|
428
|
1 @c -*-texinfo-*-
|
|
|
2 @c This is part of the XEmacs Lisp Reference Manual.
|
|
|
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
|
|
|
4 @c See the file lispref.texi for copying conditions.
|
|
|
5 @setfilename ../../info/compile.info
|
|
|
6 @node Byte Compilation, Debugging, Loading, Top
|
|
|
7 @chapter Byte Compilation
|
|
|
8 @cindex byte-code
|
|
|
9 @cindex compilation
|
|
|
10
|
|
|
11 XEmacs Lisp has a @dfn{compiler} that translates functions written
|
|
|
12 in Lisp into a special representation called @dfn{byte-code} that can be
|
|
|
13 executed more efficiently. The compiler replaces Lisp function
|
|
|
14 definitions with byte-code. When a byte-coded function is called, its
|
|
|
15 definition is evaluated by the @dfn{byte-code interpreter}.
|
|
|
16
|
|
|
17 Because the byte-compiled code is evaluated by the byte-code
|
|
|
18 interpreter, instead of being executed directly by the machine's
|
|
|
19 hardware (as true compiled code is), byte-code is completely
|
|
|
20 transportable from machine to machine without recompilation. It is not,
|
|
|
21 however, as fast as true compiled code.
|
|
|
22
|
|
|
23 In general, any version of Emacs can run byte-compiled code produced
|
|
|
24 by recent earlier versions of Emacs, but the reverse is not true. In
|
|
|
25 particular, if you compile a program with XEmacs 20, the compiled code
|
|
|
26 may not run in earlier versions.
|
|
|
27
|
|
|
28 The first time a compiled-function object is executed, the byte-code
|
|
|
29 instructions are validated and the byte-code is further optimized. An
|
|
|
30 @code{invalid-byte-code} error is signaled if the byte-code is invalid,
|
|
|
31 for example if it contains invalid opcodes. This usually means a bug in
|
|
|
32 the byte compiler.
|
|
|
33
|
|
|
34 @iftex
|
|
|
35 @xref{Docs and Compilation}.
|
|
|
36 @end iftex
|
|
|
37
|
|
|
38 @xref{Compilation Errors}, for how to investigate errors occurring in
|
|
|
39 byte compilation.
|
|
|
40
|
|
|
41 @menu
|
|
|
42 * Speed of Byte-Code:: An example of speedup from byte compilation.
|
|
|
43 * Compilation Functions:: Byte compilation functions.
|
|
|
44 * Docs and Compilation:: Dynamic loading of documentation strings.
|
|
|
45 * Dynamic Loading:: Dynamic loading of individual functions.
|
|
|
46 * Eval During Compile:: Code to be evaluated when you compile.
|
|
|
47 * Compiled-Function Objects:: The data type used for byte-compiled functions.
|
|
|
48 * Disassembly:: Disassembling byte-code; how to read byte-code.
|
|
446
|
49 * Different Behavior:: When compiled code gives different results.
|
|
428
|
50 @end menu
|
|
|
51
|
|
|
52 @node Speed of Byte-Code
|
|
|
53 @section Performance of Byte-Compiled Code
|
|
|
54
|
|
|
55 A byte-compiled function is not as efficient as a primitive function
|
|
|
56 written in C, but runs much faster than the version written in Lisp.
|
|
|
57 Here is an example:
|
|
|
58
|
|
|
59 @example
|
|
|
60 @group
|
|
|
61 (defun silly-loop (n)
|
|
|
62 "Return time before and after N iterations of a loop."
|
|
|
63 (let ((t1 (current-time-string)))
|
|
|
64 (while (> (setq n (1- n))
|
|
|
65 0))
|
|
|
66 (list t1 (current-time-string))))
|
|
|
67 @result{} silly-loop
|
|
|
68 @end group
|
|
|
69
|
|
|
70 @group
|
|
|
71 (silly-loop 5000000)
|
|
|
72 @result{} ("Mon Sep 14 15:51:49 1998"
|
|
|
73 "Mon Sep 14 15:52:07 1998") ; @r{18 seconds}
|
|
|
74 @end group
|
|
|
75
|
|
|
76 @group
|
|
|
77 (byte-compile 'silly-loop)
|
|
|
78 @result{} #<compiled-function
|
|
|
79 (n)
|
|
|
80 "...(23)"
|
|
|
81 [current-time-string t1 n 0]
|
|
|
82 2
|
|
|
83 "Return time before and after N iterations of a loop.">
|
|
|
84 @end group
|
|
|
85
|
|
|
86 @group
|
|
|
87 (silly-loop 5000000)
|
|
|
88 @result{} ("Mon Sep 14 15:53:43 1998"
|
|
|
89 "Mon Sep 14 15:53:49 1998") ; @r{6 seconds}
|
|
|
90 @end group
|
|
|
91 @end example
|
|
|
92
|
|
|
93 In this example, the interpreted code required 18 seconds to run,
|
|
|
94 whereas the byte-compiled code required 6 seconds. These results are
|
|
|
95 representative, but actual results will vary greatly.
