TraitFn

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src/lib.rs

@@ -2,3 +2,4 @@ pub mod model_00;
 pub mod model_01;
 #[cfg(any())]
 pub mod model_02; // ICE
+pub mod model_03;

src/model_03.rs

@@ -0,0 +1,273 @@
+use std::{
+    marker::PhantomData,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use futures::Future;
+use pin_project::pin_project;
+
+pub trait Trait {
+    type Associated: ?Sized + Trait;
+    type In<'out: 'tmp, 'tmp, I: 'tmp>;
+    type Out<'out, A>;
+}
+
+pub trait Impl<T: ?Sized + Trait>: Sized {
+    type Associated: Impl<T::Associated>;
+    fn method<'out: 'tmp, 'tmp>(_: T::In<'out, 'tmp, Self>) -> T::Out<'out, Self::Associated>
+    where
+        Self: 'tmp;
+}
+
+pub enum Empty {}
+
+impl Trait for Empty {
+    type Associated = Self;
+    type In<'out: 'tmp, 'tmp, I: 'tmp> = Self;
+    type Out<'out, A> = Self;
+}
+
+impl<I> Impl<Empty> for I {
+    type Associated = I;
+    fn method<'out: 'tmp, 'tmp>(
+        empty: <Empty as Trait>::In<'out, 'tmp, Self>,
+    ) -> <Empty as Trait>::Out<'out, Self::Associated>
+    where
+        Self: 'tmp,
+    {
+        empty
+    }
+}
+
+pub struct Is<That, T: ?Sized>(That, T);
+
+impl<That, T: ?Sized + Trait> Trait for Is<That, T> {
+    type Associated = T;
+    type In<'out: 'tmp, 'tmp, I: 'tmp> = I;
+    type Out<'out, A> = That;
+}
+
+impl<That: Impl<T>, T: ?Sized + Trait> Impl<Is<Self, T>> for That {
+    type Associated = Self;
+
+    fn method<'out: 'tmp, 'tmp>(
+        this: <Is<That, T> as Trait>::In<'out, 'tmp, Self>,
+    ) -> <Is<That, T> as Trait>::Out<'out, Self::Associated>
+    where
+        Self: 'tmp,
+    {
+        this
+    }
+}
+
+pub struct To<T: ?Sized>(T);
+
+impl<T: ?Sized + Trait> Trait for To<T> {
+    type Associated = T;
+    type In<'out: 'tmp, 'tmp, I: 'tmp> = I;
+    type Out<'out, A> = A;
+}
+
+impl<I: FnOnce() -> Output, Output: Impl<T>, T: ?Sized + Trait> Impl<To<T>> for I {
+    type Associated = Output;
+
+    fn method<'out: 'tmp, 'tmp>(
+        this: <To<T> as Trait>::In<'out, 'tmp, Self>,
+    ) -> <To<T> as Trait>::Out<'out, Self::Associated>
+    where
+        Self: 'tmp,
+    {
+        this()
+    }
+}
+
+pub trait TraitFn<In: ?Sized + Trait> {
+    type Out: ?Sized + Trait;
+    fn run(self, _: impl Impl<In>) -> impl Impl<Self::Out>;
+}
+
+pub trait Functor {
+    type W<T: ?Sized + Trait>: ?Sized + Trait;
+    fn pure<A: ?Sized + Trait>(_: impl Impl<A>) -> impl Impl<Self::W<A>>;
+    fn map<A: ?Sized + Trait, F: TraitFn<A>>(
+        _: impl Impl<Self::W<A>>,
+        _: F,
+    ) -> impl Impl<Self::W<F::Out>>;
+}
+
+pub struct Verbatim;
+
+impl Functor for Verbatim {
+    type W<T: ?Sized + Trait> = T;
+
+    fn pure<A: ?Sized + Trait>(a: impl Impl<A>) -> impl Impl<Self::W<A>> {
+        a
+    }
+
+    fn map<A: ?Sized + Trait, F: TraitFn<A>>(
+        a: impl Impl<Self::W<A>>,
+        f: F,
+    ) -> impl Impl<Self::W<F::Out>> {
+        f.run(a)
+    }
+}
+
+pub trait Call<T: ?Sized + Trait> {
+    type Output: Impl<T>;
+    fn call(self) -> Self::Output;
+}
+
+impl<T: ?Sized + Trait, I: Impl<To<T>>> Call<T> for I {
+    type Output = I::Associated;
+
+    fn call(self) -> Self::Output {
+        I::method(self)
+    }
+}
+
+pub struct Lazy;
+
+impl Functor for Lazy {
+    type W<T: ?Sized + Trait> = To<T>;
+
+    fn pure<A: ?Sized + Trait>(a: impl Impl<A>) -> impl Impl<Self::W<A>> {
+        || a
+    }
+
+    fn map<A: ?Sized + Trait, F: TraitFn<A>>(
+        a: impl Impl<Self::W<A>>,
+        f: F,
+    ) -> impl Impl<Self::W<F::Out>> {
