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Re: symbols are not generic functions
- To: Moon@STONY-BROOK.SCRC.Symbolics.COM
- Subject: Re: symbols are not generic functions
- From: Gregor.pa@Xerox.COM
- Date: 29 Jan 87 16:05 PST
- Cc: Common-Lisp-Object-System@Sail.Stanford.edu
- In-reply-to: David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>'s message of Tue, 27 Jan 87 23:05 EST
in reference to ensure-generic-function, Moon says:
I don't completely understand. Suppose symbol-function of the
is already a generic function, but it is of a different class than
kind that you get by default, because someone is using
meta-objects. Would ensure-generic-function accept that generic
function, signal an error, or clobber it with a generic function of
the default kind?
Well, the short lazy answer is ensure-generic-function does whatever
add-method was going to do.
The long answer is we need to figure this out.
1. perhaps ensure-generic-function should take a second argument which
would be the class of the generic function to make if there isn't one.
2. There is a part of the meta-object protocol which deals with whether
or not is is permissible to change the class of a generic function, that
part of the protocol should be called here when there is already a
generic function but its the wrong class.
3. Perhaps ensure-generic-function should take another argument which
could be used to specify that if there is a function in the place, but
its not a generic-function, it should become the default method for the
new generic function.
Also, does ensure-generic-function ever alter the symbol-function of
a symbol, or is it just a side-effect free coercion? If the latter,
it might be cleaner to use the existing COERCE function, thus
(add-method (coerce <arg> 'generic-function) <method>).
I am not sure about this given what I said above.