|
|
|
96
|
|
|
97 @node Compilation Functions
|
|
|
98 @comment node-name, next, previous, up
|
|
|
99 @section The Compilation Functions
|
|
|
100 @cindex compilation functions
|
|
|
101
|
|
|
102 You can byte-compile an individual function or macro definition with
|
|
|
103 the @code{byte-compile} function. You can compile a whole file with
|
|
|
104 @code{byte-compile-file}, or several files with
|
|
|
105 @code{byte-recompile-directory} or @code{batch-byte-compile}.
|
|
|
106
|
|
|
107 When you run the byte compiler, you may get warnings in a buffer
|
|
|
108 called @samp{*Compile-Log*}. These report things in your program that
|
|
|
109 suggest a problem but are not necessarily erroneous.
|
|
|
110
|
|
|
111 @cindex macro compilation
|
|
|
112 Be careful when byte-compiling code that uses macros. Macro calls are
|
|
|
113 expanded when they are compiled, so the macros must already be defined
|
|
|
114 for proper compilation. For more details, see @ref{Compiling Macros}.
|
|
|
115
|
|
|
116 Normally, compiling a file does not evaluate the file's contents or
|
|
|
117 load the file. But it does execute any @code{require} calls at top
|
|
|
118 level in the file. One way to ensure that necessary macro definitions
|
|
|
119 are available during compilation is to @code{require} the file that defines
|
|
|
120 them (@pxref{Named Features}). To avoid loading the macro definition files
|
|
|
121 when someone @emph{runs} the compiled program, write
|
|
|
122 @code{eval-when-compile} around the @code{require} calls (@pxref{Eval
|
|
|
123 During Compile}).
|
|
|
124
|
|
|
125 @defun byte-compile symbol
|
|
|
126 This function byte-compiles the function definition of @var{symbol},
|
|
|
127 replacing the previous definition with the compiled one. The function
|
|
|
128 definition of @var{symbol} must be the actual code for the function;
|
|
|
129 i.e., the compiler does not follow indirection to another symbol.
|
|
|
130 @code{byte-compile} returns the new, compiled definition of
|
|
|
131 @var{symbol}.
|
|
|
132
|
|
|
133 If @var{symbol}'s definition is a compiled-function object,
|
|
|
134 @code{byte-compile} does nothing and returns @code{nil}. Lisp records
|
|
|
135 only one function definition for any symbol, and if that is already
|
|
|
136 compiled, non-compiled code is not available anywhere. So there is no
|
|
|
137 way to ``compile the same definition again.''
|
|
|
138
|
|
|
139 @example
|
|
|
140 @group
|
|
|
141 (defun factorial (integer)
|
|
|
142 "Compute factorial of INTEGER."
|
|
|
143 (if (= 1 integer) 1
|
|
|
144 (* integer (factorial (1- integer)))))
|
|
|
145 @result{} factorial
|
|
|
146 @end group
|
|
|
147
|
|
|
148 @group
|
|
|
149 (byte-compile 'factorial)
|
|
|
150 @result{} #<compiled-function
|
|
|
151 (integer)
|
|
|
152 "...(21)"
|
|
|
153 [integer 1 factorial]
|
|
|
154 3
|
|
|
155 "Compute factorial of INTEGER.">
|
|
|
156 @end group
|
|
|
157 @end example
|
|
|
158
|
|
|
159 @noindent
|
|
|
160 The result is a compiled-function object. The string it contains is
|
|
|
161 the actual byte-code; each character in it is an instruction or an
|
|
|
162 operand of an instruction. The vector contains all the constants,
|
|
|
163 variable names and function names used by the function, except for
|
|
|
164 certain primitives that are coded as special instructions.
|
|
|
165 @end defun
|
|
|
166
|
|
|
167 @deffn Command compile-defun &optional arg
|
|
|
168 This command reads the defun containing point, compiles it, and
|
|
|
169 evaluates the result. If you use this on a defun that is actually a
|
|
|
170 function definition, the effect is to install a compiled version of that
|
|
|
171 function.
|
|
|
172
|
|
|
173 @c XEmacs feature
|
|
|
174 If @var{arg} is non-@code{nil}, the result is inserted in the current
|
|
|
175 buffer after the form; otherwise, it is printed in the minibuffer.
|
|
|
176 @end deffn
|
|
|
177
|
|
|
178 @deffn Command byte-compile-file filename &optional load
|
|
|
179 This function compiles a file of Lisp code named @var{filename} into
|
|
|
180 a file of byte-code. The output file's name is made by appending
|
|
|
181 @samp{c} to the end of @var{filename}.
|
|
|
182
|
|
|
183 @c XEmacs feature
|
|
|
184 If @code{load} is non-@code{nil}, the file is loaded after having been
|
|
|
185 compiled.
|
|
|
186
|
|
|
187 Compilation works by reading the input file one form at a time. If it
|
|
|
188 is a definition of a function or macro, the compiled function or macro
|
|
|
189 definition is written out. Other forms are batched together, then each
|
|
|
190 batch is compiled, and written so that its compiled code will be
|
|
|
191 executed when the file is read. All comments are discarded when the
|
|
|
192 input file is read.
