[Sbcl-devel] Re: simple method combination and :AROUND methods

[Gerd M. <ger...@t-...>]

William Harold Newman <wil...@ai...> writes:

> > >I'd like to patch the
> > >(COMPUTE-EFFECTIVE-METHOD SHORT-METHOD-COMBINATION T) method either
> > >with a NO-APPLICABLE-METHOD call or with a comment recording once and
> > >for all why it can't be done.
> > >
> > >When I do 
> > >  (defgeneric foo (x))
> > >  (defmethod foo :around ((x integer)) (+ 1 x)) ; never does 
> > >  CALL-NEXT-METHOD
> > >  (foo 12)
> > >in sbcl-0.8.0.72 it fails: "There is no primary method...".
> > 
> > Section 7.6.6.2, paragraph 15:  "In standard method combination, if there
> > is an applicable method but no applicable primary method, an error is 
> > signaled."
> 
> OK, it's even in the same section as what I quoted.:-(
> 
> Now I guess I'll just put the citations to the standard into the
> comments at the code which I found confusing, and wonder why ANSI did
> this thing.

Just wanted to add one thing...

Your example above uses standard method combination, but you also say
you'd like to patch a method for SHORT-METHOD-COMBINATION.  That
method is used for the short form of DEFINE-METHOD-COMBINATION, which
includes the standardized method combinations like PROGN, LIST, etc.

For these short method combination cases, the description of
DEFINE-METHOD-COMBINATION says that an error should be signaled:

    A method combination procedure defined in this way recognizes two roles
    for methods. A method whose one qualifier is the symbol naming this type
    of method combination is defined to be a primary method. At least one
    primary method must be applicable or an error is signaled.