A portable, annotation-based, visual stepper for Common Lisp

Many programming systems feature a stepping debugger, a tool that lets users execute code, section by section, in steps of their own choosing. Despite many attempts throughout the decades, the Common Lisp language is still lacking in this regard. We propose and describe the workings of a new, portable, visual stepping facility for Common Lisp, realized as an extension to SLY, a cross-implementation Common Lisp IDE for the Emacs editor. This facility is realized as an increment to an existing source code annotation system known as “stickers”, whose working principles we also describe in this work. As part of the solution arrived at for the main objective, we also present two reusable software components: (1) a simple, near portable technique for constructing a source-tracking Common Lisp expression reader in terms of a preexisting compliant expression reader and (2) a technique to carry over source-tracking information to the expansion of macro expressions.