Spatial Model

A feature which constructs the fundamental spatial model used by IF, to represent containment, support, carrying, wearing, and incorporation.

§1. Introduction. The "spatial model" is the aspect of the IF model world which represents containment, support, carrying, wearing, and incorporation; say, a button which is part of a shirt which is in a tumble-drier which is in a room called the Laundry, where there's also a man carrying a box of washing powder and wearing a dressing gown. That's quite a lot of concepts, but note that it doesn't include the geographical model of directions, the map, regions, and so on.

void Spatial::start(void) {
    SpatialInferences::create();

    PluginCalls::plug(CREATE_INFERENCE_SUBJECTS_PLUG, Spatial::create_inference_subjects);
    PluginCalls::plug(NEW_BASE_KIND_NOTIFY_PLUG, Spatial::new_base_kind_notify);
    PluginCalls::plug(ACT_ON_SPECIAL_NPS_PLUG, Spatial::act_on_special_NPs);
    PluginCalls::plug(COMPLETE_MODEL_PLUG, Spatial::IF_complete_model);
    PluginCalls::plug(DEFAULT_APPEARANCE_PLUG, Spatial::default_appearance);
    PluginCalls::plug(NAME_TO_EARLY_INFS_PLUG, Spatial::name_to_early_infs);
    PluginCalls::plug(NEW_SUBJECT_NOTIFY_PLUG, Spatial::new_subject_notify);
    PluginCalls::plug(NEW_PROPERTY_NOTIFY_PLUG, Spatial::new_property_notify);
    PluginCalls::plug(PARSE_COMPOSITE_NQS_PLUG, Spatial::parse_composite_NQs);
    PluginCalls::plug(SET_KIND_NOTIFY_PLUG, Spatial::set_kind_notify);
    PluginCalls::plug(SET_SUBKIND_NOTIFY_PLUG, Spatial::set_subkind_notify);
    PluginCalls::plug(INTERVENE_IN_ASSERTION_PLUG, Spatial::intervene_in_assertion);
}

§2. Kinds of interest. These are kind names to do with spatial layout which Inform provides special support for; it recognises the English name when defined by the Standard Rules. (So there is no need to translate this to other languages.)

<notable-spatial-kinds> ::=
    room |
    thing |
    container |
    supporter |
    person |
    player's holdall

This is Preform grammar, not regular C code.

§3.

kind *K_room = NULL;
kind *K_thing = NULL;
kind *K_container = NULL;
kind *K_supporter = NULL;
kind *K_person = NULL;
kind *K_players_holdall = NULL;

§4.

int Spatial::new_base_kind_notify(kind *new_base, text_stream *name, wording W) {
    if (<notable-spatial-kinds>(W)) {
        switch (<<r>>) {
            case 0: K_room = new_base; return TRUE;
            case 1: K_thing = new_base; return TRUE;
            case 2: K_container = new_base; return TRUE;
            case 3: K_supporter = new_base; return TRUE;
            case 4: K_person = new_base; return TRUE;
            case 5: K_players_holdall = new_base; return TRUE;
        }
    }
    return FALSE;
}

§5. When the rest of Inform makes something a room, for instance in response to an explicit sentence like "The Hall of Mirrors is a room.", we take notice; if it turns out to be news, we infer is_room_inf with certainty.

int Spatial::set_kind_notify(instance *I, kind *k) {
    kind *kw = Instances::to_kind(I);
    if ((!(Kinds::Behaviour::is_object_of_kind(kw, K_room))) &&
        (Kinds::Behaviour::is_object_of_kind(k, K_room)))
        SpatialInferences::infer_is_room(Instances::as_subject(I), CERTAIN_CE);
    return FALSE;
}

§6. Nothing in the core Inform language prevents room from being made a kind of vehicle, and so on, but this would cause mayhem in the model world. So:

int Spatial::set_subkind_notify(kind *sub, kind *super) {
    if ((sub == K_thing) && (super != K_object)) {
        if (problem_count == 0)
            StandardProblems::sentence_problem(Task::syntax_tree(), _p_(PM_ThingAdrift),
                "'thing' is not allowed to be a kind of anything (other than "
                "'object')",
                "because it's too fundamental to the way Inform uses rooms "
                "and things to model the physical world.");
        return TRUE;
    }
    if ((sub == K_room) && (super != K_object)) {
        if (problem_count == 0)
            StandardProblems::sentence_problem(Task::syntax_tree(), _p_(PM_RoomAdrift),
                "'room' is not allowed to be a kind of anything (other than "
                "'object')",
                "because it's too fundamental to the way Inform uses rooms "
                "and things to model the physical world.");
        return TRUE;
    }
    if (((sub == K_container) && (super == K_supporter)) ||
        ((sub == K_supporter) && (super == K_container))) {
        if (problem_count == 0)
            StandardProblems::sentence_problem(Task::syntax_tree(), _p_(PM_ContainerAdrift),
                "'container' and 'supporter' are not allowed to be kinds "
                "of each other",
                "because they're too fundamental to the way Inform models the "
                "physical world. Both are kinds of 'thing', but they are "
                "different, and no object is allowed to belong to both at once.");
        return TRUE;
    }
    return FALSE;
}

§7. This tests whether an object is an instance of "room":

int Spatial::object_is_a_room(instance *I) {
    if ((K_room) && (I) && (Instances::of_kind(I, K_room))) return TRUE;
    return FALSE;
}

§8. This is where we give Inform the numbers it needs to write the "a world with 5 rooms and 27 things"-style text in a successful report on its run.

void Spatial::get_world_size(int *rooms, int *things) {
    instance *I;
    *rooms = 0; *things = 0;
    LOOP_OVER_INSTANCES(I, K_room) (*rooms)++;
    LOOP_OVER_INSTANCES(I, K_thing) (*things)++;
}

§9. We also need inference subjects to refer to those kinds, but there's a timing issue with that: the kinds will not exist until Inform's run is fairly advanced, since they are created by source text. We need the subjects earlier than that, and so we have to have placeholders until the real thing is ready:

inference_subject *infs_room = NULL;
inference_subject *infs_thing = NULL;
inference_subject *infs_supporter = NULL;
inference_subject *infs_person = NULL;

§10.

int Spatial::create_inference_subjects(void) {
    infs_room =      InferenceSubjects::new_fundamental(global_constants, "room(early)");
    infs_thing =     InferenceSubjects::new_fundamental(global_constants, "thing(early)");
    infs_supporter = InferenceSubjects::new_fundamental(global_constants, "supporter(early)");
    infs_person =    InferenceSubjects::new_fundamental(global_constants, "person(early)");
    return FALSE;
}

