Xref: utzoo comp.object:3439 comp.lang.misc:7705 comp.lang.eiffel:1568 Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!spool.mu.edu!uunet!mcsun!ukc!pyrltd!tetrauk!rick From: rick@tetrauk.UUCP (Rick Jones) Newsgroups: comp.object,comp.lang.misc,comp.lang.eiffel Subject: Re: A Hard Problem for Static Type Systems Message-ID: <1152@tetrauk.UUCP> Date: 2 May 91 09:06:04 GMT Article-I.D.: tetrauk.1152 References: <1991Apr20.010347.28984@leland.Stanford.EDU> <554@eiffel.UUCP> <1991Apr26.203642.17387@leland.Stanford.EDU> <556@eiffel.UUCP> <1146@tetrauk.UUCP> Reply-To: rick@tetrauk.UUCP (Rick Jones) Organization: Tetra Ltd., Maidenhead, UK Lines: 21 In article boehm@parc.xerox.com (Hans Boehm) writes: } rick@tetrauk.UUCP (Rick Jones) writes: } >... It is worth noting that } >Craig Chambers' "hard problem" is only irresolvable in a static type system if } >you demand contravariance (which he did in his initial posting) - but then most } >problems are irresolvable in a useful way with contravariance... } The original sentence strikes me as a substantial overgeneralization. The } problem appears to be unsolvable in a straightforward way using a version of } Eiffel's type system that enforces contravariance. Nothing else has been } established. Criticism accepted - I was assuming a context of types related by inheritance, which was the general context of the discussion. The statement was not intended to be as sweeping as it might sound. -- Rick Jones, Tetra Ltd. Maidenhead, Berks, UK rick@tetrauk.uucp Any fool can provide a solution - the problem is to understand the problem