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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
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3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 2002, 2003, 2004, |
4 | @c 2005 Free Software Foundation, Inc. | |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/compile | |
a9f0a989 | 7 | @node Byte Compilation, Advising Functions, Loading, Top |
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8 | @chapter Byte Compilation |
9 | @cindex byte-code | |
10 | @cindex compilation | |
11 | ||
969fe9b5 | 12 | Emacs Lisp has a @dfn{compiler} that translates functions written |
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13 | in Lisp into a special representation called @dfn{byte-code} that can be |
14 | executed more efficiently. The compiler replaces Lisp function | |
15 | definitions with byte-code. When a byte-code function is called, its | |
16 | definition is evaluated by the @dfn{byte-code interpreter}. | |
17 | ||
18 | Because the byte-compiled code is evaluated by the byte-code | |
19 | interpreter, instead of being executed directly by the machine's | |
20 | hardware (as true compiled code is), byte-code is completely | |
21 | transportable from machine to machine without recompilation. It is not, | |
22 | however, as fast as true compiled code. | |
23 | ||
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24 | Compiling a Lisp file with the Emacs byte compiler always reads the |
25 | file as multibyte text, even if Emacs was started with @samp{--unibyte}, | |
26 | unless the file specifies otherwise. This is so that compilation gives | |
27 | results compatible with running the same file without compilation. | |
28 | @xref{Loading Non-ASCII}. | |
29 | ||
53f60086 | 30 | In general, any version of Emacs can run byte-compiled code produced |
b57bdd74 | 31 | by recent earlier versions of Emacs, but the reverse is not true. |
53f60086 | 32 | |
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33 | @vindex no-byte-compile |
34 | If you do not want a Lisp file to be compiled, ever, put a file-local | |
35 | variable binding for @code{no-byte-compile} into it, like this: | |
36 | ||
37 | @example | |
38 | ;; -*-no-byte-compile: t; -*- | |
39 | @end example | |
40 | ||
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41 | @xref{Compilation Errors}, for how to investigate errors occurring in |
42 | byte compilation. | |
43 | ||
44 | @menu | |
a0acfc98 | 45 | * Speed of Byte-Code:: An example of speedup from byte compilation. |
53f60086 | 46 | * Compilation Functions:: Byte compilation functions. |
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47 | * Docs and Compilation:: Dynamic loading of documentation strings. |
48 | * Dynamic Loading:: Dynamic loading of individual functions. | |
53f60086 | 49 | * Eval During Compile:: Code to be evaluated when you compile. |
d7810bda | 50 | * Compiler Errors:: Handling compiler error messages. |
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51 | * Byte-Code Objects:: The data type used for byte-compiled functions. |
52 | * Disassembly:: Disassembling byte-code; how to read byte-code. | |
53 | @end menu | |
54 | ||
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55 | @node Speed of Byte-Code |
56 | @section Performance of Byte-Compiled Code | |
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57 | |
58 | A byte-compiled function is not as efficient as a primitive function | |
59 | written in C, but runs much faster than the version written in Lisp. | |
a0acfc98 | 60 | Here is an example: |
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61 | |
62 | @example | |
63 | @group | |
64 | (defun silly-loop (n) | |
65 | "Return time before and after N iterations of a loop." | |
66 | (let ((t1 (current-time-string))) | |
177c0ea7 | 67 | (while (> (setq n (1- n)) |
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68 | 0)) |
69 | (list t1 (current-time-string)))) | |
70 | @result{} silly-loop | |
71 | @end group | |
72 | ||
73 | @group | |
74 | (silly-loop 100000) | |
a0acfc98 RS |
75 | @result{} ("Fri Mar 18 17:25:57 1994" |
76 | "Fri Mar 18 17:26:28 1994") ; @r{31 seconds} | |
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77 | @end group |
78 | ||
79 | @group | |
80 | (byte-compile 'silly-loop) | |
81 | @result{} @r{[Compiled code not shown]} | |
82 | @end group | |
83 | ||
84 | @group | |
85 | (silly-loop 100000) | |
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86 | @result{} ("Fri Mar 18 17:26:52 1994" |
87 | "Fri Mar 18 17:26:58 1994") ; @r{6 seconds} | |
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88 | @end group |
89 | @end example | |
90 | ||
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91 | In this example, the interpreted code required 31 seconds to run, |
92 | whereas the byte-compiled code required 6 seconds. These results are | |
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93 | representative, but actual results will vary greatly. |
