Re: Loading database from string (C API)

2013/12/6 Edd Barrett <[email protected]>

> Hi,
>
> I am writing a VM which embeds SWI-prolog using the C interface (I am
> actually calling the SWI C interface via Python-CFFI, but it is all the
> same).
>
> I need to be able to parse Prolog source code (in a C string) into the
> Prolog
> database. Looking at the FFI documentation [1] I don't see an obvious way
> to do
> this. I guess one way is to write the Prolog source code to a file and
> construct a query to consult/1.
>
> Maybe it is possible to write the code to a memory file and use load_file/2
> to load from a stream, but that seems convoluted too.
>
> Is there a better way?
>
>
I think you could benefit from using the C++ interface: for instance, here
is how I load code from memory (Qt resources, mostly)

bool SwiPrologEngine::in_thread::named_load(QString n, QString t, bool
silent_yn) {
    try {
        PlTerm cs, s, opts;
        if (    atom_codes(A(t), cs) &&
                open_chars_stream(cs, s)) {
            PlTail l(opts);
            l.append(stream(s));
            if (silent_yn)
                l.append(silent(A("true")));
            l.close();
            bool rc = load_files(A(n), opts);
            close(s);
            return rc;
        }
    }
    catch(PlException ex) {
        qDebug() << t2w(ex);
    }
    return false;
...

I get such a natural interface with a bit of syntax sugar, found in
PREDICATE.h <https://github.com/CapelliC/pqConsole/blob/master/PREDICATE.h>
Just declare as visible to working scope what symbols you need to access

structure1(stream)
structure1(silent)

predicate2(atom_codes)
predicate2(open_chars_stream)
predicate2(load_files)
predicate1(current_module)
predicate1(close)

bye Carlo


Thanks
>
> P.S. Typo in documentation:
> "security riscs" -> "security risks"
> http://www.swi-prolog.org/pldoc/man?section=memory-files
>
> [1] http://www.swi-prolog.org/pldoc/man?section=foreign
> --
> Best Regards
> Edd Barrett
>
> http://www.theunixzoo.co.uk
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