# Re: no-applicable-method

• To: CHEEWEEI%ITIVAX.BITNET@CUNYVM.CUNY.EDU
• Subject: Re: no-applicable-method
• From: Gregor.pa@Xerox.COM
• Date: Wed, 9 Aug 89 20:12 PDT
• Cc: commonloops.pa@Xerox.COM
• In-reply-to: The message of 9 Aug 89 19:41 PDT from CHEEWEEI%ITIVAX.BITNET@CUNYVM.CUNY.EDU
• Line-fold: no

    Date: Thu, 10 Aug 89 10:41 U
From: <CHEEWEEI%ITIVAX.BITNET@CUNYVM.CUNY.EDU>

If defining a method for the gen func NO-APPLICABLE-METHOD, specialised
on STANDARD-GENERIC-FUNCTION is illegal, I assume that specialising
on the class T is illegal too then since T is specified in CLOS.

Yes, the following excerpt from the current draft version of chapter 3
(which, unfortunately, still isn't available) may be helpful to you.

These principles govern inheritance relationships among CLOS classes, and
the corresponding method applicability relationships of methods specialized
to those classes.  Other principles which govern the calling relationships
among generic functions are defined in the Protocols'' section.

These principles are based on a division of classes, methods and generic
functions into three categories.  Classes, methods and generic functions
defined by this specification are called {\bit specified classes}, {\bit
specified methods} and {\bit specified generic-functions}.  Classes, methods
and generic functions which are defined by a particular implementation of
CLOS are called {\bit implementation-specific classes}, {\bit
implementation-specific methods} and {\bit implementation-specific
generic-functions}.  Classes, methods and generic functions which are
defined by portable programs are called {\bit portable classes}, {\bit
portable methods} and {\bit portable generic-functions}.

\item{4}  Implementations are not free to override a specified method with an
unspecified method if that will affect the specified method's applicability
to any specified class.

\item{5} Implementations are free to define unspecified {\bf :before} and
{\bf :after} methods on specified generic functions.

\item{6} Portable programs are not free to redefine any specified methods or
classes.  Portable programs are not free to define methods on specified
generic functions which are specialized to specified classes.

So, when the specification says methods may be written for it, does
that imply that only methods specialised on a user defined metaclass
for gf objects may be written?

Yes, if the generic function is a specified one, you can write methods
on user defined metaobject classes only.  So, you could say:

(defclass my-generic-function (standard-generic-function)
()
(:metaclass funcallable-standard-class))

(defmethod no-applicable-method ((gf my-generic-function) args)
...)

Then, using defgeneric, you can make a generic function like FOO be an
instance of my-generic-function rather than standard-generic-function.
In the PCL you are using, you may need to say the following instead: