www.neuron.yale.edu

The two easiest ways to figure out where you code is going wrong is to print variables, or to print an arbitrary message after certain flow control statements. But I can't figure out how to do this in from NMODL. Is there a way?

Just insert printf() statements into the NMODL source code. Syntax is same as in C. Example:
printf("flag=%d t=%g\n", flag, t)