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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/loading.info
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6 @node Loading, Byte Compilation, Macros, Top
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7 @chapter Loading
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8 @cindex loading
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9 @cindex library
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10 @cindex Lisp library
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11
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12 Loading a file of Lisp code means bringing its contents into the Lisp
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13 environment in the form of Lisp objects. XEmacs finds and opens the
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14 file, reads the text, evaluates each form, and then closes the file.
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15
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16 The load functions evaluate all the expressions in a file just
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17 as the @code{eval-current-buffer} function evaluates all the
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18 expressions in a buffer. The difference is that the load functions
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19 read and evaluate the text in the file as found on disk, not the text
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20 in an Emacs buffer.
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21
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22 @cindex top-level form
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23 The loaded file must contain Lisp expressions, either as source code
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24 or as byte-compiled code. Each form in the file is called a
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25 @dfn{top-level form}. There is no special format for the forms in a
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26 loadable file; any form in a file may equally well be typed directly
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27 into a buffer and evaluated there. (Indeed, most code is tested this
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28 way.) Most often, the forms are function definitions and variable
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29 definitions.
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30
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31 A file containing Lisp code is often called a @dfn{library}. Thus,
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32 the ``Rmail library'' is a file containing code for Rmail mode.
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33 Similarly, a ``Lisp library directory'' is a directory of files
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34 containing Lisp code.
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35
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36 @menu
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37 * How Programs Do Loading:: The @code{load} function and others.
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38 * Autoload:: Setting up a function to autoload.
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39 * Repeated Loading:: Precautions about loading a file twice.
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40 * Named Features:: Loading a library if it isn't already loaded.
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41 * Unloading:: How to ``unload'' a library that was loaded.
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42 * Hooks for Loading:: Providing code to be run when
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43 particular libraries are loaded.
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44 @end menu
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45
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46 @node How Programs Do Loading
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47 @section How Programs Do Loading
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48
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49 XEmacs Lisp has several interfaces for loading. For example,
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50 @code{autoload} creates a placeholder object for a function in a file;
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51 trying to call the autoloading function loads the file to get the
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52 function's real definition (@pxref{Autoload}). @code{require} loads a
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53 file if it isn't already loaded (@pxref{Named Features}). Ultimately, all
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54 these facilities call the @code{load} function to do the work.
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55
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56 @defun load filename &optional missing-ok nomessage nosuffix
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57 This function finds and opens a file of Lisp code, evaluates all the
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58 forms in it, and closes the file.
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59
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60 To find the file, @code{load} first looks for a file named
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61 @file{@var{filename}.elc}, that is, for a file whose name is
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62 @var{filename} with @samp{.elc} appended. If such a file exists, it is
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63 loaded. If there is no file by that name, then @code{load} looks for a
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64 file named @file{@var{filename}.el}. If that file exists, it is loaded.
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65 Finally, if neither of those names is found, @code{load} looks for a
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66 file named @var{filename} with nothing appended, and loads it if it
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67 exists. (The @code{load} function is not clever about looking at
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68 @var{filename}. In the perverse case of a file named @file{foo.el.el},
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69 evaluation of @code{(load "foo.el")} will indeed find it.)
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70
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71 If the optional argument @var{nosuffix} is non-@code{nil}, then the
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72 suffixes @samp{.elc} and @samp{.el} are not tried. In this case, you
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73 must specify the precise file name you want.
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74
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75 If @var{filename} is a relative file name, such as @file{foo} or
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76 @file{baz/foo.bar}, @code{load} searches for the file using the variable
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77 @code{load-path}. It appends @var{filename} to each of the directories
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78 listed in @code{load-path}, and loads the first file it finds whose name
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79 matches. The current default directory is tried only if it is specified
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80 in @code{load-path}, where @code{nil} stands for the default directory.
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81 @code{load} tries all three possible suffixes in the first directory in
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82 @code{load-path}, then all three suffixes in the second directory, and
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83 so on.
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84
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85 If you get a warning that @file{foo.elc} is older than @file{foo.el}, it
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86 means you should consider recompiling @file{foo.el}. @xref{Byte
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87 Compilation}.
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88
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89 Messages like @samp{Loading foo...} and @samp{Loading foo...done} appear
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90 in the echo area during loading unless @var{nomessage} is
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91 non-@code{nil}.
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92
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93 @cindex load errors
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94 Any unhandled errors while loading a file terminate loading. If the
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95 load was done for the sake of @code{autoload}, any function definitions
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96 made during the loading are undone.
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97
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98 @kindex file-error
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99 If @code{load} can't find the file to load, then normally it signals the
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100 error @code{file-error} (with @samp{Cannot open load file
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101 @var{filename}}). But if @var{missing-ok} is non-@code{nil}, then
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102 @code{load} just returns @code{nil}.
