless, preceding any character without | |
338 | a special escape meaning; thus, @samp{?\+} is equivalent to @samp{?+}. | |
339 | There is no reason to add a backslash before most characters. However, | |
340 | you should add a backslash before any of the characters | |
341 | @samp{()\|;'`"#.,} to avoid confusing the Emacs commands for editing | |
342 | Lisp code. You can also add a backslash before whitespace characters such as | |
343 | space, tab, newline and formfeed. However, it is cleaner to use one of | |
344 | the easily readable escape sequences, such as @samp{\t} or @samp{\s}, | |
345 | instead of an actual whitespace character such as a tab or a space. | |
346 | (If you do write backslash followed by a space, you should write | |
347 | an extra space after the character constant to separate it from the | |
348 | following text.) | |
349 | ||
350 | @node General Escape Syntax | |
351 | @subsubsection General Escape Syntax | |
352 | ||
49ea0074 | 353 | In addition to the specific escape sequences for special important |
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354 | control characters, Emacs provides several types of escape syntax that |
355 | you can use to specify non-ASCII text characters. | |
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356 | |
357 | @cindex unicode character escape | |
fb080b28 | 358 | You can specify characters by their Unicode values. |
b8d4c8d0 | 359 | @code{?\u@var{nnnn}} represents a character that maps to the Unicode |
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360 | code point @samp{U+@var{nnnn}} (by convention, Unicode code points are |
361 | given in hexadecimal). There is a slightly different syntax for | |
362 | specifying characters with code points higher than | |
363 | @code{U+@var{ffff}}: @code{\U00@var{nnnnnn}} represents the character | |
f14589fa | 364 | whose code point is @samp{U+@var{nnnnnn}}. The Unicode Standard only |
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365 | defines code points up to @samp{U+@var{10ffff}}, so if you specify a |
366 | code point higher than that, Emacs signals an error. | |
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367 | |
368 | This peculiar and inconvenient syntax was adopted for compatibility | |
369 | with other programming languages. Unlike some other languages, Emacs | |
47dbc044 | 370 | Lisp supports this syntax only in character literals and strings. |
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371 | |
372 | @cindex @samp{\} in character constant | |
4963495d | 373 | @cindex backslash in character constants |
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374 | @cindex octal character code |
375 | The most general read syntax for a character represents the | |
376 | character code in either octal or hex. To use octal, write a question | |
377 | mark followed by a backslash and the octal character code (up to three | |
378 | octal digits); thus, @samp{?\101} for the character @kbd{A}, | |
379 | @samp{?\001} for the character @kbd{C-a}, and @code{?\002} for the | |
380 | character @kbd{C-b}. Although this syntax can represent any | |
381 | @acronym{ASCII} character, it is preferred only when the precise octal | |
382 | value is more important than the @acronym{ASCII} representation. | |
383 | ||
384 | @example | |
385 | @group | |
386 | ?\012 @result{} 10 ?\n @result{} 10 ?\C-j @result{} 10 | |
387 | ?\101 @result{} 65 ?A @result{} 65 | |
388 | @end group | |
389 | @end example | |
390 | ||
391 | To use hex, write a question mark followed by a backslash, @samp{x}, | |
392 | and the hexadecimal character code. You can use any number of hex | |
393 | digits, so you can represent any character code in this way. | |
394 | Thus, @samp{?\x41} for the character @kbd{A}, @samp{?\x1} for the | |
f987fde4 | 395 | character @kbd{C-a}, and @code{?\xe0} for the Latin-1 character |
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396 | @iftex |
397 | @samp{@`a}. | |
398 | @end iftex | |
399 | @ifnottex | |
400 | @samp{a} with grave accent. | |
401 | @end ifnottex | |
402 | ||
403 | @node Ctl-Char Syntax | |
404 | @subsubsection Control-Character Syntax | |
405 | ||
406 | @cindex control characters | |
407 | Control characters can be represented using yet another read syntax. | |
408 | This consists of a question mark followed by a backslash, caret, and the | |
409 | corresponding non-control character, in either upper or lower case. For | |
410 | example, both @samp{?\^I} and @samp{?\^i} are valid read syntax for the | |
411 | character @kbd{C-i}, the character whose value is 9. | |
412 | ||
413 | Instead of the @samp{^}, you can use @samp{C-}; thus, @samp{?\C-i} is | |
414 | equivalent to @samp{?\^I} and to @samp{?\^i}: | |
415 | ||
416 | @example | |
417 | ?\^I @result{} 9 ?\C-I @result{} 9 | |
418 | @end example | |
419 | ||
420 | In strings and buffers, the only control characters allowed are those | |
421 | that exist in @acronym{ASCII}; but for keyboard input purposes, you can turn | |
422 | any character into a control character with @samp{C-}. The character | |
423 | codes for these non-@acronym{ASCII} control characters include the | |
424 | @tex | |
425 | @math{2^{26}} | |
426 | @end tex | |
427 | @ifnottex | |
428 | 2**26 | |
429 | @end ifnottex | |
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430 | bit as well as the code for the corresponding non-control character. |
431 | Ordinary text terminals have no way of generating non-@acronym{ASCII} | |
432 | control characters, but you can generate them straightforwardly using | |
433 | X and other window systems. | |
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434 | |
435 | For historical reasons, Emacs treats the @key{DEL} character as | |
436 | the control equivalent of @kbd{?}: | |
437 | ||
438 | @example | |
439 | ?\^? @result{} 127 ?\C-? @result{} 127 | |
440 | @end example | |
441 | ||
442 | @noindent | |
443 | As a result, it is currently not possible to represent the character | |
444 | @kbd{Control-?}, which is a meaningful input character under X, using | |
445 | @samp{\C-}. It is not easy to change this, as various Lisp files refer | |
446 | to @key{DEL} in this way. | |
447 | ||
448 | For representing control characters to be found in files or strings, | |
449 | we recommend the @samp{^} syntax; for control characters in keyboard | |
450 | input, we prefer the @samp{C-} syntax. Which one you use does not | |
451 | affect the meaning of the program, but may guide the understanding of | |
452 | people who read it. | |
453 | ||
454 | @node Meta-Char Syntax | |
455 | @subsubsection Meta-Character Syntax | |
456 | ||
457 | @cindex meta characters | |
458 | A @dfn{meta character} is a character typed with the @key{META} | |
459 | modifier key. The integer that represents such a character has the | |
460 | @tex | |
461 | @math{2^{27}} | |
462 | @end tex | |
463 | @ifnottex | |
464 | 2**27 | |
465 | @end ifnottex | |
466 | bit set. We use high bits for this and other modifiers to make | |
467 | possible a wide range of basic character codes. | |
468 | ||
469 | In a string, the | |
470 | @tex | |
471 | @math{2^{7}} | |
472 | @end tex | |
473 | @ifnottex | |
474 | 2**7 | |
475 | @end ifnottex | |
476 | bit attached to an @acronym{ASCII} character indicates a meta | |
477 | character; thus, the meta characters that can fit in a string have | |
478 | codes in the range from 128 to 255, and are the meta versions of the | |
417f77e6 CY |
479 | ordinary @acronym{ASCII} characters. @xref{Strings of Events}, for |
480 | details about @key{META}-handling in strings. | |
b8d4c8d0 GM |
481 | |
482 | The read syntax for meta characters uses @samp{\M-}. For example, | |
483 | @samp{?\M-A} stands for @kbd{M-A}. You can use @samp{\M-} together with | |
484 | octal character codes (see below), with @samp{\C-}, or with any other | |
485 | syntax for a character. Thus, you can write @kbd{M-A} as @samp{?\M-A}, | |
486 | or as @samp{?\M-\101}. Likewise, you can write @kbd{C-M-b} as | |
487 | @samp{?\M-\C-b}, @samp{?\C-\M-b}, or @samp{?\M-\002}. | |
488 | ||
489 | @node Other Char Bits | |
490 | @subsubsection Other Character Modifier Bits | |
491 | ||
492 | The case of a graphic character is indicated by its character code; | |
493 | for example, @acronym{ASCII} distinguishes between the characters @samp{a} | |
494 | and @samp{A}. But @acronym{ASCII} has no way to represent whether a control | |
495 | character is upper case or lower case. Emacs uses the | |
496 | @tex | |
497 | @math{2^{25}} | |
498 | @end tex | |
499 | @ifnottex | |
500 | 2**25 | |
501 | @end ifnottex | |
502 | bit to indicate that the shift key was used in typing a control | |
503 | character. This distinction is possible only when you use X terminals | |
fead402d CY |
504 | or other special terminals; ordinary text terminals do not report the |
505 | distinction. The Lisp syntax for the shift bit is @samp{\S-}; thus, | |
506 | @samp{?\C-\S-o} or @samp{?\C-\S-O} represents the shifted-control-o | |
507 | character. | |
b8d4c8d0 GM |
508 | |
509 | @cindex hyper characters | |
510 | @cindex super characters | |
511 | @cindex alt characters | |
512 | The X Window System defines three other | |
513 | @anchor{modifier bits}modifier bits that can be set | |
514 | in a character: @dfn{hyper}, @dfn{super} and @dfn{alt}. The syntaxes | |
515 | for these bits are @samp{\H-}, @samp{\s-} and @samp{\A-}. (Case is | |
516 | significant in these prefixes.) Thus, @samp{?\H-\M-\A-x} represents | |
517 | @kbd{Alt-Hyper-Meta-x}. (Note that @samp{\s} with no following @samp{-} | |
518 | represents the space character.) | |
519 | @tex | |
520 | Numerically, the bit values are @math{2^{22}} for alt, @math{2^{23}} | |
521 | for super and @math{2^{24}} for hyper. | |
522 | @end tex | |
523 | @ifnottex | |
524 | Numerically, the | |
525 | bit values are 2**22 for alt, 2**23 for super and 2**24 for hyper. | |
526 | @end ifnottex | |
527 | ||
528 | @node Symbol Type | |
529 | @subsection Symbol Type | |
530 | ||
