Implementing traits for function types?

fn_trait.rs

// Based on:
//   https://github.com/emk/jit.rs/blob/master/src/macros.rs#L41-L64
//   https://github.com/emk/jit.rs/blob/master/src/compile.rs#L105-L109
//   https://github.com/emk/jit.rs/blob/master/examples/hello_world.rs#L22
// Build on branch:
//   https://github.com/emk/jit.rs/tree/rust-beta-updates

trait Foo {}

impl Foo for fn() {}

fn do_foo<T: Foo>(t: T) {}

fn example() {}

fn main() {
    do_foo(example);
}

# fn_impl.rs:10:5: 10:11 error: the trait `Foo` is not implemented for the type `fn() {example}` [E0277]
# fn_impl.rs:10     do_foo(example);
#                   ^~~~~~
# error: aborting due to previous error