Monadic Mealy Machine
Demo for Souzoh iOS Talk 2017: メルカリ アッテを支えるオートマトン
Requirement
Swift 4 / Xcode 9
Summary
State Monad
struct State<S, A> {
private let run: (S) -> (S, A)
init(f: @escaping (S) -> (S, A)) {
self.run = f
}
func run(s: S) -> (S, A) {
return self.run(s)
}
func map<B>(g: @escaping (A) -> B) -> State<S, B> {
return State<S, B> { s in
let (s1, val) = self.run(s)
return (s1, g(val))
}
}
func flatMap<B>(g: @escaping (A) -> State<S, B>) -> State<S, B> {
return State<S, B> { s in
let (s1, val) = self.run(s)
return g(val).run(s1)
}
}
}Monadic Mealy Machine
struct MonadicAutomaton<S, A, B> {
typealias T = (A) -> State<S, B>
private var f : T
init(f: @escaping T) {
self.f = f
}
func transition(from: S, by: A) -> (S, B) {
return f(by).run(s: from)
}
}