Error handling with `ocaml-github`

Learning
,
1

Hi,

I am trying to use https://github.com/mirage/ocaml-github/ and it works fine for the happy path, but I am having some trouble catching exceptions and assume that I misunderstand something about ocaml-githubs monadic interface?

Both compile, both work fine when given a real commits sha, but both are seemingly failing in catching the exception for invalid commit shas; I’d except an exception to be printed, preceeded by "ERROR ", but the output I get is just
Fatal error: exception GitHub API error: 422 Unprocessable Entity (WebDAV) (RFC 4918) -- No commit found for SHA: not-a-real-commit - without my prefix.

I tried using Github.Monad.catch as in

let t =
  let open Github.Monad in
  let token = Github.Token.of_string "my-token"
  and user = "ocaml"
  and repo = "opam"
  in
  run Github_t.(
      catch
        (fun () ->
           let sha = "not-a-real-commit" in
           Github.Repo.get_commit ~token ~user ~repo ~sha ()
           >>~ fun commit ->
           return (Printf.eprintf "commit url: %s\n" commit.commit_url))
        (function
          | e -> return (Printf.eprintf "ERROR %s\n" (Printexc.to_string e)))
    )

let () =
  Lwt_main.run t

As well as a conventional try-catch-clause:

let t =
  let open Github.Monad in
  let token = Github.Token.of_string "my-token"
  and user = "ocaml"
  and repo = "opam"
  in
  run Github_t.( 
     try
        let sha = "not-a-real-commit" in
        Github.Repo.get_commit ~token ~user ~repo ~sha ()
        >>~ fun commit ->
        return (Printf.eprintf "commit url: %s\n" commit.commit_url)
      with
      | e -> return (Printf.eprintf "ERROR %s\n" (Printexc.to_string e))
    )

let () =
  Lwt_main.run t

Thanks for reading, looking forward to any pointers :slight_smile: