The following works, and will soon be on stable Rust 
:
#![feature(min_type_alias_impl_trait)]
type Add2 = impl Fn(u32) -> Add1;
type Add1 = impl Fn(u32) -> u32;
fn add3 (x: u32)
-> Add2
{
move |y: u32| {
move |z: u32| {
x + y + z
}
}
}
fn main ()
{
assert_eq!(6, add3 (1) (2) (3));
}