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Some portions of the Scheme community favor a much more dynamic semantics for macros, more in the Lisp tradition; others favor building macros on top of a more compilation-friendly semantics

Forgive my ignorance, but aren't Lisp's semantics very compilation-friendly? Doesn't macro expansion happen at read-time?

EDIT: I think that's the case for Common Lisp. By "the Lisp tradition" did you mean prior dialects?

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you still can have dynamic semantics at read-time -- eg, does the macro-expand in reading the first form load new macros that affect the next form? Eg, in (progn (M) (M)), is it ever the case that the second M will dispatch to a different macro definition than the first M?

In the world of Common Lisp, yes. In the world of R6RS's more static semantics, no.

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