Very basic thing to ask for, but right now I'm just getting
*** - =: "ROUND" is not a number
as a description of my error.
Does GNU Common Lisp not support stacktraces?
As comment mentioned, the solution is to run the script with -on-error debug and then use :bt to get a backtrace, like this:
$ clisp -on-error debug test.lisp
Break 1 [3]> :bt