|
|
|
193
|
|
|
194 This command returns @code{t}. When called interactively, it prompts
|
|
|
195 for the file name.
|
|
|
196
|
|
|
197 @example
|
|
|
198 @group
|
|
|
199 % ls -l push*
|
|
|
200 -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
|
|
|
201 @end group
|
|
|
202
|
|
|
203 @group
|
|
|
204 (byte-compile-file "~/emacs/push.el")
|
|
|
205 @result{} t
|
|
|
206 @end group
|
|
|
207
|
|
|
208 @group
|
|
|
209 % ls -l push*
|
|
|
210 -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
|
|
|
211 -rw-r--r-- 1 lewis 638 Oct 8 20:25 push.elc
|
|
|
212 @end group
|
|
|
213 @end example
|
|
|
214 @end deffn
|
|
|
215
|
|
|
216 @c flag is not optional in FSF Emacs
|
|
444
|
217 @deffn Command byte-recompile-directory directory &optional flag norecursion force
|
|
428
|
218 @cindex library compilation
|
|
|
219 This function recompiles every @samp{.el} file in @var{directory} that
|
|
|
220 needs recompilation. A file needs recompilation if a @samp{.elc} file
|
|
|
221 exists but is older than the @samp{.el} file.
|
|
|
222
|
|
444
|
223 Files in subdirectories of @var{directory} are also processed unless
|
|
|
224 optional argument @var{norecursion} is non-@code{nil}.
|
|
|
225
|
|
428
|
226 When a @samp{.el} file has no corresponding @samp{.elc} file, then
|
|
|
227 @var{flag} says what to do. If it is @code{nil}, these files are
|
|
|
228 ignored. If it is non-@code{nil}, the user is asked whether to compile
|
|
|
229 each such file.
|
|
|
230
|
|
444
|
231 If the fourth optional argument @var{force} is non-@code{nil},
|
|
|
232 recompile every @samp{.el} file that already has a @samp{.elc} file.
|
|
|
233
|
|
428
|
234 The return value of this command is unpredictable.
|
|
|
235 @end deffn
|
|
|
236
|
|
|
237 @defun batch-byte-compile
|
|
|
238 This function runs @code{byte-compile-file} on files specified on the
|
|
|
239 command line. This function must be used only in a batch execution of
|
|
|
240 Emacs, as it kills Emacs on completion. An error in one file does not
|
|
|
241 prevent processing of subsequent files. (The file that gets the error
|
|
|
242 will not, of course, produce any compiled code.)
|
|
|
243
|
|
|
244 @example
|
|
442
|
245 % xemacs -batch -f batch-byte-compile *.el
|
|
428
|
246 @end example
|
|
|
247 @end defun
|
|
|
248
|
|
|
249 @c XEmacs feature
|
|
|
250 @defun batch-byte-recompile-directory
|
|
|
251 This function is similar to @code{batch-byte-compile} but runs the
|
|
|
252 command @code{byte-recompile-directory} on the files remaining on the
|
|
|
253 command line.
|
|
|
254 @end defun
|
|
|
255
|
|
|
256 @c XEmacs feature
|
|
|
257 @defvar byte-recompile-directory-ignore-errors-p
|
|
|
258 If non-@code{nil}, this specifies that @code{byte-recompile-directory}
|
|
|
259 will continue compiling even when an error occurs in a file. This is
|
|
|
260 normally @code{nil}, but is bound to @code{t} by
|
|
|
261 @code{batch-byte-recompile-directory}.
|
|
|
262 @end defvar
|
|
|
263
|
|
444
|
264 @defun byte-code instructions constants stack-depth
|
|
428
|
265 @cindex byte-code interpreter
|
|
|
266 This function actually interprets byte-code.
|
|
|
267 Don't call this function yourself. Only the byte compiler knows how to
|
|
|
268 generate valid calls to this function.
|
|
|
269
|
|
|
270 In newer Emacs versions (19 and up), byte code is usually executed as
|
|
|
271 part of a compiled-function object, and only rarely due to an explicit
|
|
|
272 call to @code{byte-code}. A byte-compiled function was once actually
|
|
|
273 defined with a body that calls @code{byte-code}, but in recent versions
|
|
|
274 of Emacs @code{byte-code} is only used to run isolated fragments of lisp
|
|
|
275 code without an associated argument list.
|
|
|
276 @end defun
|
|
|
277
|
|
|
278 @node Docs and Compilation
|
|
|
279 @section Documentation Strings and Compilation
|
|
|
280 @cindex dynamic loading of documentation
|
|
|
281
|
|
|
282 Functions and variables loaded from a byte-compiled file access their
|
|
|
283 documentation strings dynamically from the file whenever needed. This
|
|
|
284 saves space within Emacs, and makes loading faster because the
|
|
|
285 documentation strings themselves need not be processed while loading the
|
|
|
286 file. Actual access to the documentation strings becomes slower as a
|
|
|
287 result, but normally not enough to bother users.
