The structure of a dialogue beat as a tree of nodes, each of which can be either a line or a choice.

§1. Inside any given beat, we have to keep track of the indentation of material in order to see what is subordinate to what. For example:

(About Elsinore.)

Marcellus: "What, has this thing appear'd again to-night?"

Bernardo: "I have seen naught but [list of things in the Battlements]."

    Marcellus: "Horatio says 'tis but our fantasy."

Here the lines are at levels 0, 0 and 1. We actually allow them to go in as far as MAX_DIALOGUE_NODE_NESTING, which is a lot of tab stops: no human author would want that many.

As we go through the beat looking for lines, we track the most recent line or choice seen at each level. These are called "precursors".

define MAX_DIALOGUE_NODE_NESTING 25

dialogue_node *precursor_dialogue_nodes[MAX_DIALOGUE_NODE_NESTING];

void DialogueNodes::clear_precursors?Usage of DialogueNodes::clear_precursors:
§3.3
Dialogue Beats - §2, §3(int from) {
    for (int i=from; i<MAX_DIALOGUE_NODE_NESTING; i++)
        precursor_dialogue_nodes[i] = NULL;
}

§2. Other than the connectivity for the tree structure, a node is basically a union type: it can either be a line, a choice or a decision.

typedef struct dialogue_node {
    struct dialogue_line *if_line;
    struct dialogue_choice *if_choice;
    struct dialogue_decision *if_decision;

    struct dialogue_beat *owning_beat;
    struct dialogue_node *parent_node;
    struct dialogue_node *child_node;
    struct dialogue_node *next_node;
    CLASS_DEFINITION
} dialogue_node;

• The structure dialogue_node is private to this section.

§3. The following should be called with exactly one non-NULL pointer. (Decision nodes are created later.)

dialogue_node *DialogueNodes::add_to_current_beat?Usage of DialogueNodes::add_to_current_beat:
Dialogue Lines - §1
Dialogue Choices - §2(int L, dialogue_line *dl, dialogue_choice *dc) {
    int w = 0; if (dl) w++; if (dc) w++;
    if (w != 1) internal_error("exactly one should be non-NULL");
    See if we are expecting a dialogue node3.4;
    See if that level of indentation is feasible3.5;
    dialogue_node *dn = CREATE(dialogue_node);
    Initialise the node3.1;
    Join the node to the current beat's tree3.2;
    Make the node a precursor3.3;
    return dn;
}

§3.1. Initialise the node3.1 =

    dn->if_line = dl;
    dn->if_choice = dc;
    dn->if_decision = NULL;
    dn->owning_beat = current_dialogue_beat;

    if (L > 0) dn->parent_node = precursor_dialogue_nodes[L-1];
    else dn->parent_node = NULL;
        dn->child_node = NULL;
    dn->next_node = NULL;

• This code is used in §3.

§3.2. Join the node to the current beat's tree3.2 =

    if (current_dialogue_beat->root == NULL)
        current_dialogue_beat->root = dn;
    else if (precursor_dialogue_nodes[L])
        precursor_dialogue_nodes[L]->next_node = dn;
    else
        precursor_dialogue_nodes[L-1]->child_node = dn;

• This code is used in §3.

§3.3. Make the node a precursor3.3 =

    precursor_dialogue_nodes[L] = dn;
    DialogueNodes::clear_precursors(L+1);

• This code is used in §3.

§3.4. Note that a DIALOGUE_LINE_NT or DIALOGUE_CHOICE_NT is only made under a section marked as containing dialogue, so the internal error here should be impossible to hit.

See if we are expecting a dialogue node3.4 =

    if (dialogue_section_being_scanned == NULL) internal_error("node outside dialogue section");
    if (current_dialogue_beat == NULL) {
        StandardProblems::sentence_problem(Task::syntax_tree(), _p_(PM_LineWithoutBeat),
            "this dialogue material seems to appear before any beat has begun",
            "which is not allowed - every line or choice has to be part of a 'beat', which "
            "has to be introduced with a bracketed paragraph looking like a stage "
            "direction in a play.");
        return NULL;
    }

• This code is used in §3.

§3.5. See if that level of indentation is feasible3.5 =

    if (L >= MAX_DIALOGUE_NODE_NESTING) {
        StandardProblems::sentence_problem(Task::syntax_tree(), _p_(PM_OvernestedLine),
            "this dialogue material is indented further than I can cope with",
            "and indeed further than any human reader could really make sense of.");
        return NULL;
    }
    if ((L > 0) && (precursor_dialogue_nodes[L-1] == NULL)) {
        StandardProblems::sentence_problem(Task::syntax_tree(), _p_(PM_OrphanLine),
            "this dialogue material is indented too far",
            "and should either not be indented at all, or indented by just one tab "
            "stop from the material it is dependent on.");
        return NULL;
    }

• This code is used in §3.

