radn-rs/src/func/instances/tryfuture.rs

use std::{future::Future, pin::Pin};

use futures::{
    future::{try_select, Either, Shared},
    try_join, FutureExt,
};

use crate::func::*;

#[derive(CovariantFunctor)]
pub struct TryFutureInstance<E>(E);

impl<E> WeakFunctor for TryFutureInstance<E> {
    type F<'a, A: 'a> = Pin<Box<dyn 'a + Future<Output = Result<A, E>>>> where Self: 'a;
}

impl<E> Functor for TryFutureInstance<E> {
    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,
    {
        Box::pin(async { Ok(f(fa.await?)) })
    }

    fn replace<'a, A: 'a, B: 'a>(fa: Self::F<'a, A>, b: B) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Box::pin(async {
            fa.await?;
            Ok(b)
        })
    }
}

impl<E> Pure for TryFutureInstance<E> {
    fn pure<'a, A: 'a>(a: A) -> Self::F<'a, A>
    where
        Self: 'a,
    {
        Box::pin(async { Ok(a) })
    }
}

impl<E> ApplicativeSeq for TryFutureInstance<E> {
    fn seq<'a, A: 'a, B: 'a>(
        ff: Self::F<'a, impl 'a + FnOnce(A) -> B>,
        fa: Self::F<'a, A>,
    ) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Box::pin(async {
            let (f, a) = try_join!(ff, fa)?;
            Ok(f(a))
        })
    }
}

impl<E> ApplicativeLA2 for TryFutureInstance<E> {
    fn la2<'a, A: 'a, B: 'a, C: 'a>(
        f: impl 'a + FnOnce(A, B) -> C,
        fa: Self::F<'a, A>,
        fb: Self::F<'a, B>,
    ) -> Self::F<'a, C>
    where
        Self: 'a,
    {
        Box::pin(async {
            let (a, b) = try_join!(fa, fb)?;
            Ok(f(a, b))
        })
    }
}

impl<E> ApplicativeTuple for TryFutureInstance<E> {
    fn tuple<'a, A: 'a, B: 'a>((fa, fb): (Self::F<'a, A>, Self::F<'a, B>)) -> Self::F<'a, (A, B)>
    where
        Self: 'a,
    {
        Box::pin(async { try_join!(fa, fb) })
    }
}

impl<E> ApplicativeSelect for TryFutureInstance<E> {
    fn select<'a, A: 'a, B: 'a>(
        fa: Self::F<'a, A>,
        fb: Self::F<'a, B>,
    ) -> SelectedWrapped<'a, A, B, Self>
    where
        Self: 'a,
    {
        Box::pin(async {
            match try_select(fa, fb).await {
                Ok(Either::Left((a, fb))) => Ok(Selected::A(a, fb)),
                Ok(Either::Right((b, fa))) => Ok(Selected::B(fa, b)),
                Err(Either::Left((e, _))) => Err(e),
                Err(Either::Right((e, _))) => Err(e),
            }
        })
    }
}

impl<E> Applicative for TryFutureInstance<E> {
    fn discard_first<'a, A: 'a, B: 'a>(fa: Self::F<'a, A>, fb: Self::F<'a, B>) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Box::pin(async { Ok(try_join!(fa, fb)?.1) })
    }

    fn discard_second<'a, A: 'a, B: 'a>(fa: Self::F<'a, A>, fb: Self::F<'a, B>) -> Self::F<'a, A>
    where
        Self: 'a,
    {
        Box::pin(async { Ok(try_join!(fa, fb)?.0) })
    }
}

impl<E> Monad for TryFutureInstance<E> {
    fn bind<'a, A: 'a, B: 'a>(
        fa: Self::F<'a, A>,
        f: impl 'a + FnOnce(A) -> Self::F<'a, B>,
    ) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Box::pin(async { f(fa.await?).await })
    }

    fn iterate<'a, B: 'a>(mut f: impl Iterative<'a, T = Self, B = B>) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Box::pin(async move {
            loop {
                match f.next().await? {
                    ControlFlow::Continue(next_f) => f = next_f,
                    ControlFlow::Break(b) => return Ok(b),
                }
            }
        })
    }

    fn join<'a, A: 'a>(ffa: Self::F<'a, Self::F<'a, A>>) -> Self::F<'a, A>
    where
        Self: 'a,
    {
        Box::pin(async { ffa.await?.await })
    }
}

impl<E: Clone> SharedFunctor for TryFutureInstance<E> {
    type Shared<'a, A: 'a + Clone> = Shared<Pin<Box<dyn 'a + Future<Output = Result<A, E>>>>>
    where
        Self: 'a;

    fn share<'a, A: 'a + Clone>(fa: Self::F<'a, A>) -> Self::Shared<'a, A>
    where
        Self: 'a,
    {
        fa.shared()
    }

    fn unshare<'a, A: 'a + Clone>(sa: Self::Shared<'a, A>) -> Self::F<'a, A>
    where
        Self: 'a,
    {
        Box::pin(sa)
    }
}

impl<E> Fail<E> for TryFutureInstance<E> {
    fn fail<'a, A: 'a>(e: E) -> Self::F<'a, A>
    where
        Self: 'a,
        E: 'a,
    {
        Box::pin(async { Err(e) })
    }
}

pub struct FutureFailAny;

impl MonadFailAny for FutureFailAny {
    type W<E> = TryFutureInstance<E>;

    type T = instances::future::FutureInstance;

    fn unstuff<'a, A: 'a, E: 'a>(wa: WrapE<'a, A, E, Self>) -> Wrap<'a, Result<A, E>, Self::T>
    where
        Self: 'a,
    {
        wa
    }

    fn stuff<'a, A: 'a, E: 'a>(fa: Wrap<'a, Result<A, E>, Self::T>) -> WrapE<'a, A, E, Self>
    where
        Self: 'a,
    {
        fa
    }

    fn map_err<'a, A: 'a, E0: 'a, E1: 'a>(
        wa: WrapE<'a, A, E0, Self>,
        f: impl 'a + FnOnce(E0) -> E1,
    ) -> WrapE<'a, A, E1, Self>
    where
        Self: 'a,
    {
        Box::pin(async { wa.await.map_err(f) })
    }

    fn bind_err<'a, A: 'a, E0: 'a, E1: 'a>(
        wa: WrapE<'a, A, E0, Self>,
        f: impl 'a + FnOnce(E0) -> WrapE<'a, A, E1, Self>,
    ) -> WrapE<'a, A, E1, Self>
    where
        Self: 'a,
    {
        Box::pin(async {
            match wa.await {
                Ok(a) => Ok(a),
                Err(e) => f(e).await,
            }
        })
    }

    fn bind<'a, A: 'a, B: 'a, E0: 'a, E1: 'a>(
        wa: WrapE<'a, A, E0, Self>,
        f: impl 'a + FnOnce(Result<A, E0>) -> WrapE<'a, B, E1, Self>,
    ) -> WrapE<'a, B, E1, Self>
    where
        Self: 'a,
    {
        Box::pin(async { f(wa.await).await })
    }

    fn rotate_out<'a, A: 'a, E0: 'a, E1: 'a>(
        wa: WrapE<'a, Result<A, E1>, E0, Self>,
    ) -> WrapE<'a, A, Result<E1, E0>, Self>
    where
        Self: 'a,
    {
        Box::pin(async {
            match wa.await {
                Ok(Ok(a)) => Ok(a),
                Ok(Err(e)) => Err(Ok(e)),
                Err(e) => Err(Err(e)),
            }
        })
    }
}