Trilean

Implementation of three-valued logic.

This type resembles Boolean, but has three values instead of two:

• Trilean.True (equivalent to true)
• Trilean.False (equivalent to false)
• Trilean.Unknown

Trilean supports the same operations that Boolean does, and as long as all values are True or False, the results will be the same. However, the truth tables have to be extended to work with unknown:

not:

-+-
T|F
U|U
F|T

and:

 |T U F
-+-----
T|T U F
U|U U F
F|F F F

or:

 |T U F
-+-----
T|T T T
U|T U U
F|T U F

Trilean is implemented as a value type, so in most cases it will only have the overhead of a single Int. However, in some situations it will be boxed.