References: DEFSETF, DEFINE-SETF-METHOD, SETF
CLtL pages 97, 102, 105
ANSI CL spec 6-162 (Sep 89 version)
Related issues: FUNCTION-NAME:LARGE
Edit history: 29-Apr-90, Version 1 by Moon
CLtL is inconsistent because pages 102 and 105 say DEFSETF and
DEFINE-SETF-METHOD can be used with a function or a macro, while page 97
says that SETF expands macros before it looks for setf-methods.
This is Symbolics issue #9.
Clarify that SETF (actually GET-SETF-METHOD-MULTIPLE-VALUE) only expands
macros after exhausting all other possibilities other than expanding into
a call to a function named (SETF reader). Clarify that it expands macros
in the style of MACROEXPAND-1 rather than MACROEXPAND (this was point 11
of FUNCTION-NAME:LARGE and is repeated here for clarity only).
(defvar *foo-trace* nil)
(defmacro foo (x y) `(aref ,x ,y))
(defun (setf foo) (z x y) ;wrong
(push `(,x ,y ,z) *foo-trace*)
(setf (aref x y) z))
(defsetf foo (x y) (z) ;right
(push `(,,x ,,y ,,z) *foo-trace*)
(setf (aref ,x ,y) ,z)))
(macroexpand-1 '(setf (foo array i) (val)))
The last form should include a push onto *foo-trace*, rather than
first macroexpanding (foo array i) into (aref array i) and then
The defun form has no effect because SETF expands macros before expanding
into a call to such a function, so this function will not be used.
In the absence of this clarification, the language specification is not
self-consistent. The example given above will not work in implementations
that chose to believe CLtL page 97 rather than page 102.
The rationale for FUNCTION-NAME:LARGE point 11 suggests that we thought
we had exchanged the two bullets on page 97, so that SETF looks for setf
methods before it expands macros. However there doesn't seem to be any
cleanup issue that explicitly addresses this.
Symbolics Genera looks for setf methods before expanding macros, I didn't
check any other implementations.
Cost to Implementors:
Cost to Users:
Cost of non-adoption:
The Common Lisp language will be a joke.