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1 @c -*-texinfo-*-
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2 @c This is part of the XEmacs Lisp Reference Manual.
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3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
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4 @c See the file lispref.texi for copying conditions.
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5 @setfilename ../../info/compile.info
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6 @node Byte Compilation, Debugging, Loading, Top
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7 @chapter Byte Compilation
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8 @cindex byte-code
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9 @cindex compilation
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10
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11 XEmacs Lisp has a @dfn{compiler} that translates functions written
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12 in Lisp into a special representation called @dfn{byte-code} that can be
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13 executed more efficiently. The compiler replaces Lisp function
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14 definitions with byte-code. When a byte-coded function is called, its
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15 definition is evaluated by the @dfn{byte-code interpreter}.
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16
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17 Because the byte-compiled code is evaluated by the byte-code
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18 interpreter, instead of being executed directly by the machine's
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19 hardware (as true compiled code is), byte-code is completely
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20 transportable from machine to machine without recompilation. It is not,
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21 however, as fast as true compiled code.
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22
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23 In general, any version of Emacs can run byte-compiled code produced
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24 by recent earlier versions of Emacs, but the reverse is not true. In
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25 particular, if you compile a program with XEmacs 20, the compiled code
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26 may not run in earlier versions.
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27
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28 The first time a compiled-function object is executed, the byte-code
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29 instructions are validated and the byte-code is further optimized. An
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30 @code{invalid-byte-code} error is signaled if the byte-code is invalid,
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31 for example if it contains invalid opcodes. This usually means a bug in
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32 the byte compiler.
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33
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34 @iftex
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35 @xref{Docs and Compilation}.
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36 @end iftex
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37
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38 @xref{Compilation Errors}, for how to investigate errors occurring in
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39 byte compilation.
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40
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41 @menu
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42 * Speed of Byte-Code:: An example of speedup from byte compilation.
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43 * Compilation Functions:: Byte compilation functions.
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44 * Docs and Compilation:: Dynamic loading of documentation strings.
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45 * Dynamic Loading:: Dynamic loading of individual functions.
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46 * Eval During Compile:: Code to be evaluated when you compile.
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47 * Compiled-Function Objects:: The data type used for byte-compiled functions.
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48 * Disassembly:: Disassembling byte-code; how to read byte-code.
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49 @end menu
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50
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51 @node Speed of Byte-Code
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52 @section Performance of Byte-Compiled Code
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53
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54 A byte-compiled function is not as efficient as a primitive function
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55 written in C, but runs much faster than the version written in Lisp.
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56 Here is an example:
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57
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58 @example
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59 @group
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60 (defun silly-loop (n)
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61 "Return time before and after N iterations of a loop."
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62 (let ((t1 (current-time-string)))
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63 (while (> (setq n (1- n))
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64 0))
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65 (list t1 (current-time-string))))
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66 @result{} silly-loop
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67 @end group
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68
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69 @group
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70 (silly-loop 5000000)
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71 @result{} ("Mon Sep 14 15:51:49 1998"
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72 "Mon Sep 14 15:52:07 1998") ; @r{18 seconds}
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73 @end group
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74
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75 @group
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76 (byte-compile 'silly-loop)
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77 @result{} #<compiled-function
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78 (n)
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79 "...(23)"
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80 [current-time-string t1 n 0]
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81 2
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82 "Return time before and after N iterations of a loop.">
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83 @end group
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84
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85 @group
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86 (silly-loop 5000000)
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87 @result{} ("Mon Sep 14 15:53:43 1998"
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88 "Mon Sep 14 15:53:49 1998") ; @r{6 seconds}
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89 @end group
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90 @end example
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91
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92 In this example, the interpreted code required 18 seconds to run,
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93 whereas the byte-compiled code required 6 seconds. These results are
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94 representative, but actual results will vary greatly.
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95
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96 @node Compilation Functions
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97 @comment node-name, next, previous, up
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98 @section The Compilation Functions
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99 @cindex compilation functions
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100
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101 You can byte-compile an individual function or macro definition with
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102 the @code{byte-compile} function. You can compile a whole file with
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103 @code{byte-compile-file}, or several files with
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104 @code{byte-recompile-directory} or @code{batch-byte-compile}.
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105
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106 When you run the byte compiler, you may get warnings in a buffer
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107 called @samp{*Compile-Log*}. These report things in your program that
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108 suggest a problem but are not necessarily erroneous.
