In this section we keep track of response texts.

• §1. Introduction
• §4. How rules gain responses
• §6. Compilation

§1. Introduction. Responses are texts — which may be either literals or text substitutions — occurring inside the body of rules, and marked out (A), (B), (C), ... within that rule. This enables them to be manipulated or changed. For example:

Report an actor taking (this is the standard report taking rule):
    if the action is not silent:
        if the actor is the player:
            say "Taken." (A);
        otherwise:
            say "[The actor] [pick] up [the noun]." (B).

In effect there is a two-element array attached to this rule, one holding the current response (A), the other (B). These are identified by an index called the "marker", which counts from 0: so (A) is 0, (B) is 1.

Those original appearances inside the rule are called the "cues". The texts are stored as Text Substitutions, even if, as in example (A) here, they do not actually involve any substituting. (It's simpler to have a common format, and in any case these are the exception.) All of the difficulties attendant on text substitutions apply here, too. Note, for example, that (B) refers to the "actor", a shared variable which is not normally visible from here:

To grab is a verb.
When play begins:
    now the standard report taking rule response (B) is "[The actor] [grab] [the noun]."

Here, "actor" has to be read in the context of the standard report taking rule's stack frame, not in the stack for the "when play begins" rule.

Each time a cue is found, a response_message object is created, as follows:

typedef struct response_message {
    struct rule *the_rule;  to which this is a response
    int the_marker;  0 for A, 1 for B, and so on up
    struct text_substitution *the_ts;
    struct stack_frame *original_stack_frame;
    struct inter_name *value_iname;
    struct inter_name *constant_iname;
    struct inter_name *launcher_iname;
    struct inter_name *parking_iname;
    struct local_parking_lot *parking_lot;
    struct inter_name *value_md_iname;
    struct inter_name *rule_md_iname;
    struct inter_name *marker_md_iname;
    struct inter_name *index_text_md_iname;
    struct inter_name *group_md_iname;
    int launcher_compiled;
    int via_Inter_routine_compiled;  if responding to a rule defined by Inter code
    CLASS_DEFINITION
} response_message;

• The structure response_message is accessed in 5/act, 5/rls and here.

§2. Note that each response has its own package, which is stored inside the package of the rule to which it responds.

It occasionally happens that assertion sentences have changed the wording of a response long before any code is compiled, and therefore before this call, through a sentence like:

The print empty inventory rule response (A) is "I got nothing."

This would cause RW, the replacement wording, below to be "I got nothing.".

response_message *Responses::response_cue?Usage of Responses::response_cue:
§4, §5(rule *R, int marker, wording W, stack_frame *frame) {
    response_message *resp = CREATE(response_message);
    resp->original_stack_frame = frame;
    resp->the_rule = R;
    resp->the_marker = marker;
    resp->launcher_compiled = FALSE;
    resp->via_Inter_routine_compiled = FALSE;

    package_request *PR = Hierarchy::package_within(RESPONSES_HAP, RTRules::package(R));
    resp->constant_iname = Hierarchy::make_iname_in(AS_CONSTANT_HL, PR);
    resp->value_iname = Hierarchy::make_iname_in(AS_BLOCK_CONSTANT_HL, PR);
    resp->parking_iname = Hierarchy::make_iname_in(PARKING_ARRAY_HL, PR);
    resp->parking_lot = NULL;
    resp->launcher_iname = Hierarchy::make_iname_in(LAUNCHER_HL, PR);
    resp->value_md_iname = Hierarchy::make_iname_in(RESP_VALUE_MD_HL, PR);
    resp->rule_md_iname = Hierarchy::make_iname_in(RULE_MD_HL, PR);
    resp->marker_md_iname = Hierarchy::make_iname_in(MARKER_MD_HL, PR);
    resp->index_text_md_iname = Hierarchy::make_iname_in(INDEX_TEXT_MD_HL, PR);
    resp->group_md_iname = Hierarchy::make_iname_in(GROUP_HL, PR);

