unspecified-object

[Jonathan Rees <jar@zohar.ai.mit.edu>]

   Date: 23 May 89 01:51:40 GMT
   From: pierce@locus.ucla.edu

      I think that the specification of Scheme, as well as many Scheme programs,
      would be made more elegant if an "unspecified-object" analogous to NaN in 
      the IEEE numeric standard were introduced. Functions which return 
      unspecified values now would be required to return an "unspecified-object"
      instead.

It doesn't make sense to specify that the object to be returned should
be unspecified.  It seems to me that if some specific object is to be
specified, then it should be a specific object, not an unspecific one.
Besides, if we specify what object should be returned, then that
object will no longer be unspecified.