default values of flavor instance vars

["William D. Gooch" <ai.gooch@MCC.COM>]

    Is there a way to programmatically determine
    the default values for the instance variables of foo?

By "determine", do you mean (1) find out what they are, (2) set them to
some computed values, or (3) select from among a reasonably small set of
possible initializations for foo.  I think you already got some answers
to (1).  I don't know a good way to do (2) except by using a specialized 
make-instance method (or destructively modifying the flavor prior to
instantiation - urk).  If you're interested in (3), you might want to
look at the flavor :mixture option, which lets you pass a keyword
argument to make-instance which selects a dependent of the specified
flavor to instantiate (the mixture dependents are automatically
defflavored).