|
|
|
288
|
|
|
289 Dynamic access to documentation strings does have drawbacks:
|
|
|
290
|
|
|
291 @itemize @bullet
|
|
|
292 @item
|
|
|
293 If you delete or move the compiled file after loading it, Emacs can no
|
|
|
294 longer access the documentation strings for the functions and variables
|
|
|
295 in the file.
|
|
|
296
|
|
|
297 @item
|
|
|
298 If you alter the compiled file (such as by compiling a new version),
|
|
|
299 then further access to documentation strings in this file will give
|
|
|
300 nonsense results.
|
|
|
301 @end itemize
|
|
|
302
|
|
|
303 If your site installs Emacs following the usual procedures, these
|
|
|
304 problems will never normally occur. Installing a new version uses a new
|
|
|
305 directory with a different name; as long as the old version remains
|
|
|
306 installed, its files will remain unmodified in the places where they are
|
|
|
307 expected to be.
|
|
|
308
|
|
|
309 However, if you have built Emacs yourself and use it from the
|
|
|
310 directory where you built it, you will experience this problem
|
|
|
311 occasionally if you edit and recompile Lisp files. When it happens, you
|
|
|
312 can cure the problem by reloading the file after recompiling it.
|
|
|
313
|
|
|
314 Versions of Emacs up to and including XEmacs 19.14 and FSF Emacs 19.28
|
|
|
315 do not support the dynamic docstrings feature, and so will not be able
|
|
|
316 to load bytecode created by more recent Emacs versions. You can turn
|
|
|
317 off the dynamic docstring feature by setting
|
|
|
318 @code{byte-compile-dynamic-docstrings} to @code{nil}. Once this is
|
|
|
319 done, you can compile files that will load into older Emacs versions.
|
|
|
320 You can do this globally, or for one source file by specifying a
|
|
|
321 file-local binding for the variable. Here's one way to do that:
|
|
|
322
|
|
|
323 @example
|
|
|
324 -*-byte-compile-dynamic-docstrings: nil;-*-
|
|
|
325 @end example
|
|
|
326
|
|
|
327 @defvar byte-compile-dynamic-docstrings
|
|
|
328 If this is non-@code{nil}, the byte compiler generates compiled files
|
|
|
329 that are set up for dynamic loading of documentation strings.
|
|
|
330 @end defvar
|
|
|
331
|
|
|
332 @cindex @samp{#@@@var{count}}
|
|
|
333 @cindex @samp{#$}
|
|
|
334 The dynamic documentation string feature writes compiled files that
|
|
|
335 use a special Lisp reader construct, @samp{#@@@var{count}}. This
|
|
|
336 construct skips the next @var{count} characters. It also uses the
|
|
|
337 @samp{#$} construct, which stands for ``the name of this file, as a
|
|
|
338 string.'' It is best not to use these constructs in Lisp source files.
|
|
|
339
|
|
|
340 @node Dynamic Loading
|
|
|
341 @section Dynamic Loading of Individual Functions
|
|
|
342
|
|
|
343 @cindex dynamic loading of functions
|
|
|
344 @cindex lazy loading
|
|
|
345 When you compile a file, you can optionally enable the @dfn{dynamic
|
|
|
346 function loading} feature (also known as @dfn{lazy loading}). With
|
|
|
347 dynamic function loading, loading the file doesn't fully read the
|
|
|
348 function definitions in the file. Instead, each function definition
|
|
|
349 contains a place-holder which refers to the file. The first time each
|
|
|
350 function is called, it reads the full definition from the file, to
|
|
|
351 replace the place-holder.
|
|
|
352
|
|
|
353 The advantage of dynamic function loading is that loading the file
|
|
|
354 becomes much faster. This is a good thing for a file which contains
|
|
|
355 many separate commands, provided that using one of them does not imply
|
|
|
356 you will soon (or ever) use the rest. A specialized mode which provides
|
|
|
357 many keyboard commands often has that usage pattern: a user may invoke
|
|
|
358 the mode, but use only a few of the commands it provides.
|
|
|
359
|
|
|
360 The dynamic loading feature has certain disadvantages:
|
|
|
361
|
|
|
362 @itemize @bullet
|
|
|
363 @item
|
|
|
364 If you delete or move the compiled file after loading it, Emacs can no
|
|
|
365 longer load the remaining function definitions not already loaded.
|
|
|
366
|
|
|
367 @item
|
|
|
368 If you alter the compiled file (such as by compiling a new version),
|
|
|
369 then trying to load any function not already loaded will get nonsense
|
|
|
370 results.
|
|
|
371 @end itemize
|
|
|
372
|
|
|
373 If you compile a new version of the file, the best thing to do is
|
|
|
374 immediately load the new compiled file. That will prevent any future
|
|
|
375 problems.
|
|
|
376
|
|
|
377 The byte compiler uses the dynamic function loading feature if the
|
|
|
378 variable @code{byte-compile-dynamic} is non-@code{nil} at compilation
|
|
|
379 time. Do not set this variable globally, since dynamic loading is
|
|
|
380 desirable only for certain files. Instead, enable the feature for
|
|
|
381 specific source files with file-local variable bindings, like this:
|
|
|
382
|
|
|
383 @example
|
|
|
384 -*-byte-compile-dynamic: t;-*-
|
|
|
385 @end example
|
|
|
386
|
|
|
387 @defvar byte-compile-dynamic
|
|
|
388 If this is non-@code{nil}, the byte compiler generates compiled files
|
|
|
389 that are set up for dynamic function loading.
