(Per the current SRFI, you first need to try to write an object, and if that fails, you get back an exception satisfying "unwritable-error?")
Sorry, that's a misleading claim on my part. The SRFI says:
(unwritable-error? object) => boolean Possible causes for the error include the following. * The port's syntax cannot encode any unreadable data at all. * The implementation does not know how to encode a stand-in for this particular object. * The programmer has set an implementation-defined flag saying that trying to write unreadable data to the port should raise an error.
But the SRFI does not provide a way to set the flag in question.
