LTK is a set of CL bindings for the Tk GUI library, which provides a complete CLOS binding to the Tk widget set. It is implemented by means of talking to a Tcl interpreter. This makes the toolkit portable and capable of working over a remote socket.

LTK was written by Peter Herth.

Although the last release is somewhat dated, the project is still under active development. Most activity happens on its mailing list

Recent improvements could could be found in svn repo at


One unfortunate problem is that LTK mysteriously fails to run on some Windows computers, depending on what programs happen to be running in the background. People are encouraged to either donate a Windows box for testing, or helpfully volunteer to track the issue down.

This may be an issue limited to certain Lisp implementations, as SBCL has not been observed to manifest this problem.

See cl-tk or clTcl for alternatives.