Ciao-users May 2003

ciao-users@cliplab.org

12 participants
18 discussions

Re: "Printing" a term to a string
by Richard A. O'Keefe 13 May '03

13 May '03

Armin Rigo <arigo(a)tunes.org> wrote: However, the stream concept of all Prolog implementations I know seems very old-fashioned to me; doesn't any give the user a way to define his own streams (i.e. objects that would be usable in lieu of streams in the built-in predicates, but whose byte-level read and write operations are user-defined predicates) ? That would nicely solve this and other problems. Quintus Prolog has *serious* (but *SERIOUS*) support for just that. I should know, I designed it. More than 10 years ago. The main motivation was porting. The IBM mainframe operating systems MVS and CMS have record-oriented file systems which are different from each other and very different from UNIX. The Vax & Alpha operating system VMS has several kinds of file, and UNIX-like streams are not the normal kind of file. Mapping Prolog I/O -> C stdio -> native I/O was giving us performance costs you'd have nightmares about; we needed a reasonably adaptable interface so that you could write just a small amount of "glue" code for each host file system and then run at native speeds. However, this was also used - to read and write encrypted files - to read and write compressed files - to do character code mapping - to implement string streams - to implement socket streams ... And not just by Quintus. The I/O extension interface is fully documented in the Quintus manuals and is definitely intended for use by customers. One difference between this and what Armin Rigo suggests is that the code you plugged in for your own stream types had to be written in C. In order to suit the host file system interfaces, we had to work in terms of packed mutable arrays of bytes (NOT a Prolog data type); the user functions had to be called from C; and there had to be no possibility of backtracking or failure. The point is that unless you want I/O to be so inefficient that you'd notice it even on a 10GHz machine, you really *REALLY* don't want to be doing byte-at-a-type operations, especially because quite a lot of operating systems don't *have* byte-at-a-time interfaces. You want to work in terms of a BLOCK at a time. If the underlying system delivers a block at a time, and if you DON'T pass stream arguments around but always read from current input and write to current output, it is possible to implement get_{byte,code,char}/1 and put_{byte,code,char}/1 so that they work at close-to-C speeds, while *still* providing user extensibility. ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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Dynamic predicates
by gff＠ruc.dk 12 May '03

12 May '03

How can I include files or libraries dynamicaly in Ciao-Prolog? ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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Re: "Printing" a term to a string
by Jonathan Hodgson 12 May '03

12 May '03

I know this is going to get me into a lot of trouble. stringifying 9or atomifying) things is soemthing one needs to do a lot. Perhaps we should look into the "informal" prolog standard group. Most implmentatation provide some way to do it so we really need a simple common name and mode for it. Jonathan ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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"Printing" a term to a string
by Armin Rigo 08 May '03

08 May '03

Hello, How can I "print" a term to a string ? In other words, how can I do the equivalent of (+Term, -String) :- open(TempFileName, write, S), write_term(S, Term), close(S), file_to_string(TempFileName, String). without using a temporary file at all ? Thanks, Armin. ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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Response to provocation
by Richard A. O'Keefe 06 May '03

06 May '03

I really have better things to do than to respond to provocation, but here goes. Richard has been advocating for ages the writing of steadfast predicates: he could be named the prophet of steadfastness. That does not mean that I have lost all vestiges of common sense. I repeat: I have advocated that *exported* predicates be steadfast. So, when Richard writes in a public forum a predicate that does not look steadfast, he should expect remarks. I was explicitly *sketching* an implementation of *one* predicate, namely between/3. It was obvious to any reader with kindergarten-level reading and conversational skills that between1/3 was part of that sketch. Some trouble was in fact taken to ensure that the predicate which was the topic of the message was steadfast. # Bart, as usual, you make such fuzz out of nothing, but actually, # you are right, between_aux/3 is not steadfast. Here is a # steadfast version: The thing is that for a predicate which is intended to be called in only one place, there is no *point* in adding overheads just to satisfy a criterion which isn't really relevant. It never occurred to me that Bart Demoen was yanking my chain. His second answer uses the "official definition of steadfastness". That definition was written at a moment that there was no standard about Prolog modules and where Prolog systems with modules typically allowed to bypass the intended hiding of non-exported predicates: Well, no. between/3 goes back to DEC-10 Prolog. Now in old DEC-10 compiled Prolog a predicate really was not visible outside its module unless you explicitly said so. (Old DEC-10 Prolog basically had the "assembler" model of name control.) Unfortunately, the file system where I keep some of this stuff suddenly disappeared this morning, so I can't quote chapter and verse. What is more, even when "The Craft of Prolog" was written, it was written in the context of Dave Bowen's XREF program (which he had adapted to Quintus Prolog), so that despite the module overriding that had been provided for the sake of the debugger, one could be quite sure that there were no *static* calls to a private predicate. (XREF goes back to DEC-10 Prolog.) To be sure, one could not be sure about dynamic calls using call/1 (although XREF did quite a good job of tracing those too), but then a dynamic call using call/1 could replace the entire module with anyone you please, as could a static call to compile/1. One of the key steps that should have been required as part of the standardisation process for ISO Prolog (and even more so for ISO Prolog modules) is the production of a version of XREF (or XREF-like functionality) working with ISO syntax and semantics. If I were rewriting The Craft of Prolog, I think that "how to use XREF" and "how to build an XREF" would not just deserve mention (as, to my regret, they were not mentioned), they would deserve an entire chapter. ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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Re: [mail@krauskopf-rainer.de: functions in Ciao Prolog]
by Richard A. O'Keefe 05 May '03

