Defining the cast construct.

• §1. Definition
• §2. Instructions
• §4. Creating from textual Inter syntax
• §5. Writing to textual Inter syntax

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

void CastInstruction::define_construct?Usage of CastInstruction::define_construct:
Inter Constructs - §15(void) {
    inter_construct *IC = InterInstruction::create_construct(CAST_IST, I"cast");
    InterInstruction::specify_syntax(IC, I"cast IDENTIFIER <- IDENTIFIER");
    InterInstruction::data_extent_always(IC, 2);
    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, CastInstruction::read);
    METHOD_ADD(IC, CONSTRUCT_VERIFY_MTID, CastInstruction::verify);
    METHOD_ADD(IC, CONSTRUCT_WRITE_MTID, CastInstruction::write);
    METHOD_ADD(IC, CONSTRUCT_VERIFY_CHILDREN_MTID, CastInstruction::verify_children);
}

§2. Instructions. In bytecode, the frame of a cast instruction is laid out with the compulsory words — see Inter Nodes — followed by:

define TO_KIND_CAST_IFLD   (DATA_IFLD + 0)
define FROM_KIND_CAST_IFLD (DATA_IFLD + 1)

inter_error_message *CastInstruction::new?Usage of CastInstruction::new:
§4(inter_bookmark *IBM, inter_type from_type,
    inter_type to_type, inter_ti level, inter_error_location *eloc) {
    inter_tree_node *P = Inode::new_with_2_data_fields(IBM, CAST_IST,
        /* TO_KIND_CAST_IFLD: */   InterTypes::to_TID_at(IBM, to_type),
        /* FROM_KIND_CAST_IFLD: */ InterTypes::to_TID_at(IBM, from_type),
        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 CastInstruction::verify?Usage of CastInstruction::verify:
§1(inter_construct *IC, inter_tree_node *P, inter_package *owner,
    inter_error_message **E) {
    *E = VerifyingInter::TID_field(owner, P, TO_KIND_CAST_IFLD);
    if (*E) return;
    *E = VerifyingInter::TID_field(owner, P, FROM_KIND_CAST_IFLD);
    if (*E) return;
}

void CastInstruction::verify_children?Usage of CastInstruction::verify_children:
§1(inter_construct *IC, inter_tree_node *P,
    inter_error_message **E) {
    int arity_as_invoked = 0;
    LOOP_THROUGH_INTER_CHILDREN(C, P) {
        arity_as_invoked++;
        if ((C->W.instruction[0] != INV_IST) &&
            (C->W.instruction[0] != VAL_IST) &&
            (C->W.instruction[0] != EVALUATION_IST) &&
            (C->W.instruction[0] != CAST_IST)) {
            *E = Inode::error(P, I"only a value can be under a cast", NULL);
            return;
        }
    }
    if (arity_as_invoked != 1) {
        *E = Inode::error(P, I"a cast should have exactly one child", NULL);
        return;
    }
}

§4. Creating from textual Inter syntax.

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

    inter_symbols_table *T = InterBookmark::scope(IBM);
    inter_type from_type = InterTypes::parse_simple(T, eloc, from_text, E);
    if (*E) return;
    inter_type to_type = InterTypes::parse_simple(T, eloc, to_text, E);
    if (*E) return;

    *E = CastInstruction::new(IBM, from_type, to_type, (inter_ti) ilp->indent_level, eloc);
}

§5. Writing to textual Inter syntax.

void CastInstruction::write?Usage of CastInstruction::write:
§1(inter_construct *IC, OUTPUT_STREAM, inter_tree_node *P) {
    WRITE("cast ");
    TextualInter::write_compulsory_type_marker(OUT, P, TO_KIND_CAST_IFLD);
    WRITE(" <- ");
    TextualInter::write_compulsory_type_marker(OUT, P, FROM_KIND_CAST_IFLD);
}