531 | A @dfn{symbol} in GNU Emacs Lisp is an object with a name. The | |
532 | symbol name serves as the printed representation of the symbol. In | |
a2afc99d | 533 | ordinary Lisp use, with one single obarray (@pxref{Creating Symbols}), |
b8d4c8d0 GM |
534 | a symbol's name is unique---no two symbols have the same name. |
535 | ||
536 | A symbol can serve as a variable, as a function name, or to hold a | |
537 | property list. Or it may serve only to be distinct from all other Lisp | |
538 | objects, so that its presence in a data structure may be recognized | |
539 | reliably. In a given context, usually only one of these uses is | |
540 | intended. But you can use one symbol in all of these ways, | |
541 | independently. | |
542 | ||
543 | A symbol whose name starts with a colon (@samp{:}) is called a | |
fead402d CY |
544 | @dfn{keyword symbol}. These symbols automatically act as constants, |
545 | and are normally used only by comparing an unknown symbol with a few | |
546 | specific alternatives. @xref{Constant Variables}. | |
b8d4c8d0 GM |
547 | |
548 | @cindex @samp{\} in symbols | |
549 | @cindex backslash in symbols | |
550 | A symbol name can contain any characters whatever. Most symbol names | |
551 | are written with letters, digits, and the punctuation characters | |
552 | @samp{-+=*/}. Such names require no special punctuation; the characters | |
553 | of the name suffice as long as the name does not look like a number. | |
554 | (If it does, write a @samp{\} at the beginning of the name to force | |
555 | interpretation as a symbol.) The characters @samp{_~!@@$%^&:<>@{@}?} are | |
556 | less often used but also require no special punctuation. Any other | |
557 | characters may be included in a symbol's name by escaping them with a | |
558 | backslash. In contrast to its use in strings, however, a backslash in | |
559 | the name of a symbol simply quotes the single character that follows the | |
560 | backslash. For example, in a string, @samp{\t} represents a tab | |
561 | character; in the name of a symbol, however, @samp{\t} merely quotes the | |
562 | letter @samp{t}. To have a symbol with a tab character in its name, you | |
563 | must actually use a tab (preceded with a backslash). But it's rare to | |
564 | do such a thing. | |
565 | ||
566 | @cindex CL note---case of letters | |
567 | @quotation | |
568 | @b{Common Lisp note:} In Common Lisp, lower case letters are always | |
569 | ``folded'' to upper case, unless they are explicitly escaped. In Emacs | |
570 | Lisp, upper case and lower case letters are distinct. | |
571 | @end quotation | |
572 | ||
573 | Here are several examples of symbol names. Note that the @samp{+} in | |
574 | the fifth example is escaped to prevent it from being read as a number. | |
575 | This is not necessary in the fourth example because the rest of the name | |
576 | makes it invalid as a number. | |
577 | ||
578 | @example | |
579 | @group | |
580 | foo ; @r{A symbol named @samp{foo}.} | |
581 | FOO ; @r{A symbol named @samp{FOO}, different from @samp{foo}.} | |
b8d4c8d0 GM |
582 | @end group |
583 | @group | |
584 | 1+ ; @r{A symbol named @samp{1+}} | |
585 | ; @r{(not @samp{+1}, which is an integer).} | |
586 | @end group | |
587 | @group | |
588 | \+1 ; @r{A symbol named @samp{+1}} | |
589 | ; @r{(not a very readable name).} | |
590 | @end group | |
591 | @group | |
592 | \(*\ 1\ 2\) ; @r{A symbol named @samp{(* 1 2)} (a worse name).} | |
593 | @c the @'s in this next line use up three characters, hence the | |
594 | @c apparent misalignment of the comment. | |
595 | +-*/_~!@@$%^&=:<>@{@} ; @r{A symbol named @samp{+-*/_~!@@$%^&=:<>@{@}}.} | |
596 | ; @r{These characters need not be escaped.} | |
597 | @end group | |
598 | @end example | |
599 | ||
ddb54206 | 600 | @cindex @samp{##} read syntax |
b8d4c8d0 GM |
601 | @ifinfo |
602 | @c This uses ``colon'' instead of a literal `:' because Info cannot | |
603 | @c cope with a `:' in a menu | |
604 | @cindex @samp{#@var{colon}} read syntax | |
605 | @end ifinfo | |
606 | @ifnotinfo | |
607 | @cindex @samp{#:} read syntax | |
608 | @end ifnotinfo | |
ddb54206 CY |
609 | As an exception to the rule that a symbol's name serves as its |
610 | printed representation, @samp{##} is the printed representation for an | |
611 | interned symbol whose name is an empty string. Furthermore, | |
612 | @samp{#:@var{foo}} is the printed representation for an uninterned | |
613 | symbol whose name is @var{foo}. (Normally, the Lisp reader interns | |
614 | all symbols; @pxref{Creating Symbols}.) | |
b8d4c8d0 GM |
615 | |
616 | @node Sequence Type | |
617 | @subsection Sequence Types | |
618 | ||
619 | A @dfn{sequence} is a Lisp object that represents an ordered set of | |
fead402d CY |
620 | elements. There are two kinds of sequence in Emacs Lisp: @dfn{lists} |
621 | and @dfn{arrays}. | |
622 | ||
623 | Lists are the most commonly-used sequences. A list can hold | |
624 | elements of any type, and its length can be easily changed by adding | |
625 | or removing elements. See the next subsection for more about lists. | |
626 | ||
627 | Arrays are fixed-length sequences. They are further subdivided into | |
628 | strings, vectors, char-tables and bool-vectors. Vectors can hold | |
629 | elements of any type, whereas string elements must be characters, and | |
630 | bool-vector elements must be @code{t} or @code{nil}. Char-tables are | |
631 | like vectors except that they are indexed by any valid character code. | |
632 | The characters in a string can have text properties like characters in | |
633 | a buffer (@pxref{Text Properties}), but vectors do not support text | |
634 | properties, even when their elements happen to be characters. | |
635 | ||
636 | Lists, strings and the other array types also share important | |
637 | similarities. For example, all have a length @var{l}, and all have | |
638 | elements which can be indexed from zero to @var{l} minus one. Several | |
639 | functions, called sequence functions, accept any kind of sequence. | |
640 | For example, the function @code{length} reports the length of any kind | |
641 | of sequence. @xref{Sequences Arrays Vectors}. | |
b8d4c8d0 GM |
642 | |
643 | It is generally impossible to read the same sequence twice, since | |
644 | sequences are always created anew upon reading. If you read the read | |
645 | syntax for a sequence twice, you get two sequences with equal contents. | |
646 | There is one exception: the empty list @code{()} always stands for the | |
647 | same object, @code{nil}. | |
648 | ||
649 | @node Cons Cell Type | |
650 | @subsection Cons Cell and List Types | |
651 | @cindex address field of register | |
652 | @cindex decrement field of register | |
653 | @cindex pointers | |
654 | ||
fead402d CY |
655 | A @dfn{cons cell} is an object that consists of two slots, called |
656 | the @sc{car} slot and the @sc{cdr} slot. Each slot can @dfn{hold} any | |
657 | Lisp object. We also say that ``the @sc{car} of this cons cell is'' | |
658 | whatever object its @sc{car} slot currently holds, and likewise for | |
659 | the @sc{cdr}. | |
b8d4c8d0 | 660 | |
fead402d | 661 | @cindex list structure |
b8d4c8d0 GM |
662 | A @dfn{list} is a series of cons cells, linked together so that the |
663 | @sc{cdr} slot of each cons cell holds either the next cons cell or the | |
664 | empty list. The empty list is actually the symbol @code{nil}. | |
fead402d CY |
665 | @xref{Lists}, for details. Because most cons cells are used as part |
666 | of lists, we refer to any structure made out of cons cells as a | |
667 | @dfn{list structure}. | |
668 | ||
669 | @cindex linked list | |
670 | @quotation | |
671 | A note to C programmers: a Lisp list thus works as a @dfn{linked list} | |
672 | built up of cons cells. Because pointers in Lisp are implicit, we do | |
673 | not distinguish between a cons cell slot ``holding'' a value versus | |
674 | ``pointing to'' the value. | |
675 | @end quotation | |
b8d4c8d0 GM |
676 | |
677 | @cindex atoms | |
678 | Because cons cells are so central to Lisp, we also have a word for | |
679 | ``an object which is not a cons cell.'' These objects are called | |
680 | @dfn{atoms}. | |
681 | ||
682 | @cindex parenthesis | |
683 | @cindex @samp{(@dots{})} in lists | |
684 | The read syntax and printed representation for lists are identical, and | |
685 | consist of a left parenthesis, an arbitrary number of elements, and a | |
686 | right parenthesis. Here are examples of lists: | |
687 | ||
688 | @example | |
689 | (A 2 "A") ; @r{A list of three elements.} | |
690 | () ; @r{A list of no elements (the empty list).} | |
691 | nil ; @r{A list of no elements (the empty list).} | |
692 | ("A ()") ; @r{A list of one element: the string @code{"A ()"}.} | |
693 | (A ()) ; @r{A list of two elements: @code{A} and the empty list.} | |
694 | (A nil) ; @r{Equivalent to the previous.} | |
695 | ((A B C)) ; @r{A list of one element} | |
696 | ; @r{(which is a list of three elements).} | |
697 | @end example | |
698 | ||
699 | Upon reading, each object inside the parentheses becomes an element | |
700 | of the list. That is, a cons cell is made for each element. The | |
701 | @sc{car} slot of the cons cell holds the element, and its @sc{cdr} | |
702 | slot refers to the next cons cell of the list, which holds the next | |
703 | element in the list. The @sc{cdr} slot of the last cons cell is set to | |
704 | hold @code{nil}. | |
705 | ||
706 | The names @sc{car} and @sc{cdr} derive from the history of Lisp. The | |
707 | original Lisp implementation ran on an @w{IBM 704} computer which | |
708 | divided words into two parts, called the ``address'' part and the | |
709 | ``decrement''; @sc{car} was an instruction to extract the contents of | |
710 | the address part of a register, and @sc{cdr} an instruction to extract | |
711 | the contents of the decrement. By contrast, ``cons cells'' are named | |
712 | for the function @code{cons} that creates them, which in turn was named | |
713 | for its purpose, the construction of cells. | |
