rust/src/test/compile-fail/issue-2149.rs

trait vec_monad<A> {
    fn bind<B>(f: fn(A) -> ~[B]);
}

impl<A> ~[A]: vec_monad<A> {
    fn bind<B>(f: fn(A) -> ~[B]) {
        let mut r = fail;
        for self.each |elt| { r += f(elt); }
        //~^ WARNING unreachable expression
        //~^^ ERROR the type of this value must be known
   }
}
fn main() {
    ["hi"].bind({|x| [x] });
}