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109
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110 @cindex macro compilation
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111 Be careful when byte-compiling code that uses macros. Macro calls are
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112 expanded when they are compiled, so the macros must already be defined
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113 for proper compilation. For more details, see @ref{Compiling Macros}.
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114
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115 Normally, compiling a file does not evaluate the file's contents or
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116 load the file. But it does execute any @code{require} calls at top
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117 level in the file. One way to ensure that necessary macro definitions
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118 are available during compilation is to @code{require} the file that defines
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119 them (@pxref{Named Features}). To avoid loading the macro definition files
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120 when someone @emph{runs} the compiled program, write
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121 @code{eval-when-compile} around the @code{require} calls (@pxref{Eval
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122 During Compile}).
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123
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124 @defun byte-compile symbol
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125 This function byte-compiles the function definition of @var{symbol},
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126 replacing the previous definition with the compiled one. The function
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127 definition of @var{symbol} must be the actual code for the function;
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128 i.e., the compiler does not follow indirection to another symbol.
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129 @code{byte-compile} returns the new, compiled definition of
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130 @var{symbol}.
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131
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132 If @var{symbol}'s definition is a compiled-function object,
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133 @code{byte-compile} does nothing and returns @code{nil}. Lisp records
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134 only one function definition for any symbol, and if that is already
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135 compiled, non-compiled code is not available anywhere. So there is no
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136 way to ``compile the same definition again.''
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137
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138 @example
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139 @group
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140 (defun factorial (integer)
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141 "Compute factorial of INTEGER."
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142 (if (= 1 integer) 1
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143 (* integer (factorial (1- integer)))))
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144 @result{} factorial
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145 @end group
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146
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147 @group
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148 (byte-compile 'factorial)
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149 @result{} #<compiled-function
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150 (integer)
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151 "...(21)"
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152 [integer 1 factorial]
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153 3
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154 "Compute factorial of INTEGER.">
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155 @end group
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156 @end example
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157
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158 @noindent
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159 The result is a compiled-function object. The string it contains is
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160 the actual byte-code; each character in it is an instruction or an
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161 operand of an instruction. The vector contains all the constants,
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162 variable names and function names used by the function, except for
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163 certain primitives that are coded as special instructions.
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164 @end defun
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165
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166 @deffn Command compile-defun &optional arg
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167 This command reads the defun containing point, compiles it, and
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168 evaluates the result. If you use this on a defun that is actually a
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169 function definition, the effect is to install a compiled version of that
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170 function.
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171
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172 @c XEmacs feature
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173 If @var{arg} is non-@code{nil}, the result is inserted in the current
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174 buffer after the form; otherwise, it is printed in the minibuffer.
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175 @end deffn
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176
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177 @deffn Command byte-compile-file filename &optional load
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178 This function compiles a file of Lisp code named @var{filename} into
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179 a file of byte-code. The output file's name is made by appending
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180 @samp{c} to the end of @var{filename}.
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181
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182 @c XEmacs feature
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183 If @code{load} is non-@code{nil}, the file is loaded after having been
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184 compiled.
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185
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186 Compilation works by reading the input file one form at a time. If it
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187 is a definition of a function or macro, the compiled function or macro
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188 definition is written out. Other forms are batched together, then each
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189 batch is compiled, and written so that its compiled code will be
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190 executed when the file is read. All comments are discarded when the
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191 input file is read.
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192
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193 This command returns @code{t}. When called interactively, it prompts
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194 for the file name.
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195
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196 @example
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197 @group
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198 % ls -l push*
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199 -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
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200 @end group
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201
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202 @group
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203 (byte-compile-file "~/emacs/push.el")
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204 @result{} t
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205 @end group
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206
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207 @group
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208 % ls -l push*
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209 -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
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210 -rw-r--r-- 1 lewis 638 Oct 8 20:25 push.elc
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211 @end group
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212 @end example
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213 @end deffn
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214
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215 @c flag is not optional in FSF Emacs
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216 @deffn Command byte-recompile-directory directory &optional flag norecursion force
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217 @cindex library compilation
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218 This function recompiles every @samp{.el} file in @var{directory} that
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219 needs recompilation. A file needs recompilation if a @samp{.elc} file
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220 exists but is older than the @samp{.el} file.
