Defining the nop construct.

§1. Definition. This instruction does nothing at all, has no textual representation and is nevertheless useful when constructing Inter in memory.

It exists as a convenience used by Inform when it needs to write simultaneously to multiple positions within the same node's child list — the idea being that a nop statement acts as a divider. For example, by placing the A write position just before a nop N, and the B write position just after, Inform will generate A1, A2, A3, ..., N, B1, B2, ..., rather than (say) A1, B1, A2, A3, B2, ... The extra N is simply ignored in code generation, so it causes no problems to have it.

void NopInstruction::define_construct(void) {
    inter_construct *IC = InterInstruction::create_construct(NOP_IST, I"nop");
    InterInstruction::data_extent_always(IC, 0);
    InterInstruction::allow_in_depth_range(IC, 0, INFINITELY_DEEP);
    InterInstruction::permit(IC, OUTSIDE_OF_PACKAGES_ICUP);
    InterInstruction::permit(IC, INSIDE_PLAIN_PACKAGE_ICUP);
    InterInstruction::permit(IC, INSIDE_CODE_PACKAGE_ICUP);
    METHOD_ADD(IC, CONSTRUCT_WRITE_MTID, NopInstruction::write);

§2. Instructions. In bytecode, the frame of a nop instruction consists only of the two compulsory words — see Inter Nodes.

inter_error_message *NopInstruction::new(inter_bookmark *IBM, inter_ti level,
    inter_error_location *eloc) {
    inter_tree_node *P = Inode::new_with_0_data_fields(IBM, NOP_IST,
        eloc, 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. Writing to textual Inter syntax. The nop construct is not expressible in textual Inter, but can be printed out all the same, purely so that a stack backtrace will show it.

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