[VersionInstruction::] The Version Construct.

Defining the version construct.

@ 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);
}

@ 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();
		WRITE_TO(erm,
			"file holds Inter written for specification v%v, but I expect v%v",
			&file_version, &current_version);
		*E = InterErrors::plain(erm, eloc);
	}
}