Using trace with functions not defined by me

Question

I'm using sbcl 1.4.6 and I have this behaviour:

*  (trace string<)

(STRING<)
*  (string< "hola" "pato")
  0: (STRING< "hola" "pato")
  0: STRING< returned 0
0
*  (defun test-without-cond (str)
           (string< "hola" str))

TEST-WITHOUT-COND
* (test-without-cond "pato")

0

If the function is allready defined in common lisp, I cannot use trace when using inside a user defined function. BUt this is not a problem if I define the function

* (defun my-string< (str) (string< str "hello"))
MY-STRING<

* (trace my-string<)

(MY-STRING<)

* (defun test-2 (str) (my-string< str))

TEST-2
* (test-2 "gato")
  0: (MY-STRING< "gato")
  0: MY-STRING< returned 0
0

Why is this happening?

Answer 1

What can be traced depends on the implementation and various settings.

For SBCL read the manual: Open Coding and Inline Expansion

But SBCL now also has an interpreter and it looks like you can trace calls to CL functions from interpreted code:

* (setf  *evaluator-mode* :interpret)

:INTERPRET
* (trace string<)

(STRING<)
* (defun test-without-cond (str)
    (string< "hola" str))

TEST-WITHOUT-COND
* (test-without-cond "pato")
  0: (STRING< "hola" "pato")
  0: STRING< returned 0
0
* 

Note that one might need to be careful with tracing core functions, since they can be called a lot...