Absolute Trivial State Derivative

absoluteTrivialStateDerivative.swift

enum Action: Int {
    case buttonDown
}

struct State {
    var counter: Int = 0
}

struct View {
    var height: Float
    var width: Float
}

// s = f(s,a) = s + (a * 1)
func updateState(state: State, action: Action) -> State {
    return State(counter: state.counter + (action == .buttonDown ? 1 : 0))
}

// v = f(s) = s * 10
func updateView(state: State) -> View {
    return View(height: 10.0 * Float(state.counter), width: 100.0)
}

var state = State()

state = updateState(state: state, action: .buttonDown)
var view = updateView(state: state)

print("1) initial")
print("state: \(state)")
print("view: \(view)")

// Dirivitives

struct State_d {
    var counter: Int = 0
}

struct View_d {
    var height: Float
    var width: Float
}

// s' = f'(s,a) = 1
func updateState_d(state: State, action: Action) -> State_d {
    return State_d(counter: 1)
}

// v' = f'(s) = 10
func updateView_d(state: State_d) -> View_d {
    return View_d(height: 10.0, width: 0.0)
}

let state_d = updateState_d(state: state, action: .buttonDown)
let view_d = updateView_d(state: state_d)
view.height += view_d.height
view.width += view_d.width
print("2) after  differential")
print("view: \(view)")