94 | ||
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95 | @node Compilation Functions |
96 | @comment node-name, next, previous, up | |
97 | @section The Compilation Functions | |
98 | @cindex compilation functions | |
99 | ||
100 | You can byte-compile an individual function or macro definition with | |
101 | the @code{byte-compile} function. You can compile a whole file with | |
102 | @code{byte-compile-file}, or several files with | |
103 | @code{byte-recompile-directory} or @code{batch-byte-compile}. | |
104 | ||
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105 | The byte compiler produces error messages and warnings about each file |
106 | in a buffer called @samp{*Compile-Log*}. These report things in your | |
107 | program that suggest a problem but are not necessarily erroneous. | |
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108 | |
109 | @cindex macro compilation | |
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110 | Be careful when writing macro calls in files that you may someday |
111 | byte-compile. Macro calls are expanded when they are compiled, so the | |
112 | macros must already be defined for proper compilation. For more | |
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113 | details, see @ref{Compiling Macros}. If a program does not work the |
114 | same way when compiled as it does when interpreted, erroneous macro | |
115 | definitions are one likely cause (@pxref{Problems with Macros}). | |
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116 | Inline (@code{defsubst}) functions are less troublesome; if you |
117 | compile a call to such a function before its definition is known, the | |
118 | call will still work right, it will just run slower. | |
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119 | |
120 | Normally, compiling a file does not evaluate the file's contents or | |
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121 | load the file. But it does execute any @code{require} calls at top |
122 | level in the file. One way to ensure that necessary macro definitions | |
123 | are available during compilation is to require the file that defines | |
124 | them (@pxref{Named Features}). To avoid loading the macro definition files | |
125 | when someone @emph{runs} the compiled program, write | |
126 | @code{eval-when-compile} around the @code{require} calls (@pxref{Eval | |
127 | During Compile}). | |
a0acfc98 | 128 | |
53f60086 | 129 | @defun byte-compile symbol |
a0acfc98 | 130 | This function byte-compiles the function definition of @var{symbol}, |
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131 | replacing the previous definition with the compiled one. The function |
132 | definition of @var{symbol} must be the actual code for the function; | |
133 | i.e., the compiler does not follow indirection to another symbol. | |
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134 | @code{byte-compile} returns the new, compiled definition of |
135 | @var{symbol}. | |
136 | ||
22697dac | 137 | If @var{symbol}'s definition is a byte-code function object, |
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138 | @code{byte-compile} does nothing and returns @code{nil}. Lisp records |
139 | only one function definition for any symbol, and if that is already | |
140 | compiled, non-compiled code is not available anywhere. So there is no | |
141 | way to ``compile the same definition again.'' | |
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142 | |
143 | @example | |
144 | @group | |
145 | (defun factorial (integer) | |
146 | "Compute factorial of INTEGER." | |
147 | (if (= 1 integer) 1 | |
148 | (* integer (factorial (1- integer))))) | |
a0acfc98 | 149 | @result{} factorial |
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150 | @end group |
151 | ||
152 | @group | |
153 | (byte-compile 'factorial) | |
a0acfc98 | 154 | @result{} |
53f60086 RS |
155 | #[(integer) |
156 | "^H\301U\203^H^@@\301\207\302^H\303^HS!\"\207" | |
157 | [integer 1 * factorial] | |
158 | 4 "Compute factorial of INTEGER."] | |
159 | @end group | |
160 | @end example | |
161 | ||
162 | @noindent | |
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163 | The result is a byte-code function object. The string it contains is |
164 | the actual byte-code; each character in it is an instruction or an | |
165 | operand of an instruction. The vector contains all the constants, | |
166 | variable names and function names used by the function, except for | |
167 | certain primitives that are coded as special instructions. | |
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168 | |
169 | If the argument to @code{byte-compile} is a @code{lambda} expression, | |
170 | it returns the corresponding compiled code, but does not store | |
171 | it anywhere. | |
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172 | @end defun |
173 | ||
e75c1a57 | 174 | @deffn Command compile-defun &optional arg |
