Common Lisp the Language, 2nd Edition
The macro define-method-combination defines new forms of method
combination. It provides a mechanism for customizing the production
of the effective method. The default procedure for producing an
effective method is described in
section 28.1.7.2.
There are two forms of
define-method-combination. The short form is a simple facility;
the long form is more powerful and more verbose. The long form
resembles defmacro in that the body is an expression that
computes a Lisp form; it provides mechanisms for implementing
arbitrary control structures within method combination and for
arbitrary processing of method qualifiers. The syntax and use of both
forms of define-method-combination are explained in
section 28.2.
