Writing GNU Emacs Extensions

Code Objects

Functions

A function is a list in the following form:

(lambda (parameters ...)
   "documentation string"
   body1 body2 ...)

The documentation string is optional.

When the function is invoked, the actual arguments will be bound to the parameters listed in the parameter list. The keyword &optional appearing in the parameter list means the following parameters are optional. If the function is called without a value for an optional parameter, the parameter is assigned nil. The last parameter may be preceded by the keyword &rest, meaning that all remaining unused arguments are placed in a list and assigned to that parameter.

The result of invoking a function is the result of the last body expression.

To define a function with a name, use defun.

(defun name (parameters ...)
   "documentation string"
   body1 body2 ...)

This creates a lambda expression and assigns it to the function value of the symbol name. This is different from name's variable value, so there is no conflict between function names and variable names.

Macro Functions

A macro function is a list like a lambda expression, but instead of lambda, macro is used. When a macro is invoked, its arguments are not evaluated. Instead, they are used in their literal form to compute a new Lisp expression. Then that is evaluated.

To define a macro with a name, use defmacro exactly like defun.