Here is an example of tracing with some of the possible options. For simplicity, this is the function:
(defun fact (n)
(declare (double-float n) (optimize speed))
(if (zerop n)
1d0
(* n (fact (1- n)))))
(compile 'fact)
This example shows how to use the :condition option:
(trace fact :condition (= 4d0 (debug:arg 0)))
(fact 10d0) ->
0: (FACT 4.0d0)
0: FACT returned 24.0d0
3628800.0d0
As we can see, we produced output when the condition was satisfied.
Here’s another example:
(untrace)
(trace fact :break (= 4d0 (debug:arg 0)))
(fact 10d0) ->
0: (FACT 5.0d0)
1: (FACT 4.0d0)
Breaking before traced call to FACT:
[Condition of type SIMPLE-CONDITION]
Restarts:
0: [CONTINUE] Return from BREAK.
1: [ABORT ] Return to Top-Level.
Debug (type H for help)
In this example, we see that normal tracing occurs until we the argument reaches 4d0, at which point, we break into the debugger.