How to use the decoders.hardcoded function in decoders

export function labeledDecoder(
  typeDecoder: Decoder,
  msgDecoder: Decoder
): Decoder> {
  return object({
    // TODO: in 4.0.0 make protocol and verison fields mandatory
    protocol: either(
      constant<'iframe-coordinator'>(API_PROTOCOL),
      hardcoded<'iframe-coordinator'>(API_PROTOCOL)
    ),
    version: either(string, hardcoded('unknown')),
    msgType: typeDecoder,
    msg: msgDecoder
  });
}

export function labeledDecoder(
  typeDecoder: Decoder,
  msgDecoder: Decoder
): Decoder> {
  return object({
    // TODO: in 4.0.0 make protocol and verison fields mandatory
    protocol: either(
      constant<'iframe-coordinator'>(API_PROTOCOL),
      hardcoded<'iframe-coordinator'>(API_PROTOCOL)
    ),
    version: either(string, hardcoded('unknown')),
    msgType: typeDecoder,
    msg: msgDecoder
  });
}

case 'circle':
            return circle;
    }
    return fail('Must be a valid shape');
});

guard(
    object({
        a0: string,
        a1: number,
        a2: optional(nullable(either4(string, email, regex(/x/, 'Must be x'), url()))),
        a3: fail('foo'),
        a4: maybe(mixed),
        a5: either3(constant('foo'), constant('bar'), constant('qux')),
        a6: exact({ c: array(poja), d: pojo }),
        a7: tuple6(hardcoded('foo'), mixed, null_, undefined_, unknown, truthy),
        a8: tuple4(integer, number, positiveInteger, positiveNumber),
        a9: either(boolean, numericBoolean),
        b0: map(
            compose(
                string,
                predicate(s => s.startsWith('x'), 'Must start with x')
            ),
            s => s.toUpperCase()
        ),
        b1: shape,
        b2: date,
        b3: dict(string),
        b4: mapping(string),
        b5: oneOf(['foo', 'bar']),
        b6: instanceOf(TypeError),
    }),