Macros that Work Together

Macros that Work Together - Compile-Time Bindings, Partial Expansion, and Definition Contexts, Matthew Flatt, Ryan Culpepper, David Darais, and Robert Bruce Findler. Under consideration for publication in J. Functional Programming.

Racket (formerly PLT Scheme) is a large language that is built mostly within itself. Unlike the usual
approach taken by non-Lisp languages, the self-hosting of Racket is not a matter of bootstrapping
one implementation through a previous implementation, but instead a matter of building a tower of
languages and libraries via macros. The upper layers of the tower include a class system, a component
system, pedagogic variants of Scheme, a statically typed dialect of Scheme, and more. The demands
of this language-construction effort require a macro system that is substantially more expressive than
previous macro systems. In particular, while conventional Scheme macro systems handle stand-alone
syntactic forms adequately, they provide weak support for macros that share information or macros
that use existing syntactic forms in new contexts.

This paper describes and models novel features of the Racket macro system, including support for
general compile-time bindings, sub-form expansion and analysis, and environment management. The
presentation assumes a basic familiarity with Lisp-style macros, and it takes for granted the need for
macros that respect lexical scope. The model, however, strips away the pattern and template system
that is normally associated with Scheme macros, isolating a core that is simpler, that can support
pattern and template forms themselves as macros, and that generalizes naturally to Racket’s other

A good description of Racket's rocket science tools for growing languages.