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Issue ADJUST-ARRAY-DISPLACEMENT (Version 3)
- To: CL-CLEANUP@SAIL.STANFORD.EDU
- Subject: Issue ADJUST-ARRAY-DISPLACEMENT (Version 3)
- From: David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>
- Date: Wed, 10 Jun 87 22:40 EDT
- In-reply-to: <FAHLMAN.12308703889.BABYL@C.CS.CMU.EDU>
Date: Sun, 7 Jun 1987 19:29 EDT
From: "Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>
Rather than wait for some resolution of Kent's question about the
omission of the :DISPLACED-TO argument, I took the liberty of guessing
that adjusting a displaced-to array without setting the :displaced-to
meant that the result was displaced to the same place. I inserted rule 3
and renumbered the rules.
The manual is pretty vague in this area, but my reading of
ADJUST-ARRAY (which says that the :DISPLACED-TO argument is the same as
in MAKE-ARRAY) is that if no :DISPLACED-TO argument is supplied, the
resulting array is never displaced, even if it had been originally.
That's what we implemented in Spice Lisp, and that's the interpretation
that seems to be consistent with the rest of this proposal (e.g. the rule
that if :DISPLACED-INDEX-ARG is not supplied, it defaults to zero rather
than the old index).
Scott, I think you're right. Also I think the second paragraph on p.298
can only be interpreted as saying that if you don't specify :DISPLACED-TO,
it doesn't retain the old displacement.
So I support the earlier version of the proposal, with the added
clarification that if no :DISPLACED-TO argument is supplied in a call to
ADJUST-ARRAY, the resulting array is not displaced, even if the original
array had been displaced. That is clear, simple, and sufficient in my