Sent the response below to Tobias privately by accident.

---------- Forwarded message ---------- From: Erik Huelsmann ehuels@gmail.com Date: Mon, Jan 11, 2010 at 11:40 PM Subject: Re: [armedbear-devel] [Bug] Identically named gensymed coalesced into same object in fasl file To: "Tobias C. Rittweiler" tcr@freebits.de

Hi Tobias,

Thanks for your report. This issue has long been in ABCL and it's not fixed yet.

I have known about this problem for a while, but was kind of hoping it wouldn't show up in practice. I guess it did.

This is what happens: when reading, the fasl loader creates an anonymous package in which it interns uninterned symbols. It "has" to do that, because ABCL doesn't store references to the actual unique objects everywhere; instead it stores the textual representation in some places. These symbols get coalesced by use of the anonymous package.

So, generally the system of coalescing is something inherent to this idea. The idea is wrong enough for you to run into and get bitten by it.

We'll have to come up with a better idea. Can you add the mail message below to our issue tracker?

BTW: Did you happen to find this issue by accident? How did you find it?

Bye,

Erik.

On Mon, Jan 11, 2010 at 10:35 PM, Tobias C. Rittweiler tcr@freebits.de wrote:

I'm currently running an old checkout ("0.17.0-dev"), so the issue may have been fixed meanwhile.

### /tmp/foo.lisp  (eval-when (:load-toplevel :execute)    (let ((a '#:foo)          (b '#:foo))      (setf (fdefinition 'foo) (lambda () (values a b)))))

(eval-when (:load-toplevel :execute)    (format t "~&(multiple-value-call #'eq (foo)) => ~S~%"            (multiple-value-call #'eq (foo))))  ###

CL-USER> (compile-file "/tmp/foo.lisp")  ; Compiling /tmp/foo.lisp ...  ; (LET (# #) ...)  ; (FORMAT T ...)

; Compilation unit finished  ;   The following functions were used but not defined:  ;     FOO

; Wrote /tmp/foo.abcl (0.034 seconds)  #P"/tmp/foo.abcl"  NIL  NIL

That warning is bogus. There some work in this area so this bit may be fixed already.

The actual issue of my mail is this one, though:

CL-USER> (load *)  (multiple-value-call #'eq (foo)) => T  T

As you can see, ABCL coalesces the two identical named gensyms into the same object in the fasl file.

While 3.2.4.2.2 does specify that

Two apparently uninterned symbols S and C are similar if their names  are similar.

ABCL's behavior is still wrong because 3.2.4.1 says

If two literal objects appearing in the source code for a single file  processed with the file compiler are the [sic] identical, the  corresponding objects in the compiled code must also be the  identical. __With the exception of symbols and packages__, any two  literal objects in code being processed by the file compiler may be  coalesced if and only if they are similar; __if they are either both  symbols or both packages, they may only be coalesced if and only if  they are identical__.

-T.

---

armedbear-devel mailing list armedbear-devel@common-lisp.net http://common-lisp.net/cgi-bin/mailman/listinfo/armedbear-devel