§4.

enum BLANK_DDT from 1
enum TEXTUAL_DDT
enum PARSED_COMMAND_DDT
enum FLOW_CONTROL_DDT
enum RANDOMISED_CONTROL_DDT
enum SHUFFLE_CONTROL_DDT
enum CYCLE_CONTROL_DDT
enum STEP_CONTROL_DDT
enum STEP_STOP_CONTROL_DDT

typedef struct dialogue_decision {
    CLASS_DEFINITION
    int decision_type;  one of the *_DDT constants above
    struct dialogue_node *as_node;
} dialogue_decision;

• The structure dialogue_decision is accessed in 6/dl, 6/dc and here.

§5.

void DialogueNodes::find_decisions_in_beat?Usage of DialogueNodes::find_decisions_in_beat:
Dialogue Beats - §6(dialogue_beat *db) {
    DialogueNodes::find_decisions_in_beat_r(db, db->root, NULL);
    DialogueNodes::examine_decisions_in_beat_r(db, db->root, NULL);
}
void DialogueNodes::find_decisions_in_beat_r(dialogue_beat *db, dialogue_node *dn, dialogue_node *parent) {
    if (dn == NULL) return;
    for (dialogue_node *c = dn, *prev = NULL; c; prev = c, c = c->next_node) {
        if (c->if_choice) {
            dialogue_node *d = c;
            if (DialogueNodes::is_divider(c)) {
                if (c->child_node) {
                    current_sentence = c->if_choice->choice_at;
                    StandardProblems::sentence_problem(Task::syntax_tree(),
                        _p_(PM_ChoiceDividerDependent),
                        "this choice can't have dependent material",
                        "that is, can't have lines or other choices indented below it.");
                    c->child_node = NULL;
                }
            } else {
                while ((d) && (d->next_node) && (d->next_node->if_choice) &&
                    (DialogueNodes::is_divider(d->next_node) == FALSE)) d = d->next_node;
            }
            dialogue_decision *dd = CREATE(dialogue_decision);
            dd->decision_type = BLANK_DDT;
            dd->as_node = CREATE(dialogue_node);
            dd->as_node->if_line = NULL;
            dd->as_node->if_choice = NULL;
            dd->as_node->if_decision = dd;
            dd->as_node->parent_node = parent;
            if (prev) prev->next_node = dd->as_node;
            else if (parent) parent->child_node = dd->as_node;
            else db->root = dd->as_node;
            dd->as_node->next_node = d->next_node; d->next_node = NULL;
            dd->as_node->child_node = c;
            for (dialogue_node *e = c; e; e = e->next_node)
                e->parent_node = dd->as_node;
            for (dialogue_node *e = c; e; e = e->next_node)
                DialogueNodes::find_decisions_in_beat_r(db, e->child_node, e);
            c = dd->as_node;
        } else {
            DialogueNodes::find_decisions_in_beat_r(db, c->child_node, c);
        }
    }
}

int DialogueNodes::is_divider(dialogue_node *dn) {
    if ((dn) && (dn->if_choice) &&
        ((dn->if_choice->selection_type == ANOTHER_CHOICE_DSEL) ||
            (dn->if_choice->selection_type == AGAIN_DSEL) ||
            (dn->if_choice->selection_type == STOP_DSEL) ||
            (dn->if_choice->selection_type == ENDING_DSEL) ||
            (dn->if_choice->selection_type == ENDING_SAYING_DSEL) ||
            (dn->if_choice->selection_type == ENDING_FINALLY_DSEL) ||
            (dn->if_choice->selection_type == ENDING_FINALLY_SAYING_DSEL) ||
            (dn->if_choice->selection_type == PERFORM_DSEL)))
        return TRUE;
    return FALSE;
}

void DialogueNodes::examine_decisions_in_beat_r(dialogue_beat *db, dialogue_node *dn, dialogue_node *parent) {
    for (dialogue_node *c = dn, *prev = NULL; c; prev = c, c = c->next_node) {
        if (c->if_decision) {
            int t = -1;
            if (c->child_node) t = DialogueNodes::decision_type(c->child_node);
            if ((t == RANDOMISED_CONTROL_DDT) ||
                (t == SHUFFLE_CONTROL_DDT) ||
                (t == CYCLE_CONTROL_DDT) ||
                (t == STEP_CONTROL_DDT) ||
                (t == STEP_STOP_CONTROL_DDT))
                Apply the rules for an or-list5.1
            else
                Apply the mixture rules5.2;
        }
        DialogueNodes::examine_decisions_in_beat_r(db, c->child_node, c);
    }
}

§5.1. Apply the rules for an or-list5.1 =

    for (dialogue_node *d = c->child_node->next_node; d; d = d->next_node)
        if (d->if_choice->selection_type != OR_DSEL) {
            current_sentence = d->if_choice->choice_at;
            StandardProblems::sentence_problem(Task::syntax_tree(),
                _p_(...),
                "this is a run of choices where all choices other than the"
                "first must be just '-- or'",
                "since it is a list of alternatives.");
        }
    c->if_decision->decision_type = t;

• This code is used in §5.

