Confusing to use && result.then

[Jedsek]

consider this following code:

fn do(x: String) -> Result(String, String) {
  // ...
}

fn main() {
  let infos: List(String)
  use str <- result.then(infos |> list.first)  
  use str <- result.then(str |> do)  // error: Type mismatched: Result(String, Nil) && Result(String, String)
  // ...
}

fn main() {
  let infos: List(String)
  use str <- result.then(infos |> list.first |> result.replace_error("")) // Here
  use str <- result.then(str |> do) // Sucessful
  // ...
}

How to avoid this result.replace_error("") for type convertion? (Because I would not use this "")
Supposing there is a different error type...(create new one every time...)

Are there any function like result.then, but Result(a, b) -> Result(c, d)

rust version code with ? operator for early return:

    fn try_from(header_line: &str) -> Result<Self, Self::Error> {
        let infos: Vec<&str> = header_line.trim().split(' ').collect();

        let signature_with_hardblank =
            HeaderLine::extract_signature_with_hardblank(infos.first().unwrap())?;

[Jedsek]

oh, I think it's enough for me now:)

fn try_from(header_line: String) -> Result(Header, String) {
  let infos = header_line |> string.trim |>  string.split(" ") |> iterator.from_list

  use <- bool.guard(when: infos |> iterator.length < 6, return: Error("headerline is illegal"))

  use str <- result.then(infos |> iterator.first |> result.replace_error("no first elem"))
  use signature_with_hardblank <- result.then(str |> extract_signature_with_hardblank)
  // ...

[lpil]

Hello! We don't do any implicit casts so you'll need to design and use your error type however is best for your code.