It should be possible to detect, at define-time, whether a function/macro has side-effects (see the ideas for a conservative purity analyzer in http://arclanguage.org/item?id=558).
So if the function/macro has side-effects, def/mac could e.g. also assign it to a second symbol with "!" appended.
'?' could also be done similarly, but would be more difficult. Here is a start:
def/mac should also assign its function/macro to a second symbol with "?" appended if:
1) The function/macro has no side-effects (no "!")
Leaving aside the issues of detecting a query, I think it's a really bad idea to have the compiler force (badly guessed) semantic knowledge on me.
It's my code, I wrote it, and I don't want any compiler telling me that a query that caches previous results must be imperative! and not end in a ? .
I also thing needlessly polluting a namespace with addition symbols is a bad idea. You only get one namespace in arc, try to preserve it for the future.
