Defining the Evaluation construct.

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

void EvaluationInstruction::define_construct(void) {
    inter_construct *IC = InterInstruction::create_construct(EVALUATION_IST, I"evaluation");
    InterInstruction::specify_syntax(IC, I"evaluation");
    InterInstruction::data_extent_always(IC, 0);
    InterInstruction::allow_in_depth_range(IC, 1, INFINITELY_DEEP);
    InterInstruction::permit(IC, INSIDE_CODE_PACKAGE_ICUP);
    InterInstruction::permit(IC, CAN_HAVE_CHILDREN_ICUP);
    METHOD_ADD(IC, CONSTRUCT_READ_MTID, EvaluationInstruction::read);
    METHOD_ADD(IC, CONSTRUCT_WRITE_MTID, EvaluationInstruction::write);
    METHOD_ADD(IC, CONSTRUCT_VERIFY_CHILDREN_MTID, EvaluationInstruction::verify_children);

§2. Instructions. In bytecode, the frame of an evaluation instruction is laid out with just the two compulsory words — see Inter Nodes.

inter_error_message *EvaluationInstruction::new(inter_bookmark *IBM, int level,
    inter_error_location *eloc) {
    inter_tree_node *P = Inode::new_with_0_data_fields(IBM, EVALUATION_IST,
        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.

void EvaluationInstruction::verify_children(inter_construct *IC, inter_tree_node *P,
    inter_error_message **E) {
        if ((C->W.instruction[0] != INV_IST) &&
            (C->W.instruction[0] != SPLAT_IST) &&
            (C->W.instruction[0] != VAL_IST) &&
            (C->W.instruction[0] != LABEL_IST) &&
            (C->W.instruction[0] != EVALUATION_IST)) {
            *E = Inode::error(C, I"only a value can be below an evaluation", NULL);

§4. Creating from textual Inter syntax.

void EvaluationInstruction::read(inter_construct *IC, inter_bookmark *IBM,
    inter_line_parse *ilp, inter_error_location *eloc, inter_error_message **E) {
    *E = EvaluationInstruction::new(IBM, ilp->indent_level, eloc);

§5. Writing to textual Inter syntax.

void EvaluationInstruction::write(inter_construct *IC, OUTPUT_STREAM, inter_tree_node *P) {