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From: bothner@sevenlayer.cs.wisc.edu (Per Bothner)
Newsgroups: comp.lang.lisp
Subject: Re: Clarification of array semantics needed
Message-ID: <11839@spool.cs.wisc.edu>
Date: 29 Nov 90 17:54:30 GMT
References: <11765@spool.cs.wisc.edu> <1990Nov20.101626.13488@hellgate.utah.edu>
Sender: news@spool.cs.wisc.edu
Organization: U of Wisconsin CS Dept
Lines: 31

In article <1990Nov20.101626.13488@hellgate.utah.edu> moore%cdr.utah.edu@cs.utah.edu (Tim Moore) writes:

... a posting that clears up some of my questions.
But there still seems to be inconsistencies in CLtL:2.

>>* Page 456, line 12: "but this may be achieved ... by creating
>>a new array and modifying the array argument to be displaced..."
>>seems to be contradicted by p 457, line 19.
>>
>p457, line 19 applies only to arrays that weren't created with the
>:adjustable argument to make-array, and thus isn't really relevent.

But p 457 lines 19- still contradict p 456 lines 12-15. The new semantics
says that one is *never* allowed to "modify the ARRAY argument to be
DISPLACED to the new array." It looks like this paragraph (on p 456)
should have been removed for the 2nd edition, but wasn't.

>>If I have:
>>	(setq B (adjust-array A ...))
>>does the phrase "the result" refer to B or A?
>>
>Both. The whole point of adjust-array is that its return value is eq
>to its array argument, as long as A is adjustable.

The question is for when A is *not* adjustable.
My reading is that then the adjust-array is equivalent to
a make-array, except that A is used as a kind of default :initial-contents.
Is this a reasonable reading?
--
	--Per Bothner
bothner@cs.wisc.edu Computer Sciences Dept, U. of Wisconsin-Madison