> It would be an interesting project to split R7RS-small into "stages" and
> describe them via implementing each stage in the last one. For example:
> assume R7RS doesn't have `read`, `eval`, `string->number`, or anything
> else that knows anything about Scheme syntax or evaluation semantics.
> How do you then implement these in terms of the other operations? This
> would be a true reference implementation of R7RS, and a useful tool for
> testing and specifications.

I've had the same idea, but both of you and many regulars on this list
are better suited for specifying it than I am.

IIRC the main parts of Gambit were written in R4RS for a long time, to
ease bootstrapping?

SRFI 211 (Scheme Macro Libraries) section `The low-level macro facility
of the R^4RS` gives rudiments that are enough to build the other macro
systems.