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comparison man/lispref/variables.texi @ 371:cc15677e0335 r21-2b1

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Import from CVS: tag r21-2b1
author cvs
date Mon, 13 Aug 2007 11:03:08 +0200
parents 1d62742628b6
children 6240c7796c7a
comparison
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370:bd866891f083 371:cc15677e0335
93 @section Variables That Never Change 93 @section Variables That Never Change
94 @vindex nil 94 @vindex nil
95 @vindex t 95 @vindex t
96 @kindex setting-constant 96 @kindex setting-constant
97 97
98 In XEmacs Lisp, some symbols always evaluate to themselves: the two 98 XEmacs Lisp has two special symbols, @code{nil} and @code{t}, that
99 special symbols @code{nil} and @code{t}, as well as @dfn{keyword 99 always evaluate to themselves. These symbols cannot be rebound, nor can
100 symbols}, that is, symbols whose name begins with the character 100 their value cells be changed. An attempt to change the value of
101 @samp{@code{:}}. These symbols cannot be rebound, nor can their value 101 @code{nil} or @code{t} signals a @code{setting-constant} error.
102 cells be changed. An attempt to change the value of @code{nil} or
103 @code{t} signals a @code{setting-constant} error.
104 102
105 @example 103 @example
106 @group 104 @group
107 nil @equiv{} 'nil 105 nil @equiv{} 'nil
108 @result{} nil 106 @result{} nil
249 binding depth exceeds max-specpdl-size"}). 247 binding depth exceeds max-specpdl-size"}).
250 248
251 This limit, with the associated error when it is exceeded, is one way 249 This limit, with the associated error when it is exceeded, is one way
252 that Lisp avoids infinite recursion on an ill-defined function. 250 that Lisp avoids infinite recursion on an ill-defined function.
253 251
254 The default value is 3000. 252 The default value is 600.
255 253
256 @code{max-lisp-eval-depth} provides another limit on depth of nesting. 254 @code{max-lisp-eval-depth} provides another limit on depth of nesting.
257 @xref{Eval}. 255 @xref{Eval}.
258 @end defvar 256 @end defvar
259 257
433 stored in the symbol's @code{variable-documentation} property. The 431 stored in the symbol's @code{variable-documentation} property. The
434 XEmacs help functions (@pxref{Documentation}) look for this property. 432 XEmacs help functions (@pxref{Documentation}) look for this property.
435 433
436 If the first character of @var{doc-string} is @samp{*}, it means that 434 If the first character of @var{doc-string} is @samp{*}, it means that
437 this variable is considered a user option. This lets users set the 435 this variable is considered a user option. This lets users set the
438 variable conveniently using the commands @code{set-variable} and 436 variable conventiently using the commands @code{set-variable} and
439 @code{edit-options}. 437 @code{edit-options}.
440 438
441 For example, this form defines @code{foo} but does not set its value: 439 For example, this form defines @code{foo} but does not set its value:
442 440
443 @example 441 @example