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From: "Peter C. Chapin" <PChapin@vtc.vsc.edu>
Subject: Re: What's wrong with C++?
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Date: 2011-10-04T20:53:28-05:00
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On Tue, 04 Oct 2011 23:00:20 +0200, Yannick Duchêne (Hibou57) wrote:

> So OK, it is formally proved that is not even sure a given C++ source
> file can really be compiled or not. That's big, ouch.

I don't think this is a big deal. It's an interesting theoretical 
observation with little practical significance. For one thing, I doubt 
any reasonably normal looking program would invoke this behavior. A 
broken program might, I suppose, but non-termination of the compiler is 
not much different than a compile error. Nobody is injured by the program 
it didn't create; it's only an inconvenience to the programmer who has to 
adjust the source.

C++ isn't alone with this problem either. I understand that Scala's type 
system is also Turing complete. It is possible, apparently, to write a 
Scala program for which type checking never terminates. Again it's an 
interesting theoretical observation but I don't think anyone really cares.

In our work at VTC on translating some NASA software to SPARK we 
encountered a situation where the SPARK simplifier took an "infinitely" 
long time to execute... well, okay, it only took about an hour. Yes it 
did terminate but it took so long that development was impractical (no 
different, really, than true non-termination). Our response: fix the 
source.

Peter