|
|
|
390 @end defvar
|
|
|
391
|
|
|
392 @defun fetch-bytecode function
|
|
|
393 This immediately finishes loading the definition of @var{function} from
|
|
|
394 its byte-compiled file, if it is not fully loaded already. The argument
|
|
|
395 @var{function} may be a compiled-function object or a function name.
|
|
|
396 @end defun
|
|
|
397
|
|
|
398 @node Eval During Compile
|
|
|
399 @section Evaluation During Compilation
|
|
|
400
|
|
|
401 These features permit you to write code to be evaluated during
|
|
|
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
|
|
|
409 and referring to that file with @code{require}. Using @code{require} is
|
|
|
410 preferable if there is a substantial amount of code to be executed in
|
|
|
411 this way.
|
|
|
412 @end defspec
|
|
|
413
|
|
|
414 @defspec eval-when-compile body
|
|
|
415 This form marks @var{body} to be evaluated at compile time and not when
|
|
|
416 the compiled program is loaded. The result of evaluation by the
|
|
|
417 compiler becomes a constant which appears in the compiled program. When
|
|
|
418 the program is interpreted, not compiled at all, @var{body} is evaluated
|
|
|
419 normally.
|
|
|
420
|
|
|
421 At top level, this is analogous to the Common Lisp idiom
|
|
|
422 @code{(eval-when (compile eval) @dots{})}. Elsewhere, the Common Lisp
|
|
|
423 @samp{#.} reader macro (but not when interpreting) is closer to what
|
|
|
424 @code{eval-when-compile} does.
|
|
|
425 @end defspec
|
|
|
426
|
|
|
427 @node Compiled-Function Objects
|
|
|
428 @section Compiled-Function Objects
|
|
|
429 @cindex compiled function
|
|
|
430 @cindex byte-code function
|
|
|
431
|
|
|
432 Byte-compiled functions have a special data type: they are
|
|
|
433 @dfn{compiled-function objects}. The evaluator handles this data type
|
|
|
434 specially when it appears as a function to be called.
|
|
|
435
|
|
|
436 The printed representation for a compiled-function object normally
|
|
|
437 begins with @samp{#<compiled-function} and ends with @samp{>}. However,
|
|
|
438 if the variable @code{print-readably} is non-@code{nil}, the object is
|
|
|
439 printed beginning with @samp{#[} and ending with @samp{]}. This
|
|
|
440 representation can be read directly by the Lisp reader, and is used in
|
|
|
441 byte-compiled files (those ending in @samp{.elc}).
|
|
|
442
|
|
|
443 In Emacs version 18, there was no compiled-function object data type;
|
|
|
444 compiled functions used the function @code{byte-code} to run the byte
|
|
|
445 code.
|
|
|
446
|
|
|
447 A compiled-function object has a number of different attributes.
|
|
|
448 They are:
|
|
|
449
|
|
|
450 @table @var
|
|
|
451 @item arglist
|
|
|
452 The list of argument symbols.
|
|
|
453
|
|
|
454 @item instructions
|
|
|
455 The string containing the byte-code instructions.
|
|
|
456
|
|
|
457 @item constants
|
|
|
458 The vector of Lisp objects referenced by the byte code. These include
|
|
|
459 symbols used as function names and variable names.
|
|
|
460
|
|
444
|
461 @item stack-depth
|
|
428
|
462 The maximum stack size this function needs.
|
|
|
463
|
|
|
464 @item doc-string
|
|
|
465 The documentation string (if any); otherwise, @code{nil}. The value may
|
|
|
466 be a number or a list, in case the documentation string is stored in a
|
|
|
467 file. Use the function @code{documentation} to get the real
|
|
|
468 documentation string (@pxref{Accessing Documentation}).
|
|
|
469
|
|
|
470 @item interactive
|
|
|
471 The interactive spec (if any). This can be a string or a Lisp
|
|
|
472 expression. It is @code{nil} for a function that isn't interactive.
|
|
|
473
|
|
|
474 @item domain
|
|
|
475 The domain (if any). This is only meaningful if I18N3 (message-translation)
|
|
|
476 support was compiled into XEmacs. This is a string defining which
|
|
|
477 domain to find the translation for the documentation string and
|
|
|
478 interactive prompt. @xref{Domain Specification}.
|
|
|
479 @end table
|
|
|
480
|
|
|
481 Here's an example of a compiled-function object, in printed
|
|
|
482 representation. It is the definition of the command
|
|
|
483 @code{backward-sexp}.
