[Openmcl-devel] Lisp User Interface LUI

[Terje Norderhaug]

On Jan 9, 2009, at 6:14 AM, Robert Goldman wrote:
> This approach looks very interesting.  A question about pushing it  
> further --- in the style sheets, would it be possible to use  
> symbolic expressions for some of the attributes (e.g., to compute  
> some of the sizes)?  I used to use the Garnet constraint-based UI  
> toolkit quite a bit, and really came to like it for that reason.   
> For example, in laying out Gantt charts, it was handy to be able to  
> have ribbons whose dimensions were computed functions of the size  
> of the window and the duration of the corresponding activities.

Adding constraints to such a stylesheet would be a natural next step.  
However, instead of allowing e.g. Garnet constraints directly in the  
stylesheet, it would be advantageous to support a simple syntax for  
the most useful constraints and perhaps provide a means for the  
developer to extend with additional constraints in the application  
and/or interface engine.

For example, rather than allowing expressions in the stylesheet like:

     <group width="(* parent.width 1/2)">

allow the stylesheet to contain e.g.

    <group width="50%">

and have a definition elsewhere (perhaps defined in the LISP  
application) that interprets this to the equivalent as (*  
parent.width 1/2).

This  keeps the stylesheets reasonably comprehensible for non- 
programmers. In addition, it encourages developers to identify the  
most useful constraints and their parameters, together with how to  
provide these in a syntax understandable for those designing the  
stylesheets.

-- Terje Norderhaug