+        || f.run(a.call())
+    }
+}
+
+pub struct Composition<Uo, Ui>(Uo, Ui);
+
+impl<Uo: Functor, Ui: Functor> Functor for Composition<Ui, Uo> {
+    type W<T: ?Sized + Trait> = Uo::W<Ui::W<T>>;
+
+    fn pure<A: ?Sized + Trait>(a: impl Impl<A>) -> impl Impl<Self::W<A>> {
+        Uo::pure(Ui::pure(a))
+    }
+
+    fn map<A: ?Sized + Trait, F: TraitFn<A>>(
+        a: impl Impl<Self::W<A>>,
+        f: F,
+    ) -> impl Impl<Self::W<F::Out>> {
+        struct Tmp<A: ?Sized, F, Uo, Ui>(F, PhantomData<(Uo, Ui, A)>);
+        impl<A: ?Sized + Trait, F: TraitFn<A>, Uo: Functor, Ui: Functor> TraitFn<Ui::W<A>>
+            for Tmp<A, F, Uo, Ui>
+        {
+            type Out = Ui::W<F::Out>;
+
+            fn run(self, a: impl Impl<Ui::W<A>>) -> impl Impl<Self::Out> {
+                Ui::map(a, self.0)
+            }
+        }
+        Uo::map(a, Tmp::<A, F, Uo, Ui>(f, PhantomData))
+    }
+}
+
+pub trait Into_<T: ?Sized + Trait> {
+    fn into_<A>(self) -> A
+    where
+        Self: Impl<Is<A, T>>,
+    {
+        Self::method(self)
+    }
+}
+
+impl<T: ?Sized + Trait, I> Into_<T> for I {}
+
+impl<A, B, F: FnOnce(A) -> B, T: ?Sized + Trait> TraitFn<Is<A, T>> for F {
+    type Out = Is<B, Empty>;
+
+    fn run(self, a: impl Impl<Is<A, T>>) -> impl Impl<Self::Out> {
+        self(a.into_())
+    }
+}
+
+#[cfg(test)]
+fn generic_test<U: Functor>() -> impl Impl<U::W<Is<i32, Empty>>> {
+    let x = U::pure::<Is<_, Empty>>(5);
+    let x = U::map(x, |x| x + 1);
+    let x = U::map(x, |x| x + 1);
+    let x = U::map(x, |x| x + 1);
+    let x = U::map(x, |x| x + 1);
+    U::map(x, |x| x + 1)
+}
+
+#[test]
+fn doubly_lazy() {
+    type U = Composition<Lazy, Lazy>;
+    let x = generic_test::<U>();
+    let x = x.call().call().into_::<i32>();
+    assert_eq!(x, 10);
+}
+
+pub struct FutureTo<T: ?Sized>(T);
+
+impl<T: ?Sized + Trait> Trait for FutureTo<T> {
+    type Associated = T;
+    type In<'out: 'tmp, 'tmp, I: 'tmp> = (Pin<&'tmp mut I>, &'tmp mut Context<'out>);
+    type Out<'out, A> = Poll<A>;
+}
+
+impl<T: ?Sized + Trait, Output: Impl<T>, F: Future<Output = Output>> Impl<FutureTo<T>> for F {
+    type Associated = F::Output;
+
+    fn method<'out: 'tmp, 'tmp>(
+        (this, cx): <FutureTo<T> as Trait>::In<'out, 'tmp, Self>,
+    ) -> <FutureTo<T> as Trait>::Out<'out, Self::Associated>
+    where
+        Self: 'tmp,
+    {
+        this.poll(cx)
+    }
+}
+
+#[pin_project]
+struct TraitFuture<F, T: ?Sized>(#[pin] F, PhantomData<T>);
+
+impl<T: ?Sized + Trait, F: Impl<FutureTo<T>>> Future for TraitFuture<F, T> {
+    type Output = F::Associated;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        F::method((self.project().0, cx))
+    }
+}
+
+pub trait IntoFuture_<T: ?Sized + Trait>: Impl<FutureTo<T>> {
+    fn into_future_(self) -> impl Future<Output = Self::Associated> {
+        TraitFuture(self, PhantomData)
+    }
+}
+
+impl<T: ?Sized + Trait, I: Impl<FutureTo<T>>> IntoFuture_<T> for I {}
+
+pub struct Futures;
+
+impl Functor for Futures {
+    type W<T: ?Sized + Trait> = FutureTo<T>;
+
+    fn pure<A: ?Sized + Trait>(a: impl Impl<A>) -> impl Impl<Self::W<A>> {
+        async { a }
+    }
+
+    fn map<A: ?Sized + Trait, F: TraitFn<A>>(
+        a: impl Impl<Self::W<A>>,
+        f: F,
+    ) -> impl Impl<Self::W<F::Out>> {
+        async { f.run(a.into_future_().await) }
+    }
+}
+
+#[test]
+fn with_futures() {
+    type U = Futures;
+    let x = generic_test::<U>();
+    let x = futures::executor::block_on(x.into_future_()).into_::<i32>();
+    assert_eq!(x, 10);
+}