dispatching on keywords

[patl@goldfish.mitron.tek.com (Patrick Logan)]

   Date: Fri, 13 Nov 1992 13:17:50 -0500
   Agreed.  Yet another role for #none (or #nothing).  For that matter,
   this gives the programmer a way of explicitly saying "I know that
   there is a keyword K, but I do not want to provide a value for it",
   not to be confused with "...and I give it the value #f":

Doesn't this lead to meta-circular madness? I mean, once there is an
object that is #nothing, then that object is something and will be
used for something, e.g., er, nothing.

The only way to ultimately step out of the problem is to have two
separate values: the data and the meta-data. The data is the value
desired and the meta-data is the separate indicator that indicates the
data is good, bad, missing, etc. It is trouble when one variable's
value is being used for both purposes.
--
Patrick Logan         patl@goldfish.mitron.tek.com
Mitron Corporation    (503) 690-8350    FAX: (503) 690-9292
15256 NW Greenbrier Pkwy, Beaverton, OR 97006