32:
The printer doesn't report closures very well. This is true in
CMU CL 18b as well:
- (PRINT #'CLASS-NAME)
+ (defstruct foo bar)
+ (print #'foo-bar)
gives
- #<Closure Over Function "DEFUN STRUCTURE-SLOT-ACCESSOR" {134D1A1}>
+ #<FUNCTION "CLOSURE" {406974D5}>
It would be nice to make closures have a settable name slot,
and make things like DEFSTRUCT and FLET, which create closures,
set helpful values into this slot.
then requesting a BACKTRACE at the debugger prompt gives no information
about where in the user program the problem occurred.
- (this is apparently mostly fixed on the SPARC and PPC architectures:
- while giving the backtrace the system complains about "unknown
+ (this is apparently mostly fixed on the SPARC, PPC, and x86 architectures:
+ while giving the backtrace the non-x86 systems complains about "unknown
source location: using block start", but apart from that the
- backtrace seems reasonable. See tests/debug.impure.lisp for a test
- case)
+ backtrace seems reasonable. On x86 this is masked by bug 353. See
+ tests/debug.impure.lisp for a test case)
64:
Using the pretty-printer from the command prompt gives funny
conformance problem, since seems hard to construct useful code
where it matters.)
+ [ partially fixed by CSR in 0.8.17.17 because of a PFD ansi-tests
+ report that (COMPLEX RATIO) was failing; still failing on types of
+ the form (AND NUMBER (SATISFIES REALP) (SATISFIES ZEROP)). ]
+
b. (fixed in 0.8.3.43)
146:
b. The same for CSUBTYPEP.
262: "yet another bug in inline expansion of local functions"
- Compiler fails on
-
- (defun foo (x y)
- (declare (integer x y))
- (+ (block nil
- (flet ((xyz (u)
- (declare (integer u))
- (if (> (1+ (the unsigned-byte u)) 0)
- (+ 1 u)
- (return (+ 38 (cos (/ u 78)))))))
- (declare (inline xyz))
- (return-from foo
- (* (funcall (eval #'xyz) x)
- (if (> x 30)
- (funcall (if (> x 5) #'xyz #'identity)
- (+ x 13))
- 38)))))
- (sin (* x y))))
-
- Urgh... It's time to write IR1-copier.
+ During inline expansion of a local function Python can try to
+ reference optimized away objects (functions, variables, CTRANs from
+ tags and blocks), which later may lead to problems. Some of the
+ cases are worked around by forbidding expansion in such cases, but
+ the better way would be to reimplement inline expansion by copying
+ IR1 structures.
266:
David Lichteblau provided (sbcl-devel 2003-06-01) a patch to fix
in the wrapper, and then to update the instance just run through
all the old wrappers in order from oldest to newest.
-331: "lazy creation of CLOS classes for user-defined conditions"
- (defstruct foo)
- (defstruct (bar (:include foo)))
- (sb-mop:class-direct-subclasses (find-class 'foo))
- returns NIL, rather than a singleton list containing the BAR class.
-
332: "fasl stack inconsistency in structure redefinition"
(reported by Tim Daly Jr sbcl-devel 2004-05-06)
Even though structure redefinition is undefined by the standard, the
(it is likely that the fault lies in PPRINT-LOGICAL-BLOCK, as
suggested by the suggested implementation of PPRINT-TABULAR)
-342: PPRINT-TABULAR / PPRINT-LOGICAL-BLOCK logical block start position
- The logical block introduced by PPRINT-LOGICAL-BLOCK should not
- include the prefix, so that
- (pprint-tabular *standard-output* '(1 2 3) t nil 2)
- should print
- "(1 2 3)" rather than "(1 2 3)".
-
343: MOP:COMPUTE-DISCRIMINATING-FUNCTION overriding causes error
Even the simplest possible overriding of
COMPUTE-DISCRIMINATING-FUNCTION, suggested in the PCL implementation
(Note: there's at least one dubious thing in room.lisp: see the
comment in VALID-OBJ)
-345: backtrace on x86 undefined function
- In sbcl-0.8.13 (and probably earlier versions), code of the form
- (flet ((test () (#:undefined-fun 42)))
- (funcall #'test))
- yields the debugger with a poorly-functioning backtrace. Brian
- Downing fixed most of the problems on non-x86 architectures, but on
- the x86 the backtrace from this evaluation does not reveal anything
- about the problem. (See tests in debug.impure.lisp)
-
346: alpha backtrace
In sbcl-0.8.13, all backtraces from errors caused by internal errors
on the alpha seem to have a "bogus stack frame".
-348:
- Structure slot setters do not preserve evaluation order:
-
- (defstruct foo (x))
-
- (let ((i (eval '-2))
- (x (make-foo)))
- (funcall #'(setf foo-x)
- (incf i)
- (aref (vector x) (incf i)))
- (foo-x x))
- => error
-
349: PPRINT-INDENT rounding implementation decisions
At present, pprint-indent (and indeed the whole pretty printer)
more-or-less assumes that it's using a monospace font. That's
pprinter and only truncated at output? (So that indenting by 1/2
then 3/2 would indent by two spaces, not one?)
-350: heap overflow when printing bignums
- (reported by Bruno Haible 2004-10-08)
- In sbcl-0.8.15.18,
- * (DEFPARAMETER *BIG* (ASH 1 1000000))
- *BIG*
- * (PRINT *BIG*)
- Argh! gc_find_freeish_pages failed (restart_page), nbytes=110152.
- It should be straightforward to push the heap overflow threshold
- up to much larger bignums; Paul Dietz pointed out it would help to
- use a bignum-printing algorithm which bisected the printed number,
- rather than stripping off digits one by one, and CSR suggested using
- iteration rather than recursion to encourage intermediate results
- to be GCed.
-
-351: suboptimal error handling/reporting when compiling (PUSH (LET ...))
- In sbcl-0.8.15.18,
- * (defvar *b*)
- *B*
- * (defun oops ()
- (push *b*
- (let ((b *b*))
- (aref b 1))))
- causes the compiler to die with a TYPE-ERROR in SB-C::EXTRACT-LET-VARS,
- The value #:G4 is not of type LIST.
- Since the (LET ...) expression is being misused in PUSH as a
- SETFable place, it would be more helpful to fail as in
- * (defun oops2 () (setf (let ((b *b*)) (aref b 1)) *b*))
- with compilation errors and warnings like
- ; in: LAMBDA NIL
- ; ((B *B*))
- ; caught ERROR:
- ; illegal function call
- and
- ; caught WARNING:
- ; The function (SETF LET) is undefined, and its name is reserved
- ; by ANSI CL so that even if it were defined later, the code
- ; doing so would not be portable.
+352: forward-referenced-class trouble
+ reported by Bruno Haible on sbcl-devel
+ (defclass c (a) ())
+ (setf (class-name (find-class 'a)) 'b)
+ (defclass a () (x))
+ (defclass b () (y))
+ (make-instance 'c)
+ Expected: an instance of c, with a slot named x
+ Got: debugger invoked on a SIMPLE-ERROR in thread 78906:
+ While computing the class precedence list of the class named C.
+ The class named B is a forward referenced class.
+ The class named B is a direct superclass of the class named C.
+
+353: debugger suboptimalities on x86
+ On x86 backtraces for undefined functions start with a bogus stack
+ frame, and backtraces for throws to unknown catch tags with a "no
+ debug information" frame. These are both due to CODE-COMPONENT-FROM-BITS
+ (used on non-x86 platforms) being a more complete solution then what
+ is done on x86.
+
+ More generally, the debugger internals suffer from excessive x86/non-x86
+ conditionalization and OAOOMization: refactoring the common parts would
+ be good.
+
+354: XEPs in backtraces
+ Under default compilation policy
+ (defun test ()
+ (throw :unknown t))
+ (test)
+ Has the XEP for TEST in the backtrace, not the TEST frame itself.
+ (sparc and x86 at least)
+
+355: change-class of generic-function
+ (reported by Bruno Haible)
+ The MOP doesn't support change-class on a generic-function. However, SBCL
+ apparently supports it, since it doesn't give an error or warning when doing
+ so so. Then, however, it produces wrong results for calls to this generic
+ function.
