Redefining an Assignment Slot?

[Rob Reiss]

Hello,
 
  Is there a way to redefine an assignment slot. 

  For instance is it possible to redefine a point's x: slot to do something
besides just assignment. Lets say I want to notify some object (a display)
when a point changes. Could I do this by changeing x: in the point to first
notify the display then do assignment... 

i.e. Do something like point x: = ( display NeedRedraw. <- )

Rob Reiss
University of California, Berkeley
rob at moray.berkeley.edu