    Rules::set_response(R, marker, resp);

    wording RW = Rules::get_response_replacement_wording(R, marker);
    if (Wordings::nonempty(RW)) W = RW;
    resp->the_ts = TextSubstitutions::new_text_substitution(W, frame, R, marker);
    TextSubstitutions::value_iname(resp->the_ts);

    text_stream *desc = Str::new();
    WRITE_TO(desc, "response (%c) to '%W'", 'A'+marker, R->name);
    Sequence::queue(&Responses::compilation_agent, STORE_POINTER_response_message(resp), desc);
    return resp;
}

§3. Some access functions:

inter_name *Responses::response_launcher_iname?Usage of Responses::response_launcher_iname:
§4(response_message *resp) {
    return resp->value_iname;
}

inter_name *Responses::response_constant_iname?Usage of Responses::response_constant_iname:
§6(rule *R, int marker) {
    response_message *resp = Rules::get_response(R, marker);
    if (resp == NULL) return NULL;
    if (resp->constant_iname == NULL) internal_error("no response value");
    return resp->constant_iname;
}

local_parking_lot *Responses::enable_private_parking(rule *R, int marker) {
    response_message *resp = Rules::get_response(R, marker);
    if (resp) {
        if (resp->parking_lot == NULL)
            resp->parking_lot = LocalParking::new_lot(resp->parking_iname);
        return resp->parking_lot;
    }
    return NULL;
}

local_parking_lot *Responses::parking_lot?Usage of Responses::parking_lot:
Text Substitutions - §7.4(rule *R, int marker) {
    response_message *resp = Rules::get_response(R, marker);
    if (resp == NULL) return NULL;
    return resp->parking_lot;
}

stack_frame *Responses::frame_for_response?Usage of Responses::frame_for_response:
Text Substitutions - §7.1(rule *R, int marker) {
    response_message *resp = Rules::get_response(R, marker);
    if (resp == NULL) return NULL;
    return resp->original_stack_frame;
}

§4. How rules gain responses. There are two ways a rule can get a new response. Firstly, and the way most Inform authors do it:

say "[The actor] [pick] up [the noun]." (B).

Will cause Responses::set_via_source_text to be called. This compiles Inter code suitable for the response to be called (i.e., printed), setting up the cue and attaching it to its rule in the process.

Note the use of Local Parking (in imperative) to stash local values before the evaluation: and see TextSubstitutions::compile_function for where those are retrieved.

void Responses::set_via_source_text(value_holster *VH, rule *R, int marker, wording SW) {
    stack_frame *frame = Frames::current_stack_frame();
    response_message *resp =
        Responses::response_cue(R, marker, SW, Frames::boxed_frame(frame));
    int downs = LocalParking::park_with_private_lot(frame, R, marker);
    EmitCode::val_iname(K_value, Responses::response_launcher_iname(resp));
    while (downs > 0) { EmitCode::up(); downs--; }
}

§5. Secondly, a lower-level technique used by extensions to give responses even to rules defined in Inter kits rather than by source text:

The requested actions require persuasion rule translates into Inter as
    "REQUESTED_ACTIONS_REQUIRE_R" with
     "[The noun] [have] better things to do." (A).

Which causes the following to be called:

void Responses::set_via_translation(rule *R, int marker, wording SW) {
    response_message *resp = Responses::response_cue(R, marker, SW, NULL);
    text_stream *desc = Str::new();
    WRITE_TO(desc, "Inter response agent function for '%W'", R->name);
    Sequence::queue(&Responses::via_Inter_compilation_agent,
        STORE_POINTER_response_message(resp), desc);
}

§6. Compilation. Values and launchers for responses are then compiled in due course by the following agent. Each response compiles to a text value like so:

                            small block:
    value ----------------> CONSTANT_PACKED_TEXT_STORAGE
                            launcher function ----------------------> ...

