The plain-vanilla code generation strategy, provided for the use of generators to imperative languages such as Inform 6 or C.

§1. The rest of this chapter is a plain-vanilla algorithm for turning Inter trees to imperative code, making method calls to the generator to handle each individual step as needed. I think this works quite elegantly, but then every beetle is a gazelle in the eyes of its mother.

The following function does everything except that the generator has already been sent the BEGIN_GENERATION_MTID method, and that the generator will subsequently be sent END_GENERATION_MTID: see Generators::go.

void Vanilla::go?Usage of Vanilla::go:
Code Generators - §4(code_generation *gen) {
    Traverse for pragmas1.1;
    Generators::declare_variables(gen, gen->global_variables);
    VanillaObjects::declare_properties(gen);
    VanillaFunctions::predeclare_functions(gen);
    General traverse1.3;
    VanillaConstants::declare_text_literals(gen);
    VanillaObjects::declare_kinds_and_instances(gen);
}

§1.1. Since pragma settings may affect what the generator does (that is the point of them, after all), we want to send those to the generator first of all. It can act on them or ignore them as it pleases.

Traverse for pragmas1.1 =

    InterTree::traverse_root_only(gen->from, Vanilla::pragma, gen, PRAGMA_IST);

• This code is used in §1.

§1.2.

void Vanilla::pragma?Usage of Vanilla::pragma:
§1.1(inter_tree *I, inter_tree_node *P, void *state) {
    code_generation *gen = (code_generation *) state;
    Generators::offer_pragma(gen, P,
        PragmaInstruction::target(P), PragmaInstruction::content(P));
}

§1.3. General traverse1.3 =

    gen->void_level = -1;
    InterTree::traverse(gen->from, Vanilla::iterate, gen, NULL, 0);

• This code is used in §1.

§2. This looks for the top level of packages which are not the code-body of functions, and calls Vanilla::node to recurse downwards through them. En route we also spot the functions, and declare those.

void Vanilla::iterate?Usage of Vanilla::iterate:
§1.3(inter_tree *I, inter_tree_node *P, void *state) {
    code_generation *gen = (code_generation *) state;
    if (Inode::is(P, PACKAGE_IST)) {
        inter_package *pack = PackageInstruction::at_this_head(P);
        if (InterPackage::is_a_function_body(pack))
            VanillaFunctions::declare_function(gen, PackageInstruction::name_symbol(pack));
    } else {
        inter_package *outer = InterPackage::container(P);
        if ((outer == NULL) || (InterPackage::is_a_function_body(outer) == FALSE)) {
            switch (Inode::get_construct_ID(P)) {
                case CONSTANT_IST:
                case VARIABLE_IST:
                case SPLAT_IST:
                case INSTANCE_IST:
                case PROPERTYVALUE_IST:
                    Vanilla::node(gen, P);
                    break;
            }
        }
    }
}

§3. The function Vanilla::node is a sort of handle-any-node function, and is the main way we iterate through the Inter tree.

Note that the general-traverse iteration above calls into this function, but that the function then recurses down through nodes. As a result, it sees pretty well the entire tree by the end.

The current node is always called P, for reasons now forgotten.

It is so often used recursively that the following abbreviation macros are helpful:

define VNODE_1C    Vanilla::node(gen, InterTree::first_child(P))
define VNODE_2C    Vanilla::node(gen, InterTree::second_child(P))
define VNODE_3C    Vanilla::node(gen, InterTree::third_child(P))
define VNODE_4C    Vanilla::node(gen, InterTree::fourth_child(P))
define VNODE_5C    Vanilla::node(gen, InterTree::fifth_child(P))
define VNODE_6C    Vanilla::node(gen, InterTree::sixth_child(P))
define VNODE_7C    Vanilla::node(gen, InterTree::seventh_child(P))
define VNODE_ALLC  LOOP_THROUGH_INTER_CHILDREN(C, P) Vanilla::node(gen, C)

void Vanilla::node?Usage of Vanilla::node:
§2
Inform 6 Code - §2, §5, §6, §7.2.1.2, §7.4, §7.6.1, §7.6.8
C References - §2.1.1, §2.1.2, §2.1.3
C Assembly - §6.2, §6.3
C Program Control - §2.7, §2.12
C Conditions - §2, §2.1, §2.2
C Function Model - §5.1, §5.2, §8.1(code_generation *gen, inter_tree_node *P) {
    switch (Inode::get_construct_ID(P)) {
        case CONSTANT_IST:      VanillaConstants::constant(gen, P); break;

        case LABEL_IST:         VanillaCode::label(gen, P); break;
        case CODE_IST:          VanillaCode::code(gen, P); break;
        case EVALUATION_IST:    VanillaCode::evaluation(gen, P); break;
        case REFERENCE_IST:     VanillaCode::reference(gen, P); break;
        case INV_IST:           VanillaCode::inv(gen, P); break;
        case CAST_IST:          VanillaCode::cast(gen, P); break;
        case VAL_IST:           VanillaCode::val_or_ref(gen, P, FALSE); break;
        case REF_IST:           VanillaCode::val_or_ref(gen, P, TRUE); break;
        case ASSEMBLY_IST:      VanillaCode::assembly(gen, P); break;
        case LAB_IST:           VanillaCode::lab(gen, P); break;

        case SPLAT_IST:         Vanilla::splat(gen, P); break;
        case PACKAGE_IST:       VNODE_ALLC; break;

        case INSTANCE_IST:      break;
        case VARIABLE_IST:      break;
        case PROPERTYVALUE_IST: break;
        case LOCAL_IST:         break;
        case NOP_IST:           break;
        case COMMENT_IST:       break;
        case PROVENANCE_IST:    VanillaCode::place_provenance(gen, P); break;

        case INVALID_IST:       InterErrors::backtrace(DL, P);
                                internal_error("INVALID node type in Inter tree");

        default:
            InterInstruction::write_construct_text(DL, P);
            internal_error("unexpected node type in Inter tree");
    }
}

§4. splat nodes are the joker in the pack. They copy material verbatim to the output, regardless of the language being generated. (In practice, of course, this means that the content of a splat must carefully have been pre-generated in the right format.) Inform uses such nodes as little as it possibly can.

A wrinkle, though, is that the special URL_SYMBOL_CHAR is used to mark out a URL for a symbol in the Inter tree: this is replaced with its properly generated name. So a splat is not quite generator-independent after all.

define URL_SYMBOL_CHAR 0x00A7

void Vanilla::splat?Usage of Vanilla::splat:
§3(code_generation *gen, inter_tree_node *P) {
    text_stream *OUT = CodeGen::current(gen);
    inter_tree *I = gen->from;
    text_stream *S = SplatInstruction::splatter(P);
    Vanilla::splat_matter(OUT, I, S);
}

void Vanilla::splat_matter?Usage of Vanilla::splat_matter:
Vanilla Objects - §5(OUTPUT_STREAM, inter_tree *I, text_stream *S) {
    int L = Str::len(S);
    for (int i=0; i<L; i++) {
        inchar32_t c = Str::get_at(S, i);
        if (c == URL_SYMBOL_CHAR) {
            TEMPORARY_TEXT(T)
            for (i++; i<L; i++) {
                inchar32_t c = Str::get_at(S, i);
                if (c == URL_SYMBOL_CHAR) break;
                PUT_TO(T, c);
            }
            inter_symbol *symb = InterSymbolsTable::URL_to_symbol(I, T);
            WRITE("%S", InterSymbol::trans(symb));
            DISCARD_TEXT(T)
        } else PUT(c);
    }
}