optional positional not working as expected?

[0x5a4]

Im having some trouble with positionals. According to my understanding
this should produce Out {first: Some("a:"), last: "b" } when run with a: b and
Out {first: None, last: "a"} when run with a.

Yet the second case fails to parse. Am I just being stupid here?

use bpaf::*;

#[derive(Debug, PartialEq, Eq)]
struct Out {
    first: Option<String>,
    last: String,
}

fn the_parser() -> OptionParser<Out> {
    let first = positional::<String>("first")
        .parse(|v| {
            if v.contains(':') {
                Ok(v)
            } else {
                Err("no colon")
            }
        })
        .optional();

    let last = positional::<String>("last");

    construct!(Out { first, last }).to_options()
}

fn main() {
    let out = the_parser().run();
    println!("{:?}", out);
}

[pacak]

By default optional would propagate parse error outwards, you can slap catch at the end to return None instead.

This should work the way you describe.

  #[derive(Debug, PartialEq, Eq)]
  struct Out {
      first: Option<String>,
      last: String,
  }

  fn the_parser() -> OptionParser<Out> {
      let first = positional::<String>("first")
          .parse(|v| {
              if v.contains(':') {
                  Ok(v)
              } else {
                  Err("no colon")
              }
          })
          .optional()
          .catch();
      let last = positional::<String>("last");
      construct!(Out { first, last }).to_options()
  }

[0x5a4]

Whoops, completely missed the existence of catch. I assumed returning None instead was the default...

[pacak]

I need to keep working on the documentation then, thank you for making a ticket :)