Thus, printing this value at runtime calls the launcher function. This in turn runs the "issuing the response text" activity, though it does it via a function defined in BasicInformKit.

void Responses::compilation_agent?Usage of Responses::compilation_agent:
§2(compilation_subtask *t) {
    response_message *resp = RETRIEVE_POINTER_response_message(t->data);
    text_substitution *ts = resp->the_ts;
    inter_name *ts_value_iname = TextSubstitutions::value_iname(ts);
    inter_name *rc_iname =
        Responses::response_constant_iname(resp->the_rule, resp->the_marker);
    Emit::numeric_constant(rc_iname, 0);

    Emit::iname_constant(resp->value_md_iname, K_value, ts_value_iname);
    Emit::iname_constant(resp->rule_md_iname, K_value, RTRules::iname(resp->the_rule));
    Emit::numeric_constant(resp->marker_md_iname, (inter_ti) resp->the_marker);
    TEMPORARY_TEXT(T)
    WRITE_TO(T, "%+W", resp->the_ts->unsubstituted_text);
    Emit::text_constant(resp->index_text_md_iname, T);
    DISCARD_TEXT(T)
    inform_extension *E = Extensions::corresponding_to(
        Lexer::file_of_origin(Wordings::first_wn(resp->the_rule->name)));
    TEMPORARY_TEXT(QT)
    if (E) WRITE_TO(QT, "%<X", E->as_copy->edition->work);
    else WRITE_TO(QT, "source text");
    EmitArrays::text_entry(QT);
    Emit::text_constant(resp->group_md_iname, QT);
    DISCARD_TEXT(QT)

    TextLiterals::compile_value_to(resp->value_iname, resp->launcher_iname);

    packaging_state save = Functions::begin(resp->launcher_iname);

    inter_name *iname = Responses::response_constant_iname(
        resp->the_rule, resp->the_marker);

    inter_name *rname = Hierarchy::find(RESPONSEVIAACTIVITY_HL);
    EmitCode::call(rname);
    EmitCode::down();
    EmitCode::val_iname(K_value, iname);
    EmitCode::up();

    Functions::end(save);
}

§7. Something skated over above is that responses can also be created when the source text defines a rule only as an Inter function. For example:

The hack mode rule translates into Inter as "HACK_MODE_ON_R" with "Hack mode on." (A).

Responses like this one are "via Inter", and they cause us to create a handler function for the rule, called (say) HACK_MODE_ON_RM. The rule then calls:

    HACK_MODE_ON_RM('A');

to produce response (A), or alternatively

    HACK_MODE_ON_RM('a');

to return the current text of (A) without printing it. Speed is not of the essence; and note that the response-handler is created in the package for the rule to which it responds.

void Responses::via_Inter_compilation_agent?Usage of Responses::via_Inter_compilation_agent:
§5(compilation_subtask *t) {
    response_message *resp = RETRIEVE_POINTER_response_message(t->data);
    if (resp->via_Inter_routine_compiled == FALSE) {
        response_message *r2;
        LOOP_OVER(r2, response_message)
            if (r2->the_rule == resp->the_rule)
                r2->via_Inter_routine_compiled = TRUE;
        Compile the response-handler function for this rule7.1;
    }
}

§7.1. Compile the response-handler function for this rule7.1 =

    inter_name *responder_iname = RTRules::response_handler_iname(resp->the_rule);
    packaging_state save = Functions::begin(responder_iname);
    inter_symbol *code_s = LocalVariables::new_other_as_symbol(I"code");
    inter_symbol *val_s = LocalVariables::new_other_as_symbol(I"val");
    inter_symbol *val2_s = LocalVariables::new_other_as_symbol(I"val2");
    inter_symbol *s_s = LocalVariables::new_internal_as_symbol(I"s");
    inter_symbol *s2_s = LocalVariables::new_internal_as_symbol(I"s2");
    inter_symbol *s3_s = LocalVariables::new_internal_as_symbol(I"s3");
    inter_symbol *str_s = LocalVariables::new_internal_as_symbol(I"str");
    inter_symbol *f_s = LocalVariables::new_internal_as_symbol(I"f");