+ ;;; The effective-methods cache:
+ (progn
+ (defgeneric testgf35 (x))
+ (defmethod testgf35 ((x integer))
+ (cons 'integer (if (next-method-p) (call-next-method))))
+ (defmethod testgf35 ((x real))
+ (cons 'real (if (next-method-p) (call-next-method))))
+ (defclass customized5-generic-function (standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ (defmethod sb-pcl:compute-effective-method ((gf customized5-generic-function) method-combination methods)
+ `(REVERSE ,(call-next-method)))
+ (list
+ (testgf35 3)
+ (progn
+ (change-class #'testgf35 'customized5-generic-function)
+ (testgf35 3))))
+ Expected: ((INTEGER REAL) (REAL INTEGER))
+ Got: ((INTEGER REAL) (INTEGER REAL))
+ ;;; The discriminating-function cache:
+ (progn
+ (defgeneric testgf36 (x))
+ (defmethod testgf36 ((x integer))
+ (cons 'integer (if (next-method-p) (call-next-method))))
+ (defmethod testgf36 ((x real))
+ (cons 'real (if (next-method-p) (call-next-method))))
+ (defclass customized6-generic-function (standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ (defmethod sb-pcl:compute-discriminating-function ((gf customized6-generic-function))
+ (let ((orig-df (call-next-method)))
+ #'(lambda (&rest arguments)
+ (reverse (apply orig-df arguments)))))
+ (list
+ (testgf36 3)
+ (progn
+ (change-class #'testgf36 'customized6-generic-function)
+ (testgf36 3))))
+ Expected: ((INTEGER REAL) (REAL INTEGER))
+ Got: ((INTEGER REAL) (INTEGER REAL))
+
+356: PCL corruption
+ (reported by Bruno Haible)
+ After the "layout depth conflict" error, the CLOS is left in a state where
+ it's not possible to define new standard-class subclasses any more.
+ Test case:
+ (defclass prioritized-dispatcher ()
+ ((dependents :type list :initform nil)))
+ (defmethod sb-pcl:validate-superclass ((c1 sb-pcl:funcallable-standard-class)
+ (c2 (eql (find-class 'prioritized-dispatcher))))
+ t)
+ (defclass prioritized-generic-function (prioritized-dispatcher standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ ;; ERROR, Quit the debugger with ABORT
+ (defclass typechecking-reader-class (standard-class)
+ ())
+ Expected: #<STANDARD-CLASS TYPECHECKING-READER-CLASS>
+ Got: ERROR "The assertion SB-PCL::WRAPPERS failed."
+
+357: defstruct inheritance of initforms
+ (reported by Bruno Haible)
+ When defstruct and defclass (with :metaclass structure-class) are mixed,
+ 1. some slot initforms are ignored by the DEFSTRUCT generated constructor
+ function, and
+ 2. all slot initforms are ignored by MAKE-INSTANCE. (This can be arguably
+ OK for initforms that were given in a DEFSTRUCT form, but for those
+ given in a DEFCLASS form, I think it qualifies as a bug.)
+ Test case:
+ (defstruct structure02a
+ slot1
+ (slot2 t)
+ (slot3 (floor pi)))
+ (defclass structure02b (structure02a)
+ ((slot4 :initform -44)
+ (slot5)
+ (slot6 :initform t)
+ (slot7 :initform (floor (* pi pi)))
+ (slot8 :initform 88))
+ (:metaclass structure-class))
+ (defstruct (structure02c (:include structure02b (slot8 -88)))
+ slot9
+ (slot10 t)
+ (slot11 (floor (exp 3))))
+ ;; 1. Form:
+ (let ((a (make-structure02c)))
+ (list (structure02c-slot4 a)
+ (structure02c-slot5 a)
+ (structure02c-slot6 a)
+ (structure02c-slot7 a)))
+ Expected: (-44 nil t 9)
+ Got: (SB-PCL::..SLOT-UNBOUND.. SB-PCL::..SLOT-UNBOUND..
+ SB-PCL::..SLOT-UNBOUND.. SB-PCL::..SLOT-UNBOUND..)
+ ;; 2. Form:
+ (let ((b (make-instance 'structure02c)))
+ (list (structure02c-slot2 b)
+ (structure02c-slot3 b)
+ (structure02c-slot4 b)
+ (structure02c-slot6 b)
+ (structure02c-slot7 b)
+ (structure02c-slot8 b)
+ (structure02c-slot10 b)
+ (structure02c-slot11 b)))
+ Expected: (t 3 -44 t 9 -88 t 20)
+ Got: (0 0 0 0 0 0 0 0)
+
+358: :DECLARE argument to ENSURE-GENERIC-FUNCTION
+ (reported by Bruno Haible)
+ According to ANSI CL, ensure-generic-function must accept a :DECLARE
+ keyword argument. In SBCL 0.8.16 it does not.
