name—a symbol.
lambda-list—a define-modify-macro lambda list
function—a symbol.
documentation—a string; not evaluated.
define-modify-macro
defines a macro named
name to read and write a place.
The arguments to the new macro are a place,
followed
by the arguments that are supplied in lambda-list.
Macros defined with define-modify-macro
correctly pass the environment parameter to
get-setf-expansion
.
When the macro is invoked, function is applied to the old contents of the place and the lambda-list arguments to obtain the new value, and the place is updated to contain the result.
Except for the issue of avoiding multiple evaluation (see below), the expansion
of a define-modify-macro
is equivalent to the following:
(defmacro name (reference . lambda-list) documentation `(setf ,reference (function ,reference ,arg1 ,arg2 ...)))
where arg1, arg2, ..., are the parameters appearing in lambda-list; appropriate provision is made for a rest parameter.
The subforms of the macro calls defined by define-modify-macro
are evaluated as specified in Section 5.1.1.1 (Evaluation of Subforms to Places).
Documentation is attached as a documentation string
to name (as kind function
)
and to the macro function.
If a define-modify-macro
form appears as a top level form,
the compiler must store the macro definition at compile time,
so that occurrences of the macro later on in the file can be expanded correctly.
(define-modify-macro appendf (&rest args) append "Append onto list") → APPENDF (setq x '(a b c) y x) → (A B C) (appendf x '(d e f) '(1 2 3)) → (A B C D E F 1 2 3) x → (A B C D E F 1 2 3) y → (A B C) (define-modify-macro new-incf (&optional (delta 1)) +) (define-modify-macro unionf (other-set &rest keywords) union)
A macro definition is assigned to name.
defsetf, define-setf-expander, documentation, Section 3.4.11 (Syntactic Interaction of Documentation Strings and Declarations)