[clpython-devel] Re: CLPython on SBCL

[Robert Brown]

The call to ensure-class without

    :metaclass 'py-core-type

succeeds.

The call with the :metaclass argument fails inside change-class:

  (defmethod change-class ((instance standard-object) (new-class standard-class)
                           &rest initargs)
    (unless (class-finalized-p new-class)
      (finalize-inheritance new-class))
    (let ((cpl (class-precedence-list new-class)))
      (dolist (class cpl)
        (macrolet
            ((frob (class-name)
               `(when (eq class (find-class ',class-name))
                 (error 'metaobject-initialization-violation
                  :format-control "~@<Cannot ~S objects into ~S
                  metaobjects.~@:>"
                  :format-arguments (list 'change-class ',class-name)
                  :references (list '(:amop :initialization ,class-name))))))
          (frob class)
          (frob generic-function)
          (frob method)
          (frob slot-definition))))
    (change-class-internal instance new-class initargs))

CLASS is on the class precedence list of PY-CORE-TYPE.

bob

====================

Willem Broekema writes:
 > Hello Bob,
 > 
 > On Thu, May 1, 2008 at 5:52 PM, Robert Brown <brown at google.com> wrote:
 > 
 > > I tried to get CLPython up and running on the latest SBCL.  The diff below
 > > contains a couple of easy fixes.  SBCL wants BREAK's argument to be a
 > > string
 > > and SBCL's LOOP does not like a negative loop increment.
 > 
 > 
 > Thanks for the patches!
 > 
 > 
 > > The real porting problem right now is CLOS related.  SBCL does not like
 > > the
 > > following code in core/classes.lisp:
 > >
 > >    ;; Fix superclass and metaclass of PY-DICT.
 > >    (ensure-class 'py-dict
 > >                  :direct-superclasses (list 'py-core-object)
 > >                  :metaclass 'py-core-type)
 > >
 > > I get the following error:
 > >
 > >    debugger invoked on a SB-PCL::METAOBJECT-INITIALIZATION-VIOLATION in
 > > thread
 > >    #<THREAD "initial thread" {11701A79}>:
 > >      Cannot CHANGE-CLASS objects into CLASS metaobjects.
 > >    See also:
 > >      AMOP, Initialization of Class Metaobjects
 > >
 > > I think the problem is that PY-DICT is a normal class and the ENSURE-CLASS
 > > call tries to turn it into a metaclass.  Anyway, I'm far from a CLOS
 > > expert.
 > 
 > 
 > Well, class py-dict is not turned into a metaclass here, at least that's not
 > the intention. :) The superclass and metaclass of it are changed but py-dict
 > remains a non-metaclass class. So I think the actual error message is
 > incorrect, but something else is wrong.
 > 
 > The problem might be that you can not change the metaclasses of a class
 > using ensure-class. Could you please check if the call to ensure-class
 > without the metaclass change is accepted?
 > 
 > (ensure-class 'py-dict
 >                     :direct-superclasses (list 'py-core-object))
 > 
 > Thanks,
 > - Willem