Mon Apr 7 12:19:22 EDT 2008

optional library code

Then, the more general problem of requiring runtime words only if
necessary. For example:

 (([qw macro]  run) macro)
 ((run)             ([cw 'runtime-run]))

Since symbols are no longer allowed, this form of late binding needs
to be handled differently. The most straightforward solution is to
have the default throw an exception, and rely on targets to implement
the word.