The long production line on which products of Inform are built, one step at a time.

§1. Having seen the top management of the factory, we now reach the factory floor, which is one long production line: over 100 steps must be performed in sequence to finish making the product. We can picture each of these steps as carried out by a worker function: each does its work and passes on to the next.

We group the steps into departments, which are in order of when they work:

enum SUBDIVIDING_CSEQ from 0
enum BUILT_IN_STUFF_CSEQ
enum SEMANTIC_ANALYSIS_CSEQ
enum ASSERTIONS_PASS_1_CSEQ
enum ASSERTIONS_PASS_2_CSEQ
enum MODEL_CSEQ
enum MODEL_COMPLETE_CSEQ
enum TABLES_CSEQ
enum AUGMENT_CSEQ
enum PHRASES_CSEQ
enum INTER1_CSEQ
enum INTER2_CSEQ
enum INTER3_CSEQ
enum INTER4_CSEQ
enum INTER5_CSEQ
enum BIBLIOGRAPHIC_CSEQ
enum FINISHED_CSEQ

§2. The aim of this section is to contain as little logic as possible other then the sequence itself.

int Sequence::carry_out?Usage of Sequence::carry_out:
What To Compile - §3(int debugging) {
    stopwatch_timer *sequence_timer =
        Time::start_stopwatch(inform7_timer, I"compilation to Inter");
    Divide into compilation units2.2;
    Build a rudimentary set of kinds, relations, verbs and inference subjects2.3;
    Pass three times through the major nodes2.4;
    Make the model world2.5;
    Tables and grammar2.6;
    Augment model world with low-level properties2.7;
    Phrases and rules2.8;
    Generate inter, part 12.9
    Generate inter, part 22.10
    Generate inter, part 32.11
    Generate inter, part 42.12
    Generate inter, part 52.13
    Generate index and bibliographic file2.14;

    Task::advance_stage_to(FINISHED_CSEQ, I"Ccmplete", -1, debugging, sequence_timer);
    int cpu_time_used = Time::stop_stopwatch(sequence_timer);
    LOG("Compile CPU time: %d centiseconds\n", cpu_time_used);
    if (problem_count > 0) return FALSE;
    return TRUE;
}

§2.1. This macro carries out a step at what we think of as "benches" in the production line: hence the name BENCH. Continuing the analogy, there is an ongoing time and motion study: any step which takes more than 1 centisecond of CPU time is reported to the debugging log. That isn't necessarily a sign of something wrong: a few of these steps are always going to take serious computation. But we want to know which ones.

As soon as any step generates problem messages, all subsequent steps are skipped, so that each of the worker functions can assume that the part-assembled state they receive is correct so far. This greatly simplifies error recovery, prevents small errors in the source text leading to cascades of problem messages, and ensures that we report problems as quickly as possible.

define BENCH(routine) {
    if (problem_count == 0) {
        TEMPORARY_TEXT(name)
        WRITE_TO(name, "//");
        WRITE_TO(name, #routine);
        WRITE_TO(name, "//");
        for (int i=0; i<Str::len(name)-1; i++)
            if ((Str::get_at(name, i) == '_') && (Str::get_at(name, i+1) == '_')) {
                Str::put_at(name, i, ':'); Str::put_at(name, i+1, ':');
            }
        stopwatch_timer *st = Time::start_stopwatch(sequence_timer, name);
        DISCARD_TEXT(name)
        routine();
        int cs = Time::stop_stopwatch(st);
        if (cs > 0) LOG(".... " #routine "() took %dcs\n", cs);
    }
}

§2.2. Here, then, are the steps in the production line, presented without commentary. For what they do, see the relevant sections. Note that at the end of each stage, plugins are allowed to add further steps; see Task::advance_stage_to.

Before anything else can be done, we must create an empty Inter hierarchy into which we will "emit" an Inter program. No actual code will be emitted for some time yet, but identifier names and type declarations need somewhere to go. We then break the source into "compilation units" — basically, one for the main source text and one for each extension — because the Inter hierarchy will divide according to these units.

Divide into compilation units2.2 =

    Task::advance_stage_to(SUBDIVIDING_CSEQ, I"Dividing source into compilation units",
        -1, debugging, sequence_timer);
    BENCH(CompilationSettings::initialise_gcs)
    BENCH(Emit::create_emission_tree)
    BENCH(Hierarchy::establish)
    BENCH(Emit::rudimentary_kinds);
    BENCH(FundamentalConstants::emit);
    BENCH(RTVerbs::ConjugateVerbDefinitions);
    BENCH(NameResolution::make_the_tree)
    BENCH(IndexHeadings::write_as_xml)
    BENCH(CompilationUnits::determine)

• This code is used in §2.

§2.3. Most of the conceptual infrastructure in Inform is created by Inform source text in the Basic Inform or Standard Rules extensions, but not basic kinds of value such as "number", or the verb "to mean", or the meaning relation, and so on. Those absolute basics are made here.

