Re: [Caml-list] ocaml toplevel: is it possible to separate what is sent on stdout from the answers from the toplevel?

[Alan Schmitt <alan.schmitt@polytechnique.org>]

Hello Jeremie,

Jeremie Dimino <jdimino@janestreet.com> writes:

> The best way is to create a custom toplevel and map the replies.
>
> "val x : int = 3" is printed using [Toploop.print_out_phrase] which is
> a reference, so you can replace by a function adding markers around
> the text.
>
> This won't catch error/warning messages. If you also want to
> distinguish these, you can redirect the standard formatters. The
> toplevel prints replies and error messages on the formatter passed to
> [Toploop.loop], which is [Format.std_formatter] by default. So you can
> either:
> (1) override [Format.std_formatter] callbacks
> (2) call [Toploop.loop] with a custom formatter
>
> You can do (1) with [Format.pp_set_all_formatter_output_functions] and
> (2) by setting the startup hook:
>
> Toploop.toplevel_startup_hook := (fun () -> Toploop.loop my_formatter;
> exit 0)
>
> Warnings are always printed on [Format.err_formatter] so you'll need
> to override its callbacks.
>
> If you can't create a custom toplevel, I guess you can also send the
> code to the toplevel at the beginning of the session.

Thanks a lot, this was most helpful. This is what I ended up doing. The
following, when evaluated, will send all the information from the
toplevel to some file, and only output in the toplevel things that are
explicitly printed.

#+begin_src ocaml
let _,_,newline,space = 
  Format.pp_get_all_formatter_output_functions Format.std_formatter ();;

let outfile = open_out "/Users/schmitta/tmp/testoutml.txt";;

let myout s p n = Printf.fprintf outfile "%s" (String.sub s p n);;

let myflush () = flush outfile;;

Format.pp_set_all_formatter_output_functions 
  Format.std_formatter 
  myout 
  myflush 
  newline 
  space;;
#+end_src

Alan