MAKE-HASH-TABLE :TEST arg

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: Mon, 12 Sep 88 11:05 EDT
    From: Barry Margolin <barmar@Think.COM>

    I suppose you COULD use SXHASH for all hash tables, since EQ objects are
    necessarily EQUAL

Not if the following program is valid Common Lisp.  I couldn't find anything
in CLtL that speaks to this.  Should this be run through the cleanup committee?

  (setq ht (make-hash-table :test #'eq))
  (setq a (cons 1 2))
  (setf (gethash a ht) 'win)
  (setf (cdr a) 3)
  (gethash a ht 'lose) => win t

If SXHASH was used, the last form would evaluate to lose nil unless
by chance (= (sxhash '(1 . 2)) (sxhash '(1 . 3))) was true.  Similar
examples can be constructed using strings and bit-vectors in place of
conses.

I would propose that modifications to components of the key do not
affect EQ and EQL hash tables, and thus are allowed, but are not
allowed for EQUAL hash tables when the modification is to a component
that is examined by the EQUAL function.