Trampoline.rs

pub enum Trampoline<A> {
    Return(A)
    , Suspend(Box<Fn() -> Trampoline<A>>)
}



impl<A> Trampoline<A> {
    pub fn now(a:A) -> Trampoline<A> {
        Trampoline::Return(a)
    }

    pub fn suspend<F>(thunk: F) -> Trampoline<A>
    where F: Fn() -> Trampoline<A> {
      Trampoline::Suspend(Box::new(thunk()))
    }
    pub fn map<B, F>(self, f: F) -> Trampoline<B>
    where F: Fn(A) -> B {
        self.flatMap(|a| Trampoline::Return(f(a)))
    }

    pub fn flatMap<B, F>(self, f: F) -> Trampoline<B>
    where F: Fn(A) -> Trampoline<B> {
        match self {
            Trampoline::Return(a) => {
                let eval = || -> Trampoline<B> { f(a) };
                Trampoline::Suspend (Box::new(eval))
            }
            , Trampoline::Suspend(thunk) => {
                let eval = || -> Trampoline<B> {
                   let a = thunk().run();
                   f(a)
               };
               Trampoline::Suspend (Box::new(eval))
              
            }
        }
    }

    pub fn run(self) -> A {
        unimplemented!()
    }
}