To define the provision relation, which determines which properties can be held by which objects.

§1. Assertions assigning properties ("A scene has a time called the expected duration") generate propositions which assert that a subject, here "scene", provides a property, here "expected duration". The relation needed is:

Global knowledge variable definitions3 +=

binary_predicate *R_provision = NULL;

§2. Family. There is just one provision relation, which is the only member of its family.

bp_family *provision_bp_family = NULL;

void ProvisionRelation::start(void) {
    provision_bp_family = BinaryPredicateFamilies::new();
    METHOD_ADD(provision_bp_family, STOCK_BPF_MTID, ProvisionRelation::stock);
    METHOD_ADD(provision_bp_family, TYPECHECK_BPF_MTID, ProvisionRelation::typecheck);
    METHOD_ADD(provision_bp_family, ASSERT_BPF_MTID, ProvisionRelation::assert);
    METHOD_ADD(provision_bp_family, SCHEMA_BPF_MTID, ProvisionRelation::schema);
    METHOD_ADD(provision_bp_family, DESCRIBE_FOR_INDEX_BPF_MTID,
        ProvisionRelation::describe_for_index);
}

§3. Initial stock. There's just one relation of this kind, and it's hard-wired in. The terms are given a very broad range of what they can accept.

void ProvisionRelation::stock(bp_family *self, int n) {
    if (n == 1) {
        R_provision =
            BinaryPredicates::make_pair(provision_bp_family,
                BPTerms::new(NULL), BPTerms::new(NULL),
                I"provides", NULL, NULL, NULL,
                PreformUtilities::wording(<relation-names>, PROVISION_RELATION_NAME));
        BinaryPredicates::set_index_details(R_provision, "value", "property");
    }
}

§4. Typechecking. Any property can in principle be assigned to any inference subject, so there's really no restriction on the left term. The right term, of course, has to be a value property. It's surprisingly tricky to provide a good problem message for the case where an either-or property has been quoted because that will have been read adjectivally, so that term 1 here will be a variable ranging over some kind (usually object) which might or might not have the either-or property: in effect, X provides open is read as X provides something open. But we can't see the whole proposition here, so we just have to make a guess at what might be a good problem message.

int ProvisionRelation::typecheck(bp_family *self, binary_predicate *bp,
    pcalc_term *terms, kind **kinds_of_terms, kind **kinds_required, tc_problem_kit *tck) {
    if (Kinds::get_construct(kinds_of_terms[1]) == CON_property) return ALWAYS_MATCH;
    if ((terms[1].variable >= 0) && (Kinds::eq(kinds_of_terms[1], K_object))) {
        Problems::quote_kind(4, kinds_of_terms[1]);
        StandardProblems::tcp_problem(_p_(PM_BadProvidesEO), tck,
            "that asks whether something provides something, and in Inform 'to provide' "
            "means that an object (or value) has a property attached - for instance, "
            "containers provide the property 'carrying capacity'. But it has to be "
            "a property with a value, not an either-or property like 'open' or 'lighted'. "
            "This doesn't seem to be a property with a value.");
    } else {
        Problems::quote_kind(4, kinds_of_terms[1]);
        StandardProblems::tcp_problem(_p_(PM_BadProvides), tck,
            "that asks whether something provides something, and in Inform 'to provide' "
            "means that an object (or value) has a property attached - for instance, "
            "containers provide the property 'carrying capacity'. But it has to be "
            "a property with a value. Here, what comes after 'provides' is %4 "
            "rather than the name of a property with a value.");
    }
    return NEVER_MATCH;
}

§5. Assertion. If we assert that, say, vehicles provide "colour", then we are implicitly enabling adjectives formed from its enumerated instances — say, "green" or "blue" — can apply to vehicles, so we must make sure any such meanings are defined.

int ProvisionRelation::assert(bp_family *self, binary_predicate *bp,
        inference_subject *infs0, parse_node *spec0,
        inference_subject *infs1, parse_node *spec1) {
    property *prn = Rvalues::to_property(spec1);
    if ((infs0) && (prn)) {
        PropertyPermissions::grant(infs0, prn, TRUE);
        Instances::update_adjectival_forms(prn);
        return TRUE;
    }
    return FALSE;
}

§6. Compilation. Run-time is too late to change which objects provide what, so this relation can't be changed at compile time.

int ProvisionRelation::schema(bp_family *self, int task, binary_predicate *bp,
    annotated_i6_schema *asch) {
    if (task == TEST_ATOM_TASK) return RTProperties::test_provision_schema(asch);
    return FALSE;
}

§7. Problem message text. Nothing special is needed here.

void ProvisionRelation::describe_for_index(bp_family *self, OUTPUT_STREAM,
    binary_predicate *bp) {
    WRITE("provision");
}