A compile time / type level NAND "function" in Swift.

TypeLevelNAND.swift

protocol Bit {}
protocol IsSet {}
protocol IsClr {}

struct Set : Bit, IsSet {}
struct Clr : Bit, IsClr {}

protocol  NandOp { typealias Result }
extension NandOp { typealias Result = Set }

struct Nand<B0: Bit, B1: Bit> : NandOp {}
extension Nand where B0: IsSet, B1: IsSet {
    typealias Result = Clr
}

print(Nand<Clr, Clr>.Result.self == Set.self) // true
print(Nand<Clr, Set>.Result.self == Set.self) // true
print(Nand<Set, Clr>.Result.self == Set.self) // true
print(Nand<Set, Set>.Result.self == Clr.self) // true

Bummer:

struct Not<B0: Bit> {
    typealias Result = Nand<B0, B0>.Result // Error: Ambigous type name 'Result' in Nand<B0, B0>
}

:´ (