michaelm@bcsaic.UUCP (michael b maxwell) (07/02/85)
> >From: vantreeck@logic.DEC > Date: 26 Jun 85 16:01:50 GMT > They also think that current implementations of Prolog are severely > lacking in features that help produce reliable and maintainable programs. But > some experts think that there is so much good work being done on the > theoretical issues of how to extend the language to make it more useful while > remaining strictly first order logic that to put Prolog into concrete at this ^^^^^^^^^^^^^^^^^^^^^^^^^^ > time would be not be productive. Can someone clear something up for me? I would have thought that Prolog was *not* "strictly first order logic," because of the existence of predicates like "call" and "=..". Clocksin and Mellish seem to say something like this (2nd. ed., pg 255; 1st. ed., pg. 226). Would someone care to comment on this?
shebs@bcsaic.UUCP (stan shebs) (07/03/85)
In article <174@bcsaic.UUCP> michaelm@bcsaic.UUCP (michael b maxwell) writes: > >Can someone clear something up for me? I would have thought that Prolog >was *not* "strictly first order logic," because of the existence of >predicates like "call" and "=..". Prolog is first-order logic in the same way that Lisp is lambda-calculus. It's amazing what a language can pick up on the way from theory to design to implementation hacking... stan shebs
rggoebel@water.UUCP (Randy Goebel LPAIG) (07/12/85)
> > remaining strictly first order logic that to put Prolog into concrete at this > ^^^^^^^^^^^^^^^^^^^^^^^^^^ > > time would be not be productive. > > Can someone clear something up for me? I would have thought that Prolog > was *not* "strictly first order logic," because of the existence of > predicates like "call" and "=.."... The semantics of pure Prolog is well understood from a first order viewpoint (e.g., see John Lloyd's book ``The Foundations of Logic Programming'', Springer-Verlag, 1984). The semantics of meta-language operations is neither standardized nor well-formalized. Relevant here is Bowen and Kowalski's paper ``Amalgamating language and metalanguage in logic programming'' in the book ``Logic Programming'' edited by Clark and Tarnlund, Academic Press, 1982. Randy Goebel Logic Programming and Artificial Intelligence Group Computer Science Department University of Waterloo Waterloo, Ontario, CANADA N2L 3G1 UUCP: {decvax,ihnp4,allegra}!watmath!water!rggoebel CSNET: rggoebel%water@waterloo.csnet ARPA: rggoebel%water%waterloo.csnet@csnet-relay.arpa
debray@sbcs.UUCP (Saumya Debray) (07/22/85)
> There are people in our department who maintain that PROLOG is not first > order *logic* since it relies on features like the ordering of clauses, > and the ordering of goals within a clause. > -- > Dave Berry. CS postgrad, Univ. of Edinburgh "Pure" Prolog has a well-defined semantics in terms of first order logic (e.g. see [van Emden & Kowalski, JACM v.23 #4 1976], [Apt & van Emden, JACM v.29 #3 1982]). Relying on a specific clause order for resolution, as Prolog does, loses completeness but not soundness, i.e. at worst, Prolog may loop on a query although a refutation exists. It turns out (as Apt & van Emden show in their proof of completeness of SLD-resolution) that the order in which literals are selected for resolution is irrelevant for completeness _as_long_as_ the clauses to be resolved against can be chosen nondeterministically. It is possible, however, to lose the logical semantics once "not" is thrown in, unless you're careful about variables inside negations. -- Saumya Debray SUNY at Stony Brook uucp: {allegra, hocsd, philabs, ogcvax} !sbcs!debray arpa: debray%suny-sb.csnet@csnet-relay.arpa CSNet: debray@sbcs.csnet
kyukawa@water.UUCP (Keitaro Yukawa) (07/22/85)
Note that Randy Goebel wrote:
The semantics of pure Prolog.....
Clearly he is referring to model theoretic or fixpoint semantics;
he mentions neither proof theory nor implementation.
Kei Yukawa
Logic Programming and Artificial Intelligence Group
University of Waterloodb@cstvax.UUCP (Dave Berry) (07/23/85)
In article <697@water.UUCP> rggoebel@water.UUCP (Randy Goebel LPAIG) writes: >> Can someone clear something up for me? I would have thought that Prolog >> was *not* "strictly first order logic," because of the existence of >> predicates like "call" and "=.."... > >The semantics of pure Prolog is well understood from a first order viewpoint >(e.g., see John Lloyd's book ``The Foundations of Logic Programming'', >Springer-Verlag, 1984). There are people in our department who maintain that PROLOG is not first order *logic* since it relies on features like the ordering of clauses, and the ordering of goals within a clause. -- Dave Berry. CS postgrad, Univ. of Edinburgh ...mcvax!ukc!{hwcs,kcl-cs}!cstvax!db