Defining the symbol 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 PlugInstruction::define_construct?Usage of PlugInstruction::define_construct:
Inter Constructs - §15(void) {
    inter_construct *IC = InterInstruction::create_construct(PLUG_IST, I"plug");
    InterInstruction::specify_syntax(IC, I"plug IDENTIFIER TOKENS");
    METHOD_ADD(IC, CONSTRUCT_READ_MTID, PlugInstruction::read);
    METHOD_ADD(IC, CONSTRUCT_VERIFY_MTID, PlugInstruction::verify);
    InterInstruction::allow_in_depth_range(IC, 0, 1);
    InterInstruction::permit(IC, INSIDE_PLAIN_PACKAGE_ICUP);
}

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

§2. What it does is to specify a symbol which is a plug in the current tree: this results in an entry in the symbols table for the current package (which will always be /main/connectors, in fact) but not an instruction.

Surprisingly, this can actually result in a socket rather than a plug, but only in the case where the plug asks to wire to something existing in the current tree already.

void PlugInstruction::read?Usage of PlugInstruction::read:
§1(inter_construct *IC, inter_bookmark *IBM,
    inter_line_parse *ilp, inter_error_location *eloc, inter_error_message **E) {
    text_stream *symbol_text = ilp->mr.exp[0];
    text_stream *equate_text = ilp->mr.exp[1];

    inter_tree *I = InterBookmark::tree(IBM);
    inter_symbols_table *T = InterBookmark::scope(IBM);
    inter_symbol *plug_s = TextualInter::new_symbol(eloc, T, symbol_text, E);
    if (*E) return;
    InterSymbol::make_plug(plug_s);

    text_stream *equate_name = NULL;
    int to_name = FALSE;
    match_results mr = Regexp::create_mr();
    if (Regexp::match(&mr, equate_text, U"~~> \"(%C+)\"")) {
        equate_name = mr.exp[0];
        to_name = TRUE;
    } else if (Regexp::match(&mr, equate_text, U"~~> (%C+)")) {
        equate_name = mr.exp[0];
    } else {
        Regexp::dispose_of(&mr);
        *E = InterErrors::plain(I"bad plug syntax", eloc); return;
    }

    if (to_name) {
        Wiring::make_plug_wanting_identifier(plug_s, equate_name);
    } else {
        inter_symbol *eq_s = InterSymbolsTable::URL_to_symbol(I, equate_name);
        if (eq_s == NULL) Wiring::wire_to_name(plug_s, equate_name);
        else Wiring::make_socket_to(plug_s, eq_s);
    }
    Regexp::dispose_of(&mr);
}

§3. The following writes a valid line of textual Inter to declare a plug or socket, appearing at level N in the hierarchy.

void PlugInstruction::write_declaration?Usage of PlugInstruction::write_declaration:
The Package Construct - §8(OUTPUT_STREAM, inter_symbol *S, int N) {
    for (int L=0; L<N; L++) WRITE("\t");
    switch (InterSymbol::get_type(S)) {
        case PLUG_ISYMT:   WRITE("plug"); break;
        case SOCKET_ISYMT: WRITE("socket"); break;
        default: internal_error("not a connector"); break;
    }
    WRITE(" %S", InterSymbol::identifier(S));
    if (Wiring::is_wired_to_name(S)) {
        WRITE(" ~~> \"%S\"", Wiring::wired_to_name(S));
    } else if (Wiring::is_wired(S)) {
        WRITE(" ~~> ");
        InterSymbolsTable::write_symbol_URL(OUT, Wiring::wired_to(S));
    } else {
        WRITE(" ?");
    }
}