Sun Aug 22 14:19:58 EDT 2004
>>>>> "Kent" == R Kent Dybvig <dyb at cs.indiana.edu> writes:
Kent> A tool can determine if the requires are necessary for a
Kent> particular build, but it cannot necessarily determine whether a
Kent> require can be eliminated from the source code, since a change
Kent> in an imported syntactic abstraction can affect whether other
Kent> module imports are used. For example, does (a x) reference x?
Kent> We can answer this question for a particular definition of a but
Kent> not for all possible definitions of a.
Well, but isn't that an obscure case? Isn't the more common case that
indeed no binding for a given import even occurs in the code? How
does this fit in with the local-import scenario?
Maybe I misunderstood you: I thought your point was that programmers
will just delete the import along with the code that relies on them as
a matter of course---because the import is part of the code. But you
seem to be hinting at a deeper issue.
Kent> Here's a simple one: Suppose I want to make sure I get the r6rs cons
Kent> and not some other cons, so I write:
Kent> ((let () (require scheme) cons) x y)
Kent> With top-level require only, I would write:
Kent> (module ---
Kent> (require (add-prefix scheme "real:"))
Kent> (real:cons x y)
Kent> I think the former is clearer, but others may not. (Plus, I don't have
Kent> to think of a prefix or remember what it was.)
I think the latter is clearer, in particular if "real" is renamed to
"r6rs." Moreover, will the former still work if "scheme" has been
rebound? (And somehow, this seems like a fairly contrived example to
me :-) )
Kent> Not at all. I'm not sure how I gave that impression, but I would
Kent> certainly want local imports to shadow local bindings. Modules create
Kent> sets of bindings; require forms make them visible.
I guess I don't understand this paragraph at all:
Kent> * Should bindings established by run-time require shadow bindings
Kent> that would otherwise be visible within transformers, and visa
Kent> versa? For example, if M exports x, does
Kent> (let ([x 3]) (require only-for-syntax M) x)
Kent> evaluate to 3 or to an out-of-context error? (I prefer error;
Kent> I'm not sure about Matthew.)
Could you elaborate?
Cheers =8-} Mike
Friede, V?lkerverst?ndigung und ?berhaupt blabla
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