Tcl/Tk error handling

[Filip Konvička]

Hi all,

while solving some issues with the TclODBC library, I've created the 
following wrappers for Tk.send and Tk.return. The problem I've been 
trying to solve was that when a Tcl/Tk call failed, an error was printed 
to stderr and the Oz script froze. The wrappers below throw an exception 
when an error occurs, and Oz--Tcltk communication is in a consistent 
state after such event.

    proc {TkSafeSend X}
       case {Tk.returnInt 'catch'(v("{") X v("}") 'tk_safe_send_msg')}
       of 0 then skip
       else
          E={Tk.returnString set('tk_safe_send_msg')}
       in
          {Wait E}
          raise tk_error(E) end
       end
    end
    fun {TkSafeReturn X}
       case {Tk.returnInt 'catch'(v('{set tk_safe_return_result ') l(X) 
v('}') 'tk_safe_return_msg')}
       of 0 then
          {Tk.return set('tk_safe_return_result')}
       else
          E={Tk.returnString set('tk_safe_return_msg')}
       in
          {Wait E}
          raise tk_error(E) end
          unit
       end
    end

Cheers,
Filip