714 | ||
715 | @menu | |
716 | * Box Diagrams:: Drawing pictures of lists. | |
717 | * Dotted Pair Notation:: A general syntax for cons cells. | |
718 | * Association List Type:: A specially constructed list. | |
719 | @end menu | |
720 | ||
721 | @node Box Diagrams | |
722 | @subsubsection Drawing Lists as Box Diagrams | |
723 | @cindex box diagrams, for lists | |
724 | @cindex diagrams, boxed, for lists | |
725 | ||
726 | A list can be illustrated by a diagram in which the cons cells are | |
727 | shown as pairs of boxes, like dominoes. (The Lisp reader cannot read | |
728 | such an illustration; unlike the textual notation, which can be | |
729 | understood by both humans and computers, the box illustrations can be | |
730 | understood only by humans.) This picture represents the three-element | |
731 | list @code{(rose violet buttercup)}: | |
732 | ||
733 | @example | |
734 | @group | |
735 | --- --- --- --- --- --- | |
736 | | | |--> | | |--> | | |--> nil | |
737 | --- --- --- --- --- --- | |
738 | | | | | |
739 | | | | | |
740 | --> rose --> violet --> buttercup | |
741 | @end group | |
742 | @end example | |
743 | ||
744 | In this diagram, each box represents a slot that can hold or refer to | |
745 | any Lisp object. Each pair of boxes represents a cons cell. Each arrow | |
746 | represents a reference to a Lisp object, either an atom or another cons | |
747 | cell. | |
748 | ||
749 | In this example, the first box, which holds the @sc{car} of the first | |
750 | cons cell, refers to or ``holds'' @code{rose} (a symbol). The second | |
751 | box, holding the @sc{cdr} of the first cons cell, refers to the next | |
752 | pair of boxes, the second cons cell. The @sc{car} of the second cons | |
753 | cell is @code{violet}, and its @sc{cdr} is the third cons cell. The | |
754 | @sc{cdr} of the third (and last) cons cell is @code{nil}. | |
755 | ||
756 | Here is another diagram of the same list, @code{(rose violet | |
757 | buttercup)}, sketched in a different manner: | |
758 | ||
759 | @smallexample | |
760 | @group | |
761 | --------------- ---------------- ------------------- | |
762 | | car | cdr | | car | cdr | | car | cdr | | |
763 | | rose | o-------->| violet | o-------->| buttercup | nil | | |
764 | | | | | | | | | | | |
765 | --------------- ---------------- ------------------- | |
766 | @end group | |
767 | @end smallexample | |
768 | ||
769 | @cindex @code{nil} as a list | |
770 | @cindex empty list | |
771 | A list with no elements in it is the @dfn{empty list}; it is identical | |
772 | to the symbol @code{nil}. In other words, @code{nil} is both a symbol | |
773 | and a list. | |
774 | ||
775 | Here is the list @code{(A ())}, or equivalently @code{(A nil)}, | |
776 | depicted with boxes and arrows: | |
777 | ||
778 | @example | |
779 | @group | |
780 | --- --- --- --- | |
781 | | | |--> | | |--> nil | |
782 | --- --- --- --- | |
783 | | | | |
784 | | | | |
785 | --> A --> nil | |
786 | @end group | |
787 | @end example | |
788 | ||
789 | Here is a more complex illustration, showing the three-element list, | |
790 | @code{((pine needles) oak maple)}, the first element of which is a | |
791 | two-element list: | |
792 | ||
793 | @example | |
794 | @group | |
795 | --- --- --- --- --- --- | |
796 | | | |--> | | |--> | | |--> nil | |
797 | --- --- --- --- --- --- | |
798 | | | | | |
799 | | | | | |
800 | | --> oak --> maple | |
801 | | | |
802 | | --- --- --- --- | |
803 | --> | | |--> | | |--> nil | |
804 | --- --- --- --- | |
805 | | | | |
806 | | | | |
807 | --> pine --> needles | |
808 | @end group | |
809 | @end example | |
810 | ||
811 | The same list represented in the second box notation looks like this: | |
812 | ||
813 | @example | |
814 | @group | |
815 | -------------- -------------- -------------- | |
816 | | car | cdr | | car | cdr | | car | cdr | | |
817 | | o | o------->| oak | o------->| maple | nil | | |
818 | | | | | | | | | | | | |
819 | -- | --------- -------------- -------------- | |
820 | | | |
821 | | | |
822 | | -------------- ---------------- | |
823 | | | car | cdr | | car | cdr | | |
824 | ------>| pine | o------->| needles | nil | | |
825 | | | | | | | | |
826 | -------------- ---------------- | |
827 | @end group | |
828 | @end example | |
829 | ||
830 | @node Dotted Pair Notation | |
831 | @subsubsection Dotted Pair Notation | |
832 | @cindex dotted pair notation | |
833 | @cindex @samp{.} in lists | |
834 | ||
835 | @dfn{Dotted pair notation} is a general syntax for cons cells that | |
836 | represents the @sc{car} and @sc{cdr} explicitly. In this syntax, | |
837 | @code{(@var{a} .@: @var{b})} stands for a cons cell whose @sc{car} is | |
838 | the object @var{a} and whose @sc{cdr} is the object @var{b}. Dotted | |
839 | pair notation is more general than list syntax because the @sc{cdr} | |
840 | does not have to be a list. However, it is more cumbersome in cases | |
841 | where list syntax would work. In dotted pair notation, the list | |
842 | @samp{(1 2 3)} is written as @samp{(1 . (2 . (3 . nil)))}. For | |
843 | @code{nil}-terminated lists, you can use either notation, but list | |
844 | notation is usually clearer and more convenient. When printing a | |
845 | list, the dotted pair notation is only used if the @sc{cdr} of a cons | |
846 | cell is not a list. | |
847 | ||
848 | Here's an example using boxes to illustrate dotted pair notation. | |
849 | This example shows the pair @code{(rose . violet)}: | |
850 | ||
851 | @example | |
852 | @group | |
853 | --- --- | |
854 | | | |--> violet | |
855 | --- --- | |
856 | | | |
857 | | | |
858 | --> rose | |
859 | @end group | |
860 | @end example | |
861 | ||
862 | You can combine dotted pair notation with list notation to represent | |
863 | conveniently a chain of cons cells with a non-@code{nil} final @sc{cdr}. | |
864 | You write a dot after the last element of the list, followed by the | |
865 | @sc{cdr} of the final cons cell. For example, @code{(rose violet | |
866 | . buttercup)} is equivalent to @code{(rose . (violet . buttercup))}. | |
867 | The object looks like this: | |
868 | ||
869 | @example | |
870 | @group | |
871 | --- --- --- --- | |
872 | | | |--> | | |--> buttercup | |
873 | --- --- --- --- | |
874 | | | | |
875 | | | | |
876 | --> rose --> violet | |
877 | @end group | |
878 | @end example | |
879 | ||
880 | The syntax @code{(rose .@: violet .@: buttercup)} is invalid because | |
881 | there is nothing that it could mean. If anything, it would say to put | |
882 | @code{buttercup} in the @sc{cdr} of a cons cell whose @sc{cdr} is already | |
883 | used for @code{violet}. | |
884 | ||
885 | The list @code{(rose violet)} is equivalent to @code{(rose . (violet))}, | |
886 | and looks like this: | |
887 | ||
888 | @example | |
889 | @group | |
890 | --- --- --- --- | |
891 | | | |--> | | |--> nil | |
892 | --- --- --- --- | |
893 | | | | |
894 | | | | |
895 | --> rose --> violet | |
896 | @end group | |
897 | @end example | |
898 | ||
899 | Similarly, the three-element list @code{(rose violet buttercup)} | |
900 | is equivalent to @code{(rose . (violet . (buttercup)))}. | |
901 | @ifnottex | |
902 | It looks like this: | |
903 | ||
904 | @example | |
905 | @group | |
906 | --- --- --- --- --- --- | |
907 | | | |--> | | |--> | | |--> nil | |
908 | --- --- --- --- --- --- | |
909 | | | | | |
910 | | | | | |
911 | --> rose --> violet --> buttercup | |
912 | @end group | |
913 | @end example | |
914 | @end ifnottex | |
915 | ||
916 | @node Association List Type | |
917 | @comment node-name, next, previous, up | |
918 | @subsubsection Association List Type | |
919 | ||
920 | An @dfn{association list} or @dfn{alist} is a specially-constructed | |
921 | list whose elements are cons cells. In each element, the @sc{car} is | |
922 | considered a @dfn{key}, and the @sc{cdr} is considered an | |
923 | @dfn{associated value}. (In some cases, the associated value is stored | |
924 | in the @sc{car} of the @sc{cdr}.) Association lists are often used as | |
925 | stacks, since it is easy to add or remove associations at the front of | |
926 | the list. | |
927 | ||
928 | For example, | |
929 | ||
930 | @example | |
931 | (setq alist-of-colors | |
932 | '((rose . red) (lily . white) (buttercup . yellow))) | |
933 | @end example | |
934 | ||
935 | @noindent | |
936 | sets the variable @code{alist-of-colors} to an alist of three elements. In the | |
937 | first element, @code{rose} is the key and @code{red} is the value. | |
938 | ||
939 | @xref{Association Lists}, for a further explanation of alists and for | |
940 | functions that work on alists. @xref{Hash Tables}, for another kind of | |
941 | lookup table, which is much faster for handling a large number of keys. | |
942 | ||
943 | @node Array Type | |
944 | @subsection Array Type | |
945 | ||
946 | An @dfn{array} is composed of an arbitrary number of slots for | |
947 | holding or referring to other Lisp objects, arranged in a contiguous block of | |
948 | memory. Accessing any element of an array takes approximately the same | |
949 | amount of time. In contrast, accessing an element of a list requires | |
950 | time proportional to the position of the element in the list. (Elements | |
951 | at the end of a list take longer to access than elements at the | |
952 | beginning of a list.) | |
953 | ||
954 | Emacs defines four types of array: strings, vectors, bool-vectors, and | |
955 | char-tables. | |
956 | ||
957 | A string is an array of characters and a vector is an array of | |
958 | arbitrary objects. A bool-vector can hold only @code{t} or @code{nil}. | |
959 | These kinds of array may have any length up to the largest integer. | |
960 | Char-tables are sparse arrays indexed by any valid character code; they | |
961 | can hold arbitrary objects. | |
962 | ||
963 | The first element of an array has index zero, the second element has | |
964 | index 1, and so on. This is called @dfn{zero-origin} indexing. For | |
965 | example, an array of four elements has indices 0, 1, 2, @w{and 3}. The | |