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175 | This command reads the defun containing point, compiles it, and |
176 | evaluates the result. If you use this on a defun that is actually a | |
177 | function definition, the effect is to install a compiled version of that | |
178 | function. | |
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179 | |
180 | @code{compile-defun} normally displays the result of evaluation in the | |
181 | echo area, but if @var{arg} is non-@code{nil}, it inserts the result | |
182 | in the current buffer after the form it compiled. | |
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183 | @end deffn |
184 | ||
e75c1a57 | 185 | @deffn Command byte-compile-file filename &optional load |
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186 | This function compiles a file of Lisp code named @var{filename} into a |
187 | file of byte-code. The output file's name is made by changing the | |
188 | @samp{.el} suffix into @samp{.elc}; if @var{filename} does not end in | |
189 | @samp{.el}, it adds @samp{.elc} to the end of @var{filename}. | |
53f60086 | 190 | |
a0acfc98 | 191 | Compilation works by reading the input file one form at a time. If it |
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192 | is a definition of a function or macro, the compiled function or macro |
193 | definition is written out. Other forms are batched together, then each | |
194 | batch is compiled, and written so that its compiled code will be | |
195 | executed when the file is read. All comments are discarded when the | |
196 | input file is read. | |
197 | ||
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198 | This command returns @code{t} if there were no errors and @code{nil} |
199 | otherwise. When called interactively, it prompts for the file name. | |
200 | ||
201 | If @var{load} is non-@code{nil}, this command loads the compiled file | |
202 | after compiling it. Interactively, @var{load} is the prefix argument. | |
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203 | |
204 | @example | |
205 | @group | |
206 | % ls -l push* | |
207 | -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el | |
208 | @end group | |
209 | ||
210 | @group | |
211 | (byte-compile-file "~/emacs/push.el") | |
212 | @result{} t | |
213 | @end group | |
214 | ||
215 | @group | |
216 | % ls -l push* | |
217 | -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el | |
218 | -rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc | |
219 | @end group | |
220 | @end example | |
221 | @end deffn | |
222 | ||
e75c1a57 | 223 | @deffn Command byte-recompile-directory directory &optional flag force |
53f60086 | 224 | @cindex library compilation |
e75c1a57 LT |
225 | This command recompiles every @samp{.el} file in @var{directory} (or |
226 | its subdirectories) that needs recompilation. A file needs | |
227 | recompilation if a @samp{.elc} file exists but is older than the | |
228 | @samp{.el} file. | |
229 | ||
230 | When a @samp{.el} file has no corresponding @samp{.elc} file, | |
231 | @var{flag} says what to do. If it is @code{nil}, this command ignores | |
232 | these files. If @var{flag} is 0, it compiles them. If it is neither | |
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233 | @code{nil} nor 0, it asks the user whether to compile each such file, |
234 | and asks about each subdirectory as well. | |
53f60086 | 235 | |
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236 | Interactively, @code{byte-recompile-directory} prompts for |
237 | @var{directory} and @var{flag} is the prefix argument. | |
53f60086 | 238 | |
e75c1a57 LT |
239 | If @var{force} is non-@code{nil}, this command recompiles every |
240 | @samp{.el} file that has a @samp{.elc} file. | |
241 | ||
242 | The returned value is unpredictable. | |
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243 | @end deffn |
244 | ||
e75c1a57 | 245 | @defun batch-byte-compile &optional noforce |
a0acfc98 RS |
246 | This function runs @code{byte-compile-file} on files specified on the |
247 | command line. This function must be used only in a batch execution of | |
248 | Emacs, as it kills Emacs on completion. An error in one file does not | |
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249 | prevent processing of subsequent files, but no output file will be |
250 | generated for it, and the Emacs process will terminate with a nonzero | |
251 | status code. | |
53f60086 | 252 | |
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253 | If @var{noforce} is non-@code{nil}, this function does not recompile |
254 | files that have an up-to-date @samp{.elc} file. | |
255 | ||
53f60086 RS |
256 | @example |
257 | % emacs -batch -f batch-byte-compile *.el | |
258 | @end example | |
259 | @end defun | |
260 | ||
261 | @defun byte-code code-string data-vector max-stack | |
262 | @cindex byte-code interpreter | |
a0acfc98 | 263 | This function actually interprets byte-code. A byte-compiled function |
