Defining the Reference construct.

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

void ReferenceInstruction::define_construct(void) {
    inter_construct *IC = InterInstruction::create_construct(REFERENCE_IST, I"reference");
    InterInstruction::specify_syntax(IC, I"reference");
    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, ReferenceInstruction::read);
    METHOD_ADD(IC, CONSTRUCT_WRITE_MTID, ReferenceInstruction::write);
    METHOD_ADD(IC, CONSTRUCT_VERIFY_CHILDREN_MTID, ReferenceInstruction::verify_children);

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

inter_error_message *ReferenceInstruction::new(inter_bookmark *IBM, int level,
    inter_error_location *eloc) {
    inter_tree_node *P = Inode::new_with_0_data_fields(IBM, REFERENCE_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 ReferenceInstruction::verify_children(inter_construct *IC, inter_tree_node *P,
    inter_error_message **E) {
        if ((C->W.instruction[0] != INV_IST) &&
            (C->W.instruction[0] != REF_IST) &&
            (C->W.instruction[0] != SPLAT_IST) &&
            (C->W.instruction[0] != VAL_IST) &&
            (C->W.instruction[0] != LABEL_IST)) {
            *E = Inode::error(C, I"instruction cannot be referenced", NULL);

§4. Creating from textual Inter syntax.

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

§5. Writing to textual Inter syntax.

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

§6. Detection. This tests whether a node P represents a reference to a primitive of a given BIP. So, for example, it can look for the configuration

        inv !propertyvalue

by being called with seek_bip equal to PROPERTYVALUE_BIP.

int ReferenceInstruction::node_is_ref_to(inter_tree *I, inter_tree_node *P,
    inter_ti seek_bip) {
    int reffed = FALSE;
    while (Inode::is(P, REFERENCE_IST)) {
        P = InterTree::first_child(P);
        reffed = TRUE;
    if (Inode::is(P, INV_IST)) {
        if (InvInstruction::method(P) == PRIMITIVE_INVMETH) {
            inter_symbol *prim = InvInstruction::primitive(P);
            inter_ti bip = Primitives::to_BIP(I, prim);
            if ((bip == seek_bip) && (reffed)) return TRUE;
    return FALSE;