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221
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444
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222 Files in subdirectories of @var{directory} are also processed unless
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223 optional argument @var{norecursion} is non-@code{nil}.
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224
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225 When a @samp{.el} file has no corresponding @samp{.elc} file, then
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226 @var{flag} says what to do. If it is @code{nil}, these files are
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227 ignored. If it is non-@code{nil}, the user is asked whether to compile
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228 each such file.
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229
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444
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230 If the fourth optional argument @var{force} is non-@code{nil},
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231 recompile every @samp{.el} file that already has a @samp{.elc} file.
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232
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233 The return value of this command is unpredictable.
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234 @end deffn
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235
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236 @defun batch-byte-compile
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237 This function runs @code{byte-compile-file} on files specified on the
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238 command line. This function must be used only in a batch execution of
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239 Emacs, as it kills Emacs on completion. An error in one file does not
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240 prevent processing of subsequent files. (The file that gets the error
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241 will not, of course, produce any compiled code.)
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242
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243 @example
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442
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244 % xemacs -batch -f batch-byte-compile *.el
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428
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245 @end example
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246 @end defun
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247
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248 @c XEmacs feature
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249 @defun batch-byte-recompile-directory
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250 This function is similar to @code{batch-byte-compile} but runs the
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251 command @code{byte-recompile-directory} on the files remaining on the
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252 command line.
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253 @end defun
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254
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255 @c XEmacs feature
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256 @defvar byte-recompile-directory-ignore-errors-p
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257 If non-@code{nil}, this specifies that @code{byte-recompile-directory}
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258 will continue compiling even when an error occurs in a file. This is
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259 normally @code{nil}, but is bound to @code{t} by
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260 @code{batch-byte-recompile-directory}.
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261 @end defvar
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262
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444
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263 @defun byte-code instructions constants stack-depth
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264 @cindex byte-code interpreter
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265 This function actually interprets byte-code.
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266 Don't call this function yourself. Only the byte compiler knows how to
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267 generate valid calls to this function.
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268
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269 In newer Emacs versions (19 and up), byte code is usually executed as
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270 part of a compiled-function object, and only rarely due to an explicit
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271 call to @code{byte-code}. A byte-compiled function was once actually
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272 defined with a body that calls @code{byte-code}, but in recent versions
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273 of Emacs @code{byte-code} is only used to run isolated fragments of lisp
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274 code without an associated argument list.
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275 @end defun
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276
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277 @node Docs and Compilation
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278 @section Documentation Strings and Compilation
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279 @cindex dynamic loading of documentation
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280
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281 Functions and variables loaded from a byte-compiled file access their
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282 documentation strings dynamically from the file whenever needed. This
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283 saves space within Emacs, and makes loading faster because the
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284 documentation strings themselves need not be processed while loading the
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285 file. Actual access to the documentation strings becomes slower as a
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286 result, but normally not enough to bother users.
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287
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288 Dynamic access to documentation strings does have drawbacks:
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289
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290 @itemize @bullet
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291 @item
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292 If you delete or move the compiled file after loading it, Emacs can no
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293 longer access the documentation strings for the functions and variables
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294 in the file.
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295
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296 @item
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297 If you alter the compiled file (such as by compiling a new version),
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298 then further access to documentation strings in this file will give
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299 nonsense results.
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300 @end itemize
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301
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302 If your site installs Emacs following the usual procedures, these
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303 problems will never normally occur. Installing a new version uses a new
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304 directory with a different name; as long as the old version remains
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305 installed, its files will remain unmodified in the places where they are
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306 expected to be.
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307
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308 However, if you have built Emacs yourself and use it from the
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309 directory where you built it, you will experience this problem
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310 occasionally if you edit and recompile Lisp files. When it happens, you
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311 can cure the problem by reloading the file after recompiling it.
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312
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313 Versions of Emacs up to and including XEmacs 19.14 and FSF Emacs 19.28
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314 do not support the dynamic docstrings feature, and so will not be able
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315 to load bytecode created by more recent Emacs versions. You can turn
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316 off the dynamic docstring feature by setting
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317 @code{byte-compile-dynamic-docstrings} to @code{nil}. Once this is
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318 done, you can compile files that will load into older Emacs versions.
