Try at a Reader Monad in Swift

Reader.swift

//this is a playground
struct Reader<R,A> {
    let f:R -> A
    
    init(_ fun:R -> A) {
        f = fun
    }
    
    static func wrap(val:A) -> Reader<R,A> {
        return Reader({_ in val})
    }
    
    func runReader(r:R) -> A {
        return f(r)
    }
}

func >>=<R,A,B>(w:Reader<R,A>, f:(R -> A) -> Reader<R,B>) -> Reader<R,B> {
    return f({(env:R) in w.runReader(env)})
    
}

func hello() -> Reader<String, String> {
    return Reader({name in "Hello \(name)!"})
}

func bye() -> Reader<String, String> {
    return Reader({name in "Bye \(name)!"})
}


func both() -> Reader<String,String> {
    return Reader({name in hello().runReader(name) +  " " + bye().runReader(name)})
}


both().runReader("terry")