§11. And this is where those placeholders give up their places for the real kind subjects. What happens is that, ordinarily, the machinery creating objects (and kinds) will allocate a new inference structure for each object, but it first invites plugins to choose an existing one instead. (The inference_subject structure is rewritten, but pointers to it remain consistent and valid.)

int Spatial::name_to_early_infs(wording W, inference_subject **infs) {
    if (<notable-spatial-kinds>(W)) {
        switch (<<r>>) {
            case 0: if (K_room == NULL) *infs = infs_room; break;
            case 1: if (K_thing == NULL) *infs = infs_thing; break;
             container isn't an early case, surprisingly
            case 3: if (K_supporter == NULL) *infs = infs_supporter; break;
            case 4: if (K_person == NULL) *infs = infs_person; break;
        }
    }
    return FALSE;
}

§12. Properties of interest.

property *P_initial_appearance = NULL;
property *P_wearable = NULL;
property *P_fixed_in_place = NULL;

property *P_component_parent = NULL;
property *P_component_child = NULL;
property *P_component_sibling = NULL;
property *P_worn = NULL;
property *P_mark_as_room = NULL;
property *P_mark_as_thing = NULL;
property *P_container = NULL;
property *P_supporter = NULL;
property *P_matching_key = NULL;

§13. These are property names to do with spatial layout which Inform provides special support for; it recognises the English names when they are defined by the Standard Rules. (So there is no need to translate this to other languages.)

"Matching key" has to appear in here because it both has a traditional I6 name and is used as relation storage. If we didn't care about it being called with_key in the I6 source code, we wouldn't need to do anything special with it at all.

<notable-spatial-properties> ::=
    initial appearance |
    wearable |
    fixed in place |
    matching key

This is Preform grammar, not regular C code.

§14.

int Spatial::new_property_notify(property *prn) {
    if (<notable-spatial-properties>(prn->name)) {
        switch (<<r>>) {
            case 0: P_initial_appearance = prn; break;
            case 1: P_wearable = prn; break;
            case 2: P_fixed_in_place = prn; break;
            case 3: P_matching_key = prn;
                Properties::set_translation(P_matching_key, U"with_key");
                break;
        }
    }
    return FALSE;
}

§15. Spatial data on instances. Every inference subject contains a pointer to its own unique copy of the following structure, though we really only use it for instance subjects, which correspond to the objects in the world model.

An important concept here is the "progenitor" of something in the model, which may be NULL: the "progenitor" is the object which immediately contains, carries, wears, supports or incorporates it.

define SPATIAL_DATA(I) FEATURE_DATA_ON_INSTANCE(spatial, I)

typedef struct spatial_data {
     fundamental spatial information about an object's location
    struct instance *progenitor;
    struct parse_node *progenitor_set_at;
    int part_flag;  is this a component part of something else?
    int here_flag;  was this declared simply as being "here"?

     temporary storage needed when compiling spatial data to Inter
    struct instance *object_tree_parent;  in/on/worn by/carried by tree structure
    struct instance *object_tree_child;
    struct instance *object_tree_sibling;
    struct instance *incorp_tree_parent;  part-of tree structure
    struct instance *incorp_tree_child;
    struct instance *incorp_tree_sibling;
    int definition_depth;

    CLASS_DEFINITION
} spatial_data;

The structure spatial_data is private to this section.

§16. The attachment of this data is done here:

int Spatial::new_subject_notify(inference_subject *subj) {
    spatial_data *sd = CREATE(spatial_data);
    sd->progenitor = NULL; sd->progenitor_set_at = NULL;
    sd->part_flag = FALSE; sd->here_flag = FALSE;
    sd->object_tree_parent = NULL; sd->object_tree_child = NULL; sd->object_tree_sibling = NULL;
    sd->incorp_tree_child = NULL; sd->incorp_tree_sibling = NULL; sd->incorp_tree_parent = NULL;
    sd->definition_depth = 0;
    ATTACH_FEATURE_DATA_TO_SUBJECT(spatial, subj, sd);
    return FALSE;
}

§17. Spatial gets to decide here what raw text following a new object will be taken to mean: for scenery it will be the "description" (i.e., the text produced on examining), for any other thing it will be the "initial appearance".

int Spatial::default_appearance(inference_subject *infs, parse_node *txt) {
    if (InferenceSubjects::is_within(infs, KindSubjects::from_kind(K_object))) {
        property *set_prn = P_description;
        if (InferenceSubjects::is_within(infs, KindSubjects::from_kind(K_thing))) {
            instance *I = InstanceSubjects::to_object_instance(infs);
            if ((I) && (Backdrops::object_is_scenery(I))) {
                inference *inf;
                KNOWLEDGE_LOOP(inf, infs, property_inf) {
                    property *prn = PropertyInferences::get_property(inf);
                    if (((prn) && (Inferences::get_certainty(inf) > 0)) &&
                        (prn == P_description)) {
                        Produce a problem for doubly described scenery17.1;
                        return TRUE;
                    }
                }
            } else set_prn = P_initial_appearance;
        }
        ValueProperties::assert(set_prn, infs, txt, CERTAIN_CE);
        return TRUE;
    }
    return FALSE;
}

§17.1. A lone string as a sentence is a description for a room, but an initial description for an object. Only now can we know which, since we have only just decided whether I is a room or not. We therefore draw the necessary inference.

Produce a problem for doubly described scenery17.1 =

    StandardProblems::object_problem(_p_(PM_SceneryDoublyDescribed),
        I,
        "is scenery, which means that it cannot sensibly have any 'initial "
        "appearance' property - being scenery, it isn't announced when the "
        "player first sees it. That means the quoted text about it has to "
        "be read as its 'description' instead, seen when the player examines "
        "it. But the source text writes out its description, too",
        "which means we have a subtle little contradiction here.");

This code is used in §17.

§18. Composite noun-quantifiers. Words like "something" or "everywhere" combine a common noun — thing, and implicitly room — with a determiner — one thing, all rooms.

"Nothing" is conspicuously absent from the possibilities below. It gets special treatment elsewhere since it can also double as a value (the "not an object" pseudo-value).

