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From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: filling area by color atack safety
Date: Sun, 17 Mar 2024 12:37:08 +0000
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On 17/03/2024 11:25, Ben Bacarisse wrote:
> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
> 
>> On 16/03/2024 13:55, Ben Bacarisse wrote:
>>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>>
>>>> Recursion make programs harder to reason about and prove correct.
>>> Are you prepared to offer any evidence to support this astonishing
>>> statement or can we just assume it's another Malcolmism?
>>
>> Example given. A recursive algorithm which is hard to reason about and
>> prove correct, because we don't really know whether under perfectly
>> reasonable assumptions it will or will not blow the stack.
> 
> Had you offered a proof that your code neither "blows the stack" nor
> runs out of any other resource we'd have a starting point for
> comparison, but you have not done that.
> 
> Mind you, had you done that, we would have something that might
> eventually become only one piece of evidence for what is an
> astonishingly general remark.  Broadly applicable remarks require either
> broadly applicable evidence or a wealth of distinct cases.
> 
> Your "rule" suggests that all reasoning is impeded by the presence of
> recursion and I don't think you can support that claim.  This is
> characteristic of many of your remarks -- they are general "rules" that
> often remain rules even when there is evidence to the contrary.
> 
> I'll make another point in the hope of clarifying the matter.  An
> algorithm or code is usually proved correct (or not!) under the
> assumption that it has adequate resources -- usually time and storage.
> Further reasoning may then be done to determine the resource
> requirements since this is so often dependent on context.  This
> separation is helpful as you don't usually want to tie "correctness" to
> some specific installation.  The code might run on a system with a
> dynamically allocated stack, for example, that has very similar
> limitations to "heap" memory.
> 
> To put is more generally, we often want to prove properties of code that
> are independent of physical constraints.  Your remark includes this kind
> reasoning.  Did you intend it to?
> 
The convetional wisdom is the opposite, But here, conventional wisdom 
fails. Because heaps are unlimited whilst stacks are not.

-- 
Check out Basic Algorithms and my other books:
https://www.lulu.com/spotlight/bgy1mm