Re: [boost] Ternary logic programming

Subject: Re: [boost] Ternary logic programming
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2015-07-06 05:21:25

> -----Original Message-----
> From: Boost [mailto:boost-bounces_at_[hidden]] On Behalf Of Bjorn Reese
> Sent: 05 July 2015 17:06
> To: boost_at_[hidden]
> Subject: Re: [boost] Ternary logic programming
> 
> On 07/05/2015 12:10 PM, Rob Stewart wrote:
> 
> > That might be legitimate, and even useful, but doesn't it seem wrong that && and || yield the
same
> results?
> 
> The three cases under discussion may be easier to understand if we look at their Venn diagrams, so
I
> have drawn them here:
> 
>    http://breese.github.io/2015/07/05/layers-of-three-valued-logic.html
> 
> (the text could be more elaborate, but I wanted to make the diagrams available as quickly as
> possible.)
> 
> > If the empty state is called the same thing in each case, different behavior will be confusing.
> Otherwise, I agree that forcing everything into the same pattern may be more trouble than it's
worth.
> 
> Indeed. The empty state may have to be called different names for the three alternatives.

Nice!

Can this be added to the tribool docs - it might avoid confusion and discussion on future Boost
lists.

Might some MetaMagic allow the user to provide a compile-time template parameter to choose if wants
tribool truth-table to be either 'don't, may, or do care'?  But provide a default to keep the
behaviour as now?

Paul

---
Paul A. Bristow
Prizet Farmhouse
Kendal UK LA8 8AB
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