When I switch the 'use' to a 'require', I can indeed determine if the module is not installed and catch that.

However, if the module *is* installed, the Tk code fails to function. There are no errors or anything - the script just exits. I actually placed a 'print' after the MainLoop call, and I see the print output.

It seems to make no difference whether I call Tk->import;
It seems to make no difference if I place Tk:: before the tk subroutines.

bizarre...