/[emacs]/emacs/lispref/intro.texi
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revision 1.30 by ttn, Wed Aug 10 14:29:00 2005 UTC revision 1.31 by rms, Sun Sep 4 01:35:18 2005 UTC
# Line 197  in Lisp programs also. Line 197  in Lisp programs also.
197  (not nil)                     ; @r{Emphasize the truth value @var{false}}  (not nil)                     ; @r{Emphasize the truth value @var{false}}
198  @end example  @end example
199    
200  @cindex @code{t} and truth  @cindex @code{t}, uses of
201  @cindex true  @cindex true
202    In contexts where a truth value is expected, any non-@code{nil} value    In contexts where a truth value is expected, any non-@code{nil} value
203  is considered to be @var{true}.  However, @code{t} is the preferred way  is considered to be @var{true}.  However, @code{t} is the preferred way
# Line 209  choosing, use @code{t}.  The symbol @cod Line 209  choosing, use @code{t}.  The symbol @cod
209    In Emacs Lisp, @code{nil} and @code{t} are special symbols that always    In Emacs Lisp, @code{nil} and @code{t} are special symbols that always
210  evaluate to themselves.  This is so that you do not need to quote them  evaluate to themselves.  This is so that you do not need to quote them
211  to use them as constants in a program.  An attempt to change their  to use them as constants in a program.  An attempt to change their
212  values results in a @code{setting-constant} error.  The same is true of  values results in a @code{setting-constant} error.  @xref{Constant
 any symbol whose name starts with a colon (@samp{:}).  @xref{Constant  
213  Variables}.  Variables}.
214    
215  @node Evaluation Notation  @node Evaluation Notation
216  @subsection Evaluation Notation  @subsection Evaluation Notation
217  @cindex evaluation notation  @cindex evaluation notation
218  @cindex documentation notation  @cindex documentation notation
219    @cindex notation
220    
221    A Lisp expression that you can evaluate is called a @dfn{form}.    A Lisp expression that you can evaluate is called a @dfn{form}.
222  Evaluating a form always produces a result, which is a Lisp object.  In  Evaluating a form always produces a result, which is a Lisp object.  In
# Line 355  indicates that the subsequent arguments Line 355  indicates that the subsequent arguments
355  arguments default to @code{nil}).  Do not write @code{&optional} when  arguments default to @code{nil}).  Do not write @code{&optional} when
356  you call the function.  you call the function.
357    
358    The keyword @code{&rest} (which must be followed by a single argument    The keyword @code{&rest} (which must be followed by a single
359  name) indicates that any number of arguments can follow.  The single  argument name) indicates that any number of arguments can follow.  The
360  following argument name will have a value, as a variable, which is a  single argument name following @code{&rest} will receive, as its
361  list of all these remaining arguments.  Do not write @code{&rest} when  value, a list of all the remaining arguments passed to the function.
362  you call the function.  Do not write @code{&rest} when you call the function.
363    
364    Here is a description of an imaginary function @code{foo}:    Here is a description of an imaginary function @code{foo}:
365    
# Line 450  from @var{body}, which includes all rema Line 450  from @var{body}, which includes all rema
450  @cindex variable descriptions  @cindex variable descriptions
451  @cindex option descriptions  @cindex option descriptions
452    
453    A @dfn{variable} is a name that can hold a value.  Although any    A @dfn{variable} is a name that can hold a value.  Although nearly
454  variable can be set by the user, certain variables that exist  all variables can be set by the user, certain variables exist
455  specifically so that users can change them are called @dfn{user  specifically so that users can change them; these are called @dfn{user
456  options}.  Ordinary variables and user options are described using a  options}.  Ordinary variables and user options are described using a
457  format like that for functions except that there are no arguments.  format like that for functions except that there are no arguments.
458    

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