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319 You can do this globally, or for one source file by specifying a
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320 file-local binding for the variable. Here's one way to do that:
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321
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322 @example
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323 -*-byte-compile-dynamic-docstrings: nil;-*-
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324 @end example
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325
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326 @defvar byte-compile-dynamic-docstrings
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327 If this is non-@code{nil}, the byte compiler generates compiled files
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328 that are set up for dynamic loading of documentation strings.
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329 @end defvar
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330
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331 @cindex @samp{#@@@var{count}}
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332 @cindex @samp{#$}
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333 The dynamic documentation string feature writes compiled files that
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334 use a special Lisp reader construct, @samp{#@@@var{count}}. This
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335 construct skips the next @var{count} characters. It also uses the
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336 @samp{#$} construct, which stands for ``the name of this file, as a
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337 string.'' It is best not to use these constructs in Lisp source files.
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338
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339 @node Dynamic Loading
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340 @section Dynamic Loading of Individual Functions
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341
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342 @cindex dynamic loading of functions
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343 @cindex lazy loading
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344 When you compile a file, you can optionally enable the @dfn{dynamic
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345 function loading} feature (also known as @dfn{lazy loading}). With
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346 dynamic function loading, loading the file doesn't fully read the
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347 function definitions in the file. Instead, each function definition
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348 contains a place-holder which refers to the file. The first time each
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349 function is called, it reads the full definition from the file, to
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350 replace the place-holder.
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351
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352 The advantage of dynamic function loading is that loading the file
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353 becomes much faster. This is a good thing for a file which contains
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354 many separate commands, provided that using one of them does not imply
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355 you will soon (or ever) use the rest. A specialized mode which provides
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356 many keyboard commands often has that usage pattern: a user may invoke
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357 the mode, but use only a few of the commands it provides.
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358
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359 The dynamic loading feature has certain disadvantages:
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360
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361 @itemize @bullet
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362 @item
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363 If you delete or move the compiled file after loading it, Emacs can no
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364 longer load the remaining function definitions not already loaded.
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365
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366 @item
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367 If you alter the compiled file (such as by compiling a new version),
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368 then trying to load any function not already loaded will get nonsense
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369 results.
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370 @end itemize
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371
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372 If you compile a new version of the file, the best thing to do is
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373 immediately load the new compiled file. That will prevent any future
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374 problems.
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375
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376 The byte compiler uses the dynamic function loading feature if the
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377 variable @code{byte-compile-dynamic} is non-@code{nil} at compilation
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378 time. Do not set this variable globally, since dynamic loading is
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379 desirable only for certain files. Instead, enable the feature for
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380 specific source files with file-local variable bindings, like this:
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381
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382 @example
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383 -*-byte-compile-dynamic: t;-*-
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384 @end example
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385
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386 @defvar byte-compile-dynamic
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387 If this is non-@code{nil}, the byte compiler generates compiled files
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388 that are set up for dynamic function loading.
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389 @end defvar
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390
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391 @defun fetch-bytecode function
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|
|
392 This immediately finishes loading the definition of @var{function} from
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|
|
393 its byte-compiled file, if it is not fully loaded already. The argument
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|
|
394 @var{function} may be a compiled-function object or a function name.
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|
|
395 @end defun
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|
|
396
|
|
|
397 @node Eval During Compile
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|
|
398 @section Evaluation During Compilation
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|
|
399
|
|
|
400 These features permit you to write code to be evaluated during
|
|
|
401 compilation of a program.
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|
|
402
|
|
|
403 @defspec eval-and-compile body
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|
|
404 This form marks @var{body} to be evaluated both when you compile the
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|
|
405 containing code and when you run it (whether compiled or not).
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|
|
406
|
|
|
407 You can get a similar result by putting @var{body} in a separate file
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|
|
408 and referring to that file with @code{require}. Using @code{require} is
|
|
|
409 preferable if there is a substantial amount of code to be executed in
|
|
|
410 this way.
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|
|
411 @end defspec
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|
|
412
|
|
|
413 @defspec eval-when-compile body
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|
|
414 This form marks @var{body} to be evaluated at compile time and not when
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|
|
415 the compiled program is loaded. The result of evaluation by the
|
|
|
416 compiler becomes a constant which appears in the compiled program. When
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|
417 the program is interpreted, not compiled at all, @var{body} is evaluated
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|
|
418 normally.
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|
|
419
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|
420 At top level, this is analogous to the Common Lisp idiom
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|
|
421 @code{(eval-when (compile eval) @dots{})}. Elsewhere, the Common Lisp
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|
|
422 @samp{#.} reader macro (but not when interpreting) is closer to what
|
|
|
423 @code{eval-when-compile} does.
