[Caml-list] How can I change the margin size in the toplevel?

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

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Hello,

I’m writing some slides for an ocaml course that contain the output sent
by the toplevel, such as the following:

# let x = 1 + "toto";;
Error: This expression has type string but an expression was expected of type
         int

As the messages are too wide to fit on the width of the slide, they are
put in an environment that wraps them. The results look like this:

Characters 12-18:
  let x = 1 + "toto";;
              ^^^^^^
Error: This expression has type string but an expression was expected of
      type
         int

I’m trying to get rid of the line break before “int”, and looking at the
code, I see that the toplevel uses Format with break hints for these
messages, so I should be able to do this by setting the margin to a big
number. Unfortunately I don’t seem to be able to change the margin of
the formatter used in the toplevel. I tried both:

Format.pp_set_margin Format.err_formatter 200

and

Format.pp_set_margin Format.std_formatter 200

inside the toplevel but it does not change the formatter for these
messages.

Is there a way to access the formatter used by the toplevel? And if not,
is it possible to change the column at which word wrap happens?

Thanks,

Alan

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