Re: [Caml-list] Understanding Format

[Olivier Andrieu <oandrieu@nerim.net>]

Salut,

On Mon, Jul 23, 2012 at 11:05 AM, Alain Frisch <alain@frisch.fr> wrote:
> Hi all,
>
> I'm trying to understand the semantics of Format boxes, and I need some
> help!  Consider the following:
>
> let () =
>   set_margin 500;
>   open_vbox 0;
>   for _i = 1 to 300 do
>     open_hbox ();
>     print_string "x";
>     close_box ()
>   done;
>   close_box ()
>
>
> Format inserts line breaks, even though the page width (margin) should be
> large enough to contain 300 characters (and there is no break hint anyway).
> Why does it do it?   Changing the value passed to set_margin does not seem
> to make a difference (except for small values < 70).

You have to increase the 'max_indent' parameter for the formatter too :
  http://caml.inria.fr/pub/docs/manual-ocaml/libref/Format.html#VALset_max_indent

When you open your hbox, you get an implicit break if the current
cursor position is past this max_ident.
Calling set_margin does not change max_indent which keeps its default
value (68).

cf. this comment in format.ml :
(* To indent no more than pp_max_indent, if one tries to open a block
   beyond pp_max_indent, then the block is rejected on the left
   by simulating a break.
*)

HTH
-- 
  Olivier