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|
|
424 @end defspec
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|
|
425
|
|
|
426 @node Compiled-Function Objects
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|
|
427 @section Compiled-Function Objects
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|
|
428 @cindex compiled function
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|
|
429 @cindex byte-code function
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|
|
430
|
|
|
431 Byte-compiled functions have a special data type: they are
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|
|
432 @dfn{compiled-function objects}. The evaluator handles this data type
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|
433 specially when it appears as a function to be called.
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|
|
434
|
|
|
435 The printed representation for a compiled-function object normally
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|
436 begins with @samp{#<compiled-function} and ends with @samp{>}. However,
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|
|
437 if the variable @code{print-readably} is non-@code{nil}, the object is
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|
|
438 printed beginning with @samp{#[} and ending with @samp{]}. This
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|
|
439 representation can be read directly by the Lisp reader, and is used in
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|
|
440 byte-compiled files (those ending in @samp{.elc}).
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|
|
441
|
|
|
442 In Emacs version 18, there was no compiled-function object data type;
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|
443 compiled functions used the function @code{byte-code} to run the byte
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|
|
444 code.
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|
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445
|
|
|
446 A compiled-function object has a number of different attributes.
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|
447 They are:
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|
|
448
|
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|
449 @table @var
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|
450 @item arglist
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|
|
451 The list of argument symbols.
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|
|
452
|
|
|
453 @item instructions
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|
|
454 The string containing the byte-code instructions.
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|
|
455
|
|
|
456 @item constants
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|
|
457 The vector of Lisp objects referenced by the byte code. These include
|
|
|
458 symbols used as function names and variable names.
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|
|
459
|
|
444
|
460 @item stack-depth
|
|
428
|
461 The maximum stack size this function needs.
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|
|
462
|
|
|
463 @item doc-string
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|
|
464 The documentation string (if any); otherwise, @code{nil}. The value may
|
|
|
465 be a number or a list, in case the documentation string is stored in a
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|
|
466 file. Use the function @code{documentation} to get the real
|
|
|
467 documentation string (@pxref{Accessing Documentation}).
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|
|
468
|
|
|
469 @item interactive
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|
|
470 The interactive spec (if any). This can be a string or a Lisp
|
|
|
471 expression. It is @code{nil} for a function that isn't interactive.
|
|
|
472
|
|
|
473 @item domain
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|
|
474 The domain (if any). This is only meaningful if I18N3 (message-translation)
|
|
|
475 support was compiled into XEmacs. This is a string defining which
|
|
|
476 domain to find the translation for the documentation string and
|
|
|
477 interactive prompt. @xref{Domain Specification}.
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|
|
478 @end table
|
|
|
479
|
|
|
480 Here's an example of a compiled-function object, in printed
|
|
|
481 representation. It is the definition of the command
|
|
|
482 @code{backward-sexp}.
|
|
|
483
|
|
|
484 @example
|
|
|
485 (symbol-function 'backward-sexp)
|
|
|
486 @result{} #<compiled-function
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|
|
487 (&optional arg)
|
|
|
488 "...(15)" [arg 1 forward-sexp] 2 854740 "_p">
|
|
|
489 @end example
|
|
|
490
|
|
|
491 The primitive way to create a compiled-function object is with
|
|
|
492 @code{make-byte-code}:
|
|
|
493
|
|
444
|
494 @defun make-byte-code arglist instructions constants stack-depth &optional doc-string interactive
|
|
428
|
495 This function constructs and returns a compiled-function object
|
|
|
496 with the specified attributes.
|
|
|
497
|
|
|
498 @emph{Please note:} Unlike all other Emacs-lisp functions, calling this with
|
|
|
499 five arguments is @emph{not} the same as calling it with six arguments,
|
|
|
500 the last of which is @code{nil}. If the @var{interactive} arg is
|
|
|
501 specified as @code{nil}, then that means that this function was defined
|
|
|
502 with @code{(interactive)}. If the arg is not specified, then that means
|
|
|
503 the function is not interactive. This is terrible behavior which is
|
|
|
504 retained for compatibility with old @samp{.elc} files which expected
|
|
|
505 these semantics.
