How the vanilla code generation strategy declares functions.

§1. The following traverses the Inter tree to discover all of the functions defined within it, and does two important things for each:

• (a) Assigns it a vanilla_function of metadata, and then
• (b) Calls Generators::predeclare_function to let the generator know that the function exists. Not all target languages require functions to be predeclared, so generators can if they choose ignore this.

void VanillaFunctions::predeclare_functions?Usage of VanillaFunctions::predeclare_functions:
Vanilla - §1(code_generation *gen) {
    InterTree::traverse(gen->from, VanillaFunctions::predeclare_this, gen, NULL, PACKAGE_IST);
}

§2.

void VanillaFunctions::predeclare_this?Usage of VanillaFunctions::predeclare_this:
§1(inter_tree *I, inter_tree_node *P, void *state) {
    code_generation *gen = (code_generation *) state;
    inter_symbol *fn_s = PackageInstruction::name_symbol(PackageInstruction::at_this_head(P));
    if (PackageInstruction::is_function(fn_s)) {
        vanilla_function *vf = VanillaFunctions::new(gen, fn_s);
        Generators::predeclare_function(gen, vf);
    }
}

§3. Each function has metadata as follows. Note that:

• (a) Phrase syntax will only exist for functions which originated in Inform 7 source text; so for functions coming from kits, phrase_syntax will be empty and formal_arity will be 0.
• (b) For I7 functions, formal_arity will be the number of arguments in the phrase preamble.
• (c) For all functions, max_arity is the total number of local variables in the function, and that is by definition the largest number of arguments which could possibly be passed to this function by a call. Note that it will always be true that max_arity >= formal_arity.
• (d) Calling conventions for Inter functions are not entirely simple: see C Function Model for discussion of how they differ from regular C functions. In particular, any function with a local variable called _vararg_count is called with a variable number of arguments, placed on the stack before the call, rather than with arguments placed into local variables in the usual way.

typedef struct vanilla_function {
    struct text_stream *identifier;
    struct text_stream *phrase_syntax;
    struct linked_list *locals;  of text_stream, the names only
    struct inter_tree_node *function_body;
    int takes_variable_arguments;
    int max_arity;
    int formal_arity;
    CLASS_DEFINITION
} vanilla_function;

• The structure vanilla_function is accessed in 2/vi, 4/i6c2, 5/clt, 5/cfm and here.

§4. This produces a synopsis of the phrase syntax which can be used in an identifier. For example, for "To award (N - number) points to (P - person)", the following writes award_X_points_to_X:

void VanillaFunctions::syntax_synopsis?Usage of VanillaFunctions::syntax_synopsis:
C Function Model - §14.3(OUTPUT_STREAM, vanilla_function *vf) {
    text_stream *md = vf->phrase_syntax;
    for (int i=3, bracketed = FALSE; i<Str::len(md); i++) {
        inchar32_t c = Str::get_at(md, i);
        if (bracketed) {
            if (c == ')') bracketed = FALSE;
        } else if (c == '(') {
            PUT('X');
            bracketed = TRUE;
        } else if (Characters::isalpha(c)) {
            PUT(c);
        } else {
            PUT('_');
        }
    }
}

§5. And on the same example, this would return 2:

int VanillaFunctions::formal_arity?Usage of VanillaFunctions::formal_arity:
§6(vanilla_function *vf) {
    int A = 0;
    LOOP_THROUGH_TEXT(pos, vf->phrase_syntax)
        if (Str::get(pos) == '(')
            A++;
    return A;
}

§6. So, then:

vanilla_function *VanillaFunctions::new?Usage of VanillaFunctions::new:
§2(code_generation *gen, inter_symbol *fn_s) {
    inter_package *P = InterPackage::container(fn_s->definition);
    inter_package *PP = InterPackage::parent(P);
    text_stream *i7_syntax = PP?(Metadata::optional_textual(PP, I"^phrase_syntax")):NULL;
    vanilla_function *vf = CREATE(vanilla_function);
    vf->takes_variable_arguments = FALSE;
    vf->identifier = Str::duplicate(InterSymbol::trans(fn_s));
    vf->locals = NEW_LINKED_LIST(text_stream);
    vf->phrase_syntax = Str::duplicate(i7_syntax);
    inter_package *code_block = PackageInstruction::which(fn_s);
    vf->function_body = InterPackage::head(code_block);
    fn_s->translation_data = STORE_POINTER_vanilla_function(vf);
    VanillaFunctions::seek_locals(gen, vf->function_body, vf);
    vf->max_arity = LinkedLists::len(vf->locals);
    vf->formal_arity = VanillaFunctions::formal_arity(vf);
    return vf;
}

§7. This performs a local traverse of the body of the function to look for local variable declarations.

Note that we look at InterSymbol::identifier(local_s) not InterSymbol::trans(local_s) when checking for _vararg_count because the translated name may have been mangled in some way by the generator. (As indeed the C generator does, mangling this to local__vararg_count.)

void VanillaFunctions::seek_locals?Usage of VanillaFunctions::seek_locals:
§6(code_generation *gen, inter_tree_node *P,
    vanilla_function *vf) {
    if (Inode::is(P, LOCAL_IST)) {
        inter_symbol *local_s = LocalInstruction::variable(P);
        ADD_TO_LINKED_LIST(InterSymbol::trans(local_s), text_stream, vf->locals);
        if (Str::eq(InterSymbol::identifier(local_s), I"_vararg_count"))
            vf->takes_variable_arguments = TRUE;
    }
    LOOP_THROUGH_INTER_CHILDREN(F, P) VanillaFunctions::seek_locals(gen, F, vf);
}

§8. Note that a pointer to vf is cached with each function name symbol for speed:

void VanillaFunctions::declare_function?Usage of VanillaFunctions::declare_function:
Vanilla - §2(code_generation *gen, inter_symbol *fn_s) {
    vanilla_function *vf = RETRIEVE_POINTER_vanilla_function(fn_s->translation_data);
    Generators::declare_function(gen, vf);
}

§9.

void VanillaFunctions::invoke_function?Usage of VanillaFunctions::invoke_function:
Vanilla Code - §3.2(code_generation *gen, inter_symbol *fn_s,
    inter_tree_node *P, int void_context) {
    inter_tree_node *D = fn_s->definition;
    if ((Inode::is(D, CONSTANT_IST)) &&
        (ConstantInstruction::list_format(D) == CONST_LIST_FORMAT_NONE)) {
        inter_pair val = ConstantInstruction::constant(D);
        if (InterValuePairs::is_symbolic(val)) {
            inter_symbol *S = InterValuePairs::to_symbol_at(val, D);
            if (S) fn_s = S;
        }
    }
    vanilla_function *vf = RETRIEVE_POINTER_vanilla_function(fn_s->translation_data);
    if (vf == NULL) internal_error("no translation data");
    Generators::invoke_function(gen, P, vf, void_context);
}