Hi!
Now It is possible! Full debugging tool in tcl.
I have written an tcl-extension to support debugging in Tcl atkdebbuger see - http://www.xdobry.de/atkdebugger/index.html unfortunately it requires some patch to tcl8.4.1
This debugger is full supported in XOTclIDE see http://www.xdobry.de/xotclIDE/extdebugger.html
this functions are possible now - invoking debugger in error case (not catched errors) - breakpoints - invoking debugger per special atk::halt command
Artur Trzewik