在SBCL中使用步进器的一个简单例子

* (proclaim '(optimize (debug 3))) 
* (defun foo (a b) (* (+ a b) b)) 
FOO 
* (step (foo 1 2)) 
; Evaluating call: 
; (FOO 1 2) 
; With arguments: 
; 1 
; 2 
1] step 
; Evaluating call: 
; (+ A B) 
; With unknown arguments 
0] step 
; Evaluating call: 
; (* (+ A B) B) 
; With unknown arguments 
0] step 
; (FOO 1 2) => 6 

命令：

Stepping: 
    START Selects the CONTINUE restart if one exists and starts 
     single-stepping. Single stepping affects only code 
     compiled with under high DEBUG optimization quality. 
     See User Manual for details. 
    STEP Steps into the current form. 
    NEXT Steps over the current form. 
    OUT Stops stepping temporarily, but resumes it when the topmost 
     frame that was stepped into returns. 
    STOP Stops single-stepping. 

参见SBCL手册：single stepping。