NaNs Just Don't Get No Respect

[Walter Bright]

On 8/19/2012 8:18 AM, Peter Alexander wrote:
> Personally, I'd prefer option 1. Walter's argument is that this "leads to the
> programmer getting annoyed with false positive error diagnostics, and he'll
> likely add an =0", which is true, but in my opinion this scenario is quite rare
> to start with, and it's even more rare that 0 isn't actually the right
> initialisation value, and even then it's only a problem if the introduced bug is
> hard to reproduce.

Rare, yes, it's rare. But it's really ugly and hard to find when it does happen.

 > I find it more likely that the NaN will go unnoticed and
 > cause rare bugs.

NaNs in your output are pretty obvious. For example, if your accounting program 
prints "NAN" for the amount on the payroll cheques, someone is guaranteed to 
notice. But if it's a few cents off in your disfavor, it might take you years to 
discover there's a problem.

Critical systems also would find a NaN command a lot easier to detect than an 
off-by-two command, and would be able to shut down and engage the backup.