Re: What's wrong with C++?

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Wed, 05 Oct 2011 06:48:43 +0200, Jeffrey Carter  
<spam.jrcarter.not@spam.not.acm.org> a écrit:
> Most people misunderstand the halting problem, thinking it proves that  
> it is impossible to prove whether a program halts. In fact, it says it's  
> impossible to write a program that, in finite time, can say whether any  
> possible program halts for all inputs. It does not say it's impossible  
> to write a program that can say whether a specific program halts for all  
> inputs, or whether a subset of programs halt for all inputs.
Yes

> In fact, there are programs now that can prove whether most sequential  
> programs halt for all inputs. See the article "Proving Program  
> Termination" by Cook, Podelski, and Rybalchenko in the 2011 May  
> /Communications of the ACM/ for an overview of current work on this  
> subject.
Thanks for the reference

> So I agree that the Turing completeness of C++ templates is unlikely to  
> be a problem for real-world programs.
Still does not change anything about the background. At least, if C++  
embeds a meta-programming language to such a level, then there should be  
two distinct languages, which should be executed separately. This should  
be required to at least be able to trace execution of both. So here, you  
have execution of a program: how do you trace its execution if ever needed  
? How do you prove it's correct if ever required ? I am not opposed to  
meta-programming (I am even in favor of it), but this should belong to  
specific layers, each. If I understand this blog paper, that is not the  
case (the time I used C++, I've never heard of something like this).


With that, you have the macro language which is a powerful way to scatter  
the source in any silly ways you want, and now, you have a meta-language  
merged into the language. I don't believe that help to trust your  
understanding of the source you are reading.

I agree this may be usable, just like the rest of C++ is usable, if you  
conscientiously keep track of traps you have to avoid (yes, I know there  
may be some traps with Ada too, like mutable records are from some point  
of views, except there are probably far few, and nothing comparable to  
that).

-- 
“Syntactic sugar causes cancer of the semi-colons.”  [Epigrams on  
Programming — Alan J. — P. Yale University]
“Structured Programming supports the law of the excluded muddle.” [Idem]
Java: Write once, Never revisit