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Date: Thu, 23 Aug 1984 13:56 EDT
From: "Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>
I don't think it would violate the standard for a particular
implementation to return nil in this case -- this sort of extension in a
situation that would otherwise be an error is generally allowed -- but I
would strongly advocate that no implementor do this without a very good
reason. Users of his system will come to depend on this trick,
sacrificing portability without realizing it.
I don't see any justification for such an extension. Extend CDR to take
the successor of a number... how is that different? NIL is clearly not
defined to be "a member of all data types" or similar. I think the
proposed extension violates the spirit of Lisp.
What do you (Scott) think are similar situations "that would otherwise
be an error" that are really parallel?