+ Test case:
+ (progn
+ (ensure-generic-function 'foo113 :declare '((optimize (speed 3))))
+ (sb-pcl:generic-function-declarations #'foo113))
+ Expected: ((OPTIMIZE (SPEED 3)))
+ Got: ERROR
+ Invalid initialization argument:
+ :DECLARE
+ in call for class #<SB-MOP:FUNCALLABLE-STANDARD-CLASS STANDARD-GENERIC-FUNCTION>.
+ See also:
+ The ANSI Standard, Section 7.1.2
+
+ Bruno notes: The MOP specifies that ensure-generic-function accepts :DECLARATIONS.
+ The easiest way to be compliant to both specs is to accept both (exclusively
+ or cumulatively).
+
+359: wrong default value for ensure-generic-function's :generic-function-class argument
+ (reported by Bruno Haible)
+ ANSI CL is silent on this, but the MOP's specification of ENSURE-GENERIC-FUNCTION says:
+ "The remaining arguments are the complete set of keyword arguments
+ received by ENSURE-GENERIC-FUNCTION."
+ and the spec of ENSURE-GENERIC-FUNCTION-USING-CLASS:
+ ":GENERIC-FUNCTION-CLASS - a class metaobject or a class name. If it is not
+ supplied, it defaults to the class named STANDARD-GENERIC-FUNCTION."
+ This is not the case in SBCL. Test case:
+ (defclass my-generic-function (standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ (setf (fdefinition 'foo1)
+ (make-instance 'my-generic-function :name 'foo1))
+ (ensure-generic-function 'foo1
+ :generic-function-class (find-class 'standard-generic-function))
+ (class-of #'foo1)
+ ; => #<SB-MOP:FUNCALLABLE-STANDARD-CLASS STANDARD-GENERIC-FUNCTION>
+ (setf (fdefinition 'foo2)
+ (make-instance 'my-generic-function :name 'foo2))
+ (ensure-generic-function 'foo2)
+ (class-of #'foo2)
+ Expected: #<SB-MOP:FUNCALLABLE-STANDARD-CLASS STANDARD-GENERIC-FUNCTION>
+ Got: #<SB-MOP:FUNCALLABLE-STANDARD-CLASS MY-GENERIC-FUNCTION>
+
+360: CALL-METHOD not recognized in method-combination body
+ (reported by Bruno Haible)
+ This method combination, which adds 'redo' and 'return' restarts for each
+ method invocation to standard method combination, gives an error in SBCL.
+ (defun prompt-for-new-values ()
+ (format *debug-io* "~&New values: ")
+ (list (read *debug-io*)))
+ (defun add-method-restarts (form method)
+ (let ((block (gensym))
+ (tag (gensym)))
+ `(BLOCK ,block
+ (TAGBODY
+ ,tag
+ (RETURN-FROM ,block
+ (RESTART-CASE ,form
+ (METHOD-REDO ()
+ :REPORT (LAMBDA (STREAM) (FORMAT STREAM "Try calling ~S again." ,method))
+ (GO ,tag))
+ (METHOD-RETURN (L)
+ :REPORT (LAMBDA (STREAM) (FORMAT STREAM "Specify return values for ~S call." ,method))
+ :INTERACTIVE (LAMBDA () (PROMPT-FOR-NEW-VALUES))
+ (RETURN-FROM ,block (VALUES-LIST L)))))))))
+ (defun convert-effective-method (efm)
+ (if (consp efm)
+ (if (eq (car efm) 'CALL-METHOD)
+ (let ((method-list (third efm)))
+ (if (or (typep (first method-list) 'method) (rest method-list))
+ ; Reduce the case of multiple methods to a single one.
+ ; Make the call to the next-method explicit.
+ (convert-effective-method
+ `(CALL-METHOD ,(second efm)
+ ((MAKE-METHOD
+ (CALL-METHOD ,(first method-list) ,(rest method-list))))))
+ ; Now the case of at most one method.
+ (if (typep (second efm) 'method)
+ ; Wrap the method call in a RESTART-CASE.
+ (add-method-restarts
+ (cons (convert-effective-method (car efm))
+ (convert-effective-method (cdr efm)))
+ (second efm))
+ ; Normal recursive processing.