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103
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104 You can use the variable @code{load-read-function} to specify a function
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105 for @code{load} to use instead of @code{read} for reading expressions.
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106 See below.
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107
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108 @code{load} returns @code{t} if the file loads successfully.
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109 @end defun
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110
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111 @ignore
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112 @deffn Command load-file filename
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113 This function loads the file @var{filename}. If @var{filename} is an
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114 absolute file name, then it is loaded. If it is relative, then the
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115 current default directory is assumed. @code{load-path} is not used, and
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116 suffixes are not appended. Use this function if you wish to specify
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117 the file to be loaded exactly.
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118 @end deffn
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119
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120 @deffn Command load-library library
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121 This function loads the library named @var{library}. A library is
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122 nothing more than a file that may be loaded as described earlier. This
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123 function is identical to @code{load}, save that it reads a file name
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124 interactively with completion.
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125 @end deffn
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126 @end ignore
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127
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128 @defopt load-path
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129 @cindex @code{EMACSLOADPATH} environment variable
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130 The value of this variable is a list of directories to search when
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131 loading files with @code{load}. Each element is a string (which must be
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132 a directory name) or @code{nil} (which stands for the current working
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133 directory). The value of @code{load-path} is initialized from the
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134 environment variable @code{EMACSLOADPATH}, if that exists; otherwise its
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135 default value is specified in @file{emacs/src/paths.h} when XEmacs is
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136 built.
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137
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138 The syntax of @code{EMACSLOADPATH} is the same as used for @code{PATH};
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139 @samp{:} (or @samp{;}, according to the operating system) separates
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140 directory names, and @samp{.} is used for the current default directory.
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141 Here is an example of how to set your @code{EMACSLOADPATH} variable from
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142 a @code{csh} @file{.login} file:
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143
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144 @c This overfull hbox is OK. --rjc 16mar92
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145 @smallexample
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146 setenv EMACSLOADPATH .:/user/bil/emacs:/usr/lib/emacs/lisp
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147 @end smallexample
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148
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149 Here is how to set it using @code{sh}:
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150
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151 @smallexample
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152 export EMACSLOADPATH
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153 EMACSLOADPATH=.:/user/bil/emacs:/usr/local/lib/emacs/lisp
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154 @end smallexample
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155
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156 Here is an example of code you can place in a @file{.emacs} file to add
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157 several directories to the front of your default @code{load-path}:
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158
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159 @smallexample
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160 @group
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161 (setq load-path
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162 (append (list nil "/user/bil/emacs"
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163 "/usr/local/lisplib"
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164 "~/emacs")
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165 load-path))
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166 @end group
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167 @end smallexample
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168
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169 @c Wordy to rid us of an overfull hbox. --rjc 15mar92
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170 @noindent
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171 In this example, the path searches the current working directory first,
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172 followed then by the @file{/user/bil/emacs} directory, the
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173 @file{/usr/local/lisplib} directory, and the @file{~/emacs} directory,
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174 which are then followed by the standard directories for Lisp code.
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175
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176 The command line options @samp{-l} or @samp{-load} specify a Lisp
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177 library to load as part of Emacs startup. Since this file might be in
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178 the current directory, Emacs 18 temporarily adds the current directory
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179 to the front of @code{load-path} so the file can be found there. Newer
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180 Emacs versions also find such files in the current directory, but
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181 without altering @code{load-path}.
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182
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183 Dumping Emacs uses a special value of @code{load-path}. If the value of
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184 @code{load-path} at the end of dumping is unchanged (that is, still the
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185 same special value), the dumped Emacs switches to the ordinary
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186 @code{load-path} value when it starts up, as described above. But if
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187 @code{load-path} has any other value at the end of dumping, that value
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188 is used for execution of the dumped Emacs also.
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189
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190 Therefore, if you want to change @code{load-path} temporarily for
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191 loading a few libraries in @file{site-init.el} or @file{site-load.el},
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192 you should bind @code{load-path} locally with @code{let} around the
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193 calls to @code{load}.
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194 @end defopt
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195
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196 @defun locate-file filename path-list &optional suffixes mode
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197 This function searches for a file in the same way that @code{load} does,
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198 and returns the file found (if any). (In fact, @code{load} uses this
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199 function to search through @code{load-path}.) It searches for
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200 @var{filename} through @var{path-list}, expanded by one of the optional
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201 @var{suffixes} (string of suffixes separated by @samp{:}s), checking for
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202 access @var{mode} (0|1|2|4 = exists|executable|writable|readable),
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203 default readable.
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204
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205 @code{locate-file} keeps hash tables of the directories it searches
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206 through, in order to speed things up. It tries valiantly to not get
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207 confused in the face of a changing and unpredictable environment, but
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208 can occasionally get tripped up. In this case, you will have to call
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209 @code{locate-file-clear-hashing} to get it back on track. See that
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210 function for details.
