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000074_icon-group-sender _Mon Apr 24 07:43:03 2000.msg
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by baskerville.CS.Arizona.EDU (8.9.1a/8.9.1) id HAA25545
for icon-group-addresses; Mon, 24 Apr 2000 07:42:14 -0700 (MST)
Message-Id: <200004241442.HAA25545@baskerville.CS.Arizona.EDU>
From: "F.G. van DORP" <F.G.van.Dorp@digimedia.nl>
X-Newsgroups: comp.lang.icon
Subject: Re: Reversible assignment really reversible ?
X-Newsreader: Forte Agent 1.7/32.534
Date: Sat, 22 Apr 2000 16:52:57 GMT
X-Complaints-To: abuse@chello.nl
X-Trace: nlnews00.chello.com 956422377 212.187.67.243 (Sat, 22 Apr 2000 15:52:57 GMT)
To: icon-group@optima.CS.Arizona.EDU
Errors-To: icon-group-errors@optima.CS.Arizona.EDU
Status: RO
On 19 Apr 2000 16:57:54 -0400, Steve Wampler <swampler@noao.edu> wrote:
First of all, I agree with Frank J. Lhota that at least the distribution list
seems to duplicate postings.
>"F.G. van DORP" wrote:
>>
>> On 17 Apr 2000 16:33:32 -0400, "Frank J. Lhota"
>> <NOSPAM.Frank.Lhota@lexma.meitech.com> wrote:
>>
>> >...
>> >expression above, where text is "queen":
>> >
>> > (i <- 3) assigns 3 to i and suspends;
>> > (j < find("q")) fails, so we resume the most recently
>> Surely you mean i <=
>
>No, he means i <- 3...
I should've known better with this mailer to try formatting with spaces again,
but what I meant was
(i <= find("q")........
Besides, this may be an unfortunate example by mr. Lhota, because according
to the Icon book data backtracking is implicit in string scanning.
>
>> However, with the present implementation the first rev.assignment that gets
>> resumed in a compound expression, will make the whole expression fail.
>
>No, it will continue performing control backtracking until all subexpressions
>have no more results.
>....
I realised I made a terrible mistake by using the term "compound expression"
which in the Icon book has exactly the opposite meaning: a context in which
subexpressions are isolated from backtracking.
The opposite would be called a "backtracking context", I guess...
At this point it would be wise to consider a "tactical retreat" in order to let
my rev.assignment version loose on some other examples from the book,
as Steve Wampler seems to suggest.
.