[a3_nm]

"(defun f x (x))" gives a Python stack trace.

[dagurp]

(defun f [x] (x))

[chrismonsanto]

(defun f (x) (x))

[a3_nm]

Yes, I wasn't expecting this wrong syntax to work, just pointing out that the stack trace looks messy (e.g., leaks the absolute path to the involved Python file).