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211 @end defun
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212
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213 @defun locate-file-clear-hashing path
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214 This function clears the hash records for the specified list of
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215 directories. @code{locate-file} uses a hashing scheme to speed lookup, and
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216 will correctly track the following environmental changes:
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217
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218 @itemize @bullet
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219 @item
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220 changes of any sort to the list of directories to be searched.
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221 @item
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222 addition and deletion of non-shadowing files (see below) from the
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223 directories in the list.
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224 @item
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225 byte-compilation of a .el file into a .elc file.
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226 @end itemize
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227
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228 @code{locate-file} will primarily get confused if you add a file that
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229 shadows (i.e. has the same name as) another file further down in the
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230 directory list. In this case, you must call
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231 @code{locate-file-clear-hashing}.
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232 @end defun
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233
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234 @defvar load-in-progress
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235 This variable is non-@code{nil} if Emacs is in the process of loading a
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236 file, and it is @code{nil} otherwise.
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237 @end defvar
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238
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239 @defvar load-read-function
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240 This variable specifies an alternate expression-reading function for
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241 @code{load} and @code{eval-region} to use instead of @code{read}.
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242 The function should accept one argument, just as @code{read} does.
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243
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244 Normally, the variable's value is @code{nil}, which means those
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245 functions should use @code{read}.
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246 @end defvar
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247
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248 @defopt load-warn-when-source-newer
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249 This variable specifies whether @code{load} should check whether the
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250 source is newer than the binary. If this variable is true, then when a
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251 @samp{.elc} file is being loaded and the corresponding @samp{.el} is
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252 newer, a warning message will be printed. The default is @code{nil},
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253 but it is bound to @code{t} during the initial loadup.
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254 @end defopt
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255
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256 @defopt load-warn-when-source-only
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257 This variable specifies whether @code{load} should warn when loading a
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258 @samp{.el} file instead of an @samp{.elc}. If this variable is true,
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259 then when @code{load} is called with a filename without an extension,
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260 and the @samp{.elc} version doesn't exist but the @samp{.el} version
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261 does, then a message will be printed. If an explicit extension is
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262 passed to @code{load}, no warning will be printed. The default is
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263 @code{nil}, but it is bound to @code{t} during the initial loadup.
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264 @end defopt
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265
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266 @defopt load-ignore-elc-files
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267 This variable specifies whether @code{load} should ignore @samp{.elc}
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268 files when a suffix is not given. This is normally used only to
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269 bootstrap the @samp{.elc} files when building XEmacs, when you use the
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270 command @samp{make all-elc}. (This forces the @samp{.el} versions to be
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271 loaded in the process of compiling those same files, so that existing
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272 out-of-date @samp{.elc} files do not make it mess things up.)
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273 @end defopt
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274
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275 To learn how @code{load} is used to build XEmacs, see @ref{Building XEmacs}.
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276
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277 @node Autoload
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278 @section Autoload
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279 @cindex autoload
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280
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281 The @dfn{autoload} facility allows you to make a function or macro
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282 known in Lisp, but put off loading the file that defines it. The first
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283 call to the function automatically reads the proper file to install the
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284 real definition and other associated code, then runs the real definition
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285 as if it had been loaded all along.
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286
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287 There are two ways to set up an autoloaded function: by calling
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288 @code{autoload}, and by writing a special ``magic'' comment in the
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289 source before the real definition. @code{autoload} is the low-level
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290 primitive for autoloading; any Lisp program can call @code{autoload} at
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291 any time. Magic comments do nothing on their own; they serve as a guide
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292 for the command @code{update-file-autoloads}, which constructs calls to
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293 @code{autoload} and arranges to execute them when Emacs is built. Magic
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294 comments are the most convenient way to make a function autoload, but
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295 only for packages installed along with Emacs.
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296
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297 @defun autoload function filename &optional docstring interactive type
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298 This function defines the function (or macro) named @var{function} so as
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299 to load automatically from @var{filename}. The string @var{filename}
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300 specifies the file to load to get the real definition of @var{function}.
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301
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302 The argument @var{docstring} is the documentation string for the
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303 function. Normally, this is identical to the documentation string in
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304 the function definition itself. Specifying the documentation string in
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305 the call to @code{autoload} makes it possible to look at the
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306 documentation without loading the function's real definition.
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307
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308 If @var{interactive} is non-@code{nil}, then the function can be called
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309 interactively. This lets completion in @kbd{M-x} work without loading
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310 the function's real definition. The complete interactive specification
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311 need not be given here; it's not needed unless the user actually calls
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312 @var{function}, and when that happens, it's time to load the real
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313 definition.
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314
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315 You can autoload macros and keymaps as well as ordinary functions.