Build a rudimentary set of kinds, relations, verbs and inference subjects2.3 =

    Task::advance_stage_to(BUILT_IN_STUFF_CSEQ, I"Making built in infrastructure",
        -1, debugging, sequence_timer);
    BENCH(InferenceSubjects::make_built_in);
    BENCH(Task::make_built_in_kind_constructors);
    BENCH(BinaryPredicateFamilies::first_stock)
    BENCH(BootVerbs::make_built_in)

• This code is used in §2.

§2.4. Pass three times through the major nodes2.4 =

    Task::advance_stage_to(SEMANTIC_ANALYSIS_CSEQ, I"Pre-pass through major nodes",
        1, debugging, sequence_timer);
    BENCH(MajorNodes::pre_pass)
    BENCH(Task::verify)
    Task::advance_stage_to(ASSERTIONS_PASS_1_CSEQ, I"First pass through major nodes",
        2, debugging, sequence_timer);
    BENCH(MajorNodes::pass_1)
    BENCH(Tables::traverse_to_stock)
    Task::advance_stage_to(ASSERTIONS_PASS_2_CSEQ, I"Second pass through major nodes",
        -1, debugging, sequence_timer);
    BENCH(MajorNodes::pass_2)

• This code is used in §2.

§2.5. Make the model world2.5 =

    Task::advance_stage_to(MODEL_CSEQ, I"Making the model world",
        -1, debugging, sequence_timer);
    BENCH(RTKinds::kind_declarations)
    BENCH(RTUseOptions::compile)
    BENCH(RTProperties::emit)
    BENCH(RTPropertyValues::allocate_attributes)
    BENCH(NounIdentifiers::name_all)
    BENCH(OrderingInstances::objects_in_definition_sequence)
    Task::advance_stage_to(MODEL_COMPLETE_CSEQ, I"Completing the model world",
        -1, debugging, sequence_timer);
    BENCH(World::stages_II_and_III)
    BENCH(World::stage_IV)

• This code is used in §2.

§2.6. Tables and grammar2.6 =

    Task::advance_stage_to(TABLES_CSEQ, I"Tables and grammar",
        -1, debugging, sequence_timer);
    BENCH(Measurements::validate_definitions)
    BENCH(BinaryPredicateFamilies::second_stock)
    BENCH(Tables::check_tables_for_kind_clashes)
    BENCH(RTTables::compile_print_table_names)

• This code is used in §2.

§2.7. Augment model world with low-level properties2.7 =

    Task::advance_stage_to(AUGMENT_CSEQ, I"Augment model world",
        -1, debugging, sequence_timer);
    BENCH(World::stage_V)

• This code is used in §2.

§2.8. Phrases and rules2.8 =

    Task::advance_stage_to(PHRASES_CSEQ, I"Phrases and rules",
        3, debugging, sequence_timer);
    BENCH(LiteralPatterns::define_named_phrases)
    BENCH(ImperativeDefinitions::assess_all)
    BENCH(Equations::traverse_to_stock)
    BENCH(Tables::traverse_to_stock)
    BENCH(RTProperties::annotate_attributes)
    BENCH(RTRules::RulebookOutcomePrintingRule)
    BENCH(RTKinds::compile_instance_counts)

• This code is used in §2.

§2.9. This proceeds in stages.

Generate inter, part 12.9 =

    Task::advance_stage_to(INTER1_CSEQ, I"Generating inter (1)",
        4, debugging, sequence_timer);
    BENCH(RTUseOptions::compile_pragmas)
    BENCH(FundamentalConstants::emit_build_number)
    BENCH(RTExtensions::ShowExtensionVersions_routine)
    BENCH(Kinds::Constructors::emit_constants)
    BENCH(RTUseOptions::TestUseOption_routine)
    BENCH(RTActivities::arrays)
    BENCH(RTRelations::compile_defined_relation_constants)
    BENCH(RTKinds::compile_data_type_support_routines)
    BENCH(RTKinds::I7_Kind_Name_routine)

• This code is used in §2.

§2.10. Generate inter, part 22.10 =

    Task::advance_stage_to(INTER2_CSEQ, I"Generating inter (2)",
        -1, debugging, sequence_timer);
    BENCH(InferenceSubjects::emit_all)
    BENCH(Tables::complete)
    BENCH(RTTables::compile)
    BENCH(RTEquations::compile_identifiers)
    BENCH(ImperativeDefinitions::compile_first_block)
    BENCH(RTRules::compile_rulebooks)
    BENCH(RTRules::rulebooks_array_array)
    BENCH(RTRules::rulebook_var_creators)
    BENCH(RTActivities::activity_var_creators)
    BENCH(RTRelations::IterateRelations)
    BENCH(RTRules::RulebookNames_array)
    BENCH(RTRules::RulePrintingRule_routine)
    BENCH(RTVerbs::ConjugateVerb)
    BENCH(RTAdjectives::agreements)
    if (debugging) {
        BENCH(InternalTests::InternalTestCases_routine)
    }

• This code is used in §2.

