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From: =?UTF-8?Q?Milan_Stanojevi=C4=87?= <milanst@gmail.com>
Date: Mon, 2 Dec 2013 10:14:41 -0500
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To: Ollie Frolovs <ollie.frolovs.2012@my.bristol.ac.uk>
Cc: caml users <caml-list@inria.fr>
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Subject: Re: [Caml-list] Extracting exception details (Async, Cohttp, Exn)

> Indeed. By saying =E2=80=9Cdescription=E2=80=9D I tried to communicate my=
 intention, obviously unsuccessfully. In the given example, I would like to=
 extract ("connection attempt timeout" 127.0.0.2:80) in some civil way, pre=
ferable as a string so that i can display the error message to the user. In=
 RWO all examples that i have seen so far, just check for Error/None and pr=
int =E2=80=9CUnexpected failure=E2=80=9D to the user (DuckDuckGo example). =
I want to give more information but not the entire sexp with the backtrace,=
 etc.
>

As I said, you can use Monitor.extract_exn.

try_with (fun () -> Cohttp_async.Client.get (Uri.of_string "http://127.0.0.=
2"))
>>=3D function
| Error exn ->
  let orig_exn =3D Monitor.extract_exn exn in
  Exn.to_string orig_exn
| Ok _ -> .....