Tcl/Tk Workshop - June 10-11, 1993 - Berkeley, CA 3
Introduction
Tcl [1][2] is a language specifically intended for
generic application control. In some applica-
tions it dominates the user’s view of the
application. Expect [3][4] is a good example of
this. Expect is always executing Tcl statements
– usually from a script. When the script ends,
Expect ends.
This type of application is common. With this
heavy reliance on Tcl, it is useful to have a de-
bugger that understands Tcl. For example, it
should be able to single-step and print values at
user discretion.
The debugger described herein works in exactly
this way. It works best with applications like
A Debugger for Tcl Applications
Don Libes
National Institute of Standards and Technology
Abstract
Tcl is a language specifically intended for generic application control. By us-
ing it, application programmers escape the dilemma of whether to design
sophisticated application-specific languages or whether to build tools more
quickly but that are limited in flexibility. Tcl is easy for application program-
mers to use, however, up to now, there has been no general-purpose debugger
for application users.
This paper describes an implementation of a debugger for Tcl applications.
The debugger has a typical front-end but with some extremely unusual com-
mands, in part because of the features and limitations of Tcl. The debugger is
modeless, allowing users to issue Tcl and application commands along with
debugger commands. Each type of command may invoke the other, allowing
debugging to be programmed, dynamically or in advance.
The debugger is written in C and is very fast. When linked in but not used, it
does not slow applications at all. The debugger requires no modifications to
the Tcl core, and can be plugged into applications with little effort.
Keywords: Tcl, Tk, Tool Command Language, Expect, debugger, interpreter
Reprinted from Proceedings of the 1993 Tcl/Tk Workshop, Berkeley, CA, June
10-11, 1993.