|
|
|
484
|
|
|
485 @example
|
|
|
486 (symbol-function 'backward-sexp)
|
|
|
487 @result{} #<compiled-function
|
|
|
488 (&optional arg)
|
|
|
489 "...(15)" [arg 1 forward-sexp] 2 854740 "_p">
|
|
|
490 @end example
|
|
|
491
|
|
|
492 The primitive way to create a compiled-function object is with
|
|
|
493 @code{make-byte-code}:
|
|
|
494
|
|
444
|
495 @defun make-byte-code arglist instructions constants stack-depth &optional doc-string interactive
|
|
428
|
496 This function constructs and returns a compiled-function object
|
|
|
497 with the specified attributes.
|
|
|
498
|
|
|
499 @emph{Please note:} Unlike all other Emacs-lisp functions, calling this with
|
|
|
500 five arguments is @emph{not} the same as calling it with six arguments,
|
|
|
501 the last of which is @code{nil}. If the @var{interactive} arg is
|
|
|
502 specified as @code{nil}, then that means that this function was defined
|
|
|
503 with @code{(interactive)}. If the arg is not specified, then that means
|
|
|
504 the function is not interactive. This is terrible behavior which is
|
|
|
505 retained for compatibility with old @samp{.elc} files which expected
|
|
|
506 these semantics.
|
|
|
507 @end defun
|
|
|
508
|
|
|
509 You should not try to come up with the elements for a compiled-function
|
|
|
510 object yourself, because if they are inconsistent, XEmacs may crash
|
|
|
511 when you call the function. Always leave it to the byte compiler to
|
|
|
512 create these objects; it makes the elements consistent (we hope).
|
|
|
513
|
|
|
514 The following primitives are provided for accessing the elements of
|
|
|
515 a compiled-function object.
|
|
|
516
|
|
|
517 @defun compiled-function-arglist function
|
|
|
518 This function returns the argument list of compiled-function object
|
|
|
519 @var{function}.
|
|
|
520 @end defun
|
|
|
521
|
|
|
522 @defun compiled-function-instructions function
|
|
|
523 This function returns a string describing the byte-code instructions
|
|
|
524 of compiled-function object @var{function}.
|
|
|
525 @end defun
|
|
|
526
|
|
|
527 @defun compiled-function-constants function
|
|
|
528 This function returns the vector of Lisp objects referenced by
|
|
|
529 compiled-function object @var{function}.
|
|
|
530 @end defun
|
|
|
531
|
|
444
|
532 @defun compiled-function-stack-depth function
|
|
428
|
533 This function returns the maximum stack size needed by compiled-function
|
|
|
534 object @var{function}.
|
|
|
535 @end defun
|
|
|
536
|
|
|
537 @defun compiled-function-doc-string function
|
|
|
538 This function returns the doc string of compiled-function object
|
|
|
539 @var{function}, if available.
|
|
|
540 @end defun
|
|
|
541
|
|
|
542 @defun compiled-function-interactive function
|
|
|
543 This function returns the interactive spec of compiled-function object
|
|
|
544 @var{function}, if any. The return value is @code{nil} or a two-element
|
|
|
545 list, the first element of which is the symbol @code{interactive} and
|
|
|
546 the second element is the interactive spec (a string or Lisp form).
|
|
|
547 @end defun
|
|
|
548
|
|
|
549 @defun compiled-function-domain function
|
|
|
550 This function returns the domain of compiled-function object
|
|
|
551 @var{function}, if any. The result will be a string or @code{nil}.
|
|
|
552 @xref{Domain Specification}.
|
|
|
553 @end defun
|
|
|
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.
|
|
|
565 It pushes values onto a stack of its own, then pops them off to use them
|
|
|
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.
|
|
|
569
|
|
|
570 In addition to the stack, byte-code functions can use, bind, and set
|
|
|
571 ordinary Lisp variables, by transferring values between variables and
|
|
|
572 the stack.
|
|
|
573
|
|
|
574 @deffn Command disassemble object &optional stream
|
|
|
575 This function prints the disassembled code for @var{object}. If
|
|
|
576 @var{stream} is supplied, then output goes there. Otherwise, the
|
|
|
577 disassembled code is printed to the stream @code{standard-output}. The
|
|
|
578 argument @var{object} can be a function name or a lambda expression.
|
|
|
579
|
|
|
580 As a special exception, if this function is used interactively,
|
|
|
581 it outputs to a buffer named @samp{*Disassemble*}.
|
|
|
582 @end deffn
|
|
|
583
|
|
|
584 Here are two examples of using the @code{disassemble} function. We
|
|
|
585 have added explanatory comments to help you relate the byte-code to the
|
|
|
586 Lisp source; these do not appear in the output of @code{disassemble}.
|
|
|
587
|
|
|
588 @example
|
|
|
589 @group
|
|
|
590 (defun factorial (integer)
|
|
|
591 "Compute factorial of an integer."
|
|
|
592 (if (= 1 integer) 1
|
|
|
593 (* integer (factorial (1- integer)))))
|
|
|
594 @result{} factorial
|
|
|
595 @end group
|
|
|
596
|
|
|
597 @group
|
|
|
598 (factorial 4)
|
|
|
599 @result{} 24
|
|
|
600 @end group
|
|
|
601
|
|
|
602 @group
|
|
|
603 (disassemble 'factorial)
|
|
|
604 @print{} byte-code for factorial:
|
|
|
605 doc: Compute factorial of an integer.