53f60086 | 264 | is actually defined with a body that calls @code{byte-code}. Don't call |
969fe9b5 | 265 | this function yourself---only the byte compiler knows how to generate |
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266 | valid calls to this function. |
267 | ||
969fe9b5 RS |
268 | In Emacs version 18, byte-code was always executed by way of a call to |
269 | the function @code{byte-code}. Nowadays, byte-code is usually executed | |
270 | as part of a byte-code function object, and only rarely through an | |
271 | explicit call to @code{byte-code}. | |
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272 | @end defun |
273 | ||
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274 | @node Docs and Compilation |
275 | @section Documentation Strings and Compilation | |
276 | @cindex dynamic loading of documentation | |
277 | ||
278 | Functions and variables loaded from a byte-compiled file access their | |
279 | documentation strings dynamically from the file whenever needed. This | |
cc8c51f1 | 280 | saves space within Emacs, and makes loading faster because the |
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281 | documentation strings themselves need not be processed while loading the |
282 | file. Actual access to the documentation strings becomes slower as a | |
283 | result, but this normally is not enough to bother users. | |
284 | ||
285 | Dynamic access to documentation strings does have drawbacks: | |
286 | ||
287 | @itemize @bullet | |
288 | @item | |
289 | If you delete or move the compiled file after loading it, Emacs can no | |
290 | longer access the documentation strings for the functions and variables | |
291 | in the file. | |
292 | ||
293 | @item | |
294 | If you alter the compiled file (such as by compiling a new version), | |
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295 | then further access to documentation strings in this file will |
296 | probably give nonsense results. | |
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297 | @end itemize |
298 | ||
299 | If your site installs Emacs following the usual procedures, these | |
300 | problems will never normally occur. Installing a new version uses a new | |
301 | directory with a different name; as long as the old version remains | |
302 | installed, its files will remain unmodified in the places where they are | |
303 | expected to be. | |
304 | ||
89dbfd18 | 305 | However, if you have built Emacs yourself and use it from the |
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306 | directory where you built it, you will experience this problem |
307 | occasionally if you edit and recompile Lisp files. When it happens, you | |
308 | can cure the problem by reloading the file after recompiling it. | |
309 | ||
b57bdd74 RS |
310 | You can turn off this feature at compile time by setting |
311 | @code{byte-compile-dynamic-docstrings} to @code{nil}; this is useful | |
312 | mainly if you expect to change the file, and you want Emacs processes | |
313 | that have already loaded it to keep working when the file changes. | |
314 | You can do this globally, or for one source file by specifying a | |
315 | file-local binding for the variable. One way to do that is by adding | |
316 | this string to the file's first line: | |
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317 | |
318 | @example | |
319 | -*-byte-compile-dynamic-docstrings: nil;-*- | |
320 | @end example | |
321 | ||
322 | @defvar byte-compile-dynamic-docstrings | |
323 | If this is non-@code{nil}, the byte compiler generates compiled files | |
324 | that are set up for dynamic loading of documentation strings. | |
325 | @end defvar | |
326 | ||
327 | @cindex @samp{#@@@var{count}} | |
328 | @cindex @samp{#$} | |
329 | The dynamic documentation string feature writes compiled files that | |
330 | use a special Lisp reader construct, @samp{#@@@var{count}}. This | |
331 | construct skips the next @var{count} characters. It also uses the | |
332 | @samp{#$} construct, which stands for ``the name of this file, as a | |
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333 | string.'' It is usually best not to use these constructs in Lisp source |
334 | files, since they are not designed to be clear to humans reading the | |
335 | file. | |
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336 | |
337 | @node Dynamic Loading | |
338 | @section Dynamic Loading of Individual Functions | |
339 | ||
340 | @cindex dynamic loading of functions | |
341 | @cindex lazy loading | |
342 | When you compile a file, you can optionally enable the @dfn{dynamic | |
343 | function loading} feature (also known as @dfn{lazy loading}). With | |
344 | dynamic function loading, loading the file doesn't fully read the | |
345 | function definitions in the file. Instead, each function definition | |
346 | contains a place-holder which refers to the file. The first time each | |
347 | function is called, it reads the full definition from the file, to | |
348 | replace the place-holder. | |
