Lambda the Ultimate

A Stepper for Scheme Macros. Ryan Culpepper, Matthias Felleisen.

In this paper, we present a macro debugger with full support for modern Scheme macros. To construct the debugger, we have extended the macro expander so that it issues a series of expansion events. A parser turns these event streams into derivations in a natural semantics for macro expansion. From these derivations, the debugger extracts a reduction-sequence (stepping) view of the expansion. A programmer can specify with simple policies which parts of a derivation to omit and which parts to show. Last but not least, the debugger includes a syntax browser that graphically displays the various pieces of information that the expander attaches to syntactic tokens.

Another paper from the Scheme workshop.

Apart from being a nice exercise for macro lovers, a good macro debugger is essential for lowering the barrier to macro programming. Since macro programming is an important technique for building DSELs and for language oriented programming in general, having better macro debugging facilities is a Good Thing.