<spatial-specifying-nouns> ::=
    _something/anything *** |               ==> { -, K_thing }
    _somewhere/anywhere *** |               ==> { -, K_room }
    _someone/anyone/somebody/anybody *** |  ==> { -, K_person }
    _everything *** |                       ==> { -, K_thing, <<quantifier:q>> = for_all_quantifier }
    _everywhere *** |                       ==> { -, K_room, <<quantifier:q>> = for_all_quantifier }
    _everyone/everybody *** |               ==> { -, K_person, <<quantifier:q>> = for_all_quantifier }
    _nowhere *** |                          ==> { -, K_room, <<quantifier:q>> = not_exists_quantifier }
    _nobody/no-one *** |                    ==> { -, K_person, <<quantifier:q>> = not_exists_quantifier }
    _no _one ***                            ==> { -, K_person, <<quantifier:q>> = not_exists_quantifier }

This is Preform grammar, not regular C code.

§19. When we detect them, we set both quantifier_used and some_kind appropriately. None can be recognised if the basic kinds are not created yet, which we check for by inspecting K_thing. (Note that the S-parser may indeed be asked to parse "something" before this point, as when it scans the domains of adjective definitions, but that it's okay that it produces a null result.)

With the "some-" words, no quantifier is set because the meaning here is the exists_quantifier. Since this is the default behaviour for unquantified descriptions anyway — "a door is in the Great Hall" means that such a door exists — we needn't set the variable.

int Spatial::parse_composite_NQs(wording *W, wording *DW,
    quantifier **quant, kind **some_kind) {
    if (K_thing) {
        <<quantifier:q>> = NULL;
        if (<spatial-specifying-nouns>(*W)) {
            *W = Wordings::from(*W,
                Wordings::first_wn(GET_RW(<spatial-specifying-nouns>, 1)));
            *quant = <<quantifier:q>>; *some_kind = <<rp>>;
            return TRUE;
        }
    }
    return FALSE;
}

§20. Nowhere. This means the same as "nothing", in a noun context, but we annotate a parse node using this wording in order to produce better problem messages if need be.

<notable-spatial-noun-phrases> ::=
    nowhere

This is Preform grammar, not regular C code.

§21.

int Spatial::act_on_special_NPs(parse_node *p) {
    if ((<notable-spatial-noun-phrases>(Node::get_text(p))) &&
        (Word::unexpectedly_upper_case(Wordings::first_wn(Node::get_text(p))) == FALSE) &&
        (K_room)) {
        Refiner::give_spec_to_noun(p, Rvalues::new_nothing_object_constant());
        Annotations::write_int(p, nowhere_ANNOT, TRUE);
        return TRUE;
    }
    return FALSE;
}

§22. Now in fact this often does get picked up:

int Spatial::intervene_in_assertion(parse_node *px, parse_node *py) {
    if (Annotations::read_int(py, nowhere_ANNOT)) {
        inference_subject *left_subject = Node::get_subject(px);
        if (left_subject) {
            if (KindSubjects::to_kind(left_subject))
                StandardProblems::subject_problem_at_sentence(_p_(PM_KindNowhere),
                    left_subject,
                    "seems to be said to be 'nowhere' in some way",
                    "which doesn't make sense. An individual thing can be 'nowhere', "
                    "but here we're talking about a whole kind, and it's not allowed "
                    "to talk about general locations of a whole kind of things at once.");
            else Assert::true_about(
                Propositions::Abstract::to_put_nowhere(), left_subject, prevailing_mood);
            return TRUE;
        }
    }
    return FALSE;
}

§23. Here. A sentence like "The sonic screwdriver is here." is not copular, but instead expresses a relationship — "here" is not a value but a relation to an unstated object. That object is the room we're currently talking about, which sounds easy to work out, but isn't: we don't yet know which of the objects being talked about will eventually turn out to be rooms. As a result, "here" needs delicate handling, and its own inference type.

The fact that rooms cannot be "here" is useful, because it means Inform can with certainty read

The washing machine is here. The shirt is in the machine.

as creating a container called "washing machine", not a room.

§24.

void Spatial::infer_presence_here(instance *I) {
    inference_subject *infs = Instances::as_subject(I);
    inference *inf;
    POSITIVE_KNOWLEDGE_LOOP(inf, infs, parentage_here_inf) {
        StandardProblems::contradiction_problem(_p_(PM_DuplicateHere),
            Inferences::where_inferred(inf),
            current_sentence,
            I,
            "can only be said to be 'here' once",
            "in a single assertion sentence. This avoids potential confusion, "
            "since 'here' can mean different things in different sentences.");
    }
    SpatialInferences::infer_parentage_here(infs, CERTAIN_CE,
        Anaphora::get_current_subject());
    SpatialInferences::infer_is_room(infs, IMPOSSIBLE_CE);
}

§25. Similarly:

void Spatial::infer_presence_nowhere(instance *I) {
    SpatialInferences::infer_is_nowhere(Instances::as_subject(I), CERTAIN_CE);
    SpatialInferences::infer_is_room(Instances::as_subject(I), IMPOSSIBLE_CE);
}

§26. Completing the world model. That's enough preliminaries; time to get on with adding a sense of space to the model world.

int Spatial::IF_complete_model(int stage) {
    switch(stage) {
        case 1: Spatial::spatial_stage_I(); break;
        case 2: Spatial::spatial_stage_II(); break;
        case 3: Spatial::spatial_stage_III(); break;
        case 4: Spatial::spatial_stage_IV(); break;
        case 5: Spatial::spatial_stage_V(); break;
    }
    return FALSE;
}

§27. Recall that as we begin stage I of model creation, all objects are, of course, created, and they have kinds associated with them if the source text has said explicitly what kind they have: but that is not good enough. It often happens that the source implicitly specifies a kind, and we need to take note. If X is in Y, then Y might be a room, or a region, or a container, and we might need to look at other sentences — say, establishing that Y is the destination of a map connection — to see which.

int Spatial::spatial_stage_I(void) {
    instance *I;
    LOOP_OVER_INSTANCES(I, K_object)
        Perform kind determination for this object27.1;
    return FALSE;
}

§27.1. Our main problem in what follows is caused by "in" being so ambiguous, or perhaps it might be said that the real problem is that we choose to distinguish between rooms and containers on a world-modelling level — when it could well be argued that they are linguistically the same thing.

It means that Inform is often reading code such as:

The croquet ball is in the Boxed Set.

and not being sure whether "Boxed Set" is a container or a room.

In the following determination, we use two sources of information. One is explicit data given by the source text or unambiguously implied in it, like so —

The Boxed Set is a container. The spoon is on the low table.

which tell us the Boxed Set is certainly a container and the table certainly a supporter. This information about an object is the "designer choice" about its kind.

