Steps toward better debugging tools for LISP

Although contemporary Lisp systems are renown for their excellent debugging facilities, better debugging tools are still urgently needed. A basic flaw with the tools found in most implementations is that they are oriented towards inspection of specific pieces of program or data. and they offer little help in the process of localizing bugs within a large body of code. Among conventional tools, a stepper is the best aid for visualizing the operation of a procedure in such a way that a bug can be found without prior knowledge of its location. But steppers have not been popular, largely because they are often too verbose and difficult to control.