PrimitiveExample.cc

Go to the documentation of this file.

/*
 * PrimitiveExample.cc
 *
 * Example code showing how declare a C++ method so that it can
 * be called from scheme.
 *
 * Copyright (C) 2009 Linas Vepstas
 */


#include <opencog/atomspace/AtomSpace.h>
#include <opencog/guile/SchemeEval.h>
#include <opencog/guile/SchemePrimitive.h>

using namespace opencog;

// Some example class
class MyTestClass
{
    private:
        AtomSpace *_as;
        int _id;  // some value in the instance
    public:

        MyTestClass(AtomSpace* as, int id) : _as(as), _id(id) {}

        // An example method -- accepts a handle, and wraps it
        // with a ListLink.
        Handle my_func(Handle h)
        {
            Handle hlist;
            Type t = h->getType();
            if (classserver().isA(t, NODE))
            {
                NodePtr n = NodeCast(h);
                std::string name = n->getName();
                printf("Info: my_func instance %d received the node: %s\n",
                       _id, name.c_str());
                hlist = _as->add_link(LIST_LINK, h);
            }
            else
            {
                printf("Warning: my_func instance %d called with invalid handle\n", _id);
            }
            return hlist;
        }

        Handle my_other_func(Handle h)
        {
            throw (RuntimeException(TRACE_INFO, "I threw an exception %d", _id));
            return Handle::UNDEFINED;
        }
};

int main ()
{
    // Need to access the atomspace to get it to initialize itself.
    AtomSpace* as = new AtomSpace();

    // Do this early, so that guile is initialized.
    SchemeEval* eval = new SchemeEval(as);

    printf("\nInfo: Start creating a scheme call into C++\n");

    // Create the example class, and define a scheme function,
    // named "bingo", that will call one of its methods
    MyTestClass *mtc = new MyTestClass(as, 42);
    define_scheme_primitive("bingo", &MyTestClass::my_func, mtc);

    // Now, call bingo, with a reasonable argument. Since
    // MyTestClass::my_func is expecting a handle, we better pass
    // bingo a handle.
    eval->eval("(define nnn (cog-new-node 'ConceptNode \"Hello World!\"))");
    std::string rslt = eval->eval("(bingo nnn)");
    if (eval->eval_error())
    {
        printf("Error: failed evaluation\n");
    }

    // Print the result of calling MyTestClass::my_func
    printf("Info: Result of scheme evaluation is %s", rslt.c_str());

    // Now try throwing an exception.
    define_scheme_primitive("whoops", &MyTestClass::my_other_func, mtc);

    rslt = eval->eval("(whoops nnn)");
    if (!eval->eval_error())
    {
        printf("XXX ERROR XXX: an error should have been thrown, but wasn't!\n");
    }

    // Print the result of calling MyTestClass::my_func
    printf("Info: Intentional throw gave the following output:\n%s", rslt.c_str());

    delete eval;
    printf("\nInfo: We are done, bye!\n");
    return  0;
}