349 | ||
350 | The advantage of dynamic function loading is that loading the file | |
351 | becomes much faster. This is a good thing for a file which contains | |
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352 | many separate user-callable functions, if using one of them does not |
353 | imply you will probably also use the rest. A specialized mode which | |
354 | provides many keyboard commands often has that usage pattern: a user may | |
355 | invoke the mode, but use only a few of the commands it provides. | |
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356 | |
357 | The dynamic loading feature has certain disadvantages: | |
358 | ||
359 | @itemize @bullet | |
360 | @item | |
361 | If you delete or move the compiled file after loading it, Emacs can no | |
362 | longer load the remaining function definitions not already loaded. | |
363 | ||
364 | @item | |
365 | If you alter the compiled file (such as by compiling a new version), | |
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366 | then trying to load any function not already loaded will usually yield |
367 | nonsense results. | |
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368 | @end itemize |
369 | ||
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370 | These problems will never happen in normal circumstances with |
371 | installed Emacs files. But they are quite likely to happen with Lisp | |
372 | files that you are changing. The easiest way to prevent these problems | |
373 | is to reload the new compiled file immediately after each recompilation. | |
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374 | |
375 | The byte compiler uses the dynamic function loading feature if the | |
376 | variable @code{byte-compile-dynamic} is non-@code{nil} at compilation | |
377 | time. Do not set this variable globally, since dynamic loading is | |
378 | desirable only for certain files. Instead, enable the feature for | |
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379 | specific source files with file-local variable bindings. For example, |
380 | you could do it by writing this text in the source file's first line: | |
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381 | |
382 | @example | |
383 | -*-byte-compile-dynamic: t;-*- | |
384 | @end example | |
385 | ||
386 | @defvar byte-compile-dynamic | |
387 | If this is non-@code{nil}, the byte compiler generates compiled files | |
388 | that are set up for dynamic function loading. | |
389 | @end defvar | |
390 | ||
391 | @defun fetch-bytecode function | |
76865de3 RS |
392 | If @var{function} is a byte-code function object, this immediately |
393 | finishes loading the byte code of @var{function} from its | |
394 | byte-compiled file, if it is not fully loaded already. Otherwise, | |
395 | it does nothing. It always returns @var{function}. | |
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396 | @end defun |
397 | ||
53f60086 RS |
398 | @node Eval During Compile |
399 | @section Evaluation During Compilation | |
400 | ||
22697dac | 401 | These features permit you to write code to be evaluated during |
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402 | compilation of a program. |
403 | ||
404 | @defspec eval-and-compile body | |
405 | This form marks @var{body} to be evaluated both when you compile the | |
406 | containing code and when you run it (whether compiled or not). | |
407 | ||
408 | You can get a similar result by putting @var{body} in a separate file | |
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409 | and referring to that file with @code{require}. That method is |
410 | preferable when @var{body} is large. | |
53f60086 RS |
411 | @end defspec |
412 | ||
413 | @defspec eval-when-compile body | |
f9f59935 | 414 | This form marks @var{body} to be evaluated at compile time but not when |
78c71a98 | 415 | the compiled program is loaded. The result of evaluation by the |
f9f59935 RS |
416 | compiler becomes a constant which appears in the compiled program. If |
417 | you load the source file, rather than compiling it, @var{body} is | |
418 | evaluated normally. | |
53f60086 | 419 | |
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420 | @strong{Common Lisp Note:} At top level, this is analogous to the Common |
421 | Lisp idiom @code{(eval-when (compile eval) @dots{})}. Elsewhere, the | |
422 | Common Lisp @samp{#.} reader macro (but not when interpreting) is closer | |
423 | to what @code{eval-when-compile} does. | |
53f60086 RS |
424 | @end defspec |
425 | ||
d7810bda RS |
426 | @node Compiler Errors |
427 | @section Compiler Errors | |
428 | @cindex compiler errors | |
429 | ||
342fd6cd | 430 | Byte compilation outputs all errors and warnings into the buffer |
d7810bda RS |
431 | @samp{*Compile-Log*}. The messages include file names and line |
432 | numbers that identify the location of the problem. The usual Emacs | |
433 | commands for operating on compiler diagnostics work properly on | |
