type Env = ^ Binding;

     Value = ^ValNode;
     
     Binding = record id :alfa; v:Value; next:Env end;

     ValueClass = (intval, boolval, charval, emptyval,
                   listval, nilval, funcval, deferval);
     
     ValNode = record case tag :ValueClass of
               intval: (n :integer );
               boolval:(b :boolean );
               charval:(ch:char );
               nilval, emptyval:();
               listval:(hd, tl :Value);
               funcval, deferval:( e:tree; r:Env )
               end;

{\fB Environment and Value Types. \fP}