macro -- compilation needs context

3.9: adda/macro/compilation needs context:

. when defining macro's that are etrees
rather than text substitutions,
a complication is the context needed:
. a macro is modular, yet it assumes
enough context to be compilable .

. but when does it need compilation?
it could instead have delayed compilation?
. for simplicity, for those reading the code,
you want it to be compilable
at least to the point so that
the etrees being formed are like those that
the reader gets when doing a mental parsing .
. back-end compilation and type-checking
can be done dynamically, at run time .