Expanding macros more than once?

[Rem@IMSSS]

Perhaps the best course is to say "it is an error" to code a macro in
such a way that it has different semantics different times it is expanded.
Then implementors will be free to expand multiple times in interpretor
and just once in compiler, or whatever other strategy they prefer,
but writers of macros will have to carefully avoid writing number-of-expand
dependent macros. This seems a better tradeoff than requiring all
interpretors to expand macros just once. Further debate welcome...
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