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316 Specify @var{type} as @code{macro} if @var{function} is really a macro.
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444
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317 Specify @var{type} as @code{keymap} if @var{function} is really a keymap.
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318 Various parts of Emacs need to know this information without loading the
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319 real definition.
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428
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320
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321 An autoloaded keymap loads automatically during key lookup when a prefix
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322 key's binding is the symbol @var{function}. Autoloading does not occur
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323 for other kinds of access to the keymap. In particular, it does not
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324 happen when a Lisp program gets the keymap from the value of a variable
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325 and calls @code{define-key}; not even if the variable name is the same
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326 symbol @var{function}.
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327
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328 @cindex function cell in autoload
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329 If @var{function} already has a non-void function definition that is not
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330 an autoload object, @code{autoload} does nothing and returns @code{nil}.
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331 If the function cell of @var{function} is void, or is already an autoload
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332 object, then it is defined as an autoload object like this:
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333
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334 @example
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335 (autoload @var{filename} @var{docstring} @var{interactive} @var{type})
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336 @end example
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337
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444
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338 For example,
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428
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339
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340 @example
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341 @group
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342 (symbol-function 'run-prolog)
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343 @result{} (autoload "prolog" 169681 t nil)
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344 @end group
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345 @end example
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346
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347 @noindent
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348 In this case, @code{"prolog"} is the name of the file to load, 169681
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349 refers to the documentation string in the @file{DOC} file
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350 (@pxref{Documentation Basics}), @code{t} means the function is
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|
351 interactive, and @code{nil} that it is not a macro or a keymap.
|
|
|
352 @end defun
|
|
|
353
|
|
|
354 @cindex autoload errors
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|
|
355 The autoloaded file usually contains other definitions and may require
|
|
|
356 or provide one or more features. If the file is not completely loaded
|
|
|
357 (due to an error in the evaluation of its contents), any function
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|
|
358 definitions or @code{provide} calls that occurred during the load are
|
|
|
359 undone. This is to ensure that the next attempt to call any function
|
|
|
360 autoloading from this file will try again to load the file. If not for
|
|
|
361 this, then some of the functions in the file might appear defined, but
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|
|
362 they might fail to work properly for the lack of certain subroutines
|
|
|
363 defined later in the file and not loaded successfully.
|
|
|
364
|
|
|
365 XEmacs as distributed comes with many autoloaded functions.
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|
|
366 The calls to @code{autoload} are in the file @file{loaddefs.el}.
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|
|
367 There is a convenient way of updating them automatically.
|
|
|
368
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|
|
369 If the autoloaded file fails to define the desired Lisp function or
|
|
|
370 macro, then an error is signaled with data @code{"Autoloading failed to
|
|
|
371 define function @var{function-name}"}.
|
|
|
372
|
|
|
373 @findex update-file-autoloads
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|
|
374 @findex update-directory-autoloads
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|
|
375 A magic autoload comment looks like @samp{;;;###autoload}, on a line
|
|
|
376 by itself, just before the real definition of the function in its
|
|
|
377 autoloadable source file. The command @kbd{M-x update-file-autoloads}
|
|
|
378 writes a corresponding @code{autoload} call into @file{loaddefs.el}.
|
|
|
379 Building Emacs loads @file{loaddefs.el} and thus calls @code{autoload}.
|
|
|
380 @kbd{M-x update-directory-autoloads} is even more powerful; it updates
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|
|
381 autoloads for all files in the current directory.
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|
|
382
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|
|
383 The same magic comment can copy any kind of form into
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|
384 @file{loaddefs.el}. If the form following the magic comment is not a
|
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|
385 function definition, it is copied verbatim. You can also use a magic
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|
386 comment to execute a form at build time @emph{without} executing it when
|
|
|
387 the file itself is loaded. To do this, write the form @dfn{on the same
|
|
|
388 line} as the magic comment. Since it is in a comment, it does nothing
|
|
|
389 when you load the source file; but @code{update-file-autoloads} copies
|
|
|
390 it to @file{loaddefs.el}, where it is executed while building Emacs.
