Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!snorkelwacker.mit.edu!ai-lab!zurich.ai.mit.edu!jaffer
From: jaffer@zurich.ai.mit.edu (Aubrey Jaffer)
Newsgroups: comp.lang.scheme
Subject: Re: open-input-file [topics from hell, part 2]
Message-ID: <JAFFER.91Apr23221610@kleph.ai.mit.edu>
Date: 24 Apr 91 02:16:10 GMT
References: <CARLTON.91Apr20004133@husc10.harvard.edu> <9104211907.AA25632@august>
	<CARLTON.91Apr23155155@scws1.harvard.edu>
Sender: news@ai.mit.edu
Organization: M.I.T. Artificial Intelligence Lab.
Lines: 18
In-reply-to: carlton@scws1.harvard.edu's message of 23 Apr 91 19:51:55 GMT

How about this as a solution:

The open-xxx functions would return special ports if the file could
not be opened.  These special ports all have reached end-of-file or
are closed (I am not sure which is better).  These special ports are
the value of the symbols:
        file-does-not-exist
        path-does-not-exist
        insufficient-priveledge-to-access-file
        insufficient-priveledge-to-access-path
        file-system-unavailable

The error conditions can be checked for by (eq? file-does-not-exist port)
and so on.

This plan has the open functions always returning a port and allows
those who want to check to do so.  For those who don't check
end-of-files await.