+ (cons (convert-effective-method (car efm))
+ (convert-effective-method (cdr efm))))))
+ (cons (convert-effective-method (car efm))
+ (convert-effective-method (cdr efm))))
+ efm))
+ (define-method-combination standard-with-restarts ()
+ ((around (:around))
+ (before (:before))
+ (primary () :required t)
+ (after (:after)))
+ (flet ((call-methods-sequentially (methods)
+ (mapcar #'(lambda (method)
+ `(CALL-METHOD ,method))
+ methods)))
+ (let ((form (if (or before after (rest primary))
+ `(MULTIPLE-VALUE-PROG1
+ (PROGN
+ ,@(call-methods-sequentially before)
+ (CALL-METHOD ,(first primary) ,(rest primary)))
+ ,@(call-methods-sequentially (reverse after)))
+ `(CALL-METHOD ,(first primary)))))
+ (when around
+ (setq form
+ `(CALL-METHOD ,(first around)
+ (,@(rest around) (MAKE-METHOD ,form)))))
+ (convert-effective-method form))))
+ (defgeneric testgf16 (x) (:method-combination standard-with-restarts))
+ (defclass testclass16a () ())
+ (defclass testclass16b (testclass16a) ())
+ (defclass testclass16c (testclass16a) ())
+ (defclass testclass16d (testclass16b testclass16c) ())
+ (defmethod testgf16 ((x testclass16a))
+ (list 'a
+ (not (null (find-restart 'method-redo)))
+ (not (null (find-restart 'method-return)))))
+ (defmethod testgf16 ((x testclass16b))
+ (cons 'b (call-next-method)))
+ (defmethod testgf16 ((x testclass16c))
+ (cons 'c (call-next-method)))
+ (defmethod testgf16 ((x testclass16d))
+ (cons 'd (call-next-method)))
+ (testgf16 (make-instance 'testclass16d))
+
+ Expected: (D B C A T T)
+ Got: ERROR CALL-METHOD outside of a effective method form
+
+ This is a bug because ANSI CL HyperSpec/Body/locmac_call-m__make-method
+ says
+ "The macro call-method invokes the specified method, supplying it with
+ arguments and with definitions for call-next-method and for next-method-p.
+ If the invocation of call-method is lexically inside of a make-method,
+ the arguments are those that were supplied to that method. Otherwise
+ the arguments are those that were supplied to the generic function."
+ and the example uses nothing more than these two cases (as you can see by
+ doing (trace convert-effective-method)).
+
+361: initialize-instance of standard-reader-method ignores :function argument
+ (reported by Bruno Haible)
+ Pass a custom :function argument to initialize-instance of a
+ standard-reader-method instance, but it has no effect.
+ ;; Check that it's possible to define reader methods that do typechecking.
+ (progn
+ (defclass typechecking-reader-method (sb-pcl:standard-reader-method)
+ ())
+ (defmethod initialize-instance ((method typechecking-reader-method) &rest initargs
+ &key slot-definition)
+ (let ((name (sb-pcl:slot-definition-name slot-definition))
+ (type (sb-pcl:slot-definition-type slot-definition)))
+ (apply #'call-next-method method
+ :function #'(lambda (args next-methods)
+ (declare (ignore next-methods))
+ (apply #'(lambda (instance)
+ (let ((value (slot-value instance name)))
+ (unless (typep value type)
+ (error "Slot ~S of ~S is not of type ~S: ~S"
+ name instance type value))
+ value))
+ args))
+ initargs)))
+ (defclass typechecking-reader-class (standard-class)
+ ())
+ (defmethod sb-pcl:validate-superclass ((c1 typechecking-reader-class) (c2 standard-class))
+ t)
+ (defmethod reader-method-class ((class typechecking-reader-class) direct-slot &rest args)
+ (find-class 'typechecking-reader-method))
+ (defclass testclass25 ()
+ ((pair :type (cons symbol (cons symbol null)) :initarg :pair :accessor testclass25-pair))
+ (:metaclass typechecking-reader-class))
+ (macrolet ((succeeds (form)
+ `(not (nth-value 1 (ignore-errors ,form)))))
+ (let ((p (list 'abc 'def))
+ (x (make-instance 'testclass25)))
+ (list (succeeds (make-instance 'testclass25 :pair '(seventeen 17)))
+ (succeeds (setf (testclass25-pair x) p))
+ (succeeds (setf (second p) 456))
+ (succeeds (testclass25-pair x))
+ (succeeds (slot-value x 'pair))))))
+ Expected: (t t t nil t)
+ Got: (t t t t t)
+
+ (inspect (first (sb-pcl:generic-function-methods #'testclass25-pair)))
+ shows that the method was created with a FAST-FUNCTION slot but with a
+ FUNCTION slot of NIL.
