CLHS: Section 3.4.2

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## 3.4.2 Generic Function Lambda Lists

A generic function lambda list is used to describe the overall shape of the argument list to be accepted by a generic function. Individual method signatures might contribute additional keyword parameters to the lambda list of the effective method.

A generic function lambda list is used by defgeneric.

A generic function lambda list has the following syntax:

    lambda-list::= (var*
                    [&optional {var | (var)}*]
                    [&rest var]
                    [&key {var | ({var | (keyword-name var)})}* [&allow-other-keys]])

A generic function lambda list can contain the lambda list keywords shown in the next figure.

    &allow-other-keys  &optional
    &key               &rest

Figure 3-14. Lambda List Keywords used by Generic Function Lambda Lists

A generic function lambda list differs from an ordinary lambda list in the following ways:

Required arguments

  Zero or more required parameters must be specified.

Optional and keyword arguments

  Optional parameters and keyword parameters may not have default initial value forms nor use supplied-p parameters.

Use of `&aux`

  The use of `&aux` is not allowed.

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