What is a "file"? Lexical package usage?

[Rem@IMSSS]

A file signals its end by an end-of-file marker of some kind (I'd have to
look in the CL manual to remind myself what it is in CL). The beginning of
a file is indicated by being right after you have done some kind of OPEN,
and is lexical extent is from that point unti the end-of-file marker occurs.
Perhaps if lexical packages are implemented, other streams can issue package
and other start-of-file stuff right after they are "opened" whatever that
means for the stream, and can signal the end of a lexical segment by an
end-of-file marker? For terminal-input and other infinite streams, the
interpretor can immediately re-open them after noting the lexical break
caused by end-of-file, flushing any info it had about the package state
from the just-now-closed segment and preparing to accept new package
declarations from the new segment to arrive next on the re-opened stream.
Would that solve the problem with "IN A FILE" being a special case?
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