+
+362: missing error when a slot-definition is created without a name
+ (reported by Bruno Haible)
+ The MOP says about slot-definition initialization:
+ "The :NAME argument is a slot name. An ERROR is SIGNALled if this argument
+ is not a symbol which can be used as a variable name. An ERROR is SIGNALled
+ if this argument is not supplied."
+ Test case:
+ (make-instance (find-class 'sb-pcl:standard-direct-slot-definition))
+ Expected: ERROR
+ Got: #<SB-MOP:STANDARD-DIRECT-SLOT-DEFINITION NIL>
+
+363: missing error when a slot-definition is created with a wrong documentation object
+ (reported by Bruno Haible)
+ The MOP says about slot-definition initialization:
+ "The :DOCUMENTATION argument is a STRING or NIL. An ERROR is SIGNALled
+ if it is not. This argument default to NIL during initialization."
+ Test case:
+ (make-instance (find-class 'sb-pcl:standard-direct-slot-definition)
+ :name 'foo
+ :documentation 'not-a-string)
+ Expected: ERROR
+ Got: #<SB-MOP:STANDARD-DIRECT-SLOT-DEFINITION FOO>
+
+364: does not support class objects as specializer names
+ (reported by Bruno Haible)
+ According to ANSI CL 7.6.2, class objects are valid specializer names,
+ and "Parameter specializer names are used in macros intended as the
+ user-level interface (defmethod)". DEFMETHOD's syntax section doesn't
+ mention this possibility in the BNF for parameter-specializer-name;
+ however, this appears to be an editorial omission, since the CLHS
+ mentions issue CLASS-OBJECT-SPECIALIZER:AFFIRM as being approved
+ by X3J13. SBCL doesn't support it:
+ (defclass foo () ())
+ (defmethod goo ((x #.(find-class 'foo))) x)
+ Expected: #<STANDARD-METHOD GOO (#<STANDARD-CLASS FOO>)>
+ Got: ERROR "#<STANDARD-CLASS FOO> is not a legal class name."
+
+365: mixin on generic-function subclass
+ (reported by Bruno Haible)
+ a mixin class
+ (defclass prioritized-dispatcher ()
+ ((dependents :type list :initform nil)))
+ on a generic-function subclass:
+ (defclass prioritized-generic-function (prioritized-dispatcher standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ SBCL gives an error on this, telling to define a method on SB-MOP:VALIDATE-SUPERCLASS. If done,
+ (defmethod sb-pcl:validate-superclass ((c1 sb-pcl:funcallable-standard-class)
+ (c2 (eql (find-class 'prioritized-dispatcher))))
+ t)
+ then, however,
+ (defclass prioritized-generic-function (prioritized-dispatcher standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ => debugger invoked on a SIMPLE-ERROR in thread 6687:
+ layout depth conflict: #(#<SB-KERNEL:LAYOUT for T {500E1E9}> ...)
+
+ Further discussion on this: http://thread.gmane.org/gmane.lisp.steel-bank.general/491
+
+366: cannot define two generic functions with user-defined class
+ (reported by Bruno Haible)
+ it is possible to define one generic function class and an instance
+ of it. But attempting to do the same thing again, in the same session,
+ leads to a "Control stack exhausted" error. Test case:
+ (defclass my-generic-function-1 (standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ (defgeneric testgf-1 (x) (:generic-function-class my-generic-function-1)
+ (:method ((x integer)) (cons 'integer nil)))
+ (defclass my-generic-function-2 (standard-generic-function)
+ ()
+ (:metaclass sb-pcl:funcallable-standard-class))
+ (defgeneric testgf-2 (x) (:generic-function-class my-generic-function-2)
+ (:method ((x integer)) (cons 'integer nil)))
+ => SB-KERNEL::CONTROL-STACK-EXHAUSTED
+