966 | largest possible index value is one less than the length of the array. | |
967 | Once an array is created, its length is fixed. | |
968 | ||
969 | All Emacs Lisp arrays are one-dimensional. (Most other programming | |
970 | languages support multidimensional arrays, but they are not essential; | |
971 | you can get the same effect with nested one-dimensional arrays.) Each | |
972 | type of array has its own read syntax; see the following sections for | |
973 | details. | |
974 | ||
975 | The array type is a subset of the sequence type, and contains the | |
976 | string type, the vector type, the bool-vector type, and the char-table | |
977 | type. | |
978 | ||
979 | @node String Type | |
980 | @subsection String Type | |
981 | ||
982 | A @dfn{string} is an array of characters. Strings are used for many | |
983 | purposes in Emacs, as can be expected in a text editor; for example, as | |
984 | the names of Lisp symbols, as messages for the user, and to represent | |
985 | text extracted from buffers. Strings in Lisp are constants: evaluation | |
986 | of a string returns the same string. | |
987 | ||
988 | @xref{Strings and Characters}, for functions that operate on strings. | |
989 | ||
990 | @menu | |
0cc8c85a GM |
991 | * Syntax for Strings:: How to specify Lisp strings. |
992 | * Non-ASCII in Strings:: International characters in strings. | |
993 | * Nonprinting Characters:: Literal unprintable characters in strings. | |
994 | * Text Props and Strings:: Strings with text properties. | |
b8d4c8d0 GM |
995 | @end menu |
996 | ||
997 | @node Syntax for Strings | |
998 | @subsubsection Syntax for Strings | |
999 | ||
1000 | @cindex @samp{"} in strings | |
1001 | @cindex double-quote in strings | |
1002 | @cindex @samp{\} in strings | |
1003 | @cindex backslash in strings | |
2bd1f99a CY |
1004 | The read syntax for a string is a double-quote, an arbitrary number |
1005 | of characters, and another double-quote, @code{"like this"}. To | |
1006 | include a double-quote in a string, precede it with a backslash; thus, | |
1007 | @code{"\""} is a string containing just a single double-quote | |
1008 | character. Likewise, you can include a backslash by preceding it with | |
1009 | another backslash, like this: @code{"this \\ is a single embedded | |
1010 | backslash"}. | |
b8d4c8d0 GM |
1011 | |
1012 | @cindex newline in strings | |
1013 | The newline character is not special in the read syntax for strings; | |
1014 | if you write a new line between the double-quotes, it becomes a | |
1015 | character in the string. But an escaped newline---one that is preceded | |
1016 | by @samp{\}---does not become part of the string; i.e., the Lisp reader | |
1017 | ignores an escaped newline while reading a string. An escaped space | |
1018 | @w{@samp{\ }} is likewise ignored. | |
1019 | ||
1020 | @example | |
1021 | "It is useful to include newlines | |
1022 | in documentation strings, | |
1023 | but the newline is \ | |
1024 | ignored if escaped." | |
1025 | @result{} "It is useful to include newlines | |
1026 | in documentation strings, | |
1027 | but the newline is ignored if escaped." | |
1028 | @end example | |
1029 | ||
1030 | @node Non-ASCII in Strings | |
1031 | @subsubsection Non-@acronym{ASCII} Characters in Strings | |
1032 | ||
fead402d CY |
1033 | You can include a non-@acronym{ASCII} international character in a |
1034 | string constant by writing it literally. There are two text | |
1035 | representations for non-@acronym{ASCII} characters in Emacs strings | |
1036 | (and in buffers): unibyte and multibyte (@pxref{Text | |
1037 | Representations}). If the string constant is read from a multibyte | |
1038 | source, such as a multibyte buffer or string, or a file that would be | |
1039 | visited as multibyte, then Emacs reads the non-@acronym{ASCII} | |
1040 | character as a multibyte character and automatically makes the string | |
1041 | a multibyte string. If the string constant is read from a unibyte | |
1042 | source, then Emacs reads the non-@acronym{ASCII} character as unibyte, | |
1043 | and makes the string unibyte. | |
1044 | ||
1045 | Instead of writing a non-@acronym{ASCII} character literally into a | |
1046 | multibyte string, you can write it as its character code using a hex | |
1047 | escape, @samp{\x@var{nnnnnnn}}, with as many digits as necessary. | |
1048 | (Multibyte non-@acronym{ASCII} character codes are all greater than | |
1049 | 256.) You can also specify a character in a multibyte string using | |
1050 | the @samp{\u} or @samp{\U} Unicode escape syntax (@pxref{General | |
1051 | Escape Syntax}). In either case, any character which is not a valid | |
1052 | hex digit terminates the construct. If the next character in the | |
1053 | string could be interpreted as a hex digit, write @w{@samp{\ }} | |
1054 | (backslash and space) to terminate the hex escape---for example, | |
1055 | @w{@samp{\xe0\ }} represents one character, @samp{a} with grave | |
1056 | accent. @w{@samp{\ }} in a string constant is just like | |
1057 | backslash-newline; it does not contribute any character to the string, | |
1058 | but it does terminate the preceding hex escape. Using any hex escape | |
1059 | in a string (even for an @acronym{ASCII} character) automatically | |
1060 | forces the string to be multibyte. | |
b8d4c8d0 GM |
1061 | |
1062 | You can represent a unibyte non-@acronym{ASCII} character with its | |
1063 | character code, which must be in the range from 128 (0200 octal) to | |
1064 | 255 (0377 octal). If you write all such character codes in octal and | |
1065 | the string contains no other characters forcing it to be multibyte, | |
fead402d | 1066 | this produces a unibyte string. |
b8d4c8d0 GM |
1067 | |
1068 | @node Nonprinting Characters | |
1069 | @subsubsection Nonprinting Characters in Strings | |
1070 | ||
1071 | You can use the same backslash escape-sequences in a string constant | |
1072 | as in character literals (but do not use the question mark that begins a | |
1073 | character constant). For example, you can write a string containing the | |
1074 | nonprinting characters tab and @kbd{C-a}, with commas and spaces between | |
1075 | them, like this: @code{"\t, \C-a"}. @xref{Character Type}, for a | |
1076 | description of the read syntax for characters. | |
1077 | ||
1078 | However, not all of the characters you can write with backslash | |
1079 | escape-sequences are valid in strings. The only control characters that | |
1080 | a string can hold are the @acronym{ASCII} control characters. Strings do not | |
1081 | distinguish case in @acronym{ASCII} control characters. | |
1082 | ||
1083 | Properly speaking, strings cannot hold meta characters; but when a | |
1084 | string is to be used as a key sequence, there is a special convention | |
1085 | that provides a way to represent meta versions of @acronym{ASCII} | |
1086 | characters in a string. If you use the @samp{\M-} syntax to indicate | |
1087 | a meta character in a string constant, this sets the | |
1088 | @tex | |
1089 | @math{2^{7}} | |
1090 | @end tex | |
1091 | @ifnottex | |
1092 | 2**7 | |
1093 | @end ifnottex | |
1094 | bit of the character in the string. If the string is used in | |
1095 | @code{define-key} or @code{lookup-key}, this numeric code is translated | |
1096 | into the equivalent meta character. @xref{Character Type}. | |
1097 | ||
1098 | Strings cannot hold characters that have the hyper, super, or alt | |
1099 | modifiers. | |
1100 | ||
1101 | @node Text Props and Strings | |
1102 | @subsubsection Text Properties in Strings | |
1103 | ||
6bfc8698 EZ |
1104 | @cindex @samp{#(} read syntax |
1105 | @cindex text properties, read syntax | |
b8d4c8d0 GM |
1106 | A string can hold properties for the characters it contains, in |
1107 | addition to the characters themselves. This enables programs that copy | |
1108 | text between strings and buffers to copy the text's properties with no | |
1109 | special effort. @xref{Text Properties}, for an explanation of what text | |
1110 | properties mean. Strings with text properties use a special read and | |
1111 | print syntax: | |
1112 | ||
1113 | @example | |
1114 | #("@var{characters}" @var{property-data}...) | |
1115 | @end example | |
1116 | ||
1117 | @noindent | |
1118 | where @var{property-data} consists of zero or more elements, in groups | |
1119 | of three as follows: | |
1120 | ||
1121 | @example | |
1122 | @var{beg} @var{end} @var{plist} | |
1123 | @end example | |
1124 | ||
1125 | @noindent | |
1126 | The elements @var{beg} and @var{end} are integers, and together specify | |
1127 | a range of indices in the string; @var{plist} is the property list for | |
1128 | that range. For example, | |
1129 | ||
1130 | @example | |
1131 | #("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic)) | |
1132 | @end example | |
1133 | ||
1134 | @noindent | |
1135 | represents a string whose textual contents are @samp{foo bar}, in which | |
1136 | the first three characters have a @code{face} property with value | |
1137 | @code{bold}, and the last three have a @code{face} property with value | |
1138 | @code{italic}. (The fourth character has no text properties, so its | |
1139 | property list is @code{nil}. It is not actually necessary to mention | |
1140 | ranges with @code{nil} as the property list, since any characters not | |
1141 | mentioned in any range will default to having no properties.) | |
1142 | ||
1143 | @node Vector Type | |
1144 | @subsection Vector Type | |
1145 | ||
1146 | A @dfn{vector} is a one-dimensional array of elements of any type. It | |
1147 | takes a constant amount of time to access any element of a vector. (In | |
1148 | a list, the access time of an element is proportional to the distance of | |
1149 | the element from the beginning of the list.) | |
1150 | ||
1151 | The printed representation of a vector consists of a left square | |
1152 | bracket, the elements, and a right square bracket. This is also the | |
1153 | read syntax. Like numbers and strings, vectors are considered constants | |