The other source of information comes from less definite sentences using words like "in", and from the spatial context in which the object appears. This is the "geography choice" for its kind.

Perform kind determination for this object27.1 =

    current_sentence = Instances::get_creating_sentence(I);

    kind *designers_choice = NULL;
    Determine the designer choice27.1.1;

    kind *geography_choice = NULL;
    inference *geography_inference = NULL;
    int geography_certainty = UNKNOWN_CE;
    Determine the geography choice27.1.2;

    if ((geography_choice) &&
        (Kinds::eq(geography_choice, designers_choice) == FALSE))
        Attempt to reconcile the two choices27.1.3;

    if (Kinds::eq(Instances::to_kind(I), K_object))
        Propositions::Abstract::assert_kind_of_instance(I, K_thing);

This code is used in §27.

§27.1.1. By this point, any explicit information is reflected in the hierarchy of kinds. We look out for four specialised kinds of thing, but failing that, we simply take its broadest kind — usually "thing", "room", "direction" or "region".

Determine the designer choice27.1.1 =

    kind *f = NULL;
    inference_subject *infs;
    for (infs = KindSubjects::from_kind(Instances::to_kind(I));
        infs; infs = InferenceSubjects::narrowest_broader_subject(infs)) {
        kind *K = KindSubjects::to_kind(infs);
        if (Kinds::Behaviour::is_subkind_of_object(K)) {
            f = K;
            if ((Kinds::eq(f, K_container)) ||
                (Kinds::eq(f, K_supporter)) ||
                (Kinds::eq(f, K_door)) ||
                (Kinds::eq(f, K_person)))
                designers_choice = f;
        }
    }
    if (designers_choice == NULL) designers_choice = f;

This code is used in §27.1.

§27.1.2. If there is any positive information that this is a room, that's the geography choice; otherwise it's whichever of room or container is more probably suggested by inferences.

Determine the geography choice27.1.2 =

    inference *inf;
    KNOWLEDGE_LOOP(inf, Instances::as_subject(I), contains_things_inf)
        if (Inferences::get_certainty(inf) > geography_certainty) {
            geography_choice = K_container;
            geography_certainty = Inferences::get_certainty(inf);
            geography_inference = inf;
        }
    KNOWLEDGE_LOOP(inf, Instances::as_subject(I), is_room_inf)
        if ((Inferences::get_certainty(inf) > UNKNOWN_CE) ||
            (Inferences::get_certainty(inf) > geography_certainty)) {
            geography_choice = K_room;
            geography_certainty = Inferences::get_certainty(inf);
            geography_inference = inf;
        }

This code is used in §27.1.

§27.1.3. Since the designer choice is the one currently in force, we have basically three choices here: impose the geography choice instead; do nothing; or issue a problem message. The case where we do nothing is if geography suggests something is a room, when it's actually a door: this is because sentences like "East is the Marble Portal" can suggest the "Marble Portal" is a room when it's legitimately a door.

Attempt to reconcile the two choices27.1.3 =

    parse_node *sentence_setting_kind = Instances::get_kind_set_sentence(I);
    if ((designers_choice == NULL) ||
        ((geography_certainty == CERTAIN_CE) &&
            (Kinds::Behaviour::is_object_of_kind(geography_choice, designers_choice))))
        Accept the geography choice, since it only refines what we already know27.1.3.1
    else if ((geography_certainty == CERTAIN_CE) &&
            (!((Kinds::eq(designers_choice, K_door)) &&
                (Kinds::eq(geography_choice, K_room)))))
        Issue a problem message, since the choices are irreconcilable27.1.3.2;

This code is used in §27.1.

§27.1.3.1. Accept the geography choice, since it only refines what we already know27.1.3.1 =

    LOGIF(KIND_CHANGES, "Accepting geography choice of kind of $O as %u\n",
        I, geography_choice);
    Propositions::Abstract::assert_kind_of_instance(I, geography_choice);

This code is used in §27.1.3.

§27.1.3.2. Issue a problem message, since the choices are irreconcilable27.1.3.2 =

    LOG("Choices: designer %u, geography %u.\n", designers_choice, geography_choice);
    parse_node *decider = Instances::get_creating_sentence(I);
    if (sentence_setting_kind) decider = sentence_setting_kind;
    if (Kinds::eq(designers_choice, K_person))
        Issue a problem message for implied containment by a person27.1.3.2.1
    else if ((Kinds::eq(designers_choice, K_supporter)) &&
                (Kinds::eq(geography_choice, K_container)))
        Issue a problem message for simultaneous containment and support27.1.3.2.2
    else
        Issue a more generic problem message for irreconcilable kinds27.1.3.2.3;

This code is used in §27.1.3.

§27.1.3.2.1. Issue a problem message for implied containment by a person27.1.3.2.1 =

    StandardProblems::contradiction_problem(_p_(PM_PersonContaining),
        sentence_setting_kind,
        Inferences::where_inferred(geography_inference), I,
        "cannot contain or support things like something inanimate",
        "which is what you are implying. Instead, people must carry or wear them: "
        "so 'The briefcase is in Daphne.' is disallowed, but 'The briefcase is "
        "carried by Daphne.' is fine, or indeed 'Daphne carries the briefcase.'");

This code is used in §27.1.3.2.

§27.1.3.2.2. A notorious problem message for a notorious limitation of the traditional Inform spatial model:

Issue a problem message for simultaneous containment and support27.1.3.2.2 =

    StandardProblems::contradiction_problem(_p_(PM_CantContainAndSupport),
        decider, Inferences::where_inferred(geography_inference), I,
        "cannot both contain things and support things",
        "which is what you're implying here. If you need both, the easiest way is "
        "to make it either a supporter with a container attached or vice versa. "
        "For instance: 'A desk is here. On the desk is a newspaper. An openable "
        "container called the drawer is part of the desk. In the drawer is a "
        "stapler.'");

This code is used in §27.1.3.2.

§27.1.3.2.3. Issue a more generic problem message for irreconcilable kinds27.1.3.2.3 =

    StandardProblems::contradiction_problem(_p_(PM_BothRoomAndSupporter),
        decider,
        Inferences::where_inferred(geography_inference), I,
        "would need to have two different and incompatible kinds to make both "
        "sentences true",
        "and this is a contradiction.");

This code is used in §27.1.3.2.

§28. Stage II at last. Now the kinds are all known, and it's time to work out the spatial arrangements. Inform's spatial model assigns every instance object a unique "progenitor", which may be NULL, representing the object which immediately contains, carries, wears, supports or incorporates it.