|
|
|
506 @end defun
|
|
|
507
|
|
|
508 You should not try to come up with the elements for a compiled-function
|
|
|
509 object yourself, because if they are inconsistent, XEmacs may crash
|
|
|
510 when you call the function. Always leave it to the byte compiler to
|
|
|
511 create these objects; it makes the elements consistent (we hope).
|
|
|
512
|
|
|
513 The following primitives are provided for accessing the elements of
|
|
|
514 a compiled-function object.
|
|
|
515
|
|
|
516 @defun compiled-function-arglist function
|
|
|
517 This function returns the argument list of compiled-function object
|
|
|
518 @var{function}.
|
|
|
519 @end defun
|
|
|
520
|
|
|
521 @defun compiled-function-instructions function
|
|
|
522 This function returns a string describing the byte-code instructions
|
|
|
523 of compiled-function object @var{function}.
|
|
|
524 @end defun
|
|
|
525
|
|
|
526 @defun compiled-function-constants function
|
|
|
527 This function returns the vector of Lisp objects referenced by
|
|
|
528 compiled-function object @var{function}.
|
|
|
529 @end defun
|
|
|
530
|
|
444
|
531 @defun compiled-function-stack-depth function
|
|
428
|
532 This function returns the maximum stack size needed by compiled-function
|
|
|
533 object @var{function}.
|
|
|
534 @end defun
|
|
|
535
|
|
|
536 @defun compiled-function-doc-string function
|
|
|
537 This function returns the doc string of compiled-function object
|
|
|
538 @var{function}, if available.
|
|
|
539 @end defun
|
|
|
540
|
|
|
541 @defun compiled-function-interactive function
|
|
|
542 This function returns the interactive spec of compiled-function object
|
|
|
543 @var{function}, if any. The return value is @code{nil} or a two-element
|
|
|
544 list, the first element of which is the symbol @code{interactive} and
|
|
|
545 the second element is the interactive spec (a string or Lisp form).
|
|
|
546 @end defun
|
|
|
547
|
|
|
548 @defun compiled-function-domain function
|
|
|
549 This function returns the domain of compiled-function object
|
|
|
550 @var{function}, if any. The result will be a string or @code{nil}.
|
|
|
551 @xref{Domain Specification}.
|
|
|
552 @end defun
|
|
|
553
|
|
|
554 @node Disassembly
|
|
|
555 @section Disassembled Byte-Code
|
|
|
556 @cindex disassembled byte-code
|
|
|
557
|
|
|
558 People do not write byte-code; that job is left to the byte compiler.
|
|
|
559 But we provide a disassembler to satisfy a cat-like curiosity. The
|
|
|
560 disassembler converts the byte-compiled code into humanly readable
|
|
|
561 form.
|
|
|
562
|
|
|
563 The byte-code interpreter is implemented as a simple stack machine.
|
|
|
564 It pushes values onto a stack of its own, then pops them off to use them
|
|
|
565 in calculations whose results are themselves pushed back on the stack.
|
|
|
566 When a byte-code function returns, it pops a value off the stack and
|
|
|
567 returns it as the value of the function.
|
|
|
568
|
|
|
569 In addition to the stack, byte-code functions can use, bind, and set
|
|
|
570 ordinary Lisp variables, by transferring values between variables and
|
|
|
571 the stack.
|
|
|
572
|
|
|
573 @deffn Command disassemble object &optional stream
|
|
|
574 This function prints the disassembled code for @var{object}. If
|
|
|
575 @var{stream} is supplied, then output goes there. Otherwise, the
|
|
|
576 disassembled code is printed to the stream @code{standard-output}. The
|
|
|
577 argument @var{object} can be a function name or a lambda expression.
|
|
|
578
|
|
|
579 As a special exception, if this function is used interactively,
|
|
|
580 it outputs to a buffer named @samp{*Disassemble*}.
|
|
|
581 @end deffn
|
|
|
582
|
|
|
583 Here are two examples of using the @code{disassemble} function. We
|
|
|
584 have added explanatory comments to help you relate the byte-code to the
|
|
|
585 Lisp source; these do not appear in the output of @code{disassemble}.
|
|
|
586
|
|
|
587 @example
|
|
|
588 @group
|
|
|
589 (defun factorial (integer)
|
|
|
590 "Compute factorial of an integer."
