Taking inspiration from haskell (http://hackage.haskell.org/package/base-4.10.0.0/docs/Control-Monad.html#v:guard), we could have a guard : fn(bool) -> Option<()> function in std

This lets us write more pleasant code. For example instead of

let x = do catch {
    if is_admin(user) {
        calculate_important_stuff()
    } else {
        None
    }
};

we can do this

let x = do catch {
    guard(is_admin(user))?;
    calculate_important_stuff()
};

basic implementation:

fn guard(b: bool) -> Option<()> {
    if b { Some(()) } else { None }
}

Or maybe even have a Try trait implementation for bool? Not sure if that's beautiful though