Re: [Sbcl-devel] DEFMETHOD with invalid qualifier

[Pascal C. <pc...@p-...>]

It's good that qualifiers are in general checked only at 'method  
combination time', because the restrictions which qualifiers are  
considered valid or not may depend on conditions that can only be  
decided then. Note that the long form of define-method-combination as  
well as methods defined on compute-effective-method in the CLOS MOP  
may add such more or less dynamic restrictions.

As always, if only instances of standard metaclasses are used, a  
compiler can be more strict. It could be that ANSI Common Lisp  
intentionally left this more open because the CLOS MOP specified  
wasn't finalized yet at that time.

Pascal

On 12 Oct 2009, at 18:33, Tobias C. Rittweiler wrote:

>
> On the following
>
>  (defgeneric foo (a b)
>    (:method-combination append))
>
>  (defmethod foo ((x (eql :foo)) b)
>    (list x b))
>
> SBCL will signal a warning
>
>  Invalid qualifiers for APPEND method combination in method ...
>
> at _load-time_.
>
> in REAL-ADD-METHODS in src/pcl/methods.lisp, there's the following
> comment by Xof:
>
>  ;; KLUDGE II: ANSI saith that it is not an error to add a
>  ;; method with invalid qualifiers to a generic function of the
>  ;; wrong kind; it's only an error at generic function
>  ;; invocation time; I dunno what the rationale was, and it
>  ;; sucks.  Nevertheless, it's probably a programmer error, so
>  ;; let's warn anyway. -- CSR, 2003-08-20
>
> and I wonder if SBCL couldn't signal the warning at compilation-time,
> too, so COMPILE-FILE will return T as failurep.
>
>  -T.
>
>
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-- 
Pascal Costanza, mailto:pc...@p-..., http://p-cos.net
Vrije Universiteit Brussel
Software Languages Lab
Pleinlaan 2, B-1050 Brussel, Belgium