[ External Interface | The ECLiPSe Built-In Predicates | Reference Manual | Alphabetic Index ]

yield(+ToC, -FromC)

Yield control to the C/C++ main program that has invoked ECLiPSe. The arguments are used for passing data in and out.
A term.
A variable.


When ECLiPSe is used as an embedded component within an application written in C/C++, the ECLiPSe execution is conceptually a thread. Therefore, a yield-resume control flow model is used. On the C/C++ side, the ec_resume()/EC_resume() functions pass control to the ECLiPSe thread, while on the ECLiPSe side, the yield/2 predicate is used to pass control back. Data can be passed both ways: the ToC argument of yield/2 is passed to C/C++ via the second argument of ec_resume()/EC_resume() when it returns. Similarly a ec_resume()/EC_resume() first argument is passed to ECLiPSe as the FromC argument of yield/2.

This mechanism is supposed to be used such that an ECLiPSe server loop is set up, and the host program resumes ECLiPSe repeatedly to have a request served.

Note that, by default, ECLiPSe is set up as a server which calls posted goals. This is such a general mechanism that it is often not necessary to write a special-purpose server loop.

Modes and Determinism


    % ECLiPSe server code
    start_server :-

    eclipse_server(PrevResult) :-
        yield(PrevResult, Request),
        process_request(Request, NewResult),

    // C++ client code
    if (EC_resume() == EC_yield)
	    // create a request
            if (EC_resume(request, result) != EC_yield);
            // use the result

See Also

xget / 3, xset / 3