Path: utzoo!mnetor!uunet!mcvax!enea!zyx!bd
From: bd@zyx.UUCP (Bjorn Danielsson)
Newsgroups: comp.lang.prolog
Subject: End-of-file handling
Message-ID: <2403@zyx.UUCP>
Date: 24 Mar 88 06:49:23 GMT
Reply-To: bd@zyx.SE (Bjorn Danielsson)
Organization: ZYX Sweden AB, Stockolm, Sweden
Lines: 22


I can't understand why there should be a "strait-jacket solution" to this
kind of problem. Why not put in enough flexibility to allow for the most
obvious cases? In Z-Prolog, (which was never designed to be Edinburgh
compatible) the "read" predicate can handle end-of-file in three different
ways, depending on an optional argument:

	(1) signal an error,
	(2) fail,
	(3) return a value supplied by the programmer.

The default action is to signal an error.
This solution, or something like it, could easily be adopted for Edinburgh
Prolog as well, only the default there should probably be returning
'end_of_file' to ensure backward compatibility.

End-of-file handling is much less problematic for character input, since
there it is possible to have an end-of-file value (like -1) which can never
be mistaken for legal input.

-- 
Bjorn Danielsson, ZYX Sweden AB, +46 (8) 665 32 05, bd@zyx.SE