05 May '03

Bart Demoen made a petty criticism of between_aux/3 in my sample implementation of between/3. He continues: Conclusion: between_aux/3 is _not_ steadfast. The invariant that _your_ code imposes, can be violated by others in the same module. Steadfastness is all about the INTERFACE seen by USERS of modules. The point is that to the extent practical, users of Prolog modules should see predicates that act logically; when that doesn't make sense (predicates that are supposed to change the state, for example) they should still see predicates that are "clean" in whatever sense is appropriate. It is entirely commonplace for modules in all sorts of languages to have internal operations which *could* do bad things but *don't* because the rest of the module ensures that they are never called in bad ways. It is important that beween/3 should be steadfast, because it is an exported predicate. It is important that between_aux/3 should be steadfast-in-context. For this purpose, it is idle chatter to talk about what other predicates in the module COULD do; they don't. Yes, a change to the module could introduce a bad call. But a change to the module could erase all the files on your disc. The module this is drawn from is 99 SLOC. between_aux/3 (actually called between1/3 in the code) is *documented* as being an internal part of between/3 and aside from recursive calls is called in precisely one place. It is precisely as steadfast as it needs to be. One thing I've often wished for in Prolog generally is the ability to make one or more predicates private to another predicate or predicates. In my early days at Edinburgh, I used to indent my code to depict the nesting that I would have liked. In a functional language, I'd write let <local defs> in <public defs> end so let's rewrite between/3 like this: :- let. between_aux(L, U, X) :- ( L =:= U -> X = L ; X = L ; M is 1 + M, between_aux(M, U, X) ). :- in. between(L, U, X) :- ( integer(L), integer(U) -> ( integer(X) -> L =< X, X =< U ; var(X) -> L =< U, between_aux(L, U, X) ; <<diagnose and report type failure in X>> ) ; integer(L), var(U), integer(X), X < L -> fail ; integer(U), var(L), integer(X), X > U -> fail ; <<diagnose and report type error or instantiation fault>> ). :- end. Think of the :-let part as a "mini module" which can only be imported by the :-in part. Let's look at the official definition of steadfastness, on page 96 of The Craft of Prolog: 'We want our predicates to be "constant, firm, unwavering" about giving the right answers; we call the property of refusing to give wrong answers even when the query has an unexpected form (typically, as here, supply values for what we normally think of as [outputs]) _steadfastness_ and say that a good predicate is _steadfast_.' Yes, there's a typo in there. [outputs] reads 'inputs', which doesn't make sense. 'outputs' is what it _should_ say. Now, since between_aux/3 is a private predicate of a module, ALL THE CALLS TO IT ARE KNOWN. Queries of "unexpected form" do not arise, so on a strict construal between_aux/3 is trivially steadfast. If someone wants to get picky about whether an encapsulated predicate with only one call is "steadfast" according to some other definition, well, let them. It doesn't matter. The *point* of encapsulating things in modules is to give us the freedom to concentrate interface issues (like argument checking and steadfastness in general) in interface predicates, and to strip purely internal predicates to just the aspects they need to do their highly constrained job. ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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Re: [mail@krauskopf-rainer.de: functions in Ciao Prolog]
by Bart Demoen 01 May '03

01 May '03

> > between_aux(L, L, L) :- !. > > what happened to steadfast code ? > > It _is_ steadfast. Or rather, it's a private _part_ of a steadfast predicate. Conclusion: between_aux/3 is _not_ steadfast. The invariant that _your_ code imposes, can be violated by others in the same module. Bart Demoen ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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Re: [mail@krauskopf-rainer.de: functions in Ciao Prolog]
by Richard A. O'Keefe 01 May '03

01 May '03

Bart Demoen <Bart.Demoen(a)cs.kuleuven.ac.be> asked: > between_aux(L, L, L) :- !. what happened to steadfast code ? It _is_ steadfast. Or rather, it's a private _part_ of a steadfast predicate. between_aux/3 is not an exported predicate, it's only called by between/3, which ensures that the 3rd argument is a variable before the call. ============================================================================== Message: Address: Action: help majordomo(a)clip.dia.fi.upm.es Info. on useful commands subscribe ciao-users-request(a)clip.dia.fi.upm.es Subscribe to this list unsubscribe ciao-users-request(a)clip.dia.fi.upm.es Unsubscribe from this list <whatever> ciao-users(a)clip.dia.fi.upm.es Send message to list ----------------------------------------------------------------------------- Archived messages: http://www.clip.dia.fi.upm.es/Mail/ciao-users/ -----------------------------------------------------------------------------

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Ciao-users May 2003