434 | these messages. | |
435 | ||
436 | However, the warnings about functions that were used but not | |
437 | defined are always ``located'' at the end of the file, so these | |
438 | commands won't find the places they are really used. To do that, | |
439 | you must search for the function names. | |
e75c1a57 | 440 | |
fe45b975 | 441 | You can suppress the compiler warning for calling an undefined |
76865de3 | 442 | function @var{func} by conditionalizing the function call on an |
fe45b975 RS |
443 | @code{fboundp} test, like this: |
444 | ||
445 | @example | |
446 | (if (fboundp '@var{func}) ...(@var{func} ...)...) | |
447 | @end example | |
448 | ||
449 | @noindent | |
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450 | The call to @var{func} must be in the @var{then-form} of the |
451 | @code{if}, and @var{func} must appear quoted in the call to | |
452 | @code{fboundp}. (This feature operates for @code{cond} as well.) | |
453 | ||
454 | Likewise, you can suppress a compiler warning for an unbound variable | |
fe45b975 RS |
455 | @var{variable} by conditionalizing its use on a @code{boundp} test, |
456 | like this: | |
457 | ||
458 | @example | |
459 | (if (boundp '@var{variable}) ...@var{variable}...) | |
460 | @end example | |
461 | ||
462 | @noindent | |
463 | The reference to @var{variable} must be in the @var{then-form} of the | |
464 | @code{if}, and @var{variable} must appear quoted in the call to | |
465 | @code{boundp}. | |
466 | ||
467 | You can suppress any compiler warnings using the construct | |
468 | @code{with-no-warnings}: | |
469 | ||
76865de3 RS |
470 | @c This is implemented with a defun, but conceptually it is |
471 | @c a special form. | |
472 | ||
473 | @defspec with-no-warnings body... | |
fe45b975 RS |
474 | In execution, this is equivalent to @code{(progn @var{body}...)}, |
475 | but the compiler does not issue warnings for anything that occurs | |
476 | inside @var{body}. | |
477 | ||
478 | We recommend that you use this construct around the smallest | |
479 | possible piece of code. | |
76865de3 | 480 | @end defspec |
fe45b975 | 481 | |
53f60086 | 482 | @node Byte-Code Objects |
bfe721d1 | 483 | @section Byte-Code Function Objects |
53f60086 RS |
484 | @cindex compiled function |
485 | @cindex byte-code function | |
486 | ||
487 | Byte-compiled functions have a special data type: they are | |
488 | @dfn{byte-code function objects}. | |
489 | ||
490 | Internally, a byte-code function object is much like a vector; | |
491 | however, the evaluator handles this data type specially when it appears | |
492 | as a function to be called. The printed representation for a byte-code | |
493 | function object is like that for a vector, with an additional @samp{#} | |
494 | before the opening @samp{[}. | |
495 | ||
53f60086 | 496 | A byte-code function object must have at least four elements; there is |
969fe9b5 | 497 | no maximum number, but only the first six elements have any normal use. |
53f60086 RS |
498 | They are: |
499 | ||
500 | @table @var | |
501 | @item arglist | |
502 | The list of argument symbols. | |
503 | ||
504 | @item byte-code | |
505 | The string containing the byte-code instructions. | |
506 | ||
507 | @item constants | |
78c71a98 RS |
508 | The vector of Lisp objects referenced by the byte code. These include |
509 | symbols used as function names and variable names. | |
53f60086 RS |
510 | |
511 | @item stacksize | |
512 | The maximum stack size this function needs. | |
513 | ||
514 | @item docstring | |
bfe721d1 KH |
515 | The documentation string (if any); otherwise, @code{nil}. The value may |
516 | be a number or a list, in case the documentation string is stored in a | |
517 | file. Use the function @code{documentation} to get the real | |
518 | documentation string (@pxref{Accessing Documentation}). | |
53f60086 RS |
519 | |
520 | @item interactive | |
521 | The interactive spec (if any). This can be a string or a Lisp | |
522 | expression. It is @code{nil} for a function that isn't interactive. | |
523 | @end table | |
524 | ||
525 | Here's an example of a byte-code function object, in printed | |
526 | representation. It is the definition of the command | |
527 | @code{backward-sexp}. | |
528 | ||
529 | @example | |
530 | #[(&optional arg) | |
531 | "^H\204^F^@@\301^P\302^H[!\207" | |
532 | [arg 1 forward-sexp] | |
533 | 2 | |
534 | 254435 | |
535 | "p"] | |
536 | @end example | |
537 | ||
538 | The primitive way to create a byte-code object is with | |
539 | @code{make-byte-code}: | |
540 | ||
541 | @defun make-byte-code &rest elements | |
542 | This function constructs and returns a byte-code function object | |
543 | with @var{elements} as its elements. | |
544 | @end defun | |
545 | ||
a0acfc98 RS |
546 | You should not try to come up with the elements for a byte-code |
547 | function yourself, because if they are inconsistent, Emacs may crash | |
78c71a98 | 548 | when you call the function. Always leave it to the byte compiler to |