|
|
|
606 args: (integer)
|
|
|
607 @end group
|
|
|
608
|
|
|
609 @group
|
|
|
610 0 varref integer ; @r{Get value of @code{integer}}
|
|
|
611 ; @r{from the environment}
|
|
|
612 ; @r{and push the value}
|
|
|
613 ; @r{onto the stack.}
|
|
|
614
|
|
|
615 1 constant 1 ; @r{Push 1 onto stack.}
|
|
|
616 @end group
|
|
|
617
|
|
|
618 @group
|
|
|
619 2 eqlsign ; @r{Pop top two values off stack,}
|
|
|
620 ; @r{compare them,}
|
|
|
621 ; @r{and push result onto stack.}
|
|
|
622 @end group
|
|
|
623
|
|
|
624 @group
|
|
|
625 3 goto-if-nil 1 ; @r{Pop and test top of stack;}
|
|
|
626 ; @r{if @code{nil},}
|
|
|
627 ; @r{go to label 1 (which is also byte 7),}
|
|
|
628 ; @r{else continue.}
|
|
|
629 @end group
|
|
|
630
|
|
|
631 @group
|
|
|
632 5 constant 1 ; @r{Push 1 onto top of stack.}
|
|
|
633
|
|
|
634 6 return ; @r{Return the top element}
|
|
|
635 ; @r{of the stack.}
|
|
|
636 @end group
|
|
|
637
|
|
|
638 7:1 varref integer ; @r{Push value of @code{integer} onto stack.}
|
|
|
639
|
|
|
640 @group
|
|
|
641 8 constant factorial ; @r{Push @code{factorial} onto stack.}
|
|
|
642
|
|
|
643 9 varref integer ; @r{Push value of @code{integer} onto stack.}
|
|
|
644
|
|
|
645 10 sub1 ; @r{Pop @code{integer}, decrement value,}
|
|
|
646 ; @r{push new value onto stack.}
|
|
|
647 @end group
|
|
|
648
|
|
|
649 @group
|
|
|
650 ; @r{Stack now contains:}
|
|
|
651 ; @minus{} @r{decremented value of @code{integer}}
|
|
|
652 ; @minus{} @r{@code{factorial}}
|
|
|
653 ; @minus{} @r{value of @code{integer}}
|
|
|
654 @end group
|
|
|
655
|
|
|
656 @group
|
|
|
657 15 call 1 ; @r{Call function @code{factorial} using}
|
|
|
658 ; @r{the first (i.e., the top) element}
|
|
|
659 ; @r{of the stack as the argument;}
|
|
|
660 ; @r{push returned value onto stack.}
|
|
|
661 @end group
|
|
|
662
|
|
|
663 @group
|
|
|
664 ; @r{Stack now contains:}
|
|
|
665 ; @minus{} @r{result of recursive}
|
|
|
666 ; @r{call to @code{factorial}}
|
|
|
667 ; @minus{} @r{value of @code{integer}}
|
|
|
668 @end group
|
|
|
669
|
|
|
670 @group
|
|
|
671 12 mult ; @r{Pop top two values off the stack,}
|
|
|
672 ; @r{multiply them,}
|
|
|
673 ; @r{pushing the result onto the stack.}
|
|
|
674 @end group
|
|
|
675
|
|
|
676 @group
|
|
|
677 13 return ; @r{Return the top element}
|
|
|
678 ; @r{of the stack.}
|
|
|
679 @result{} nil
|
|
|
680 @end group
|
|
|
681 @end example
|
|
|
682
|
|
|
683 The @code{silly-loop} function is somewhat more complex:
|
|
|
684
|
|
|
685 @example
|
|
|
686 @group
|
|
|
687 (defun silly-loop (n)
|
|
|
688 "Return time before and after N iterations of a loop."
|
|
|
689 (let ((t1 (current-time-string)))
|
|
|
690 (while (> (setq n (1- n))
|
|
|
691 0))
|
|
|
692 (list t1 (current-time-string))))
|
|
|
693 @result{} silly-loop
|
|
|
694 @end group
|
|
|
695
|
|
|
696 @group
|
|
|
697 (disassemble 'silly-loop)
|
|
|
698 @print{} byte-code for silly-loop:
|
|
|
699 doc: Return time before and after N iterations of a loop.