|
|
|
591 (if (= 1 integer) 1
|
|
|
592 (* integer (factorial (1- integer)))))
|
|
|
593 @result{} factorial
|
|
|
594 @end group
|
|
|
595
|
|
|
596 @group
|
|
|
597 (factorial 4)
|
|
|
598 @result{} 24
|
|
|
599 @end group
|
|
|
600
|
|
|
601 @group
|
|
|
602 (disassemble 'factorial)
|
|
|
603 @print{} byte-code for factorial:
|
|
|
604 doc: Compute factorial of an integer.
|
|
|
605 args: (integer)
|
|
|
606 @end group
|
|
|
607
|
|
|
608 @group
|
|
|
609 0 varref integer ; @r{Get value of @code{integer}}
|
|
|
610 ; @r{from the environment}
|
|
|
611 ; @r{and push the value}
|
|
|
612 ; @r{onto the stack.}
|
|
|
613
|
|
|
614 1 constant 1 ; @r{Push 1 onto stack.}
|
|
|
615 @end group
|
|
|
616
|
|
|
617 @group
|
|
|
618 2 eqlsign ; @r{Pop top two values off stack,}
|
|
|
619 ; @r{compare them,}
|
|
|
620 ; @r{and push result onto stack.}
|
|
|
621 @end group
|
|
|
622
|
|
|
623 @group
|
|
|
624 3 goto-if-nil 1 ; @r{Pop and test top of stack;}
|
|
|
625 ; @r{if @code{nil},}
|
|
|
626 ; @r{go to label 1 (which is also byte 7),}
|
|
|
627 ; @r{else continue.}
|
|
|
628 @end group
|
|
|
629
|
|
|
630 @group
|
|
|
631 5 constant 1 ; @r{Push 1 onto top of stack.}
|
|
|
632
|
|
|
633 6 return ; @r{Return the top element}
|
|
|
634 ; @r{of the stack.}
|
|
|
635 @end group
|
|
|
636
|
|
|
637 7:1 varref integer ; @r{Push value of @code{integer} onto stack.}
|
|
|
638
|
|
|
639 @group
|
|
|
640 8 constant factorial ; @r{Push @code{factorial} onto stack.}
|
|
|
641
|
|
|
642 9 varref integer ; @r{Push value of @code{integer} onto stack.}
|
|
|
643
|
|
|
644 10 sub1 ; @r{Pop @code{integer}, decrement value,}
|
|
|
645 ; @r{push new value onto stack.}
|
|
|
646 @end group
|
|
|
647
|
|
|
648 @group
|
|
|
649 ; @r{Stack now contains:}
|
|
|
650 ; @minus{} @r{decremented value of @code{integer}}
|
|
|
651 ; @minus{} @r{@code{factorial}}
|
|
|
652 ; @minus{} @r{value of @code{integer}}
|
|
|
653 @end group
|
|
|
654
|
|
|
655 @group
|
|
|
656 15 call 1 ; @r{Call function @code{factorial} using}
|
|
|
657 ; @r{the first (i.e., the top) element}
|
|
|
658 ; @r{of the stack as the argument;}
|
|
|
659 ; @r{push returned value onto stack.}
|
|
|
660 @end group
|
|
|
661
|
|
|
662 @group
|
|
|
663 ; @r{Stack now contains:}
|
|
|
664 ; @minus{} @r{result of recursive}
|
|
|
665 ; @r{call to @code{factorial}}
|
|
|
666 ; @minus{} @r{value of @code{integer}}
|
|
|
667 @end group
|
|
|
668
|
|
|
669 @group
|
|
|
670 12 mult ; @r{Pop top two values off the stack,}
|
|
|
671 ; @r{multiply them,}
|
|
|
672 ; @r{pushing the result onto the stack.}
|
|
|
673 @end group
|
|
|
674
|
|
|
675 @group
|
|
|
676 13 return ; @r{Return the top element}
|
|
|
677 ; @r{of the stack.}
|
|
|
678 @result{} nil
|
|
|
679 @end group
|
|
|
680 @end example
|
|
|
681
|
|
|
682 The @code{silly-loop} function is somewhat more complex:
|
|
|
683
|
|
|
684 @example
|
|
|
685 @group
|
|
|
686 (defun silly-loop (n)
|
|
|
687 "Return time before and after N iterations of a loop."
|
|
|
688 (let ((t1 (current-time-string)))
|
|
|
689 (while (> (setq n (1- n))
|
|
|
690 0))
|
|
|
691 (list t1 (current-time-string))))
|
|
|
692 @result{} silly-loop
|
|
|
693 @end group
|
|
|
694
|
|
|
695 @group
|
|
|
696 (disassemble 'silly-loop)
|
|
|
697 @print{} byte-code for silly-loop:
|
|
|
698 doc: Return time before and after N iterations of a loop.
|
|
|
699 args: (n)
|
|
|
700
|
|
|
701 0 constant current-time-string ; @r{Push}
|
|
|
702 ; @r{@code{current-time-string}}
|
|
|
703 ; @r{onto top of stack.}
|
|
|
704 @end group
|
|
|
705
|
|
|
706 @group
|
|
|
707 1 call 0 ; @r{Call @code{current-time-string}}
|
|
|
708 ; @r{ with no argument,}
|
|
|
709 ; @r{ pushing result onto stack.}
|
|
|
710 @end group
|
|
|
711
|
|
|
712 @group
|
|
|
713 2 varbind t1 ; @r{Pop stack and bind @code{t1}}
|
|
|
714 ; @r{to popped value.}
|
|
|
715 @end group
|
|
|
716
|
|
|
717 @group
|
|
|
718 3:1 varref n ; @r{Get value of @code{n} from}
|
|
|
719 ; @r{the environment and push}
|
|
|
720 ; @r{the value onto the stack.}
|
|
|
721 @end group
|
|
|
722
|
|
|
723 @group
|
|
|
724 4 sub1 ; @r{Subtract 1 from top of stack.}
|
|
|
725 @end group
|
|
|
726
|
|
|
727 @group
|
|
|
728 5 dup ; @r{Duplicate the top of the stack;}
|
|
|
729 ; @r{i.e., copy the top of}
|
|
|
730 ; @r{the stack and push the}
|
|
|
731 ; @r{copy onto the stack.}
|
|
|
732
|
|
|
733 6 varset n ; @r{Pop the top of the stack,}
|
|
|
734 ; @r{and set @code{n} to the value.}
|
|
|
735
|
|
|
736 ; @r{In effect, the sequence @code{dup varset}}
|
|
|
737 ; @r{copies the top of the stack}
|
|
|
738 ; @r{into the value of @code{n}}
|
|
|
739 ; @r{without popping it.}
|
|
|
740 @end group
|
|
|
741
|
|
|
742 @group
|
|
|
743 7 constant 0 ; @r{Push 0 onto stack.}
|
|
|
744
|
|
|
745 8 gtr ; @r{Pop top two values off stack,}
|
|
|
746 ; @r{test if @var{n} is greater than 0}
|
|
|
747 ; @r{and push result onto stack.}
|
|
|
748 @end group
|
|
|
749
|
|
|
750 @group
|
|
|
751 9 goto-if-not-nil 1 ; @r{Goto label 1 (byte 3) if @code{n} <= 0}
|
|
|
752 ; @r{(this exits the while loop).}
|
|
|
753 ; @r{else pop top of stack}
|
|
|
754 ; @r{and continue}
|
|
|
755 @end group
|
|
|
756
|
|
|
757 @group
|
|
|
758 11 varref t1 ; @r{Push value of @code{t1} onto stack.}
|
|
|
759 @end group
|
|
|
760
|
|
|
761 @group
|
|
|
762 12 constant current-time-string ; @r{Push}
|
|
|
763 ; @r{@code{current-time-string}}
|
|
|
764 ; @r{onto top of stack.}
|
|
|
765 @end group
|
|
|
766
|
|
|
767 @group
|
|
|
768 13 call 0 ; @r{Call @code{current-time-string} again.}
|
|
|
769
|
|
|
770 14 unbind 1 ; @r{Unbind @code{t1} in local environment.}
|
|
|
771 @end group
|
|
|
772
|
|
|
773 @group
|
|
|
774 15 list2 ; @r{Pop top two elements off stack,}
|
|
|
775 ; @r{create a list of them,}
|
|
|
776 ; @r{and push list onto stack.}
|
|
|
777 @end group
|
|
|
778
|
|
|
779 @group
|
|
|
780 16 return ; @r{Return the top element of the stack.}
|
|
|
781
|
|
|
782 @result{} nil
|
|
|
783 @end group
|
|
|
784 @end example
|
|
|
785
|
|
|
786
|
