Old readme.txt:

README file for TDebug, an alternative tcl/tk-debugger.

Copyright (C) 1993 Gregor Schmid 

This software is copyrighted by Gregor Schmid. The following terms
apply to all files associated with the software unless explicitly
disclaimed in individual files.

The authors hereby grant permission to use, copy, modify, distribute,
and license this software and its documentation for any purpose,
provided that existing copyright notices are retained in all copies
and that this notice is included verbatim in any distributions. No
written agreement, license, or royalty fee is required for any of the
authorized uses. Modifications to this software may be copyrighted by
their authors and need not follow the licensing terms described here,
provided that the new terms are clearly indicated on the first page of
each file where they apply.

IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND
NON-INFRINGEMENT. THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, AND
THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.


General
-------

TDebug uses a different approach than any other debugger I've seen for
Tcl/Tk. If you know the emacs-lisp debugger `edebug' the following may
seem familiar.

TDebug is solely based on Tcl/Tk, there is no C-code, which makes it
very easy to install. It works by parsing and redefining Tcl/Tk-procs,
inserting calls to `td_eval' at certain points, which takes care of
the display, stepping, breakpoints, variables etc.

The advantages are that TDebug knows which statement in what proc is
currently being executed and can give visual feedback by highlighting
it. All currently accessible variables and their values are displayed
as well. Code can be evaluated in the context of the current
proc. Breakpoints can be set and deleted with the mouse.

Unfortunately there are back-draws to this approach. Preparation of
large procs is slow and due to Tcl's dynamic nature there is no
guarantee that a proc can be prepared at all.

This problem has been alleviated somewhat with the introduction of
partial preparation of procs. There is still no possibility to get at
code running in global context, but I'm not sure if that would be
useful anyway.