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me: > I think it might be realistic to label ports not with > the encoding scheme they want, but with the set of > code-values they can transmit -- in other words > with their framing constraints. John: The difficulty here is that an ISO-8859-1 port {produces,accepts} a different set of characters from an ISO-8859-2 port. Unless a port is labeled with an encoding, you can't know what characters it will and won't {accept,produce}, and you are stuck with some system default. There is no reason I can see why the implementation must provide the kind of labeling you like. I have no trouble imagining many applications that don't need it --- they either won't need the system to enforce a restriction because they'll know what their ports are talking to or they are robust in the case that they get wrong what the ports expect. The goal here isn't to try to prevent programmers from making mistakes. The whole "port encoding labeling" thing seems plausible to many of us but I think there is precious little actual experience in how to do it, that multiple ways are possible, and that the goal for R6RS should be to enable experimentation in this area by portable programs. For example, a common suggestion is that you specify when first creating a port what encoding it is. Well, what if I hope to send traffic over that port that will use different encodings at different points during the run? Clearly labeling is not trivial -- I'd say, not well understood. -t