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|
391
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|
|
392 The following example shows how @code{doctor} is prepared for
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|
|
393 autoloading with a magic comment:
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394
|
|
|
395 @smallexample
|
|
|
396 ;;;###autoload
|
|
|
397 (defun doctor ()
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|
|
398 "Switch to *doctor* buffer and start giving psychotherapy."
|
|
|
399 (interactive)
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|
|
400 (switch-to-buffer "*doctor*")
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|
|
401 (doctor-mode))
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|
|
402 @end smallexample
|
|
|
403
|
|
|
404 @noindent
|
|
|
405 Here's what that produces in @file{loaddefs.el}:
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|
|
406
|
|
|
407 @smallexample
|
|
|
408 (autoload 'doctor "doctor"
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|
|
409 "\
|
|
|
410 Switch to *doctor* buffer and start giving psychotherapy."
|
|
|
411 t)
|
|
|
412 @end smallexample
|
|
|
413
|
|
|
414 @noindent
|
|
|
415 The backslash and newline immediately following the double-quote are a
|
|
|
416 convention used only in the preloaded Lisp files such as
|
|
|
417 @file{loaddefs.el}; they tell @code{make-docfile} to put the
|
|
|
418 documentation string in the @file{DOC} file. @xref{Building XEmacs}.
|
|
|
419
|
|
|
420 @node Repeated Loading
|
|
|
421 @section Repeated Loading
|
|
|
422 @cindex repeated loading
|
|
|
423
|
|
|
424 You may load one file more than once in an Emacs session. For
|
|
|
425 example, after you have rewritten and reinstalled a function definition
|
|
|
426 by editing it in a buffer, you may wish to return to the original
|
|
|
427 version; you can do this by reloading the file it came from.
|
|
|
428
|
|
|
429 When you load or reload files, bear in mind that the @code{load} and
|
|
|
430 @code{load-library} functions automatically load a byte-compiled file
|
|
|
431 rather than a non-compiled file of similar name. If you rewrite a file
|
|
|
432 that you intend to save and reinstall, remember to byte-compile it if
|
|
|
433 necessary; otherwise you may find yourself inadvertently reloading the
|
|
|
434 older, byte-compiled file instead of your newer, non-compiled file!
|
|
|
435
|
|
|
436 When writing the forms in a Lisp library file, keep in mind that the
|
|
|
437 file might be loaded more than once. For example, the choice of
|
|
|
438 @code{defvar} vs.@: @code{defconst} for defining a variable depends on
|
|
|
439 whether it is desirable to reinitialize the variable if the library is
|
|
|
440 reloaded: @code{defconst} does so, and @code{defvar} does not.
|
|
|
441 (@xref{Defining Variables}.)
|
|
|
442
|
|
|
443 The simplest way to add an element to an alist is like this:
|
|
|
444
|
|
|
445 @example
|
|
|
446 (setq minor-mode-alist
|
|
|
447 (cons '(leif-mode " Leif") minor-mode-alist))
|
|
|
448 @end example
|
|
|
449
|
|
|
450 @noindent
|
|
|
451 But this would add multiple elements if the library is reloaded.
|
|
|
452 To avoid the problem, write this:
|
|
|
453
|
|
|
454 @example
|
|
|
455 (or (assq 'leif-mode minor-mode-alist)
|
|
|
456 (setq minor-mode-alist
|
|
|
457 (cons '(leif-mode " Leif") minor-mode-alist)))
|
|
|
458 @end example
|
|
|
459
|
|
|
460 To add an element to a list just once, use @code{add-to-list}
|
|
|
461 (@pxref{Setting Variables}).
|
|
|
462
|
|
|
463 Occasionally you will want to test explicitly whether a library has
|
|
|
464 already been loaded. Here's one way to test, in a library, whether it
|
|
|
465 has been loaded before:
|
|
|
466
|
|
|
467 @example
|
|
|
468 (defvar foo-was-loaded)
|
|
|
469
|
|
|
470 (if (not (boundp 'foo-was-loaded))
|
|
|
471 @var{execute-first-time-only})
|
|
|
472
|
|
|
473 (setq foo-was-loaded t)
|
|
|
474 @end example
|
|
|
475
|
|
|
476 @noindent
|
|
|
477 If the library uses @code{provide} to provide a named feature, you can
|
|
|
478 use @code{featurep} to test whether the library has been loaded.
|
|
|
479 @ifinfo
|
|
|
480 @xref{Named Features}.
|
|
|
481 @end ifinfo
|
|
|
482
|
|
|
483 @node Named Features
|
|
|
484 @section Features
|
|
|
485 @cindex features
|
|
|
486 @cindex requiring features
|
|
|
487 @cindex providing features
|
|
|
488
|
|
|
489 @code{provide} and @code{require} are an alternative to
|
|
|
490 @code{autoload} for loading files automatically. They work in terms of
|
|
|
491 named @dfn{features}. Autoloading is triggered by calling a specific
|
|
|
492 function, but a feature is loaded the first time another program asks
|
|
|
493 for it by name.
|
|
|
494
|
|
|
495 A feature name is a symbol that stands for a collection of functions,
|
|
|
496 variables, etc. The file that defines them should @dfn{provide} the
|
|
|
497 feature. Another program that uses them may ensure they are defined by
|
|
|
498 @dfn{requiring} the feature. This loads the file of definitions if it
|
|
|
499 hasn't been loaded already.
