declare
[Tree QTk]={Module.link ["Tree.ozf" "http://www.info.ucl.ac.be/people/ned/qtk/QTk.ozf"]}
TreeNode=Tree.treeNode
C
{{QTk.build td(canvas(glue:nswe
		      handle:C
		      tdscrollbar:true
		      lrscrollbar:true))} show}


class CustomNode
   from TreeNode
   feat
      calc
      current:{NewCell unit}
   meth init(...)=M
      TreeNode,M
      {self bind(event:"<1>"
		 action:self#selectNode)}
   end
   meth selectNode
      if {Access self.current}\=unit then
	 {{Access self.current} select(state:false)}
      end
      {Assign self.current self}
      {self select(state:true)}
      if {Access self.current}==self then
	 {self switch}
      end
   end
   meth expand(...)=M
      if {IsFree self.calc} then
	 Label={self get(label:$)}
      in
	 {self addLeaf(
		  nodes:{List.map ["a" "b" "c" "d"]
			 fun{$ C}
			    {New CustomNode init(parent:self
					       label:Label#" "#C)}
			 end})}
	 self.calc=unit
      end
      TreeNode,M
   end
end

CurrentNode={NewCell unit}

RootNode={New CustomNode init(canvas:C
			      font:"Helvetica 10"
			      height:18
			      label:"Node"
			     )}

{RootNode draw(x:2 y:2 height:_)}
   
{RootNode expand}