Tristate - wanna?

[Walter Bright]

On 10/26/2013 8:42 AM, Andrei Alexandrescu wrote:
> While messing with std.allocator I explored the type below. I ended up not using
> it, but was surprised that implementing it was quite nontrivial. Should we add
> it to stdlib?
>
> Theory: http://en.wikipedia.org/wiki/Three-state_logic

When I worked on the ABEL programming language, which was for designing 
programmable logic devices, we found it useful to have an additional state, 
"don't care".