ANSI Common Lisp   3 Evaluation and Compilation   3.4 Lambda Lists

3.4.4 Macro Lambda Lists

With the additional restriction that an environment parameter may appear only once (at any of the positions indicated), a macro lambda list has the following syntax:

reqvars::=

{var | pattern}

optvars::=

[&optional {var | ({var | pattern} [init-form [supplied-p-parameter ] ])}*]

restvar::=

[{&rest | &body} ]{var | pattern}

keyvars::=	[&key {var | ({var | (keyword-name{var | pattern} )} [init-form [supplied-p-parameter ] ])}*
	[&allow-other-keys]]

lambda-list::=	(wholevar envvar reqvars envvar optvars envvar
	restvar envvar keyvars envvar auxvars envvar) |
	(wholevar envvar reqvars envvar optvars envvar . var)

pattern::=	(wholevarreqvarsoptvarsrestvarkeyvarsauxvars) |
	(wholevar reqvars optvars . var)

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

Optional parameters (introduced by &optional) and keyword parameters (introduced by &key) can be supplied in a macro lambda list, just as in an ordinary lambda list. Both may contain default initialization forms and supplied-p parameters.

&body is identical in function to &rest, but it can be used to inform certain output-formatting and editing functions that the remainder of the form is treated as a body, and should be indented accordingly. Only one of &body or &rest can be used at any particular level; see Section 3.4.4.1 Destructuring by Lambda Lists. &body can appear at any level of a macro lambda list; for details, see Section 3.4.4.1 Destructuring by Lambda Lists.

&whole is followed by a single variable that is bound to the entire macro-call form; this is the value that the macro function receives as its first argument. If &whole and a following variable appear, they must appear first in lambda-list, before any other parameter or lambda list keyword. &whole can appear at any level of a macro lambda list. At inner levels, the &whole variable is bound to the corresponding part of the argument, as with &rest, but unlike &rest, other arguments are also allowed. The use of &whole does not affect the pattern of arguments specified.

&environment is followed by a single variable that is bound to an environment representing the lexical environment in which the macro call is to be interpreted. This environment should be used with macro-function, get-setf-expansion, compiler-macro-function, and macroexpand (for example) in computing the expansion of the macro, to ensure that any lexical bindings or definitions established in the compilation environment are taken into account. &environment can only appear at the top level of a macro lambda list, and can only appear once, but can appear anywhere in that list; the &environment parameter is bound along with &whole before any other variables in the lambda list, regardless of where &environment appears in the lambda list. The object that is bound to the environment parameter has dynamic extent.

Destructuring allows a macro lambda list to express the structure of a macro call syntax. If no lambda list keywords appear, then the macro lambda list is a tree containing parameter names at the leaves. The pattern and the macro form must have compatible tree structure; that is, their tree structure must be equivalent, or it must differ only in that some leaves of the pattern match non-atomic objects of the macro form. For information about error detection in this situation, see Section 3.5.1.7 Destructuring Mismatch.

A destructuring lambda list (whether at top level or embedded) can be dotted, ending in a parameter name. This situation is treated exactly as if the parameter name that ends the list had appeared preceded by &rest.

It is permissible for a macro form (or a subexpression of a macro form) to be a dotted list only when (... &rest var) or (... . var) is used to match it. It is the responsibility of the macro to recognize and deal with such situations.

3.4.4.1  Destructuring by Lambda Lists