The case where (car a) is a string wasn't handled correctly. The error was provoked by sicp-manual.scrbl.
original commit: 9a4f6b1a194cda0b841bac36df18fa4b822bf469
This changed make `(require scribble/manual)` work in an executable,
although actually rendering documents requires the "scribble"
collection.
original commit: 9ca0aa52250c18dd05c2a19bea654ca770aecf0c
The "racket" directory contains a pared-back version of the
repository, roughly.
The "pkgs" directory everything else in the repository, but
organized into packages.
original commit: b2ebb0a28bf8136e75cd98316c22fe54c30eacb2