Linear.swift

struct Linear<A> {
    let x: A
    let c: A // c stands for 'constant', it's the constant factor to the linear function
}

extension Linear: CustomStringConvertible where A: CustomStringConvertible {
    var description: String { return "f(x) = \(x)x + \(c)" }
}

extension Linear: Equatable where A: Equatable {}

extension Linear: TwoDimensions {
    typealias ComponentVal = A
    static func make2D(_ fst: A, _ snd: A) -> Linear {
        return Linear(x: fst, c: snd)
    }
    var fst: A { return x }
    var snd: A { return c }
}

extension Linear: Additive where A: Additive {}

extension Linear: Scalar where A: Multiplicative { typealias ScalarVal = A }