§5.2. Apply the mixture rules5.2 =

    int t = -1;
    dialogue_node *bad_otherwise = NULL, *mixed_choices = NULL;
    for (dialogue_node *d = c->child_node; d; d = d->next_node) {
        if (d->if_choice->selection_type == OTHERWISE_DSEL) {
            if (t != PARSED_COMMAND_DDT) bad_otherwise = d;
            if (d->next_node) bad_otherwise = d;
        } else {
            int ddt = DialogueNodes::decision_type(d);
            if (t == -1) t = ddt;
            else if (t != ddt) mixed_choices = d;
        }
    }
    if (bad_otherwise) {
        current_sentence = bad_otherwise->if_choice->choice_at;
        StandardProblems::sentence_problem(Task::syntax_tree(),
            _p_(PM_ChoiceOtherwiseUnexpected),
            "this run of choices uses 'otherwise' unexpectedly",
            "since 'otherwise' can only be used as the last option, and "
            "only where the options are written in terms of actions.");
    }
    if (mixed_choices) {
        current_sentence = mixed_choices->if_choice->choice_at;
        StandardProblems::sentence_problem(Task::syntax_tree(), _p_(PM_ChoicesMixed),
            "this run of choices mixes up the possible sorts of choice",
            "and should either all be action-dependent choices (perhaps "
            "finishing with an 'otherwise'), or else all textual choices.");
    }
    if ((c->child_node) && (c->child_node->if_choice->selection_type == ANOTHER_CHOICE_DSEL)) {
        if ((prev == NULL) || (prev->if_line) ||
            (c->next_node == NULL) || (c->next_node->if_line)) {
            current_sentence = c->child_node->if_choice->choice_at;
            StandardProblems::sentence_problem(Task::syntax_tree(),
                _p_(PM_ChoiceBlankRedundant),
                "this use of '-> another choice' looks redundant",
                "occurring at the start or end of a set of options. "
                "'-> another choice' should be used only where there's "
                "a need to mark a division point between two sets "
                "of options running on from one to the other.");
        }
    }
    c->if_decision->decision_type = t;

• This code is used in §5.

§6.

void DialogueNodes::log_node_tree(dialogue_node *dn) {
    for (; dn; dn=dn->next_node) {
        DialogueNodes::log_node(dn); LOG("\n");
        if (dn->child_node) {
            LOG_INDENT;
            DialogueNodes::log_node_tree(dn->child_node);
            LOG_OUTDENT;
        }
    }
}

void DialogueNodes::log_node(dialogue_node *dn) {
    if (dn == NULL) LOG("<null>");
    else if (dn->if_line) LOG("line %d %W", dn->if_line->allocation_id, Node::get_text(dn->if_line->line_at));
    else if (dn->if_choice) LOG("choice %d %W", dn->if_choice->allocation_id, Node::get_text(dn->if_choice->choice_at));
    else if (dn->if_decision) LOG("decision %d", dn->if_decision->allocation_id);
}

int DialogueNodes::decision_type?Usage of DialogueNodes::decision_type:
§5, §5.2(dialogue_node *dn) {
    if ((dn == NULL) || (dn->if_choice == NULL)) return -1;
    switch (dn->if_choice->selection_type) {
        case ANOTHER_CHOICE_DSEL: return PARSED_COMMAND_DDT;
        case TEXTUAL_DSEL: return TEXTUAL_DDT;
        case AGAIN_DSEL: return FLOW_CONTROL_DDT;
        case STOP_DSEL: return FLOW_CONTROL_DDT;
        case ENDING_DSEL: return FLOW_CONTROL_DDT;
        case ENDING_SAYING_DSEL: return FLOW_CONTROL_DDT;
        case ENDING_FINALLY_DSEL: return FLOW_CONTROL_DDT;
        case ENDING_FINALLY_SAYING_DSEL: return FLOW_CONTROL_DDT;
        case OTHERWISE_DSEL: return FLOW_CONTROL_DDT;
        case INSTEAD_OF_DSEL: return PARSED_COMMAND_DDT;
        case AFTER_DSEL: return PARSED_COMMAND_DDT;
        case BEFORE_DSEL: return PARSED_COMMAND_DDT;
        case PERFORM_DSEL: return FLOW_CONTROL_DDT;
        case CHOOSE_RANDOMLY_DSEL: return RANDOMISED_CONTROL_DDT;
        case SHUFFLE_THROUGH_DSEL: return SHUFFLE_CONTROL_DDT;
        case CYCLE_THROUGH_DSEL: return CYCLE_CONTROL_DDT;
        case STEP_THROUGH_DSEL: return STEP_CONTROL_DDT;
        case STEP_THROUGH_AND_STOP_DSEL: return STEP_STOP_CONTROL_DDT;
        case OR_DSEL: return RANDOMISED_CONTROL_DDT;
        default: internal_error("unimplemented DSEL");
    }
    return -1;
}