fn nonlocal_symbol(&self, name: SharedSymbol) -> Option<UniqueSymbol> {
        for nonlocal in self.borrow_local_scope().nonlocals.items().iter() {
            let nonlocal_name = self.symbol_table.name(nonlocal);
            if nonlocal_name == name {
                return Some(*nonlocal);
            }
        }

        return None;
    }
Looks to see whether a name is used as a nonlocal in
the current scope.
passerine/src/compiler/hoist.rs