Clearly if we know every object's progenitor, then we know the whole spatial layout — it's all just elaboration from there. (See Stage III below.) But since other features can decide on this, not just Spatial, we had better provide access routines to read and write:

instance *Spatial::progenitor(instance *I) {
    if (I == NULL) return NULL;
    if (FEATURE_INACTIVE(spatial)) return NULL;
    return SPATIAL_DATA(I)->progenitor;
}

parse_node *Spatial::progenitor_set_at(instance *I) {
    if (I == NULL) return NULL;
    if (FEATURE_INACTIVE(spatial)) return NULL;
    return SPATIAL_DATA(I)->progenitor_set_at;
}

void Spatial::set_progenitor(instance *of, instance *to, inference *reason) {
    if (FEATURE_INACTIVE(spatial))
        internal_error("spatial feature inactive");
    if (to == NULL) internal_error("set progenitor of nothing");
    SPATIAL_DATA(of)->progenitor = to;
    SPATIAL_DATA(of)->progenitor_set_at =
        (reason)?Inferences::where_inferred(reason):NULL;
}

§29. This is used for error recovery only.

void Spatial::void_progenitor(instance *of) {
    if (FEATURE_INACTIVE(spatial))
        internal_error("spatial feature inactive");
    SPATIAL_DATA(of)->progenitor = NULL;
    SPATIAL_DATA(of)->progenitor_set_at = NULL;
}

§30. We need to establish what the rooms are before we worry about objects which are "here"; rooms are never "here", so there's no circularity in that, and we solve this problem by determining the kind of non-here objects before the kind of here-objects.

int Spatial::spatial_stage_II(void) {
    Set the here flag for all those objects whose parentage is only thus known30.1;
    instance *I;
    LOOP_OVER_INSTANCES(I, K_object)
        if (SPATIAL_DATA(I)->here_flag == FALSE)
            Position this object spatially30.3;
    LOOP_OVER_INSTANCES(I, K_object)
        if (SPATIAL_DATA(I)->here_flag)
            Position this object spatially30.3;
    Issue problem messages if non-physical objects are spatially enclosed30.2;
    return FALSE;
}

§30.1. Set the here flag for all those objects whose parentage is only thus known30.1 =

    instance *I;
    LOOP_OVER_INSTANCES(I, K_object) {
        SPATIAL_DATA(I)->here_flag = FALSE;
        inference *inf;
        POSITIVE_KNOWLEDGE_LOOP(inf, Instances::as_subject(I), parentage_here_inf)
            SPATIAL_DATA(I)->here_flag = TRUE;
    }

This code is used in §30.

§30.2. Issue problem messages if non-physical objects are spatially enclosed30.2 =

    instance *I;
    LOOP_OVER_INSTANCES(I, K_object) {
        if ((Spatial::progenitor(I)) &&
            (Instances::of_kind(I, K_thing) == FALSE) &&
            (Instances::of_kind(I, K_room) == FALSE) &&
            (Regions::object_is_a_region(I) == FALSE)) {
            Problems::quote_source(1, Instances::get_creating_sentence(I));
            Problems::quote_object(2, I);
            Problems::quote_object(3, Spatial::progenitor(I));
            Problems::quote_kind(4, Instances::to_kind(I));
            StandardProblems::handmade_problem(Task::syntax_tree(), _p_(PM_NonThingInModel));
            Problems::issue_problem_segment(
                "In the sentence %1, you create an object '%2' which you then seem "
                "to place in or on or as part of '%3', but the kind of '%2' is %4. "
                "Since %4 is not a kind of thing, it follows that %2 is not a thing, "
                "so it doesn't represent something physical and can't be put in spatial "
                "relationships like this. (For the same reason that you can't put "
                "'southeast', the direction, inside a kitchen cupboard.)");
            Problems::issue_problem_end();
        }
    }

This code is used in §30.

§30.3. At last we come to it: determining the progenitor, and part-flag, for the object under investigation.

Position this object spatially30.3 =

    inference *parent_setting_inference = NULL;
    Find the inference which will decide the progenitor30.3.1;
    if (parent_setting_inference) {
        instance *whereabouts =
            SpatialInferences::get_inferred_progenitor(parent_setting_inference);
        if (SPATIAL_DATA(I)->here_flag) Find the whereabouts of something here30.3.2;
        if (whereabouts) {
            Spatial::set_progenitor(I, whereabouts, parent_setting_inference);
            LOGIF(OBJECT_TREE, "Progenitor of $O is $O\n", I, whereabouts);
        }
    }
    Determine whether the object in question is a component part30.3.3;

This code is used in §30 (twice).

§30.3.1. Find the inference which will decide the progenitor30.3.1 =

    inference *inf;
    POSITIVE_KNOWLEDGE_LOOP(inf, Instances::as_subject(I), parentage_nowhere_inf)
        Make this the determining inference30.3.1.1;
    POSITIVE_KNOWLEDGE_LOOP(inf, Instances::as_subject(I), parentage_here_inf)
        Make this the determining inference30.3.1.1;
    POSITIVE_KNOWLEDGE_LOOP(inf, Instances::as_subject(I), parentage_inf)
        Make this the determining inference30.3.1.1;

This code is used in §30.3.

§30.3.1.1. Make this the determining inference30.3.1.1 =

    if (parent_setting_inference) {
        StandardProblems::contradiction_problem(_p_(PM_DuplicateParentage),
            Inferences::where_inferred(parent_setting_inference),
            Inferences::where_inferred(inf),
            I,
            "can only be given its position once",
            "in a single assertion sentence.");
    }
    parent_setting_inference = inf;

This code is used in §30.3.1 (three times).

§30.3.2. Find the whereabouts of something here30.3.2 =

    if (Spatial::object_is_a_room(whereabouts) == FALSE) whereabouts = NULL;
    if (whereabouts == NULL) {
        parse_node *here_sentence =
            Inferences::where_inferred(parent_setting_inference);
        Set the whereabouts to the last discussed room prior to this inference being drawn30.3.2.1;
        if (whereabouts == NULL) {
            current_sentence = here_sentence;
            StandardProblems::object_problem_at_sentence(_p_(PM_NoHere),
                I,
                "was described as being 'here', and there doesn't seem to be any "
                "location being talked about at this point in the source text",
                "so there's nowhere you can call 'here'.");
        }
    }

This code is used in §30.3.

§30.3.2.1. This runs through the source text from the beginning up to the "here" sentence, setting whereabouts to any rooms it finds along the way, so that when it finishes this will be set to the most recently mentioned.

