The depth to which nested objects are printed in trace output.
*trace-print-level* controls the depth to which nested objects are printed during output from tracing. If its value is a positive integer then components at or above that level are suppressed. By definition an object to be printed is considered to be at level 0, its components are at level 1, their subcomponents are at level 2, and so on.
*print-level* is bound to the value of
*trace-print-level* while printing tracing information. If
nil then objects are printed without regard to depth.
USER 8 > (trace append)
USER 9 > (dotimes (i 10) (setq li (if (zerop i)
(list i li))))
USER 10 > (append li '(a b))
0 APPEND > ((9 (8 (7 (6 #)))) (A B))
0 APPEND < ((9 (8 (7 (6 #))) A B))
(9 (8 (7 (6 (5 (4 (3 (2 (1 NIL)))))))) A B)
*trace-print-level* is an extension to Common Lisp.
LispWorks User Guide and Reference Manual - 20 Sep 2017