pub fn decoder(
  ok_decoder: fn(Dynamic) -> Result(a, List(DecodeError)),
  error_decoder: fn(Dynamic) -> Result(b, List(DecodeError)),
) -> fn(Dynamic) -> Result(Result(a, b), List(DecodeError))

pub fn to_json(
  ok_encoder: fn(a) -> Json,
  error_encoder: fn(b) -> Json,
) -> fn(Result(a, b)) -> Json