interface kit { 
    
      int eval(char* cmd);       // to evaluate script commands
      char* result();            // to fetch the result of eval
      void result(char* s);      // to set the result of eval
      char* evaluate(char* cmd)  // combines eval and result
      int source(char* f);       // to load a script from file
      
      void bind(char* name, handler* h); // to bind Tcl command
      
      widget* root();            // returns toplevel (root) widget
      widget* pack(widget* w, char* options = "-side top -fill x");
      widget* pack(char* wp, char* options = "-side top -fill x";
      
      char* selection(char* options="");         // X environment
      
      void after(int msecs, char* cmd); 
      void after(int n, handler* h);
      
      void update(char* options="");
      
      char* send(char* it, char* cmd);
      
      void trace(int level = 1); 
      void notrace(); 
      void quit()                      // to terminate the session
    };