§2.11. Generate inter, part 32.11 =

    Task::advance_stage_to(INTER3_CSEQ, I"Generating inter (3)",
        -1, debugging, sequence_timer);
    BENCH(Lists::check)
    BENCH(ConstantLists::compile)
    BENCH(PhraseRequests::invoke_to_begin)
    BENCH(Closures::compile_closures)
    BENCH(Sequence::compile_function_resources)
    BENCH(Strings::compile_responses)
    BENCH(Lists::check)
    BENCH(ConstantLists::compile)
    BENCH(RTRelations::compile_defined_relations)
    BENCH(Sequence::compile_function_resources)
    BENCH(TextSubstitutions::allow_no_further_text_subs)
    BENCH(Deferrals::allow_no_further_deferrals)

• This code is used in §2.

§2.12. Generate inter, part 42.12 =

    Task::advance_stage_to(INTER4_CSEQ, I"Generating inter (4)",
        -1, debugging, sequence_timer);
    BENCH(Chronology::past_actions_i6_routines)
    BENCH(Chronology::compile_runtime)

• This code is used in §2.

§2.13. Generate inter, part 52.13 =

    Task::advance_stage_to(INTER5_CSEQ, I"Generating inter (5)",
        -1, debugging, sequence_timer);
    BENCH(RTMeasurements::compile_test_functions)
    BENCH(Lists::check)
    BENCH(ConstantLists::compile)
    BENCH(TextLiterals::compile)
    BENCH(RTKinds::compile_heap_allocator)
    BENCH(RTKinds::compile_structures)
    BENCH(Rules::check_response_usages)
    BENCH(RTUseOptions::configure_template)
    BENCH(LocalParking::compile_array)
    BENCH(RTBibliographicData::IFID_text)

• This code is used in §2.

§2.14. Generate index and bibliographic file2.14 =

    Task::advance_stage_to(BIBLIOGRAPHIC_CSEQ, I"Bibliographic work",
        -1, debugging, sequence_timer);
    BENCH(Hierarchy::log);
    BENCH(I6T::produce_index);

• This code is used in §2.

§3. We will define just one of the above steps here, because it works in a way which breaks the pattern of doing everything just once. For one thing, it's actually called twice in the above sequence.

The issue here is that each time an imperative definition is compiled to a function, that can require other resources to be compiled in turn. The code compiled into the function body can involve calls to functions derived from other imperative definitions, or even the same one reinterpreted:

To expose (X - a value):
    say "You admire [X]."

To advertise (T - text):
    expose T;
    let the price be "the price tag of [a random number between 5 and 10] pounds";
    expose the price.

Every turn:
    advertise "a valuable antique silver coffee pot".

Phrases are compiled on demand, but rules are always demanded, so the "every turn" rule here is compiled; that requires "advertise" to be compiled; which in turn requires a form of "expose X" to be compiled for X a text. But "advertise" also needs the text substitution "the price tag of [a random number between 5 and 10] pounds" to be compiled, and that in turn creates a further function compilation in order to provide a context for execution of the phrase "a random number between 5 and 10", which in turn... and so on.

The only way to be sure of handling all needs here is to keep on compiling until the process exhausts itself, and this we do. The process is structured as a set of coroutines¹ which each carry out as much as they can of the work which has arisen since they were last called, then return how much they did. Each may indirectly create work for the others, so we repeat until they are all happy.

The result terminates since eventually every "To..." phrase definition will have been compiled with every possible interpretation of its kinds. After that, everything fizzles out quickly, because none of the other resources here are able to create new work for each other. The safety cutout in this function is just defensive programming, and has never been activated. Typically only one or two iterations are needed in practical cases.

• ¹ C does not support coroutines, though that hasn't stopped hackers from using assembly language to manipulate return addresses on the C call stack, and/or use Duff's device. We avoid all that by using regular C functions which merely imitate coroutines by cooperatively giving way to each other. They return to the central organising function Sequence::compile_function_resources, not directly into each other's bodies. But I think the term "coroutine" is reasonable just the same. ↩

void Sequence::compile_function_resources?Usage of Sequence::compile_function_resources:
§2.11(void) {
    int repeat = TRUE, iterations = 0;
    while (repeat) {
        repeat = FALSE; iterations++;

        if (PhraseRequests::compilation_coroutine() > 0)       repeat = TRUE;
        if (ListTogether::compilation_coroutine() > 0)         repeat = TRUE;
        if (LoopingOverScope::compilation_coroutine() > 0)     repeat = TRUE;
        if (TextSubstitutions::compilation_coroutine() > 0)    repeat = TRUE;
        if (DeferredPropositions::compilation_coroutine() > 0) repeat = TRUE;

        if ((problem_count > 0) && (iterations > 10)) repeat = FALSE;
    }
    iterations--;  since the final round is one where everyone does nothing
    if (iterations > 0)
        LOG(".... Sequence::compile_function_resources completed in %d iteration%s\n",
            iterations, (iterations == 1)?"":"s");
}