Trilean - yes, no, maybe

Three-valued logic for Swift

Trileans are similar in many ways to standard booleans except that instead of 2 possible values they have 3: yes, no or maybe. They allow for three-valued logic which may be useful to make assertions where not all variables are known. Applications include artificial intelligence for games or simulations, where an agent must make decisions without a full knowledge of its environment.

Initialization

Trileans are typically initialized by assigning a trilean literal.

var yesTrilean = yes
var noTrilean = no
var maybeTrilean = maybe

As a convenience, trileans can also be initialized from booleans.

var yesTrilean: Trilean = true
var noTrilean: Trilean = false

Control Flow - Sure Statements

The Trilean class provides 3 control flow functions, sure(), sureNot() and unsure() that you can use to perform code that is dependent on a trilean value.

sure(myTrilean) {
    // preform the yes case
}
sureNot(myTrilean) {
    // perform the no case
}
unsure(myTrilean) {
    // perform the maybe case
} 

Control Flow - If Statements

You can use trileans almost everywhere you would use booleans, including if statements.

if myTrilean {
    // perform the yes case
}
else {
    // perform the no or maybe case
}

By default only the yes trilean is converted to true and both no and maybe are converted to false. You can however make an optimistic conversion where the maybe trilean will be converted to true.

if myTrilean.optimistically {
    // perform the yes or maybe case
}
else {
    // perform the no case
}

Logic Operators

Trileans support the &&, || and ! operators, meaning you can make compound assertions such as:

sure((trileanA || trileanB) && (trileanC || trileanD)) {
    // perform code
}

The result of conjunction, disjunction and negation are implemented according to Łukasiewicz logic:

Conjunction - A AND B

AND	yes	maybe	no
yes	yes	maybe	no
maybe	maybe	maybe	no
no	no	no	no

Disjunction - A OR B

OR	yes	maybe	no
yes	yes	yes	yes
maybe	yes	maybe	maybe
no	yes	maybe	no

Negation - NOT A

A	NOT A
yes	no
maybe	maybe
no	yes

Installation

Using CocoaPods 0.36 or above, add Trilean to your podfile:

pod 'Trilean'

License

Copyright © 2014-2015 @phelgo. MIT licensed to you.