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Message-ID: <3F4F86FE.2080202@ucdavis.edu>
Date: Fri, 29 Aug 2003 10:01:50 -0700
From: Issac Trotts <ijtrotts@ucdavis.edu>
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To: caml-list@inria.fr
Subject: Re: [Caml-list] Polymorphic graph widget problem
References: <20030829115446.GA879@redhat.com>
In-Reply-To: <20030829115446.GA879@redhat.com>
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X-Spam: no; 0.00; issac:01 trotts:01 ijtrotts:01 caml-list:01 widget:01 graphing:01 floats:01 floats:01 widget:01 lablgtk:01 plots:01 gobj:01 generalise:01 gobj:01 int':01 
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Precedence: bulk

If you'll only be graphing ints and floats, why not just use floats and 
cast to them?  To support both, you could try this:


type number = Int of int | Float of float

class chart :
...
  number array ->  (* the data being plotted *)
  object
    method repaint : Gdk.Rectangle.t option -> unit
  end



It might also help to think of the array as a map from ints to floats.  
Then you could write this instead:



class chart :
...
  (int * int * (int -> float)) ->  (* x0, x1, the data being plotted *)
  object
    method repaint : Gdk.Rectangle.t option -> unit
  end



- ijt


Richard Jones wrote:

>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.
>
>  
>


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