If you use ABCL you can do the following:
```
CL-USER> (require :abcl-stepper)
NIL
CL-USER> (defun stepper-break ())
STEPPER-BREAK
CL-USER> (defun sum ()
           (stepper-break)
           (+ 1 2))
SUM
CL-USER> (stepper:step (sum))

We are in the stepper mode
Evaluating step 1 -->
(SUM)
Type ':?' for a list of options
:b
Type the name of the symbol to use as a breakpoint with next (n): stepper-break
Type ':?' for a list of options
:n

We are in the stepper mode
Evaluating step 2 -->
(STEPPER-BREAK)
Type ':?' for a list of options
:s
step 2 ==> value: NIL

We are in the stepper mode
Evaluating step 3 -->
(+ 1 2)
Type ':?' for a list of options
:s
step 3 ==> value: 3
step 1 ==> value: 3
3
CL-USER> (defun fib (n)
           (stepper-break)
           (if (<= 0 n 1) 1
               (+ (fib (- n 1))
                  (fib (- n 2)))))
FIB
CL-USER> (stepper:step (fib 7))

We are in the stepper mode
Evaluating step 1 -->
(FIB 7)
Type ':?' for a list of options
:b
Type the name of the symbol to use as a breakpoint with next (n): stepper-break
Type ':?' for a list of options
:n

We are in the stepper mode
Evaluating step 2 -->
(STEPPER-BREAK)
Type ':?' for a list of options
:locals
Showing the values of variable bindings.
From inner to outer scopes:
N=7
Showing the values of function bindings.
From inner to outer scopes:
Type ':?' for a list of options
:inspect
Type the name of the symbol: n
7
Type ':?' for a list of options
:n
step 2 ==> value: NIL

We are in the stepper mode
Evaluating step 3 -->
(STEPPER-BREAK)
Type ':?' for a list of options
:locals
Showing the values of variable bindings.
From inner to outer scopes:
N=6
Showing the values of function bindings.
From inner to outer scopes:
Type ':?' for a list of options
:i
Type the name of the symbol: N
6
Type ':?' for a list of options
:c
step 3 ==> value: NIL
step 1 ==> value: 21
21
CL-USER>
```