EQ-preservation

[MOON at SCRC-TENEX]

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    Date: Sat, 11 Jun 1983  18:05 EDT
    From: Scott E. Fahlman <Fahlman@CMU-CS-C>
    To:   David.Dill@CMU-CS-A (L170DD60)
    Cc:   common-lisp@su-ai
    Subject: EQ-preservation
    In-reply-to: Msg of 11 Jun 1983 1416-EDT () from David.Dill at CMU-CS-A (L170DD60)

    The question is not whether two distinct numbers are EQ, but whether
    and in what conditions you can count on (EQ X X).  If X has the
    semantics of a variable reference, then you can count on this,
    regardless of what is put in X.
Not so in Maclisp, as I understand it.  And maybe not so on the LM-2
in a certain weird case involving an interrupt between the two references
to X (I forget whether or not it can happen).  In both cases this only
happens when X is a number of course.

Does Common Lisp really undertake to guarantee (EQ X X) if the value of X
is a number?  The writeup on EQ in the Laser edition could be interpreted
as either confirming or denying this.

On an unrelated note, did you notice that someone sabotaged your mail
header by putting backspaces into the "To Dill" line?  I know I shouldn't
throw stones, the header of this message I'm sending now is going to have
a host you don't know about in it, because of Babyl.