Set the whereabouts to the last discussed room prior to this inference being drawn30.3.2.1 =

    SyntaxTree::traverse_up_to_ip(Task::syntax_tree(), here_sentence,
        Spatial::seek_room, (void **) &whereabouts);

This code is used in §30.3.2.

§30.3.3. Determine whether the object in question is a component part30.3.3 =

    inference *inf;
    POSITIVE_KNOWLEDGE_LOOP(inf, Instances::as_subject(I), part_of_inf) {
        if ((Spatial::object_is_a_room(I)) || (Map::instance_is_a_door(I))) {
            StandardProblems::object_problem(_p_(PM_RoomOrDoorAsPart),
                I,
                "was set up as being part of something else, which doors and rooms "
                "are not allowed to be",
                "because they are part of the fixed map of the world - if they were "
                "parts of something else, they might move around. (Of course, it's "
                "easy to make a door look as if it's part of something to the player - "
                "describing it as part of a wall, or bulkhead, or cottage, say - "
                "and if there really is an entrance that needs to move around - say, "
                "the hatchway on a tank - it's probably best to make it an enterable "
                "container.)");
        }
        SPATIAL_DATA(I)->part_flag = TRUE;
    }

This code is used in §30.3.

§31.

void Spatial::seek_room(parse_node *sent, void **v_I) {
    instance **I = (instance **) v_I;
    inference_subject *isub = Node::get_interpretation_of_subject(sent);
    instance *sub = InstanceSubjects::to_object_instance(isub);
    if (Spatial::object_is_a_room(sub)) *I = sub;
}

§32. Completing the model, stages III and IV. By the beginning of Stage III, the progenitor of every object is known, and so is whether it is a part. It's time to start work on compiling the I6 representation of all this, but unfortunately that will need to be quite a bit more complicated. So we're going to do this in two stages, the first of which is to construct a pair of object trees as an intermediate state.

We have a main object tree, in fact a forest (i.e., it's probably disconnected), to represent containment, support, carrying and wearing; and a secondary tree for incorporation only. In this source code, we'll use the language of family trees (parent, children, siblings) rather than horticulture (branches, leaves, grafting). Both trees must be well-founded, and must be such that each object is the parent of all its children. But the trees aren't independent of each other: an object is not allowed to have a parent in both trees at once. If it has a parent in either one, then that parent is required to be its progenitor.

§33. The following logs the more interesting tree:

void Spatial::log_object_tree(void) {
    instance *I;
    LOOP_OVER_INSTANCES(I, K_object)
        if (SPATIAL_DATA(I)->object_tree_parent == NULL)
            Spatial::log_object_tree_recursively(I, 0);
}

void Spatial::log_object_tree_recursively(instance *I, int depth) {
    int i = depth;
    while (i>0) { LOG("  "); i--; }
    LOG("$O\n", I);
    if (SPATIAL_DATA(I)->object_tree_child)
        Spatial::log_object_tree_recursively(SPATIAL_DATA(I)->object_tree_child, depth+1);
    if (SPATIAL_DATA(I)->object_tree_sibling)
        Spatial::log_object_tree_recursively(SPATIAL_DATA(I)->object_tree_sibling, depth);
}

§34. The initial state of both trees is total disconnection. They are then produced using only two operations, which we'll call "adoption" and "parting".

The adoption routine moves X and its children to become the youngest child of Y. The tree is grown entirely from its root by repeated use of this one operation.

void Spatial::adopt_object(instance *orphan, instance *foster) {
    LOGIF(OBJECT_TREE, "Grafting $O to be child of $O\n", orphan, foster);
    if (orphan == NULL) internal_error("orphan is null in adoption");
    if (foster == NULL) internal_error("foster is null in adoption");

    instance *former_parent = SPATIAL_DATA(orphan)->object_tree_parent;
    if (former_parent) Remove the object from the main object tree34.2;
    Adopt the object into the main object tree34.3;
}

§34.1. "Parting" is the operation of being removed from the main tree and placed in the incorporation tree instead, but with the same parent.

void Spatial::part_object(instance *orphan) {
    LOGIF(OBJECT_TREE, "Parting $O\n", orphan);
    if (orphan == NULL) internal_error("new part is null in parting");

    instance *former_parent = SPATIAL_DATA(orphan)->object_tree_parent;
    if (former_parent == NULL) internal_error("new part is without parent");

    Remove the object from the main object tree34.2;
    Adopt the object into the incorporation tree34.1.1;
}

§34.2. Remove the object from the main object tree34.2 =

    if (SPATIAL_DATA(former_parent)->object_tree_child == orphan) {
        SPATIAL_DATA(former_parent)->object_tree_child =
            SPATIAL_DATA(orphan)->object_tree_sibling;
    } else {
        instance *elder = SPATIAL_DATA(former_parent)->object_tree_child;
        while (elder) {
            if (SPATIAL_DATA(elder)->object_tree_sibling == orphan)
                SPATIAL_DATA(elder)->object_tree_sibling =
                    SPATIAL_DATA(orphan)->object_tree_sibling;
            elder = SPATIAL_DATA(elder)->object_tree_sibling;
        }
    }
    SPATIAL_DATA(orphan)->object_tree_parent = NULL;
    SPATIAL_DATA(orphan)->object_tree_sibling = NULL;

This code is used in §34, §34.1.

§34.3. Adopt the object into the main object tree34.3 =

    if (SPATIAL_DATA(foster)->object_tree_child == NULL) {
        SPATIAL_DATA(foster)->object_tree_child = orphan;
    } else {
        instance *elder = SPATIAL_DATA(foster)->object_tree_child;
        while (SPATIAL_DATA(elder)->object_tree_sibling)
            elder = SPATIAL_DATA(elder)->object_tree_sibling;
        SPATIAL_DATA(elder)->object_tree_sibling = orphan;
    }
    SPATIAL_DATA(orphan)->object_tree_parent = foster;

This code is used in §34.

§34.1.1. Adopt the object into the incorporation tree34.1.1 =

    if (SPATIAL_DATA(former_parent)->incorp_tree_child == NULL) {
        SPATIAL_DATA(former_parent)->incorp_tree_child = orphan;
    } else {
        instance *existing_part = SPATIAL_DATA(former_parent)->incorp_tree_child;
        while (SPATIAL_DATA(existing_part)->incorp_tree_sibling)
            existing_part = SPATIAL_DATA(existing_part)->incorp_tree_sibling;
        SPATIAL_DATA(existing_part)->incorp_tree_sibling = orphan;
    }
    SPATIAL_DATA(orphan)->incorp_tree_parent = former_parent;

This code is used in §34.1.