1154 | for evaluation. | |
1155 | ||
1156 | @example | |
1157 | [1 "two" (three)] ; @r{A vector of three elements.} | |
1158 | @result{} [1 "two" (three)] | |
1159 | @end example | |
1160 | ||
1161 | @xref{Vectors}, for functions that work with vectors. | |
1162 | ||
1163 | @node Char-Table Type | |
1164 | @subsection Char-Table Type | |
1165 | ||
1166 | A @dfn{char-table} is a one-dimensional array of elements of any type, | |
1167 | indexed by character codes. Char-tables have certain extra features to | |
1168 | make them more useful for many jobs that involve assigning information | |
1169 | to character codes---for example, a char-table can have a parent to | |
1170 | inherit from, a default value, and a small number of extra slots to use for | |
1171 | special purposes. A char-table can also specify a single value for | |
1172 | a whole character set. | |
1173 | ||
1174 | The printed representation of a char-table is like a vector | |
1175 | except that there is an extra @samp{#^} at the beginning. | |
1176 | ||
1177 | @xref{Char-Tables}, for special functions to operate on char-tables. | |
1178 | Uses of char-tables include: | |
1179 | ||
1180 | @itemize @bullet | |
1181 | @item | |
1182 | Case tables (@pxref{Case Tables}). | |
1183 | ||
1184 | @item | |
1185 | Character category tables (@pxref{Categories}). | |
1186 | ||
1187 | @item | |
1188 | Display tables (@pxref{Display Tables}). | |
1189 | ||
1190 | @item | |
1191 | Syntax tables (@pxref{Syntax Tables}). | |
1192 | @end itemize | |
1193 | ||
1194 | @node Bool-Vector Type | |
1195 | @subsection Bool-Vector Type | |
1196 | ||
96b1842d CY |
1197 | A @dfn{bool-vector} is a one-dimensional array whose elements must |
1198 | be @code{t} or @code{nil}. | |
b8d4c8d0 GM |
1199 | |
1200 | The printed representation of a bool-vector is like a string, except | |
1201 | that it begins with @samp{#&} followed by the length. The string | |
1202 | constant that follows actually specifies the contents of the bool-vector | |
1203 | as a bitmap---each ``character'' in the string contains 8 bits, which | |
1204 | specify the next 8 elements of the bool-vector (1 stands for @code{t}, | |
1205 | and 0 for @code{nil}). The least significant bits of the character | |
1206 | correspond to the lowest indices in the bool-vector. | |
1207 | ||
1208 | @example | |
1209 | (make-bool-vector 3 t) | |
1210 | @result{} #&3"^G" | |
1211 | (make-bool-vector 3 nil) | |
1212 | @result{} #&3"^@@" | |
1213 | @end example | |
1214 | ||
1215 | @noindent | |
1216 | These results make sense, because the binary code for @samp{C-g} is | |
1217 | 111 and @samp{C-@@} is the character with code 0. | |
1218 | ||
1219 | If the length is not a multiple of 8, the printed representation | |
1220 | shows extra elements, but these extras really make no difference. For | |
1221 | instance, in the next example, the two bool-vectors are equal, because | |
1222 | only the first 3 bits are used: | |
1223 | ||
1224 | @example | |
1225 | (equal #&3"\377" #&3"\007") | |
1226 | @result{} t | |
1227 | @end example | |
1228 | ||
1229 | @node Hash Table Type | |
1230 | @subsection Hash Table Type | |
1231 | ||
1232 | A hash table is a very fast kind of lookup table, somewhat like an | |
1233 | alist in that it maps keys to corresponding values, but much faster. | |
16d1ff5f CY |
1234 | The printed representation of a hash table specifies its properties |
1235 | and contents, like this: | |
b8d4c8d0 GM |
1236 | |
1237 | @example | |
1238 | (make-hash-table) | |
16d1ff5f CY |
1239 | @result{} #s(hash-table size 65 test eql rehash-size 1.5 |
1240 | rehash-threshold 0.8 data ()) | |
b8d4c8d0 GM |
1241 | @end example |
1242 | ||
16d1ff5f CY |
1243 | @noindent |
1244 | @xref{Hash Tables}, for more information about hash tables. | |
1245 | ||
b8d4c8d0 GM |
1246 | @node Function Type |
1247 | @subsection Function Type | |
1248 | ||
1249 | Lisp functions are executable code, just like functions in other | |
1250 | programming languages. In Lisp, unlike most languages, functions are | |
1251 | also Lisp objects. A non-compiled function in Lisp is a lambda | |
1252 | expression: that is, a list whose first element is the symbol | |
1253 | @code{lambda} (@pxref{Lambda Expressions}). | |
1254 | ||
1255 | In most programming languages, it is impossible to have a function | |
1256 | without a name. In Lisp, a function has no intrinsic name. A lambda | |
1257 | expression can be called as a function even though it has no name; to | |
1258 | emphasize this, we also call it an @dfn{anonymous function} | |
1259 | (@pxref{Anonymous Functions}). A named function in Lisp is just a | |
1260 | symbol with a valid function in its function cell (@pxref{Defining | |
1261 | Functions}). | |
1262 | ||
1263 | Most of the time, functions are called when their names are written in | |
1264 | Lisp expressions in Lisp programs. However, you can construct or obtain | |
1265 | a function object at run time and then call it with the primitive | |
1266 | functions @code{funcall} and @code{apply}. @xref{Calling Functions}. | |
1267 | ||
1268 | @node Macro Type | |
1269 | @subsection Macro Type | |
1270 | ||
1271 | A @dfn{Lisp macro} is a user-defined construct that extends the Lisp | |
1272 | language. It is represented as an object much like a function, but with | |
1273 | different argument-passing semantics. A Lisp macro has the form of a | |
1274 | list whose first element is the symbol @code{macro} and whose @sc{cdr} | |
1275 | is a Lisp function object, including the @code{lambda} symbol. | |
1276 | ||
1277 | Lisp macro objects are usually defined with the built-in | |
1278 | @code{defmacro} function, but any list that begins with @code{macro} is | |
1279 | a macro as far as Emacs is concerned. @xref{Macros}, for an explanation | |
1280 | of how to write a macro. | |
1281 | ||
1282 | @strong{Warning}: Lisp macros and keyboard macros (@pxref{Keyboard | |
1283 | Macros}) are entirely different things. When we use the word ``macro'' | |
1284 | without qualification, we mean a Lisp macro, not a keyboard macro. | |
1285 | ||
1286 | @node Primitive Function Type | |
1287 | @subsection Primitive Function Type | |
45e46036 | 1288 | @cindex primitive function |
b8d4c8d0 GM |
1289 | |
1290 | A @dfn{primitive function} is a function callable from Lisp but | |
1291 | written in the C programming language. Primitive functions are also | |
1292 | called @dfn{subrs} or @dfn{built-in functions}. (The word ``subr'' is | |
1293 | derived from ``subroutine.'') Most primitive functions evaluate all | |
1294 | their arguments when they are called. A primitive function that does | |
1295 | not evaluate all its arguments is called a @dfn{special form} | |
1296 | (@pxref{Special Forms}).@refill | |
1297 | ||
1298 | It does not matter to the caller of a function whether the function is | |
1299 | primitive. However, this does matter if you try to redefine a primitive | |
1300 | with a function written in Lisp. The reason is that the primitive | |
1301 | function may be called directly from C code. Calls to the redefined | |
1302 | function from Lisp will use the new definition, but calls from C code | |
1303 | may still use the built-in definition. Therefore, @strong{we discourage | |
1304 | redefinition of primitive functions}. | |
1305 | ||
1306 | The term @dfn{function} refers to all Emacs functions, whether written | |
1307 | in Lisp or C. @xref{Function Type}, for information about the | |
1308 | functions written in Lisp. | |
1309 | ||
1310 | Primitive functions have no read syntax and print in hash notation | |
1311 | with the name of the subroutine. | |
1312 | ||
1313 | @example | |
1314 | @group | |
1315 | (symbol-function 'car) ; @r{Access the function cell} | |
1316 | ; @r{of the symbol.} | |
1317 | @result{} #<subr car> | |
1318 | (subrp (symbol-function 'car)) ; @r{Is this a primitive function?} | |
1319 | @result{} t ; @r{Yes.} | |
1320 | @end group | |
1321 | @end example | |
1322 | ||
1323 | @node Byte-Code Type | |
1324 | @subsection Byte-Code Function Type | |
1325 | ||
25dec365 CY |
1326 | @dfn{Byte-code function objects} are produced by byte-compiling Lisp |
1327 | code (@pxref{Byte Compilation}). Internally, a byte-code function | |
1328 | object is much like a vector; however, the evaluator handles this data | |
1329 | type specially when it appears in a function call. @xref{Byte-Code | |
1330 | Objects}. | |
b8d4c8d0 GM |
1331 | |
1332 | The printed representation and read syntax for a byte-code function | |
1333 | object is like that for a vector, with an additional @samp{#} before the | |
1334 | opening @samp{[}. | |
1335 | ||
1336 | @node Autoload Type | |
1337 | @subsection Autoload Type | |
1338 | ||
1339 | An @dfn{autoload object} is a list whose first element is the symbol | |
1340 | @code{autoload}. It is stored as the function definition of a symbol, | |
1341 | where it serves as a placeholder for the real definition. The autoload | |
1342 | object says that the real definition is found in a file of Lisp code | |
1343 | that should be loaded when necessary. It contains the name of the file, | |
1344 | plus some other information about the real definition. | |
1345 | ||
1346 | After the file has been loaded, the symbol should have a new function | |
1347 | definition that is not an autoload object. The new definition is then | |
1348 | called as if it had been there to begin with. From the user's point of | |
1349 | view, the function call works as expected, using the function definition | |
1350 | in the loaded file. | |
1351 | ||
1352 | An autoload object is usually created with the function | |
1353 | @code{autoload}, which stores the object in the function cell of a | |
1354 | symbol. @xref{Autoload}, for more details. | |
1355 | ||
1356 | @node Editing Types | |
1357 | @section Editing Types | |
1358 | @cindex editing types | |
1359 | ||
1360 | The types in the previous section are used for general programming | |
