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[Caml-list] Why I cannot open a graph with a specific title
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Date: 2004-06-28 (21:01)
From: Matt Gushee <mgushee@h...>
Subject: Re: [Caml-list] Why I cannot open a graph with a specific title
On Mon, Jun 28, 2004 at 12:57:34PM -0700, Andy Yang wrote:
> I found that with the following  code is OK:
> open Graphics;;
> let _ = open_graph "";;
> However, if I set a title for a widnow
> open Graphics;;
> let _ = open_graph "hello";;
> Ocaml will report "Fatal error: exception
> Graphics.Graphic_failure("Cannot open display hello").
> open_graph has a signature  string -> unit.

Yes, and did you read what the manual says about that string? The string
is not supposed to be the window title. On X11, it's the the name of an
X display and/or a geometry specification. I'm not sure what it's
supposed to be on Win32 platforms.

Nonetheless, the behavior of open_graph leaves something to be desired.
For example,

  # open_graph " 400x600" (* Note the leading space. *);;
  - : unit = ()
  # open_graph "400x600";;      
  Exception: Graphics.Graphic_failure "Cannot open display 400x600".

So the function distinguishes a display name from a geometry spec by
whether there is a leading space? Yech. Maybe the signature should be

  open_graph : ?display:string -> ?geometry:string -> unit -> unit

And at least one of the following should work:

  # open_graph "0";;  
  Exception: Graphics.Graphic_failure "Cannot open display 0".
  # open_graph "0.0";;  
  Exception: Graphics.Graphic_failure "Cannot open display 0.0".
  # open_graph "localhost:0.0";;
  Exception: Graphics.Graphic_failure "Cannot open display localhost:0.0".
  # open_graph "";;
  Exception: Graphics.Graphic_failure "Cannot open display".
  # open_graph "localhost:0";;
  Signal 13

P.S. When asking questions of this sort, it would be helpful if you gave
  some information about your system, e.g. the platform and version of
  OCaml--especially with libraries like Graphics that have
  platform-dependent features.

Matt Gushee                 When a nation follows the Way,
Englewood, Colorado, USA    Horses bear manure through
mgushee@havenrock.com           its fields;
http://www.havenrock.com/   When a nation ignores the Way,
                            Horses bear soldiers through
                                its streets.
                            --Lao Tzu (Peter Merel, trans.)

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