... [compile-time lexical environment]

[Ram@c.cs.cmu.edu]

If a form is implcitly evaluated at compile time, then it cannot
access the lexical environment, since the environment doesn't exist
until run-time.  Given this, the only alternative to requiring that
the null environment be used is stating that the environment is
undefined.  I see no advantage in the latter, and no reason to resolve
the problem in a different way than DEFMACRO currently does.

  Rob