1361 | purposes, and most of them are common to most Lisp dialects. Emacs Lisp | |
1362 | provides several additional data types for purposes connected with | |
1363 | editing. | |
1364 | ||
1365 | @menu | |
1366 | * Buffer Type:: The basic object of editing. | |
1367 | * Marker Type:: A position in a buffer. | |
1368 | * Window Type:: Buffers are displayed in windows. | |
eba64e97 EZ |
1369 | * Frame Type:: Windows subdivide frames. |
1370 | * Terminal Type:: A terminal device displays frames. | |
b8d4c8d0 GM |
1371 | * Window Configuration Type:: Recording the way a frame is subdivided. |
1372 | * Frame Configuration Type:: Recording the status of all frames. | |
6fdbd4c6 | 1373 | * Process Type:: A subprocess of Emacs running on the underlying OS. |
b8d4c8d0 GM |
1374 | * Stream Type:: Receive or send characters. |
1375 | * Keymap Type:: What function a keystroke invokes. | |
1376 | * Overlay Type:: How an overlay is represented. | |
2bd1f99a | 1377 | * Font Type:: Fonts for displaying text. |
b8d4c8d0 GM |
1378 | @end menu |
1379 | ||
1380 | @node Buffer Type | |
1381 | @subsection Buffer Type | |
1382 | ||
1383 | A @dfn{buffer} is an object that holds text that can be edited | |
1384 | (@pxref{Buffers}). Most buffers hold the contents of a disk file | |
1385 | (@pxref{Files}) so they can be edited, but some are used for other | |
1386 | purposes. Most buffers are also meant to be seen by the user, and | |
2bd1f99a CY |
1387 | therefore displayed, at some time, in a window (@pxref{Windows}). But |
1388 | a buffer need not be displayed in any window. Each buffer has a | |
1389 | designated position called @dfn{point} (@pxref{Positions}); most | |
1390 | editing commands act on the contents of the current buffer in the | |
1391 | neighborhood of point. At any time, one buffer is the @dfn{current | |
1392 | buffer}. | |
b8d4c8d0 GM |
1393 | |
1394 | The contents of a buffer are much like a string, but buffers are not | |
1395 | used like strings in Emacs Lisp, and the available operations are | |
1396 | different. For example, you can insert text efficiently into an | |
1397 | existing buffer, altering the buffer's contents, whereas ``inserting'' | |
2bd1f99a CY |
1398 | text into a string requires concatenating substrings, and the result |
1399 | is an entirely new string object. | |
b8d4c8d0 | 1400 | |
2bd1f99a CY |
1401 | Many of the standard Emacs functions manipulate or test the |
1402 | characters in the current buffer; a whole chapter in this manual is | |
1403 | devoted to describing these functions (@pxref{Text}). | |
b8d4c8d0 GM |
1404 | |
1405 | Several other data structures are associated with each buffer: | |
1406 | ||
1407 | @itemize @bullet | |
1408 | @item | |
1409 | a local syntax table (@pxref{Syntax Tables}); | |
1410 | ||
1411 | @item | |
1412 | a local keymap (@pxref{Keymaps}); and, | |
1413 | ||
1414 | @item | |
1415 | a list of buffer-local variable bindings (@pxref{Buffer-Local Variables}). | |
1416 | ||
1417 | @item | |
1418 | overlays (@pxref{Overlays}). | |
1419 | ||
1420 | @item | |
1421 | text properties for the text in the buffer (@pxref{Text Properties}). | |
1422 | @end itemize | |
1423 | ||
1424 | @noindent | |
1425 | The local keymap and variable list contain entries that individually | |
1426 | override global bindings or values. These are used to customize the | |
1427 | behavior of programs in different buffers, without actually changing the | |
1428 | programs. | |
1429 | ||
1430 | A buffer may be @dfn{indirect}, which means it shares the text | |
1431 | of another buffer, but presents it differently. @xref{Indirect Buffers}. | |
1432 | ||
1433 | Buffers have no read syntax. They print in hash notation, showing the | |
1434 | buffer name. | |
1435 | ||
1436 | @example | |
1437 | @group | |
1438 | (current-buffer) | |
1439 | @result{} #<buffer objects.texi> | |
1440 | @end group | |
1441 | @end example | |
1442 | ||
1443 | @node Marker Type | |
1444 | @subsection Marker Type | |
1445 | ||
1446 | A @dfn{marker} denotes a position in a specific buffer. Markers | |
1447 | therefore have two components: one for the buffer, and one for the | |
1448 | position. Changes in the buffer's text automatically relocate the | |
1449 | position value as necessary to ensure that the marker always points | |
1450 | between the same two characters in the buffer. | |
1451 | ||
1452 | Markers have no read syntax. They print in hash notation, giving the | |
1453 | current character position and the name of the buffer. | |
1454 | ||
1455 | @example | |
1456 | @group | |
1457 | (point-marker) | |
1458 | @result{} #<marker at 10779 in objects.texi> | |
1459 | @end group | |
1460 | @end example | |
1461 | ||
1462 | @xref{Markers}, for information on how to test, create, copy, and move | |
1463 | markers. | |
1464 | ||
1465 | @node Window Type | |
1466 | @subsection Window Type | |
1467 | ||
1468 | A @dfn{window} describes the portion of the terminal screen that Emacs | |
1469 | uses to display a buffer. Every window has one associated buffer, whose | |
1470 | contents appear in the window. By contrast, a given buffer may appear | |
1471 | in one window, no window, or several windows. | |
1472 | ||
1473 | Though many windows may exist simultaneously, at any time one window | |
1474 | is designated the @dfn{selected window}. This is the window where the | |
1475 | cursor is (usually) displayed when Emacs is ready for a command. The | |
1476 | selected window usually displays the current buffer, but this is not | |
1477 | necessarily the case. | |
1478 | ||
1479 | Windows are grouped on the screen into frames; each window belongs to | |
1480 | one and only one frame. @xref{Frame Type}. | |
1481 | ||
1482 | Windows have no read syntax. They print in hash notation, giving the | |
1483 | window number and the name of the buffer being displayed. The window | |
1484 | numbers exist to identify windows uniquely, since the buffer displayed | |
1485 | in any given window can change frequently. | |
1486 | ||
1487 | @example | |
1488 | @group | |
1489 | (selected-window) | |
1490 | @result{} #<window 1 on objects.texi> | |
1491 | @end group | |
1492 | @end example | |
1493 | ||
1494 | @xref{Windows}, for a description of the functions that work on windows. | |
1495 | ||
1496 | @node Frame Type | |
1497 | @subsection Frame Type | |
1498 | ||
1499 | A @dfn{frame} is a screen area that contains one or more Emacs | |
1500 | windows; we also use the term ``frame'' to refer to the Lisp object | |
1501 | that Emacs uses to refer to the screen area. | |
1502 | ||
1503 | Frames have no read syntax. They print in hash notation, giving the | |
1504 | frame's title, plus its address in core (useful to identify the frame | |
1505 | uniquely). | |
1506 | ||
1507 | @example | |
1508 | @group | |
1509 | (selected-frame) | |
1510 | @result{} #<frame emacs@@psilocin.gnu.org 0xdac80> | |
1511 | @end group | |
1512 | @end example | |
1513 | ||
1514 | @xref{Frames}, for a description of the functions that work on frames. | |
1515 | ||
eba64e97 EZ |
1516 | @node Terminal Type |
1517 | @subsection Terminal Type | |
1518 | @cindex terminal type | |
1519 | ||
1520 | A @dfn{terminal} is a device capable of displaying one or more | |
1521 | Emacs frames (@pxref{Frame Type}). | |
1522 | ||
1523 | Terminals have no read syntax. They print in hash notation giving | |
1524 | the terminal's ordinal number and its TTY device file name. | |
1525 | ||
1526 | @example | |
1527 | @group | |
1528 | (get-device-terminal nil) | |
1529 | @result{} #<terminal 1 on /dev/tty> | |
1530 | @end group | |
1531 | @end example | |
1532 | ||
1533 | @c FIXME: add an xref to where terminal-related primitives are described. | |
1534 | ||
b8d4c8d0 GM |
1535 | @node Window Configuration Type |
1536 | @subsection Window Configuration Type | |
1537 | @cindex window layout in a frame | |
1538 | ||
1539 | A @dfn{window configuration} stores information about the positions, | |
1540 | sizes, and contents of the windows in a frame, so you can recreate the | |
1541 | same arrangement of windows later. | |
1542 | ||
1543 | Window configurations do not have a read syntax; their print syntax | |
1544 | looks like @samp{#<window-configuration>}. @xref{Window | |
1545 | Configurations}, for a description of several functions related to | |
1546 | window configurations. | |
1547 | ||
1548 | @node Frame Configuration Type | |
1549 | @subsection Frame Configuration Type | |
1550 | @cindex screen layout | |
1551 | @cindex window layout, all frames | |
1552 | ||
1553 | A @dfn{frame configuration} stores information about the positions, | |
2bd1f99a CY |
1554 | sizes, and contents of the windows in all frames. It is not a |
1555 | primitive type---it is actually a list whose @sc{car} is | |
1556 | @code{frame-configuration} and whose @sc{cdr} is an alist. Each alist | |
1557 | element describes one frame, which appears as the @sc{car} of that | |
1558 | element. | |
b8d4c8d0 GM |
1559 | |
1560 | @xref{Frame Configurations}, for a description of several functions | |
1561 | related to frame configurations. | |
1562 | ||
1563 | @node Process Type | |
1564 | @subsection Process Type | |
1565 | ||
1566 | The word @dfn{process} usually means a running program. Emacs itself | |
1567 | runs in a process of this sort. However, in Emacs Lisp, a process is a | |
1568 | Lisp object that designates a subprocess created by the Emacs process. | |
1569 | Programs such as shells, GDB, ftp, and compilers, running in | |
1570 | subprocesses of Emacs, extend the capabilities of Emacs. | |
1571 | ||
1572 | An Emacs subprocess takes textual input from Emacs and returns textual | |
1573 | output to Emacs for further manipulation. Emacs can also send signals | |
1574 | to the subprocess. | |
1575 | ||
1576 | Process objects have no read syntax. They print in hash notation, | |
1577 | giving the name of the process: | |
1578 | ||
1579 | @example | |
1580 | @group | |
1581 | (process-list) | |
1582 | @result{} (#<process shell>) | |
1583 | @end group | |
1584 | @end example | |
