Defining the Lab construct.

§1. Definition. For what this does and why it is used, see Textual Inter (in inter).

void LabInstruction::define_construct(void) {
    inter_construct *IC = InterInstruction::create_construct(LAB_IST, I"lab");
    InterInstruction::specify_syntax(IC, I"lab .IDENTIFIER");
    InterInstruction::data_extent_always(IC, 1);
    InterInstruction::allow_in_depth_range(IC, 1, INFINITELY_DEEP);
    InterInstruction::permit(IC, INSIDE_CODE_PACKAGE_ICUP);
    METHOD_ADD(IC, CONSTRUCT_READ_MTID, LabInstruction::read);
    METHOD_ADD(IC, CONSTRUCT_VERIFY_MTID, LabInstruction::verify);
    METHOD_ADD(IC, CONSTRUCT_WRITE_MTID, LabInstruction::write);

§2. Instructions. In bytecode, the frame of a lab instruction is laid out with the compulsory words — see Inter Nodes — followed by:

inter_error_message *LabInstruction::new(inter_bookmark *IBM, inter_symbol *label,
    inter_ti level, inter_error_location *eloc) {
    inter_tree_node *P = Inode::new_with_1_data_field(IBM, LAB_IST,
        /* LABEL_LAB_IFLD: */ InterSymbolsTable::id_at_bookmark(IBM, label),
        eloc, (inter_ti) level);
    inter_error_message *E = VerifyingInter::instruction(InterBookmark::package(IBM), P);
    if (E) return E;
    NodePlacement::move_to_moving_bookmark(P, IBM);
    return NULL;

§3. Verification consists only of sanity checks. Note that we do not make the customary call to VerifyingInter::SID_field on LABEL_LAB_IFLD for timing reasons: it may refer to a symbol not yet defined.

void LabInstruction::verify(inter_construct *IC, inter_tree_node *P, inter_package *owner,
    inter_error_message **E) {
    inter_symbol *label = LabInstruction::label_symbol(P);
    if (InterSymbol::is_label(label) == FALSE) {
        *E = Inode::error(P, I"no such label", NULL);

§4. Creating from textual Inter syntax. Note that a lab can occur either before or after the creation point for the label it refers to; so if we have an unknown label name, we create it as a label in expectation that the position will be declared in a future instruction.

void LabInstruction::read(inter_construct *IC, inter_bookmark *IBM, inter_line_parse *ilp,
    inter_error_location *eloc, inter_error_message **E) {
    text_stream *label_name = ilp->mr.exp[0];
    inter_symbol *label_s =
        InterSymbolsTable::symbol_from_name(InterBookmark::scope(IBM), label_name);
    if (label_s == NULL) {
        label_s = TextualInter::new_symbol(eloc, InterBookmark::scope(IBM), label_name, E);
        if (*E) return;
    if (InterSymbol::is_label(label_s) == FALSE) {
        *E = InterErrors::plain(I"not a label", eloc);
    *E = LabInstruction::new(IBM, label_s, (inter_ti) ilp->indent_level, eloc);

§5. Writing to textual Inter syntax.

void LabInstruction::write(inter_construct *IC, OUTPUT_STREAM, inter_tree_node *P) {
    inter_symbol *label_s = LabInstruction::label_symbol(P);
    WRITE("lab %S", InterSymbol::identifier(label_s));

§6. Access function.

inter_symbol *LabInstruction::label_symbol(inter_tree_node *P) {
    if (P == NULL) return NULL;
    if (Inode::isnt(P, LAB_IST)) return NULL;
    return InterSymbolsTable::symbol_from_ID_at_node(P, LABEL_LAB_IFLD);