A macro lambda list is used in describing macros defined by the operators in Figure 3--17.
define-compiler-macro defmacro macrolet define-setf-expander
Figure 3--17: Operators that use 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]]
{ auxvars ::=[{&aux {var | ({var} [init-form])}{*}]} } envvar ::=[{&environment var]}
wholevar ::=[{&whole var]}
lambda-list ::=(!wholevar !envvar !reqvars !envvar !optvars !envvar !restvar !envvar !keyvars !envvar !auxvars !envvar) | (!wholevar !envvar !reqvars !envvar !optvars !envvar . var)
pattern ::=(!wholevar !reqvars !optvars !restvar !keyvars !auxvars) | (!wholevar !reqvars !optvars . var)
}
A macro lambda list can contain the lambda list keywords shown in Figure 3--18.
&allow-other-keys &environment &rest &aux &key &whole &body &optional
Figure 3--18: Lambda List Keywords used by Macro Lambda Lists
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 Destructuring by Lambda Lists.
&body can appear at any level of a macro lambda list; for details, see section 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 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.
[Editorial Note by KMP: Apparently the dotted-macro-forms cleanup doesn't allow for the macro to `manually' notice dotted forms and fix them as well. It shouldn't be required that this be done only by &REST or a dotted pattern; it should only matter that ultimately the non-macro result of a full-macro expansion not contain dots. Anyway, I plan to address this editorially unless someone raises an objection.]
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