ANSI Common Lisp 7 Objects 7.6 Generic Functions and Methods 7.6.6 Method Selection and Combination
220.127.116.11 Built-in Method Combination TypesThe object system provides a set of built-in method combination types. To specify that a generic function is to use one of these method combination types, the name of the method combination type is given as the argument to the :method-combination option to defgeneric or to the :method-combination option to any of the other operators that specify generic function options.
The names of the built-in method combination types are listed in the next figure.
The semantics of the standard built-in method combination type is described in Section 18.104.22.168 Standard Method Combination. The other built-in method combination types are called simple built-in method combination types.
The semantics of the simple built-in method combination types is as follows:
The simple built-in method combination types require exactly one qualifier per method. An error is signaled if there are applicable methods with no qualifiers or with qualifiers that are not supported by the method combination type. An error is signaled if there are applicable around methods and no applicable primary methods.