— Macro: gv-define-simple-setter name setter &optional fix-return

This macro enables you to easily define setf methods for simple cases. name is the name of a function, macro, or special form. You can use this macro whenever name has a directly corresponding setter function that updates it, e.g., (gv-define-simple-setter car setcar).

This macro translates a call of the form

          (setf (name args...) value)

into

          (setter args... value)

Such a setf call is documented to return value. This is no problem with, e.g., car and setcar, because setcar returns the value that it set. If your setter function does not return value, use a non-nil value for the fix-return argument of gv-define-simple-setter. This expands into something equivalent to

          (let ((temp value))
            (setter args... temp)
            temp)

so ensuring that it returns the correct result.

— Macro: gv-define-setter name arglist &rest body

This macro allows for more complex setf expansions than the previous form. You may need to use this form, for example, if there is no simple setter function to call, or if there is one but it requires different arguments to the place form.

This macro expands the form (setf (name args...) value) by first binding the setf argument forms (value args...) according to arglist, and then executing body. body should return a Lisp form that does the assignment, and finally returns the value that was set. An example of using this macro is:

          (gv-define-setter caar (val x) `(setcar (car ,x) ,val))