a0acfc98 | 549 | create these objects; it makes the elements consistent (we hope). |
53f60086 RS |
550 | |
551 | You can access the elements of a byte-code object using @code{aref}; | |
552 | you can also use @code{vconcat} to create a vector with the same | |
553 | elements. | |
554 | ||
555 | @node Disassembly | |
556 | @section Disassembled Byte-Code | |
557 | @cindex disassembled byte-code | |
558 | ||
559 | People do not write byte-code; that job is left to the byte compiler. | |
560 | But we provide a disassembler to satisfy a cat-like curiosity. The | |
561 | disassembler converts the byte-compiled code into humanly readable | |
562 | form. | |
563 | ||
564 | The byte-code interpreter is implemented as a simple stack machine. | |
a0acfc98 | 565 | It pushes values onto a stack of its own, then pops them off to use them |
78c71a98 RS |
566 | in calculations whose results are themselves pushed back on the stack. |
567 | When a byte-code function returns, it pops a value off the stack and | |
568 | returns it as the value of the function. | |
53f60086 | 569 | |
78c71a98 | 570 | In addition to the stack, byte-code functions can use, bind, and set |
a0acfc98 RS |
571 | ordinary Lisp variables, by transferring values between variables and |
572 | the stack. | |
53f60086 | 573 | |
e75c1a57 LT |
574 | @deffn Command disassemble object &optional buffer-or-name |
575 | This command displays the disassembled code for @var{object}. In | |
576 | interactive use, or if @var{buffer-or-name} is @code{nil} or omitted, | |
577 | the output goes in a buffer named @samp{*Disassemble*}. If | |
578 | @var{buffer-or-name} is non-@code{nil}, it must be a buffer or the | |
579 | name of an existing buffer. Then the output goes there, at point, and | |
580 | point is left before the output. | |
53f60086 | 581 | |
e75c1a57 | 582 | The argument @var{object} can be a function name, a lambda expression |
76865de3 RS |
583 | or a byte-code object. If it is a lambda expression, @code{disassemble} |
584 | compiles it and disassembles the resulting compiled code. | |
53f60086 RS |
585 | @end deffn |
586 | ||
587 | Here are two examples of using the @code{disassemble} function. We | |
588 | have added explanatory comments to help you relate the byte-code to the | |
589 | Lisp source; these do not appear in the output of @code{disassemble}. | |
590 | These examples show unoptimized byte-code. Nowadays byte-code is | |
591 | usually optimized, but we did not want to rewrite these examples, since | |
592 | they still serve their purpose. | |
593 | ||
594 | @example | |
595 | @group | |
596 | (defun factorial (integer) | |
597 | "Compute factorial of an integer." | |
598 | (if (= 1 integer) 1 | |
599 | (* integer (factorial (1- integer))))) | |
600 | @result{} factorial | |
601 | @end group | |
602 | ||
603 | @group | |
604 | (factorial 4) | |
605 | @result{} 24 | |
606 | @end group | |
607 | ||
608 | @group | |
609 | (disassemble 'factorial) | |
610 | @print{} byte-code for factorial: | |
611 | doc: Compute factorial of an integer. | |
612 | args: (integer) | |
613 | @end group | |
614 | ||
615 | @group | |
616 | 0 constant 1 ; @r{Push 1 onto stack.} | |
617 | ||
177c0ea7 | 618 | 1 varref integer ; @r{Get value of @code{integer}} |
53f60086 RS |
619 | ; @r{from the environment} |
620 | ; @r{and push the value} | |
621 | ; @r{onto the stack.} | |
622 | @end group | |
623 | ||
624 | @group | |
625 | 2 eqlsign ; @r{Pop top two values off stack,} | |
626 | ; @r{compare them,} | |
627 | ; @r{and push result onto stack.} | |
628 | @end group | |
629 | ||
630 | @group | |
631 | 3 goto-if-nil 10 ; @r{Pop and test top of stack;} | |
632 | ; @r{if @code{nil}, go to 10,} | |
633 | ; @r{else continue.} | |
634 | @end group | |
635 | ||
636 | @group | |
637 | 6 constant 1 ; @r{Push 1 onto top of stack.} | |
638 | ||
639 | 7 goto 17 ; @r{Go to 17 (in this case, 1 will be} | |
640 | ; @r{returned by the function).} | |
641 | @end group | |
642 | ||
643 | @group | |
644 | 10 constant * ; @r{Push symbol @code{*} onto stack.} | |
645 | ||
646 | 11 varref integer ; @r{Push value of @code{integer} onto stack.} | |
647 | @end group | |
648 | ||
649 | @group | |
650 | 12 constant factorial ; @r{Push @code{factorial} onto stack.} | |
651 | ||
652 | 13 varref integer ; @r{Push value of @code{integer} onto stack.} | |
653 | ||
654 | 14 sub1 ; @r{Pop @code{integer}, decrement value,} | |
655 | ; @r{push new value onto stack.} | |
656 | @end group | |
657 | ||
658 | @group | |
659 | ; @r{Stack now contains:} | |
660 | ; @minus{} @r{decremented value of @code{integer}} | |
177c0ea7 | 661 | ; @minus{} @r{@code{factorial}} |
53f60086 RS |
662 | ; @minus{} @r{value of @code{integer}} |
663 | ; @minus{} @r{@code{*}} | |
664 | @end group | |
665 | ||
666 | @group | |
667 | 15 call 1 ; @r{Call function @code{factorial} using} | |
668 | ; @r{the first (i.e., the top) element} | |
669 | ; @r{of the stack as the argument;} | |
670 | ; @r{push returned value onto stack.} | |
671 | @end group | |