§35. What will we use the trees for? Well, one use is to tell other features which depend on Spatial whether or not one object spatially contains another:

int Spatial::encloses(instance *I1, instance *I2) {
    while (I1) {
        I1 = Spatial::progenitor(I1);
        if (I1 == I2) return TRUE;
    }
    return FALSE;
}

§36. But the main use for the trees is, as noted above, to form a convenient intermediate state between the mass of progenitor data and the messy Inter code it turns into. Here goes:

int Spatial::spatial_stage_III(void) {
    int well_founded = TRUE;
    Check the well-foundedness of the hierarchy of the set of progenitors36.1;
    if (well_founded) Expand the progenitor data into the two object trees36.2;
    Assert the portability of any item carried or supported by a person36.3;
    Assert Inter-level properties to express the spatial structure36.4;
    Set up the compilation sequence so that it traverses the main object tree36.5;
    if (Log::aspect_switched_on(OBJECT_TREE_DA)) Spatial::log_object_tree();
    return FALSE;
}

§36.1. The following verifies, in a brute-force way, that there are no cycles in the directed graph formed by the objects and progeniture. (We're doing this now, rather than at Stage II above, because other features may also have changed progenitors at Stage II.)

Check the well-foundedness of the hierarchy of the set of progenitors36.1 =

    instance *I;
    int max_loop = NUMBER_CREATED(instance) + 1;
    LOOP_OVER_INSTANCES(I, K_object) {
        int k;
        instance *I2;
        for (I2 = Spatial::progenitor(I), k=0; (I2) && (k<max_loop);
            I2 = Spatial::progenitor(I2), k++) {
            if (I2 == I) {
                Diagnose the ill-foundedness with a problem message36.1.1;
                Spatial::void_progenitor(I);  thus cutting the cycle
                well_founded = FALSE;
            }
        }
    }

This code is used in §36.

§36.1.1. The cutest of all the object problem messages, really:

Diagnose the ill-foundedness with a problem message36.1.1 =

    Problems::quote_object(1, I);
    StandardProblems::handmade_problem(Task::syntax_tree(), _p_(PM_IllFounded));
    Problems::issue_problem_segment("The %1 seems to be containing itself: ");
    instance *I3 = I;
    while (TRUE) {
        wording IW = Instances::get_name(I3, FALSE);
        parse_node *creator = Diagrams::new_UNPARSED_NOUN(IW);
        Problems::quote_object(2, I3);
        Problems::quote_source(3, creator);
        Problems::issue_problem_segment("%2 (created by %3) ");
        if (SPATIAL_DATA(I3)->part_flag) Problems::issue_problem_segment("part of ");
        else Problems::issue_problem_segment("in ");
        I3 = Spatial::progenitor(I3);
        if (I3 == I) break;
    }
    Problems::issue_problem_segment("%1... and so on. This is forbidden.");
    Problems::issue_problem_end();

This code is used in §36.1.

§36.2. Intermediate states are always suspect in program design, and we might ask what's wrong with simply making the trees as we go along, rather than storing all of those progenitors and then converting them into the trees. We don't do that because (for reasons to do with "here" and with how work is shared among the features) the progenitors are determined in an undefined order; if we made the object tree as we went along, the spatial model would be perfectly correct, but siblings — say, the three things on the grass in the Croquet Lawn — would be compiled in the Inter code in some undefined order. This order matters because it affects the text produced by typical room descriptions: "You can also see a box, a ball and a peg here." might become "You can also see a ball, a box and a peg here."

Inform therefore needs a definite rule of ordering, and this rule is that siblings appear in their order of creation in the I7 source text, with the first created being the eldest child. Looping over the objects to add them to the trees in creation order achieves this nicely:

Expand the progenitor data into the two object trees36.2 =

    instance *I;
    LOOP_OVER_INSTANCES(I, K_object) {
        if (Spatial::progenitor(I))
            Spatial::adopt_object(I, Spatial::progenitor(I));
        if (SPATIAL_DATA(I)->part_flag)
            Spatial::part_object(I);
    }

This code is used in §36.

§36.3. As a brief aside: if something is carried by a living person, we can reasonably assume it's portable. (This is needed in particular to ensure that supporters which are initially carried don't pick up "fixed in place" in the absence of other information.)

Assert the portability of any item carried or supported by a person36.3 =

    instance *I;
    LOOP_OVER_INSTANCES(I, K_object) {
        int portable = FALSE;
        instance *J = I;
        if (SPATIAL_DATA(I)->part_flag == FALSE)
            for (J = Spatial::progenitor(I); J; J = Spatial::progenitor(J)) {
                if (SPATIAL_DATA(J)->part_flag) break;
                if (Instances::of_kind(J, K_person)) {
                    portable = TRUE;
                    break;
                }
            }
        if (portable) {
            current_sentence = SPATIAL_DATA(I)->progenitor_set_at;
            EitherOrProperties::assert(
                P_fixed_in_place, Instances::as_subject(I), FALSE, CERTAIN_CE);
        }
    }

This code is used in §36.

§36.4. Assert Inter-level properties to express the spatial structure36.4 =

    Assert an explicit default description value for the room kind36.4.1;
    Assert room and thing indicator properties36.4.2;
    Assert container and supporter indicator properties36.4.3;
    Assert incorporation tree properties36.4.4;

This code is used in §36.

§36.4.1. We need to make sure that every room does have an Inter description value which can be written to (i.e., we need to avoid accidental use of the Z-machine's readable-only default properties feature); hence the following, which ensures that any room with no explicit description will inherit EMPTY_TEXT_VALUE as a value for description from the room class.

Assert an explicit default description value for the room kind36.4.1 =

    if (K_room) {
        inference *inf;
        int desc_seen = FALSE;
        POSITIVE_KNOWLEDGE_LOOP(inf, KindSubjects::from_kind(K_room), property_inf)
            if (PropertyInferences::get_property(inf) == P_description)
                desc_seen = TRUE;
        if (desc_seen == FALSE) {
            TEMPORARY_TEXT(val)
            WRITE_TO(val, "\"\"");
            ValueProperties::assert(P_description, KindSubjects::from_kind(K_room),
                Rvalues::from_unescaped_wording(Feeds::feed_text(val)), LIKELY_CE);
            DISCARD_TEXT(val)
        }
    }

This code is used in §36.4.

