Article: 47247 of comp.lang.prolog
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From: ulrich@mips.complang.tuwien.ac.at (Ulrich Neumerkel)
Newsgroups: comp.lang.prolog
Subject: Prolog portability quest 3
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
Date: Thu, 14 Apr 2011 17:41:22 GMT
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Start up your Prolog, issue the directive op(1105,xfy,'|') and type
in the following query:

writeq((a-->b,c|d)).

This should be a syntax error according to ISO/IEC 13211-1:1995.  But
then, many systems succeed and write a term.  Are they all wrong?

No more!  The recently approved DTC2 provides the extra syntax needed!
This time it was the standard that moved towards implementations.

http://www.complang.tuwien.ac.at/ulrich/iso-prolog/dtc2#C2

ISO/IEC syntax now supports alternation in DCGs and the commit
operator of CHR.

Nevertheless, there are still tiny differences between
implementations.  The currently known are:

http://www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_assessment

Should you find some more - please tell me!

Prologs moved quite a bit in 2010, hopefully this trend will continue!

http://www.complang.tuwien.ac.at/ulrich/iso-prolog/ppq/