pub fn cancel(
  reader: Reader(a),
  reason reason: r,
) -> promise.Promise(Nil)

pub fn closed(of reader: Reader(a)) -> promise.Promise(Nil)

pub fn read(
  reader: Reader(a),
) -> promise.Promise(Result(read_result.ReadResult(a), String))

pub fn release_lock(reader: Reader(a)) -> Reader(a)