§36.4.2. These Inter-only properties exist for speed. They're implemented in Inter as attributes, which means that testing them is very fast and there is no memory overhead for their storage. That shaves a little time off route-finding in extensive maps.

Assert room and thing indicator properties36.4.2 =

    P_mark_as_room = EitherOrProperties::new_nameless(I"mark_as_room");
	RTProperties::recommend_storing_as_attribute(P_mark_as_room, TRUE);
    P_mark_as_thing = EitherOrProperties::new_nameless(I"mark_as_thing");
	RTProperties::recommend_storing_as_attribute(P_mark_as_thing, TRUE);
    instance *I;
    LOOP_OVER_INSTANCES(I, K_object) {
        if (Instances::of_kind(I, K_room))
            EitherOrProperties::assert(
                P_mark_as_room, Instances::as_subject(I), TRUE, CERTAIN_CE);
        if (Instances::of_kind(I, K_thing))
            EitherOrProperties::assert(
                P_mark_as_thing, Instances::as_subject(I), TRUE, CERTAIN_CE);
    }

This code is used in §36.4.

§36.4.3. Assert container and supporter indicator properties36.4.3 =

    P_container = EitherOrProperties::new_nameless(I"container");
	RTProperties::recommend_storing_as_attribute(P_container, TRUE);
    P_supporter = EitherOrProperties::new_nameless(I"supporter");
	RTProperties::recommend_storing_as_attribute(P_supporter, TRUE);
    instance *I;
    LOOP_OVER_INSTANCES(I, K_object) {
        if (Instances::of_kind(I, K_container))
            EitherOrProperties::assert(
                P_container, Instances::as_subject(I), TRUE, CERTAIN_CE);
        if (Instances::of_kind(I, K_supporter))
            EitherOrProperties::assert(
                P_supporter, Instances::as_subject(I), TRUE, CERTAIN_CE);
    }

This code is used in §36.4.

§36.4.4. The main spatial tree is expressed in the compiled Inter code in an implicit way, using the Inter object tree, but the incorporation tree is expressed using a triplet of Inter-only properties:

Assert incorporation tree properties36.4.4 =

    P_component_parent =
        ValueProperties::new_nameless(I"component_parent", K_object);
    P_component_child =
        ValueProperties::new_nameless(I"component_child", K_object);
    P_component_sibling =
        ValueProperties::new_nameless(I"component_sibling", K_object);

    if (K_thing) {
        parse_node *nothing_constant = Rvalues::new_nothing_object_constant();
        ValueProperties::assert(P_component_parent, KindSubjects::from_kind(K_thing),
            nothing_constant, CERTAIN_CE);
        ValueProperties::assert(P_component_child, KindSubjects::from_kind(K_thing),
            nothing_constant, CERTAIN_CE);
        ValueProperties::assert(P_component_sibling, KindSubjects::from_kind(K_thing),
            nothing_constant, CERTAIN_CE);
    }

    instance *I;
    LOOP_OVER_INSTANCES(I, K_object) {
        instance *cp = SPATIAL_DATA(I)->incorp_tree_parent;
        if (cp) ValueProperties::assert(P_component_parent, Instances::as_subject(I),
            Rvalues::from_instance(cp), CERTAIN_CE);
        instance *cc = SPATIAL_DATA(I)->incorp_tree_child;
        if (cc) ValueProperties::assert(P_component_child, Instances::as_subject(I),
            Rvalues::from_instance(cc), CERTAIN_CE);
        instance *cs = SPATIAL_DATA(I)->incorp_tree_sibling;
        if (cs) ValueProperties::assert(P_component_sibling, Instances::as_subject(I),
            Rvalues::from_instance(cs), CERTAIN_CE);
    }

This code is used in §36.4.

§36.5. Because Inform 6 requires objects to be defined in a traversal order for the main spatial tree (only the main one because Inter has no concept of incorporation), we use the main tree to determine the compilation sequence for objects:

Set up the compilation sequence so that it traverses the main object tree36.5 =

    OrderingInstances::begin();
    instance *I;
    LOOP_OVER_INSTANCES(I, K_object)
        if (SPATIAL_DATA(I)->object_tree_parent == NULL)
            Spatial::add_to_object_sequence(I, 0);

This code is used in §36.

§37.

void Spatial::add_to_object_sequence(instance *I, int depth) {
    OrderingInstances::place_next(I);
    SPATIAL_DATA(I)->definition_depth = depth;

    if (SPATIAL_DATA(I)->object_tree_child)
        Spatial::add_to_object_sequence(SPATIAL_DATA(I)->object_tree_child, depth+1);
    if (SPATIAL_DATA(I)->object_tree_sibling)
        Spatial::add_to_object_sequence(SPATIAL_DATA(I)->object_tree_sibling, depth);
}

§38. The "definition depth" is the same thing as the depth in the main tree; 0 for a room, 1 for a player standing in that room, 2 for his hat, and so on.

int Spatial::get_definition_depth(instance *I) {
    if (FEATURE_ACTIVE(spatial))
        return SPATIAL_DATA(I)->definition_depth;
    return 0;
}

§39. By Stage IV we're nearly all done, except for a little checking of the degenerate case where Inform is just binding up an existing story file, so that there's really no spatial model at all — the world is, or should be, empty.

int Spatial::spatial_stage_IV(void) {
    if (Task::wraps_existing_storyfile()) {
        instance *I;
        LOOP_OVER_INSTANCES(I, K_object)
            if (Spatial::object_is_a_room(I)) {
                StandardProblems::unlocated_problem(Task::syntax_tree(),
                    _p_(PM_RoomInIgnoredSource),
                    "This is supposed to be a source text which only contains "
                    "release instructions to bind up an existing story file "
                    "(for instance, one produced using Inform 6). That's because "
                    "the instruction 'Release along with an existing story file' "
                    "is present. So the source text must not contain rooms or "
                    "other game design - these would be ignored.");
                break;
            }
    }
    return FALSE;
}

§40. At last Stage V, where the only remaining task is to set the benchmark room. It's where the player begins, or if the player begins out of play for some reason, it's the first-created room. (The benchmark is used only in indexing.)

instance *benchmark_room = NULL;
int Spatial::spatial_stage_V(void) {
    benchmark_room = Player::get_start_room();
    if (benchmark_room == NULL) {
        instance *R;
        LOOP_OVER_INSTANCES(R, K_room) {
            benchmark_room = R;
            break;
        }
    }
    return FALSE;
}

instance *Spatial::get_benchmark_room(void) {
    return benchmark_room;
}