How does one find a loop in a gettable chain?

[Dirk Laurie <dirk.laurie@...>]

I'm getting the following error:

   gettable chain too long; possible loop

It's difficult to locate the error by my usual technique
of sprinkling print statements around. This may be
a case where the debug library is needed.

The traceback is of little use. It contains only the
outermost call, which is almost the only statement
in the main chunk.