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What is a compiler (vol. 63827) meets what are gensyms.
- To: Common-Lisp@SU-AI.arpa
- Subject: What is a compiler (vol. 63827) meets what are gensyms.
- From: Gregor.pa@Xerox.COM
- Date: Thu, 17 Apr 86 14:15 PST
- Cc: Gregor.pa@Xerox.COM
- Line-fold: no
In this issue the subject of what compile file is required to do with
top-level forms meets the subject of top-level calls to macros which
expand into code containing gensyms.
Suppose I have the following macro.
(defmacro foo (x y)
(let ((var (gensym))
(defun ,x ..)
(defun ,y ..)
(defsetf ,x (,var) (,nv-var) `(,',y ,,var ,,nv-var)))))
And I have a file that includes the form:
(FOO BAR SET-BAR)
[ For clarities sake, the point is that the macro expands
to a progn that includes a defsetf that has gensyms for
the access-function-args and storing-variables, like this:
(DEFSETF BAR (#:G1890) (#:G1891) `(SET-BAR ,#:G1890 ,#:G1891))
Is compiling and loading the file legal Common Lisp?
Is the original foo macro legal Common Lisp?
I claim that the answer to both questions is yes. After all, it is
clearly legal interpreted/compiled to core Common Lisp.
I believe that CLtL is "silent" on this issue.
I got bit by a Common Lisp compiler which macroexpands top-level forms,
but which does not necessarily compile the entire result of the
macroexpansion. In this particular case the compiler expanded the two
defuns, but left the defsetf as (store-setf '<list with gensyms in it>)
Then the dumper dumped that list in such a way that when the file was
loaded the gensyms which should have been eq were not.