non/spire — pull request #288 by non (2014-07-26 22:01:25+00:00)
Title: Initial implementation of a three-valued logic type (Trilean).

The main objective is just to see how well this works using a value
class implementation (wrapping an Int). The representation is:

0 = false (all bits 0)
-1 = true (all bits 1)
1 = unknown (last bit 1)

This might not be something that is generally-useful enough to include in
Spire. I just wanted to code it up and see how it looked.