It’s also a basic characteristic of Prolog module systems that each module have a unique identity (an atom). This is the most basic characteristic of an object in any OOP language. How is the OOP notion of a prototype materialized by a Prolog module? Let’s consider the defining characteristics of a prototype one-by-one: Identity It turns out that modules systems define a simple, limited, prototype-based OOP language. Self and JavaScript) instead of class-based. But OOP can also be declarative (as exemplified by Logtalk) and OOP languages can also be prototype-based (e.g. This often leads to the idea that Prolog modules are fundamentally distinct from objects. There is a partial but widespread view of not only OOP being a synonymous of imperative OOP but also OOP languages being a synonymous of class-based languages. But what modules are is a function of their characteristics, not a function of their design intentions 1. It is not the case that the creators of Prolog module systems intended to create an object-oriented extension to Prolog. From past experience, it will also annoy some Prolog practitioners. The full name would be “Logtalk idiom for deterministic finally”.Prolog modules are objects. Shielded Logtalk idiom is not yet practically tested. unshield/1 reverts shield/1, I didn’t find it yet I guess it corresponds to sig_atomic/1 in SWI-Prolog and sys_atomic/1 Protect an awaitable object from being cancelled. Shield/1 is a new meta predicate inspired by Python: Proposal how to extend the Logtalk idiom by atomicity: shield(Ĭatch(unshield(read_term(Input, Term, Options)), Error, So why is catch/3įaster? Maybe it has to do with the atomicity of the setup. Not figure out determinism only at runtime.īut catch/3 has a similar bookkeeping problem. That would infer some determinism information at compile time, and You could only make it faster with some Mercury compilation techniques, In some bookkeeping for the case when the goal is non-deterministic. It detects that its goal argument is deterministic, it has already wasted time Unless setup_call_cleanup/3 can be made faster.īut I don’t think that setup_call_cleanup/3 can be made faster, because when Here and then by other Prolog systems, that have setup_call_cleanup/3, That it is probably faster could be a motivation to adopt the Logtalk idiom Currently setup_call_cleanup/3 is buggy in Is probably one of the few cases where this matters.Īnd it also matters for Prolog systems that don’t have a working % 6,000,000 inferences, 0.500 CPU in 0.497 seconds (101% CPU, 12000000 Lips)įindall/3 with a fast generator and just a couple solutions I can measure right now: /* N215 Solution */ Idiom, since catch/3 seems to be still faster. The SWI-Prolog findall/3 could possibly get a speed-up by using the Logtalk Also the atomicity problem needs to be solved. But if catch/3 is slower than setup_call_cleanup/3, then Setup_call_cleanup/3 is currently used in findall/3: findall(Templ, Goal, List, Tail) :-īut the findall_loop/4 is deterministic. It is mostly useful to discover that your application does not close all streams. SWI-Prolog currently allows closing streams by GC if the flag agc_close_streams is set to true. As I have discovered, GC also comes with the problem that in case of an error there is no good place for delivering the exception. The downside is that notably file handles come in limited numbers and sometimes need to be closed before we can do the next step (notably on Windows to avoid sharing violations). That was proposed by Joachim if I recall correctly. The only sensible alternative is to leave resource cleanup to GC. Performance-wise, the call_cleanup/2 family is about the same as catch/3. I infrequently use setup_call_catcher_cleanup/4, mainly in cases where I do not want to cleanup in case of success. However, you cannot deal with non-determinism. You can deal with an exception in the goal as well as success or failure. Think of the reasons that setup_call_catcher_cleanup/4 provides. Still, getting resources cleaned regardless of how the accessing predicate finishes cannot be done. Ok, it also does not defined interrupts, so that is solved. ISO Prolog just doesn’t have a answer to this. This was considered insufficient as interrupts may happen between creating the resource and entering the call_cleanup/2. The origin comes (AFAIK) from SICStus that has call_cleanup/2. I think the idea should be to use setup_call_cleanup/3 as the “standard” and implement that as good as you can on each system.
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