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

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

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

pub fn release_lock(
  reader: Reader(a),
) -> Result(Reader(a), String)