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Date: Fri, 29 Aug 2003 12:54:46 +0100
To: caml-list@inria.fr
Subject: [Caml-list] Polymorphic graph widget problem
Message-ID: <20030829115446.GA879@redhat.com>
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From: Richard Jones <rich@annexia.org>
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X-Spam: no; 0.00; widget:01 widget:01 lablgtk:01 plots:01 gobj:01 generalise:01 gobj:01 int':01 freshmeat:01 ltd:98 bool:01 bool:01 ints:01 irrelevant:01 gtk:01 
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As part of a project I'm doing at the moment, I've written a Gtk graph
widget using lablgtk. The graph currently plots ints, so the type
looks something like this:

class chart :
  ?width:int ->
  ?height:int ->
  ?packing:(GObj.widget -> unit) ->
  ?show:bool ->
  int array ->  (* the data being plotted *)
  object
    method repaint : Gdk.Rectangle.t option -> unit
  end

All fine, but now I'd like to generalise this so it can plot floating
point values as well as int, thus:

class ['a] chart :
  ?width:int ->
  ?height:int ->
  ?packing:(GObj.widget -> unit) ->
  ?show:bool ->
  'a array ->  (* the data being plotted *)
  object
    method repaint : Gdk.Rectangle.t option -> unit
  end

The problem with this is that at various places in the implementation
we need to break the polymorphism. eg. To plot Y labels we call
'string_of_int', and to work out the height of the Y axis we do some
sums on the values using the (+) operator.

What I need is some way to isolate the parts which break the
polymorphism.  How do I do that?

Rich.

-- 
Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
Merjis Ltd. http://www.merjis.com/ - all your business data are belong to you.
 All new technology is irrelevant until it is taken up by the public.

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