|
|
|
500
|
|
|
501 To require the presence of a feature, call @code{require} with the
|
|
|
502 feature name as argument. @code{require} looks in the global variable
|
|
|
503 @code{features} to see whether the desired feature has been provided
|
|
|
504 already. If not, it loads the feature from the appropriate file. This
|
|
|
505 file should call @code{provide} at the top level to add the feature to
|
|
|
506 @code{features}; if it fails to do so, @code{require} signals an error.
|
|
|
507 @cindex load error with require
|
|
|
508
|
|
|
509 Features are normally named after the files that provide them, so that
|
|
|
510 @code{require} need not be given the file name.
|
|
|
511
|
|
444
|
512 For example, in @file{emacs/lisp/prolog.el},
|
|
428
|
513 the definition for @code{run-prolog} includes the following code:
|
|
|
514
|
|
|
515 @smallexample
|
|
|
516 (defun run-prolog ()
|
|
|
517 "Run an inferior Prolog process, input and output via buffer *prolog*."
|
|
|
518 (interactive)
|
|
|
519 (require 'comint)
|
|
|
520 (switch-to-buffer (make-comint "prolog" prolog-program-name))
|
|
|
521 (inferior-prolog-mode))
|
|
|
522 @end smallexample
|
|
|
523
|
|
|
524 @noindent
|
|
|
525 The expression @code{(require 'comint)} loads the file @file{comint.el}
|
|
|
526 if it has not yet been loaded. This ensures that @code{make-comint} is
|
|
|
527 defined.
|
|
|
528
|
|
|
529 The @file{comint.el} file contains the following top-level expression:
|
|
|
530
|
|
|
531 @smallexample
|
|
|
532 (provide 'comint)
|
|
|
533 @end smallexample
|
|
|
534
|
|
|
535 @noindent
|
|
|
536 This adds @code{comint} to the global @code{features} list, so that
|
|
|
537 @code{(require 'comint)} will henceforth know that nothing needs to be
|
|
|
538 done.
|
|
|
539
|
|
|
540 @cindex byte-compiling @code{require}
|
|
|
541 When @code{require} is used at top level in a file, it takes effect
|
|
|
542 when you byte-compile that file (@pxref{Byte Compilation}) as well as
|
|
|
543 when you load it. This is in case the required package contains macros
|
|
|
544 that the byte compiler must know about.
|
|
|
545
|
|
|
546 Although top-level calls to @code{require} are evaluated during
|
|
|
547 byte compilation, @code{provide} calls are not. Therefore, you can
|
|
|
548 ensure that a file of definitions is loaded before it is byte-compiled
|
|
|
549 by including a @code{provide} followed by a @code{require} for the same
|
|
|
550 feature, as in the following example.
|
|
|
551
|
|
|
552 @smallexample
|
|
|
553 @group
|
|
|
554 (provide 'my-feature) ; @r{Ignored by byte compiler,}
|
|
|
555 ; @r{evaluated by @code{load}.}
|
|
|
556 (require 'my-feature) ; @r{Evaluated by byte compiler.}
|
|
|
557 @end group
|
|
|
558 @end smallexample
|
|
|
559
|
|
|
560 @noindent
|
|
|
561 The compiler ignores the @code{provide}, then processes the
|
|
|
562 @code{require} by loading the file in question. Loading the file does
|
|
|
563 execute the @code{provide} call, so the subsequent @code{require} call
|
|
|
564 does nothing while loading.
|
|
|
565
|
|
|
566 @defun provide feature
|
|
|
567 This function announces that @var{feature} is now loaded, or being
|
|
|
568 loaded, into the current XEmacs session. This means that the facilities
|
|
|
569 associated with @var{feature} are or will be available for other Lisp
|
|
|
570 programs.
|
|
|
571
|
|
|
572 The direct effect of calling @code{provide} is to add @var{feature} to
|
|
|
573 the front of the list @code{features} if it is not already in the list.
|
|
|
574 The argument @var{feature} must be a symbol. @code{provide} returns
|
|
|
575 @var{feature}.
|
|
|
576
|
|
|
577 @smallexample
|
|
|
578 features
|
|
|
579 @result{} (bar bish)
|
|
|
580
|
|
|
581 (provide 'foo)
|
|
|
582 @result{} foo
|
|
|
583 features
|
|
|
584 @result{} (foo bar bish)
|
|
|
585 @end smallexample
|
|
|
586
|
|
|
587 When a file is loaded to satisfy an autoload, and it stops due to an
|
|
|
588 error in the evaluating its contents, any function definitions or
|
|
|
589 @code{provide} calls that occurred during the load are undone.
|
|
|
590 @xref{Autoload}.