|
|
|
700 args: (n)
|
|
|
701
|
|
|
702 0 constant current-time-string ; @r{Push}
|
|
|
703 ; @r{@code{current-time-string}}
|
|
|
704 ; @r{onto top of stack.}
|
|
|
705 @end group
|
|
|
706
|
|
|
707 @group
|
|
|
708 1 call 0 ; @r{Call @code{current-time-string}}
|
|
|
709 ; @r{ with no argument,}
|
|
|
710 ; @r{ pushing result onto stack.}
|
|
|
711 @end group
|
|
|
712
|
|
|
713 @group
|
|
|
714 2 varbind t1 ; @r{Pop stack and bind @code{t1}}
|
|
|
715 ; @r{to popped value.}
|
|
|
716 @end group
|
|
|
717
|
|
|
718 @group
|
|
|
719 3:1 varref n ; @r{Get value of @code{n} from}
|
|
|
720 ; @r{the environment and push}
|
|
|
721 ; @r{the value onto the stack.}
|
|
|
722 @end group
|
|
|
723
|
|
|
724 @group
|
|
|
725 4 sub1 ; @r{Subtract 1 from top of stack.}
|
|
|
726 @end group
|
|
|
727
|
|
|
728 @group
|
|
|
729 5 dup ; @r{Duplicate the top of the stack;}
|
|
|
730 ; @r{i.e., copy the top of}
|
|
|
731 ; @r{the stack and push the}
|
|
|
732 ; @r{copy onto the stack.}
|
|
|
733
|
|
|
734 6 varset n ; @r{Pop the top of the stack,}
|
|
|
735 ; @r{and set @code{n} to the value.}
|
|
|
736
|
|
|
737 ; @r{In effect, the sequence @code{dup varset}}
|
|
|
738 ; @r{copies the top of the stack}
|
|
|
739 ; @r{into the value of @code{n}}
|
|
|
740 ; @r{without popping it.}
|
|
|
741 @end group
|
|
|
742
|
|
|
743 @group
|
|
|
744 7 constant 0 ; @r{Push 0 onto stack.}
|
|
|
745
|
|
|
746 8 gtr ; @r{Pop top two values off stack,}
|
|
|
747 ; @r{test if @var{n} is greater than 0}
|
|
|
748 ; @r{and push result onto stack.}
|
|
|
749 @end group
|
|
|
750
|
|
|
751 @group
|
|
|
752 9 goto-if-not-nil 1 ; @r{Goto label 1 (byte 3) if @code{n} <= 0}
|
|
|
753 ; @r{(this exits the while loop).}
|
|
|
754 ; @r{else pop top of stack}
|
|
|
755 ; @r{and continue}
|
|
|
756 @end group
|
|
|
757
|
|
|
758 @group
|
|
|
759 11 varref t1 ; @r{Push value of @code{t1} onto stack.}
|
|
|
760 @end group
|
|
|
761
|
|
|
762 @group
|
|
|
763 12 constant current-time-string ; @r{Push}
|
|
|
764 ; @r{@code{current-time-string}}
|
|
|
765 ; @r{onto top of stack.}
|
|
|
766 @end group
|
|
|
767
|
|
|
768 @group
|
|
|
769 13 call 0 ; @r{Call @code{current-time-string} again.}
|
|
|
770
|
|
|
771 14 unbind 1 ; @r{Unbind @code{t1} in local environment.}
|
|
|
772 @end group
|
|
|
773
|
|
|
774 @group
|
|
|
775 15 list2 ; @r{Pop top two elements off stack,}
|
|
|
776 ; @r{create a list of them,}
|
|
|
777 ; @r{and push list onto stack.}
|
|
|
778 @end group
|
|
|
779
|
|
|
780 @group
|
|
|
781 16 return ; @r{Return the top element of the stack.}
|
|
|
782
|
|
|
783 @result{} nil
|
|
|
784 @end group
|
|
|
785 @end example
|
|
|
786
|
|
|
787
|
|
446
|
788 @node Different Behavior
|
|
|
789 @section Different Behavior
|
|
|
790
|
|
|
791 The intent is that compiled byte-code and the corresponding code
|
|
|
792 executed by the Lisp interpreter produce identical results. However,
|
|
|
793 there are some circumstances where the results will differ.
|
|
|
794
|
|
|
795 @itemize @bullet
|
|
|
796 @item
|
|
|
797 Arithmetic operations may be rearranged for efficiency or compile-time
|
|
|
798 evaluation. When floating point numbers are involved, this may produce
|
|
|
799 different values or an overflow.
|
|
|
800 @item
|
|
|
801 Some arithmetic operations may be optimized away. For example, the
|
|
|
802 expression @code{(+ x)} may be optimized to simply @code{x}. If the
|
|
|
803 value of @code{x} is a marker, then the value will be a marker instead
|
|
|
804 of an integer. If the value of @samp{x} is a cons cell, then the
|
|
|
805 interpreter will issue an error, while the bytecode will not.
|
|
|
806
|
|
|
807 If you're trying to use @samp{(+ @var{object} 0)} to convert
|
|
|
808 @var{object} to integer, consider using an explicit conversion function,
|
|
|
809 which is clearer and guaranteed to work.
|
|
|
810 Instead of @samp{(+ @var{marker} 0)}, use @samp{(marker-position @var{marker})}.
|
|
|
811 Instead of @samp{(+ @var{char} 0)}, use @samp{(char-int @var{char})}.
|
|
|
812 @end itemize
|
|
|
813
|
|
|
814 For maximal equivalence between interpreted and compiled code, the
|
|
|
815 variables @code{byte-compile-delete-errors} and
|
|
|
816 @code{byte-compile-optimize} can be set to @code{nil}, but this is not
|
|
|
817 recommended.
|
