Defining the version construct.

§1. This is a pseudo-construct: it looks like an instruction in textual Inter syntax, but specifies something else, and does not result in an inter_tree_node.

void VersionInstruction::define_construct(void) {
    inter_construct *IC = InterInstruction::create_construct(VERSION_IST, I"version");
    InterInstruction::specify_syntax(IC, I"version TOKEN");
    InterInstruction::permit(IC, OUTSIDE_OF_PACKAGES_ICUP);
    METHOD_ADD(IC, CONSTRUCT_READ_MTID, VersionInstruction::read);
    METHOD_ADD(IC, CONSTRUCT_VERIFY_MTID, VersionInstruction::verify);

void VersionInstruction::verify(inter_construct *IC, inter_tree_node *P,
    inter_package *owner, inter_error_message **E) {
    *E = Inode::error(P, I"VERSION_IST structures cannot exist", NULL);

§2. What it does is to specify the version of the Inter language used in the file of textual Inter being read in. Now, we can only read a version compatible with the version we use ourselves: so we throw an error if it is not.

void VersionInstruction::read(inter_construct *IC, inter_bookmark *IBM,
    inter_line_parse *ilp, inter_error_location *eloc, inter_error_message **E) {
    semantic_version_number file_version = VersionNumbers::from_text(ilp->mr.exp[0]);
    if (InterVersion::check_readable(file_version) == FALSE) {
        semantic_version_number current_version = InterVersion::current();
        text_stream *erm = Str::new();
            "file holds Inter written for specification v%v, but I expect v%v",
            &file_version, &current_version);
        *E = InterErrors::plain(erm, eloc);