fn foo<'a>() {
    let _: 'a ||; // for comparison
    let _: <'a> ||;
    // let _: Option<'a ||>;
    // let _: Option<<'a>||>;
    let _: Option< <'a>||>;
}
fn main() {foo()}Uncommenting the first and second commented lines gives, respectively:
option-closure.rs:5:21: 5:23 error: expected `,` or `>` after lifetime name, got: OROR
option-closure.rs:5     let _: Option<'a ||>;
                                         ^~
option-closure.rs:6:17: 6:19 error: expected `;` but found `<<`
option-closure.rs:6     let _: Option<<'a>||>;
                                     ^~