672 | ||
673 | @group | |
674 | ; @r{Stack now contains:} | |
78c71a98 | 675 | ; @minus{} @r{result of recursive} |
53f60086 RS |
676 | ; @r{call to @code{factorial}} |
677 | ; @minus{} @r{value of @code{integer}} | |
678 | ; @minus{} @r{@code{*}} | |
679 | @end group | |
680 | ||
681 | @group | |
682 | 16 call 2 ; @r{Using the first two} | |
683 | ; @r{(i.e., the top two)} | |
684 | ; @r{elements of the stack} | |
685 | ; @r{as arguments,} | |
686 | ; @r{call the function @code{*},} | |
687 | ; @r{pushing the result onto the stack.} | |
688 | @end group | |
689 | ||
690 | @group | |
691 | 17 return ; @r{Return the top element} | |
692 | ; @r{of the stack.} | |
693 | @result{} nil | |
694 | @end group | |
695 | @end example | |
696 | ||
697 | The @code{silly-loop} function is somewhat more complex: | |
698 | ||
699 | @example | |
700 | @group | |
701 | (defun silly-loop (n) | |
702 | "Return time before and after N iterations of a loop." | |
703 | (let ((t1 (current-time-string))) | |
177c0ea7 | 704 | (while (> (setq n (1- n)) |
53f60086 RS |
705 | 0)) |
706 | (list t1 (current-time-string)))) | |
707 | @result{} silly-loop | |
708 | @end group | |
709 | ||
710 | @group | |
711 | (disassemble 'silly-loop) | |
712 | @print{} byte-code for silly-loop: | |
713 | doc: Return time before and after N iterations of a loop. | |
714 | args: (n) | |
715 | ||
716 | 0 constant current-time-string ; @r{Push} | |
717 | ; @r{@code{current-time-string}} | |
718 | ; @r{onto top of stack.} | |
719 | @end group | |
720 | ||
721 | @group | |
722 | 1 call 0 ; @r{Call @code{current-time-string}} | |
723 | ; @r{ with no argument,} | |
724 | ; @r{ pushing result onto stack.} | |
725 | @end group | |
726 | ||
727 | @group | |
728 | 2 varbind t1 ; @r{Pop stack and bind @code{t1}} | |
729 | ; @r{to popped value.} | |
730 | @end group | |
731 | ||
732 | @group | |
733 | 3 varref n ; @r{Get value of @code{n} from} | |
734 | ; @r{the environment and push} | |
735 | ; @r{the value onto the stack.} | |
736 | @end group | |
737 | ||
738 | @group | |
739 | 4 sub1 ; @r{Subtract 1 from top of stack.} | |
740 | @end group | |
741 | ||
742 | @group | |
743 | 5 dup ; @r{Duplicate the top of the stack;} | |
a0acfc98 | 744 | ; @r{i.e., copy the top of} |
53f60086 RS |
745 | ; @r{the stack and push the} |
746 | ; @r{copy onto the stack.} | |
747 | @end group | |
748 | ||
749 | @group | |
750 | 6 varset n ; @r{Pop the top of the stack,} | |
751 | ; @r{and bind @code{n} to the value.} | |
752 | ||
753 | ; @r{In effect, the sequence @code{dup varset}} | |
754 | ; @r{copies the top of the stack} | |
755 | ; @r{into the value of @code{n}} | |
756 | ; @r{without popping it.} | |
757 | @end group | |
758 | ||
759 | @group | |
760 | 7 constant 0 ; @r{Push 0 onto stack.} | |
761 | @end group | |
762 | ||
763 | @group | |
764 | 8 gtr ; @r{Pop top two values off stack,} | |
765 | ; @r{test if @var{n} is greater than 0} | |
766 | ; @r{and push result onto stack.} | |
767 | @end group | |
768 | ||
769 | @group | |
78c71a98 RS |
770 | 9 goto-if-nil-else-pop 17 ; @r{Goto 17 if @code{n} <= 0} |
771 | ; @r{(this exits the while loop).} | |
53f60086 RS |
772 | ; @r{else pop top of stack} |
773 | ; @r{and continue} | |
53f60086 RS |
774 | @end group |
775 | ||
776 | @group | |
777 | 12 constant nil ; @r{Push @code{nil} onto stack} | |
778 | ; @r{(this is the body of the loop).} | |
779 | @end group | |
780 | ||
781 | @group | |
782 | 13 discard ; @r{Discard result of the body} | |
783 | ; @r{of the loop (a while loop} | |
784 | ; @r{is always evaluated for} | |
785 | ; @r{its side effects).} | |
786 | @end group | |
787 | ||
788 | @group | |
789 | 14 goto 3 ; @r{Jump back to beginning} | |
790 | ; @r{of while loop.} | |
791 | @end group | |
792 | ||
793 | @group | |
794 | 17 discard ; @r{Discard result of while loop} | |
795 | ; @r{by popping top of stack.} | |
78c71a98 RS |
796 | ; @r{This result is the value @code{nil} that} |
797 | ; @r{was not popped by the goto at 9.} | |
53f60086 RS |
798 | @end group |
799 | ||
800 | @group | |
801 | 18 varref t1 ; @r{Push value of @code{t1} onto stack.} | |
802 | @end group | |
803 | ||
804 | @group | |
177c0ea7 | 805 | 19 constant current-time-string ; @r{Push} |
53f60086 RS |
806 | ; @r{@code{current-time-string}} |
807 | ; @r{onto top of stack.} | |
808 | @end group | |
809 | ||
810 | @group | |
811 | 20 call 0 ; @r{Call @code{current-time-string} again.} | |
812 | @end group | |
813 | ||
814 | @group | |
815 | 21 list2 ; @r{Pop top two elements off stack,} | |
816 | ; @r{create a list of them,} | |
817 | ; @r{and push list onto stack.} | |
818 | @end group | |
819 | ||
820 | @group | |
821 | 22 unbind 1 ; @r{Unbind @code{t1} in local environment.} | |
822 | ||
823 | 23 return ; @r{Return value of the top of stack.} | |
824 | ||
825 | @result{} nil | |
826 | @end group | |
827 | @end example | |
828 | ||
829 | ||
ab5796a9 MB |
830 | @ignore |
831 | arch-tag: f78e3050-2f0a-4dee-be27-d9979a0a2289 | |
832 | @end ignore |