DEFGENERIC

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: 06 Feb 88  1146 PST
    From: Dick Gabriel <RPG@SAIL.Stanford.EDU>


    The material for the behavior Moon specified does not look too bad
    when presented this way: defgeneric does an ensure-generic-function,
    it removes all methods defined by any previous defgeneric, and then
    it adds the methods specified by the :methods. The DEFCLASS description
    is similar.  The presentation is clear and more concise than the
    desciption of the previous behavior. 

I prefer to add new methods before removing old ones, to avoid a transient
state in which methods are missing.  Remove-method is specified not to error
if the method is already gone.  Defining a method is specified (page 1-27) to
create a new method object and discard any existing method object, rather
than modifying the object as defining a class does.  Those two facts mean
it's safe to do the add before the remove.