|
|
|
591 @end defun
|
|
|
592
|
|
|
593 @defun require feature &optional filename
|
|
|
594 This function checks whether @var{feature} is present in the current
|
|
|
595 XEmacs session (using @code{(featurep @var{feature})}; see below). If it
|
|
|
596 is not, then @code{require} loads @var{filename} with @code{load}. If
|
|
|
597 @var{filename} is not supplied, then the name of the symbol
|
|
|
598 @var{feature} is used as the file name to load.
|
|
|
599
|
|
|
600 If loading the file fails to provide @var{feature}, @code{require}
|
|
|
601 signals an error, @samp{Required feature @var{feature} was not
|
|
|
602 provided}.
|
|
|
603 @end defun
|
|
|
604
|
|
|
605 @defun featurep fexp
|
|
|
606 This function returns @code{t} if feature @var{fexp} is present in this
|
|
|
607 Emacs. Use this to conditionalize execution of lisp code based on the
|
|
|
608 presence or absence of emacs or environment extensions.
|
|
|
609
|
|
|
610 @var{fexp} can be a symbol, a number, or a list.
|
|
|
611
|
|
444
|
612 If @var{fexp} is a symbol, it is looked up in the @code{features} variable,
|
|
428
|
613 and @code{t} is returned if it is found, @code{nil} otherwise.
|
|
|
614
|
|
|
615 If @var{fexp} is a number, the function returns @code{t} if this Emacs
|
|
444
|
616 has an equal or greater number than @var{fexp}, @code{nil} otherwise.
|
|
428
|
617 Note that minor Emacs version is expected to be 2 decimal places wide,
|
|
|
618 so @code{(featurep 20.4)} will return @code{nil} on XEmacs 20.4---you
|
|
|
619 must write @code{(featurep 20.04)}, unless you wish to match for XEmacs
|
|
|
620 20.40.
|
|
|
621
|
|
|
622 If @var{fexp} is a list whose car is the symbol @code{and}, the function
|
|
|
623 returns @code{t} if all the features in its cdr are present, @code{nil}
|
|
|
624 otherwise.
|
|
|
625
|
|
|
626 If @var{fexp} is a list whose car is the symbol @code{or}, the function
|
|
|
627 returns @code{t} if any the features in its cdr are present, @code{nil}
|
|
|
628 otherwise.
|
|
|
629
|
|
444
|
630 If @var{fexp} is a list whose car is the symbol @code{not}, the function
|
|
428
|
631 returns @code{t} if the feature is not present, @code{nil} otherwise.
|
|
|
632
|
|
|
633 Examples:
|
|
|
634
|
|
|
635 @example
|
|
|
636 (featurep 'xemacs)
|
|
|
637 @result{} ; @r{t on XEmacs.}
|
|
|
638
|
|
|
639 (featurep '(and xemacs gnus))
|
|
|
640 @result{} ; @r{t on XEmacs with Gnus loaded.}
|
|
|
641
|
|
|
642 (featurep '(or tty-frames (and emacs 19.30)))
|
|
|
643 @result{} ; @r{t if this Emacs supports TTY frames.}
|
|
|
644
|
|
|
645 (featurep '(or (and xemacs 19.15) (and emacs 19.34)))
|
|
|
646 @result{} ; @r{t on XEmacs 19.15 and later, or on}
|
|
|
647 ; @r{FSF Emacs 19.34 and later.}
|
|
|
648 @end example
|
|
|
649
|
|
|
650 @strong{Please note:} The advanced arguments of this function (anything other than a
|
|
|
651 symbol) are not yet supported by FSF Emacs. If you feel they are useful
|
|
|
652 for supporting multiple Emacs variants, lobby Richard Stallman at
|
|
|
653 @samp{<bug-gnu-emacs@@prep.ai.mit.edu>}.
|
|
|
654 @end defun
|
|
|
655
|
|
|
656 @defvar features
|
|
|
657 The value of this variable is a list of symbols that are the features
|
|
|
658 loaded in the current XEmacs session. Each symbol was put in this list
|
|
|
659 with a call to @code{provide}. The order of the elements in the
|
|
|
660 @code{features} list is not significant.
|
|
|
661 @end defvar
|
|
|
662
|
|
|
663 @node Unloading
|
|
|
664 @section Unloading
|
|
|
665 @cindex unloading
|
|
|
666
|
|
|
667 @c Emacs 19 feature
|
|
|
668 You can discard the functions and variables loaded by a library to
|
|
|
669 reclaim memory for other Lisp objects. To do this, use the function
|
|
|
670 @code{unload-feature}:
|
|
|
671
|
|
|
672 @deffn Command unload-feature feature &optional force
|
|
|
673 This command unloads the library that provided feature @var{feature}.
|
|
|
674 It undefines all functions, macros, and variables defined in that
|
|
|
675 library with @code{defconst}, @code{defvar}, @code{defun},
|
|
442
|
676 @code{defmacro}, @code{defsubst}, @code{define-function} and
|
|
428
|
677 @code{defalias}. It then restores any autoloads formerly associated
|
|
|
678 with those symbols. (Loading saves these in the @code{autoload}
|
|
|
679 property of the symbol.)
