use super::*;

/// Represents iteration state.
pub enum IState<P, D> {
    /// Loop running.
    Pending(P),
    /// Loop finished.
    Done(D),
}

pub struct IStateClass<P>(P);

impl<P> WeakFunctor for IStateClass<P> {
    type F<'a, A: 'a> = IState<P, A>
    where
        Self: 'a;
}

impl<P> Functor for IStateClass<P> {
    fn fmap<'a, A: 'a, B: 'a>(f: impl 'a + FnOnce(A) -> B, fa: Self::F<'a, A>) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        match fa {
            IState::Pending(p) => IState::Pending(p),
            IState::Done(d) => IState::Done(f(d)),
        }
    }
}

impl<P> Pure for IStateClass<P> {
    fn pure<'a, A: 'a>(a: A) -> Self::F<'a, A>
    where
        Self: 'a,
    {
        IState::Done(a)
    }
}