1585 | ||
1586 | @xref{Processes}, for information about functions that create, delete, | |
1587 | return information about, send input or signals to, and receive output | |
1588 | from processes. | |
1589 | ||
1590 | @node Stream Type | |
1591 | @subsection Stream Type | |
1592 | ||
1593 | A @dfn{stream} is an object that can be used as a source or sink for | |
1594 | characters---either to supply characters for input or to accept them as | |
1595 | output. Many different types can be used this way: markers, buffers, | |
1596 | strings, and functions. Most often, input streams (character sources) | |
1597 | obtain characters from the keyboard, a buffer, or a file, and output | |
1598 | streams (character sinks) send characters to a buffer, such as a | |
1599 | @file{*Help*} buffer, or to the echo area. | |
1600 | ||
1601 | The object @code{nil}, in addition to its other meanings, may be used | |
1602 | as a stream. It stands for the value of the variable | |
1603 | @code{standard-input} or @code{standard-output}. Also, the object | |
1604 | @code{t} as a stream specifies input using the minibuffer | |
1605 | (@pxref{Minibuffers}) or output in the echo area (@pxref{The Echo | |
1606 | Area}). | |
1607 | ||
1608 | Streams have no special printed representation or read syntax, and | |
1609 | print as whatever primitive type they are. | |
1610 | ||
1611 | @xref{Read and Print}, for a description of functions | |
1612 | related to streams, including parsing and printing functions. | |
1613 | ||
1614 | @node Keymap Type | |
1615 | @subsection Keymap Type | |
1616 | ||
1617 | A @dfn{keymap} maps keys typed by the user to commands. This mapping | |
1618 | controls how the user's command input is executed. A keymap is actually | |
1619 | a list whose @sc{car} is the symbol @code{keymap}. | |
1620 | ||
1621 | @xref{Keymaps}, for information about creating keymaps, handling prefix | |
1622 | keys, local as well as global keymaps, and changing key bindings. | |
1623 | ||
1624 | @node Overlay Type | |
1625 | @subsection Overlay Type | |
1626 | ||
1627 | An @dfn{overlay} specifies properties that apply to a part of a | |
1628 | buffer. Each overlay applies to a specified range of the buffer, and | |
1629 | contains a property list (a list whose elements are alternating property | |
1630 | names and values). Overlay properties are used to present parts of the | |
1631 | buffer temporarily in a different display style. Overlays have no read | |
1632 | syntax, and print in hash notation, giving the buffer name and range of | |
1633 | positions. | |
1634 | ||
1635 | @xref{Overlays}, for how to create and use overlays. | |
1636 | ||
2bd1f99a CY |
1637 | @node Font Type |
1638 | @subsection Font Type | |
1639 | ||
1640 | A @dfn{font} specifies how to display text on a graphical terminal. | |
1641 | There are actually three separate font types---@dfn{font objects}, | |
1642 | @dfn{font specs}, and @dfn{font entities}---each of which has slightly | |
1643 | different properties. None of them have a read syntax; their print | |
1644 | syntax looks like @samp{#<font-object>}, @samp{#<font-spec>}, and | |
1645 | @samp{#<font-entity>} respectively. @xref{Low-Level Font}, for a | |
1646 | description of these Lisp objects. | |
1647 | ||
b8d4c8d0 GM |
1648 | @node Circular Objects |
1649 | @section Read Syntax for Circular Objects | |
1650 | @cindex circular structure, read syntax | |
1651 | @cindex shared structure, read syntax | |
1652 | @cindex @samp{#@var{n}=} read syntax | |
1653 | @cindex @samp{#@var{n}#} read syntax | |
1654 | ||
1655 | To represent shared or circular structures within a complex of Lisp | |
1656 | objects, you can use the reader constructs @samp{#@var{n}=} and | |
1657 | @samp{#@var{n}#}. | |
1658 | ||
1659 | Use @code{#@var{n}=} before an object to label it for later reference; | |
1660 | subsequently, you can use @code{#@var{n}#} to refer the same object in | |
1661 | another place. Here, @var{n} is some integer. For example, here is how | |
1662 | to make a list in which the first element recurs as the third element: | |
1663 | ||
1664 | @example | |
1665 | (#1=(a) b #1#) | |
1666 | @end example | |
1667 | ||
1668 | @noindent | |
1669 | This differs from ordinary syntax such as this | |
1670 | ||
1671 | @example | |
1672 | ((a) b (a)) | |
1673 | @end example | |
1674 | ||
1675 | @noindent | |
1676 | which would result in a list whose first and third elements | |
1677 | look alike but are not the same Lisp object. This shows the difference: | |
1678 | ||
1679 | @example | |
1680 | (prog1 nil | |
1681 | (setq x '(#1=(a) b #1#))) | |
1682 | (eq (nth 0 x) (nth 2 x)) | |
1683 | @result{} t | |
1684 | (setq x '((a) b (a))) | |
1685 | (eq (nth 0 x) (nth 2 x)) | |
1686 | @result{} nil | |
1687 | @end example | |
1688 | ||
1689 | You can also use the same syntax to make a circular structure, which | |
1690 | appears as an ``element'' within itself. Here is an example: | |
1691 | ||
1692 | @example | |
1693 | #1=(a #1#) | |
1694 | @end example | |
1695 | ||
1696 | @noindent | |
1697 | This makes a list whose second element is the list itself. | |
1698 | Here's how you can see that it really works: | |
1699 | ||
1700 | @example | |
1701 | (prog1 nil | |
1702 | (setq x '#1=(a #1#))) | |
1703 | (eq x (cadr x)) | |
1704 | @result{} t | |
1705 | @end example | |
1706 | ||
1707 | The Lisp printer can produce this syntax to record circular and shared | |
1708 | structure in a Lisp object, if you bind the variable @code{print-circle} | |
1709 | to a non-@code{nil} value. @xref{Output Variables}. | |
1710 | ||
1711 | @node Type Predicates | |
1712 | @section Type Predicates | |
1713 | @cindex type checking | |
1714 | @kindex wrong-type-argument | |
1715 | ||
1716 | The Emacs Lisp interpreter itself does not perform type checking on | |
1717 | the actual arguments passed to functions when they are called. It could | |
1718 | not do so, since function arguments in Lisp do not have declared data | |
1719 | types, as they do in other programming languages. It is therefore up to | |
1720 | the individual function to test whether each actual argument belongs to | |
1721 | a type that the function can use. | |
1722 | ||
1723 | All built-in functions do check the types of their actual arguments | |
1724 | when appropriate, and signal a @code{wrong-type-argument} error if an | |
1725 | argument is of the wrong type. For example, here is what happens if you | |
1726 | pass an argument to @code{+} that it cannot handle: | |
1727 | ||
1728 | @example | |
1729 | @group | |
1730 | (+ 2 'a) | |
1731 | @error{} Wrong type argument: number-or-marker-p, a | |
1732 | @end group | |
1733 | @end example | |
1734 | ||
1735 | @cindex type predicates | |
1736 | @cindex testing types | |
1737 | If you want your program to handle different types differently, you | |
1738 | must do explicit type checking. The most common way to check the type | |
1739 | of an object is to call a @dfn{type predicate} function. Emacs has a | |
1740 | type predicate for each type, as well as some predicates for | |
1741 | combinations of types. | |
1742 | ||
1743 | A type predicate function takes one argument; it returns @code{t} if | |
1744 | the argument belongs to the appropriate type, and @code{nil} otherwise. | |
1745 | Following a general Lisp convention for predicate functions, most type | |
1746 | predicates' names end with @samp{p}. | |
1747 | ||
1748 | Here is an example which uses the predicates @code{listp} to check for | |
1749 | a list and @code{symbolp} to check for a symbol. | |
1750 | ||
1751 | @example | |
1752 | (defun add-on (x) | |
1753 | (cond ((symbolp x) | |
1754 | ;; If X is a symbol, put it on LIST. | |
1755 | (setq list (cons x list))) | |
1756 | ((listp x) | |
1757 | ;; If X is a list, add its elements to LIST. | |
1758 | (setq list (append x list))) | |
1759 | (t | |
1760 | ;; We handle only symbols and lists. | |
1761 | (error "Invalid argument %s in add-on" x)))) | |
1762 | @end example | |
1763 | ||
1764 | Here is a table of predefined type predicates, in alphabetical order, | |
1765 | with references to further information. | |
1766 | ||
1767 | @table @code | |
1768 | @item atom | |
1769 | @xref{List-related Predicates, atom}. | |
1770 | ||
1771 | @item arrayp | |
1772 | @xref{Array Functions, arrayp}. | |
1773 | ||
1774 | @item bool-vector-p | |
1775 | @xref{Bool-Vectors, bool-vector-p}. | |
1776 | ||
1777 | @item bufferp | |
1778 | @xref{Buffer Basics, bufferp}. | |
1779 | ||
1780 | @item byte-code-function-p | |
1781 | @xref{Byte-Code Type, byte-code-function-p}. | |
1782 | ||
1783 | @item case-table-p | |
1784 | @xref{Case Tables, case-table-p}. | |
1785 | ||
1786 | @item char-or-string-p | |
1787 | @xref{Predicates for Strings, char-or-string-p}. | |
1788 | ||
1789 | @item char-table-p | |
1790 | @xref{Char-Tables, char-table-p}. | |
1791 | ||
1792 | @item commandp | |
1793 | @xref{Interactive Call, commandp}. | |
1794 | ||
1795 | @item consp | |
1796 | @xref{List-related Predicates, consp}. | |
1797 | ||
1021c761 CY |
1798 | @item custom-variable-p |
1799 | @xref{Variable Definitions, custom-variable-p}. | |
1800 | ||
b8d4c8d0 GM |
1801 | @item display-table-p |
1802 | @xref{Display Tables, display-table-p}. | |
1803 | ||
1804 | @item floatp | |
1805 | @xref{Predicates on Numbers, floatp}. | |
1806 | ||
2bd1f99a CY |
1807 | @item fontp |
1808 | @xref{Low-Level Font}. | |
1809 | ||
b8d4c8d0 GM |
1810 | @item frame-configuration-p |
1811 | @xref{Frame Configurations, frame-configuration-p}. | |
1812 | ||
1813 | @item frame-live-p | |
1814 | @xref{Deleting Frames, frame-live-p}. | |
1815 | ||
1816 | @item framep | |
1817 | @xref{Frames, framep}. | |
1818 | ||
1819 | @item functionp | |
1820 | @xref{Functions, functionp}. | |
1821 | ||
1822 | @item hash-table-p | |
1823 | @xref{Other Hash, hash-table-p}. | |
1824 | ||
1825 | @item integer-or-marker-p | |
1826 | @xref{Predicates on Markers, integer-or-marker-p}. | |
1827 | ||
1828 | @item integerp | |
1829 | @xref{Predicates on Numbers, integerp}. | |