|
|
|
680
|
|
|
681 Ordinarily, @code{unload-feature} refuses to unload a library on which
|
|
|
682 other loaded libraries depend. (A library @var{a} depends on library
|
|
|
683 @var{b} if @var{a} contains a @code{require} for @var{b}.) If the
|
|
|
684 optional argument @var{force} is non-@code{nil}, dependencies are
|
|
|
685 ignored and you can unload any library.
|
|
|
686 @end deffn
|
|
|
687
|
|
|
688 The @code{unload-feature} function is written in Lisp; its actions are
|
|
|
689 based on the variable @code{load-history}.
|
|
|
690
|
|
|
691 @defvar load-history
|
|
|
692 This variable's value is an alist connecting library names with the
|
|
|
693 names of functions and variables they define, the features they provide,
|
|
|
694 and the features they require.
|
|
|
695
|
|
|
696 Each element is a list and describes one library. The @sc{car} of the
|
|
|
697 list is the name of the library, as a string. The rest of the list is
|
|
|
698 composed of these kinds of objects:
|
|
|
699
|
|
|
700 @itemize @bullet
|
|
|
701 @item
|
|
|
702 Symbols that were defined by this library.
|
|
|
703 @item
|
|
|
704 Lists of the form @code{(require . @var{feature})} indicating
|
|
|
705 features that were required.
|
|
|
706 @item
|
|
|
707 Lists of the form @code{(provide . @var{feature})} indicating
|
|
|
708 features that were provided.
|
|
|
709 @end itemize
|
|
|
710
|
|
|
711 The value of @code{load-history} may have one element whose @sc{car} is
|
|
|
712 @code{nil}. This element describes definitions made with
|
|
|
713 @code{eval-buffer} on a buffer that is not visiting a file.
|
|
|
714 @end defvar
|
|
|
715
|
|
|
716 The command @code{eval-region} updates @code{load-history}, but does so
|
|
|
717 by adding the symbols defined to the element for the file being visited,
|
|
|
718 rather than replacing that element.
|
|
|
719
|
|
|
720 @node Hooks for Loading
|
|
|
721 @section Hooks for Loading
|
|
|
722 @cindex loading hooks
|
|
|
723 @cindex hooks for loading
|
|
|
724
|
|
|
725 @ignore @c Not currently in XEmacs. JWZ hates it.
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726 You can ask for code to be executed if and when a particular library is
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727 loaded, by calling @code{eval-after-load}.
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728
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729 @defun eval-after-load library form
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730 This function arranges to evaluate @var{form} at the end of loading the
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731 library @var{library}, if and when @var{library} is loaded. If
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732 @var{library} is already loaded, it evaluates @var{form} right away.
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733
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734 The library name @var{library} must exactly match the argument of
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735 @code{load}. To get the proper results when an installed library is
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736 found by searching @code{load-path}, you should not include any
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737 directory names in @var{library}.
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738
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739 An error in @var{form} does not undo the load, but does prevent
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740 execution of the rest of @var{form}.
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741 @end defun
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742
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743 In general, well-designed Lisp programs should not use this feature.
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744 The clean and modular ways to interact with a Lisp library are (1)
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745 examine and set the library's variables (those which are meant for
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746 outside use), and (2) call the library's functions. If you wish to
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747 do (1), you can do it immediately---there is no need to wait for when
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748 the library is loaded. To do (2), you must load the library (preferably
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749 with @code{require}).
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750
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751 But it is ok to use @code{eval-after-load} in your personal customizations
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752 if you don't feel they must meet the design standards of programs to be
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753 released.
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754 @end ignore
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755
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756 @defvar after-load-alist
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757 An alist of expressions to evaluate if and when particular libraries are
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758 loaded. Each element looks like this:
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759
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760 @example
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761 (@var{filename} @var{forms}@dots{})
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762 @end example
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763
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764 When @code{load} is run and the file-name argument is @var{filename},
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765 the @var{forms} in the corresponding element are executed at the end of
|
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766 loading.
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767
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768 @var{filename} must match exactly! Normally @var{filename} is the name
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769 of a library, with no directory specified, since that is how @code{load}
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770 is normally called. An error in @var{forms} does not undo the load, but
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771 does prevent execution of the rest of the @var{forms}.
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772
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773 @ignore @c eval-after-load not in XEmacs
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774 The function @code{load} checks @code{after-load-alist} in order to
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775 implement @code{eval-after-load}.
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776 @end ignore
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777 @end defvar
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778
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779 @c Emacs 19 feature
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