gistfile1.rs

use std::marker::PhantomFn;

trait Tr<T> : PhantomFn<(Self,T)> { type O; }

trait Hello : PhantomFn<Self> {

fn pr<A>(x : A) -> <Self as Tr<A>>::O   where Self : Tr<A>;

fn ap<'a, A, B, F : Fn(A)->B> (f : <Self as Tr<&'a F>>::O, x : <Self as Tr<A>>::O) -> <Self as Tr<B>>::O
   where Self : Tr<A> + Tr<B> + Tr<&'a F>;

fn foo<A, B>(x : <Self as Tr<A>>::O, y : <Self as Tr<B>>::O) -> <Self as Tr<B>>::O
   where Self : Tr<A> + Tr<B> 
{
        let id : &Fn(B)->B = &|x|{x};      // conceptually: id :: Fn(B) -> B
        let di = &|discard:A|{id};         // conceptually: di :: Fn(A) -> Fn(B) -> B
        let fdi = <Self as Hello>::pr(di); // conceptually: fdi :: Tr<Fn(A)->Fn(B)->B>::O

        let fa = <Self as Hello>::ap(fdi, x); // conceptually: fa :: Tr<Fn(B)->B>::O
        let res = <Self as Hello>::ap(fa, y); // conceptually: res :: Tr<B>::O
}

}

// ERRORS:
smallf.rs:17:12: 17:32 error: the trait `Tr<&[closure smallf.rs:16:19: 16:34]>` is not implemented for the type `Self` [E0277]
smallf.rs:17    let fdi = <Self as Hello>::pr(di); // conceptually: fdi :: Tr<Fn(A)->Fn(B)->B>::O
                          ^~~~~~~~~~~~~~~~~~~~
smallf.rs:17:12: 17:32 error: the trait `Tr<&[closure smallf.rs:16:19: 16:34]>` is not implemented for the type `Self` [E0277]
smallf.rs:17    let fdi = <Self as Hello>::pr(di); // conceptually: fdi :: Tr<Fn(A)->Fn(B)->B>::O
                          ^~~~~~~~~~~~~~~~~~~~
smallf.rs:19:11: 19:31 error: the trait `Tr<&_>` is not implemented for the type `Self` [E0277]
smallf.rs:19    let fa = <Self as Hello>::ap(fdi, x); // conceptually: fa :: Tr<Fn(B)->B>::O
                         ^~~~~~~~~~~~~~~~~~~~
smallf.rs:20:12: 20:32 error: the trait `Tr<&_>` is not implemented for the type `Self` [E0277]
smallf.rs:20    let res = <Self as Hello>::ap(fa, y); // conceptually: res :: Tr<B>::O
                          ^~~~~~~~~~~~~~~~~~~~