Improving the ISO Prolog standard by analyzing compliance test results

Part 1 of the ISO Prolog standard (ISO/IEC 13211) published in 1995 covers the core of Prolog, including syntax, operational semantics, streams and some built-in predicates. Libraries, DCGs, and global mutables are current standardization topics. Most Prolog implementations provide an ISO mode in which they adhere to the standard. Our goal is to improve parts of the Prolog standard already published by finding and fixing ambiguities and missing details. To do so, we have compiled a suite of more than 1000 test cases covering part 1, and ran it on several free and commercial Prolog implementations. In this study we summarize the reasons of the test case failures, and discuss which of these indicate possible flaws in the standard. We also discuss test framework and test case development issues specific to Prolog, as well as some portability issues encountered.