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The @deffn command is used for definitions of entities that
resemble functions. To write a definition using the @deffn
command, write the @deffn command at the beginning of a line
and follow it on the same line by the category of the entity, the name
of the entity itself, and its arguments (if any). Then write the body
of the definition on succeeding lines. (You may embed examples in the
body.) Finally, end the definition with an @end deffn command
written on a line of its own. (The other definition commands follow
the same format.)
The template for a definition looks like this:
@deffn category name arguments... body-of-definition @end deffn
For example,
@deffn Command forward-word count
This command moves point forward @var{count} words
(or backward if @var{count} is negative). ...
@end deffn
produces
forward-word count Command
This function moves point forward count words (or backward if count is negative). ...
Capitalize the category name like a title. If the name of the
category contains spaces, as in the phrase `Interactive Command',
write braces around it. For example:
@deffn {Interactive Command} isearch-forward
...
@end deffn
Otherwise, the second word will be mistaken for the name of the entity.
Some of the definition commands are more general than others. The
@deffn command, for example, is the general definition command
for functions and the like--for entities that may take arguments. When
you use this command, you specify the category to which the entity
belongs. The @deffn command possesses three predefined,
specialized variations, @defun, @defmac, and
@defspec, that specify the category for you: "Function",
"Macro", and "Special Form" respectively. (In Lisp, a special form
is an entity much like a function.) The @defvr command also is
accompanied by several predefined, specialized variations for describing
particular kinds of variables.
The template for a specialized definition, such as @defun, is
similar to the template for a generalized definition, except that you
do not need to specify the category:
@defun name arguments... body-of-definition @end defun
Thus,
@defun buffer-end flag
This function returns @code{(point-min)} if @var{flag}
is less than 1, @code{(point-max)} otherwise.
...
@end defun
produces
buffer-end flag Function
This function returns (point-min)if flag is less than 1,(point-max)otherwise. ...
See Sample Function Definition, for a more detailed example of a function
definition, including the use of @example inside the
definition.
The other specialized commands work like @defun.
Note that, due to implementation difficulties, macros are not expanded
in @deffn and all the other definition commands.