flag_constraint which maps the value

[ollie-dot-earth]

I've used glint quite a bit and I just used a flag constraint for the first time.

I was hoping id be able to do something like this:

use url <- glint.flag(
  glint.string_flag("url")
  |> glint.flag_constraint(fn(url) {
    case uri.parse(url) {
      Error(_) -> snag.error("Invalid url")
      Ok(url) -> Ok(url)
    }
  }),
)

But I don't think this is available at the moment.

It would, however, be quite nice I think. As I currently have to either handle the impossible parse error later on or assert it. Both of which are less than optimal IMO.