1830 | ||
1831 | @item keymapp | |
1832 | @xref{Creating Keymaps, keymapp}. | |
1833 | ||
1834 | @item keywordp | |
1835 | @xref{Constant Variables}. | |
1836 | ||
1837 | @item listp | |
1838 | @xref{List-related Predicates, listp}. | |
1839 | ||
1840 | @item markerp | |
1841 | @xref{Predicates on Markers, markerp}. | |
1842 | ||
1843 | @item wholenump | |
1844 | @xref{Predicates on Numbers, wholenump}. | |
1845 | ||
1846 | @item nlistp | |
1847 | @xref{List-related Predicates, nlistp}. | |
1848 | ||
1849 | @item numberp | |
1850 | @xref{Predicates on Numbers, numberp}. | |
1851 | ||
1852 | @item number-or-marker-p | |
1853 | @xref{Predicates on Markers, number-or-marker-p}. | |
1854 | ||
1855 | @item overlayp | |
1856 | @xref{Overlays, overlayp}. | |
1857 | ||
1858 | @item processp | |
1859 | @xref{Processes, processp}. | |
1860 | ||
1861 | @item sequencep | |
1862 | @xref{Sequence Functions, sequencep}. | |
1863 | ||
1864 | @item stringp | |
1865 | @xref{Predicates for Strings, stringp}. | |
1866 | ||
1867 | @item subrp | |
1868 | @xref{Function Cells, subrp}. | |
1869 | ||
1870 | @item symbolp | |
1871 | @xref{Symbols, symbolp}. | |
1872 | ||
1873 | @item syntax-table-p | |
1874 | @xref{Syntax Tables, syntax-table-p}. | |
1875 | ||
b8d4c8d0 GM |
1876 | @item vectorp |
1877 | @xref{Vectors, vectorp}. | |
1878 | ||
1879 | @item window-configuration-p | |
1880 | @xref{Window Configurations, window-configuration-p}. | |
1881 | ||
1882 | @item window-live-p | |
1883 | @xref{Deleting Windows, window-live-p}. | |
1884 | ||
1885 | @item windowp | |
1886 | @xref{Basic Windows, windowp}. | |
1887 | ||
1888 | @item booleanp | |
1889 | @xref{nil and t, booleanp}. | |
1890 | ||
1891 | @item string-or-null-p | |
1892 | @xref{Predicates for Strings, string-or-null-p}. | |
1893 | @end table | |
1894 | ||
1895 | The most general way to check the type of an object is to call the | |
1896 | function @code{type-of}. Recall that each object belongs to one and | |
1897 | only one primitive type; @code{type-of} tells you which one (@pxref{Lisp | |
1898 | Data Types}). But @code{type-of} knows nothing about non-primitive | |
1899 | types. In most cases, it is more convenient to use type predicates than | |
1900 | @code{type-of}. | |
1901 | ||
1902 | @defun type-of object | |
1903 | This function returns a symbol naming the primitive type of | |
2bd1f99a CY |
1904 | @var{object}. The value is one of the symbols @code{bool-vector}, |
1905 | @code{buffer}, @code{char-table}, @code{compiled-function}, | |
1906 | @code{cons}, @code{float}, @code{font-entity}, @code{font-object}, | |
1907 | @code{font-spec}, @code{frame}, @code{hash-table}, @code{integer}, | |
1908 | @code{marker}, @code{overlay}, @code{process}, @code{string}, | |
1909 | @code{subr}, @code{symbol}, @code{vector}, @code{window}, or | |
b8d4c8d0 GM |
1910 | @code{window-configuration}. |
1911 | ||
1912 | @example | |
1913 | (type-of 1) | |
1914 | @result{} integer | |
1915 | @group | |
1916 | (type-of 'nil) | |
1917 | @result{} symbol | |
1918 | (type-of '()) ; @r{@code{()} is @code{nil}.} | |
1919 | @result{} symbol | |
1920 | (type-of '(x)) | |
1921 | @result{} cons | |
1922 | @end group | |
1923 | @end example | |
1924 | @end defun | |
1925 | ||
1926 | @node Equality Predicates | |
1927 | @section Equality Predicates | |
1928 | @cindex equality | |
1929 | ||
fead402d CY |
1930 | Here we describe functions that test for equality between two |
1931 | objects. Other functions test equality of contents between objects of | |
1932 | specific types, e.g.@: strings. For these predicates, see the | |
1933 | appropriate chapter describing the data type. | |
b8d4c8d0 GM |
1934 | |
1935 | @defun eq object1 object2 | |
1936 | This function returns @code{t} if @var{object1} and @var{object2} are | |
fead402d CY |
1937 | the same object, and @code{nil} otherwise. |
1938 | ||
1939 | If @var{object1} and @var{object2} are integers with the same value, | |
1940 | they are considered to be the same object (i.e.@: @code{eq} returns | |
1941 | @code{t}). If @var{object1} and @var{object2} are symbols with the | |
1942 | same name, they are normally the same object---but see @ref{Creating | |
1943 | Symbols} for exceptions. For other types (e.g.@: lists, vectors, | |
1944 | strings), two arguments with the same contents or elements are not | |
1945 | necessarily @code{eq} to each other: they are @code{eq} only if they | |
1946 | are the same object, meaning that a change in the contents of one will | |
1947 | be reflected by the same change in the contents of the other. | |
b8d4c8d0 GM |
1948 | |
1949 | @example | |
1950 | @group | |
1951 | (eq 'foo 'foo) | |
1952 | @result{} t | |
1953 | @end group | |
1954 | ||
1955 | @group | |
1956 | (eq 456 456) | |
1957 | @result{} t | |
1958 | @end group | |
1959 | ||
1960 | @group | |
1961 | (eq "asdf" "asdf") | |
1962 | @result{} nil | |
1963 | @end group | |
1964 | ||
f2b480f4 RS |
1965 | @group |
1966 | (eq "" "") | |
1967 | @result{} t | |
1968 | ;; @r{This exception occurs because Emacs Lisp} | |
1969 | ;; @r{makes just one multibyte empty string, to save space.} | |
1970 | @end group | |
1971 | ||
b8d4c8d0 GM |
1972 | @group |
1973 | (eq '(1 (2 (3))) '(1 (2 (3)))) | |
1974 | @result{} nil | |
1975 | @end group | |
1976 | ||
1977 | @group | |
1978 | (setq foo '(1 (2 (3)))) | |
1979 | @result{} (1 (2 (3))) | |
1980 | (eq foo foo) | |
1981 | @result{} t | |
1982 | (eq foo '(1 (2 (3)))) | |
1983 | @result{} nil | |
1984 | @end group | |
1985 | ||
1986 | @group | |
1987 | (eq [(1 2) 3] [(1 2) 3]) | |
1988 | @result{} nil | |
1989 | @end group | |
1990 | ||
1991 | @group | |
1992 | (eq (point-marker) (point-marker)) | |
1993 | @result{} nil | |
1994 | @end group | |
1995 | @end example | |
1996 | ||
fead402d | 1997 | @noindent |
b8d4c8d0 GM |
1998 | The @code{make-symbol} function returns an uninterned symbol, distinct |
1999 | from the symbol that is used if you write the name in a Lisp expression. | |
2000 | Distinct symbols with the same name are not @code{eq}. @xref{Creating | |
2001 | Symbols}. | |
2002 | ||
2003 | @example | |
2004 | @group | |
2005 | (eq (make-symbol "foo") 'foo) | |
2006 | @result{} nil | |
2007 | @end group | |
2008 | @end example | |
2009 | @end defun | |
2010 | ||
2011 | @defun equal object1 object2 | |
2012 | This function returns @code{t} if @var{object1} and @var{object2} have | |
fead402d CY |
2013 | equal components, and @code{nil} otherwise. Whereas @code{eq} tests |
2014 | if its arguments are the same object, @code{equal} looks inside | |
2015 | nonidentical arguments to see if their elements or contents are the | |
2016 | same. So, if two objects are @code{eq}, they are @code{equal}, but | |
2017 | the converse is not always true. | |
b8d4c8d0 GM |
2018 | |
2019 | @example | |
2020 | @group | |
2021 | (equal 'foo 'foo) | |
2022 | @result{} t | |
2023 | @end group | |
2024 | ||
2025 | @group | |
2026 | (equal 456 456) | |
2027 | @result{} t | |
2028 | @end group | |
2029 | ||
2030 | @group | |
2031 | (equal "asdf" "asdf") | |
2032 | @result{} t | |
2033 | @end group | |
2034 | @group | |
2035 | (eq "asdf" "asdf") | |
2036 | @result{} nil | |
2037 | @end group | |
2038 | ||
2039 | @group | |
2040 | (equal '(1 (2 (3))) '(1 (2 (3)))) | |
2041 | @result{} t | |
2042 | @end group | |
2043 | @group | |
2044 | (eq '(1 (2 (3))) '(1 (2 (3)))) | |
2045 | @result{} nil | |
2046 | @end group | |
2047 | ||
2048 | @group | |
2049 | (equal [(1 2) 3] [(1 2) 3]) | |
2050 | @result{} t | |
2051 | @end group | |
2052 | @group | |
2053 | (eq [(1 2) 3] [(1 2) 3]) | |
2054 | @result{} nil | |
2055 | @end group | |
2056 | ||
2057 | @group | |
2058 | (equal (point-marker) (point-marker)) | |
2059 | @result{} t | |
2060 | @end group | |
2061 | ||
2062 | @group | |
2063 | (eq (point-marker) (point-marker)) | |
2064 | @result{} nil | |
2065 | @end group | |
2066 | @end example | |
2067 | ||
2068 | Comparison of strings is case-sensitive, but does not take account of | |
fead402d CY |
2069 | text properties---it compares only the characters in the strings. |
2070 | @xref{Text Properties}. Use @code{equal-including-properties} to also | |
2071 | compare text properties. For technical reasons, a unibyte string and | |
2072 | a multibyte string are @code{equal} if and only if they contain the | |
2073 | same sequence of character codes and all these codes are either in the | |
2074 | range 0 through 127 (@acronym{ASCII}) or 160 through 255 | |
2075 | (@code{eight-bit-graphic}). (@pxref{Text Representations}). | |
b8d4c8d0 GM |
2076 | |
2077 | @example | |
2078 | @group | |
2079 | (equal "asdf" "ASDF") | |
2080 | @result{} nil | |
2081 | @end group | |
2082 | @end example | |
2083 | ||
2084 | However, two distinct buffers are never considered @code{equal}, even if | |
2085 | their textual contents are the same. | |
2086 | @end defun | |
2087 | ||
2088 | The test for equality is implemented recursively; for example, given | |
2089 | two cons cells @var{x} and @var{y}, @code{(equal @var{x} @var{y})} | |
2090 | returns @code{t} if and only if both the expressions below return | |
2091 | @code{t}: | |
2092 | ||
2093 | @example | |
2094 | (equal (car @var{x}) (car @var{y})) | |
2095 | (equal (cdr @var{x}) (cdr @var{y})) | |
2096 | @end example | |
2097 | ||
2098 | Because of this recursive method, circular lists may therefore cause | |
2099 | infinite recursion (leading to an error). | |
2100 | ||
46c0aa17 GM |
2101 | @defun equal-including-properties object1 object2 |
2102 | This function behaves like @code{equal} in all cases but also requires | |
2103 | that for two strings to be equal, they have the same text properties. | |
2104 | ||
2105 | @example | |
2106 | @group | |
2107 | (equal "asdf" (propertize "asdf" '(asdf t))) | |
2108 | @result{} t | |
2109 | @end group | |
2110 | @group | |
2111 | (equal-including-properties "asdf" | |
2112 | (propertize "asdf" '(asdf t))) | |
2113 | @result{} nil | |
2114 | @end group | |
2115 | @end example | |
2116 | @end defun |