14.1 The Template for a Definition

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: a line with the @def… command and whatever arguments are appropriate for that command; the body of the definition; and a corresponding @end line.

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

Command: forward-word count

This command 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’, enclose it in braces. For example:

@deffn {Interactive Command} isearch-forward
…
@end deffn

Otherwise, the second word will be mistaken for the name of the entity. As a general rule, when any of the arguments in the heading line except the last one are more than one word, you need to enclose them in braces. This may also be necessary if the text contains commands, for example, ‘{declaraci@'on}’ if you are writing in Spanish.

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. Three predefined, specialized variations (@defun, @defmac, and @defspec) specify the category for you: “Function”, “Macro”, and “Special Form” respectively. (In Lisp, a special form is an entity much like a function.) Similarly, the general @defvr command is accompanied by several specialized variations for describing particular kinds of variables.

See Sample Function Definition, for a detailed example of a function definition, including the use of @example inside the definition.