Froglet: A Source Level Stepper for Lisp

Froglet is a source-level stepper for Common Lisp. Unlike previous steppers, which used pretty-printed reconstructions of definitions to show the progress of execution, Froglet uses the text from which the definition was read. This means that forms can be shown under evaluation in the right context, complete with comments and related functions. It also provides views onto the stack and onto the lexical environment of the form currently being evaluated. This paper describes the background to Froglet and how it is related to steppers for conventional languages, gives an overview of its implementation and interface, and shows that it could form a key addition to Lisp environments.