The Tcl/tk language is not built into TCC, and must be obtained separately. The version supported by TCC is ActiveTcl 8.6 (free from www.activestate.com).
You must enable Tcl support in the OPTION / Startup page. If it is enabled, TCC will automatically load a Tcl interpreter when it starts. If a suitable library is found, TCC checks to see if you are running a .TCL file. If so, TCC passes the file to your Tcl interpreter for processing.
It's not possible for TCC to determine in advance whether you're running a Tcl or a Tk script. After executing the script, TCC checks if a Tk window is running. If so, it enters a Tk event loop and waits for the window to be closed. If not, TCC assumes it was a Tcl script and TCC returns immediately.
Because of the way the Tk interpreter works, it is not possible for TCC to maintain a persistent interpreter after executing a Tk script. TCC will close the current Tcl/tk interpreter and create a new one the next time a Tcl / tk script is executed.