    EmitCode::inv(IF_BIP);
    EmitCode::down();
        EmitCode::inv(AND_BIP);
        EmitCode::down();
            EmitCode::inv(GE_BIP);
            EmitCode::down();
                EmitCode::val_symbol(K_value, code_s);
                EmitCode::val_number((inter_ti) 'a');
            EmitCode::up();
            EmitCode::inv(LE_BIP);
            EmitCode::down();
                EmitCode::val_symbol(K_value, code_s);
                EmitCode::val_number((inter_ti) 'z');
            EmitCode::up();
        EmitCode::up();
        EmitCode::code();
        EmitCode::down();
            EmitCode::inv(STORE_BIP);
            EmitCode::down();
                EmitCode::ref_symbol(K_value, f_s);
                EmitCode::val_true();
            EmitCode::up();
            EmitCode::inv(STORE_BIP);
            EmitCode::down();
                EmitCode::ref_symbol(K_value, code_s);
                EmitCode::inv(MINUS_BIP);
                EmitCode::down();
                    EmitCode::val_symbol(K_value, code_s);
                    EmitCode::val_number((inter_ti) ('a'-'A'));
                EmitCode::up();
            EmitCode::up();
        EmitCode::up();
    EmitCode::up();

    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_symbol(K_value, s_s);
        EmitCode::val_iname(K_object, Hierarchy::find(NOUN_HL));
    EmitCode::up();
    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_symbol(K_value, s2_s);
        EmitCode::val_iname(K_value, Hierarchy::find(SECOND_HL));
    EmitCode::up();
    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_symbol(K_value, s3_s);
        EmitCode::val_iname(K_object, Hierarchy::find(PARSED_NUMBER_HL));
    EmitCode::up();
    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_iname(K_object, Hierarchy::find(NOUN_HL));
        EmitCode::val_symbol(K_value, val_s);
    EmitCode::up();
    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_iname(K_object, Hierarchy::find(SECOND_HL));
        EmitCode::val_symbol(K_value, val2_s);
    EmitCode::up();
    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_iname(K_object, Hierarchy::find(PARSED_NUMBER_HL));
        EmitCode::val_symbol(K_value, val_s);
    EmitCode::up();

    EmitCode::inv(SWITCH_BIP);
    EmitCode::down();
        EmitCode::val_symbol(K_value, code_s);
        EmitCode::code();
        EmitCode::down();
            response_message *r2;
            LOOP_OVER(r2, response_message) {
                if (r2->the_rule == resp->the_rule) {
                    EmitCode::inv(CASE_BIP);
                    EmitCode::down();
                        EmitCode::val_number((inter_ti) ('A' + r2->the_marker));
                        EmitCode::code();
                        EmitCode::down();
                            EmitCode::inv(STORE_BIP);
                            EmitCode::down();
                                EmitCode::ref_symbol(K_value, str_s);
                                EmitCode::val_iname(K_value, r2->value_iname);
                            EmitCode::up();
                        EmitCode::up();
                    EmitCode::up();
                }
            }
        EmitCode::up();
    EmitCode::up();

    EmitCode::inv(IF_BIP);
    EmitCode::down();
        EmitCode::inv(AND_BIP);
        EmitCode::down();
            EmitCode::val_symbol(K_value, str_s);
            EmitCode::inv(EQ_BIP);
            EmitCode::down();
                EmitCode::val_symbol(K_value, f_s);
                EmitCode::val_false();
            EmitCode::up();
        EmitCode::up();
        EmitCode::code();
        EmitCode::down();
            EmitCode::call(Hierarchy::find(TEXT_TY_SAY_HL));
            EmitCode::down();
                EmitCode::val_symbol(K_value, str_s);
            EmitCode::up();
        EmitCode::up();
    EmitCode::up();

    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_iname(K_object, Hierarchy::find(NOUN_HL));
        EmitCode::val_symbol(K_value, s_s);
    EmitCode::up();
    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_iname(K_object, Hierarchy::find(SECOND_HL));
        EmitCode::val_symbol(K_value, s2_s);
    EmitCode::up();
    EmitCode::inv(STORE_BIP);
    EmitCode::down();
        EmitCode::ref_iname(K_object, Hierarchy::find(PARSED_NUMBER_HL));
        EmitCode::val_symbol(K_value, s3_s);
    EmitCode::up();

    EmitCode::inv(RETURN_BIP);
    EmitCode::down();
        EmitCode::val_symbol(K_value, str_s);
    EmitCode::up();

    Functions::end(save);

• This code is used in §7.