// Comptime type construction — SELF-REFERENCE: a recursive enum minted via
// declare/define. `declare("List")` names a forward type the compiler registers
// at compile time, so the body can reference it as `*List` (a pointer to a type
// that isn't defined yet — legal, since a pointer needs no layout). `define`
// then fills the body in place. A by-VALUE self-reference would be infinite-size
// and rejected; `*List` is the idiom.
//
// Builds a 3-node cons-list (c -> b -> a -> nil), matches through the pointer
// payload directly (`if p ==`) and via deref (`n.*`), and counts it recursively.
#import "modules/std.sx";
#import "modules/std/meta.sx";

make_list :: () -> Type {
    h := declare("List");
    return define(h, .enum(.{ variants = .[
        EnumVariant.{ name = "cons", payload = *List },   // self-reference
        EnumVariant.{ name = "nil",  payload = void },
    ] }));
}

List :: make_list();

// Recursive traversal: `count` matches `n.*` (deref) into the same nominal type.
count :: (n: *List) -> i64 {
    if n.* == {
        case .cons: (next) { return 1 + count(next); }
        case .nil:  { return 0; }
    }
    return 0;
}

main :: () -> i32 {
    a : List = .nil;
    b : List = .cons(@a);
    c : List = .cons(@b);

    // Match the payload pointer directly (match auto-derefs).
    if c == {
        case .cons: (p) {
            if p == {
                case .cons: { print("c -> cons\n"); }
                case .nil:  { print("c -> nil\n"); }
            }
        }
        case .nil: { print("c is nil\n"); }
    }

    print("len = {}\n", count(@c));
    return 0;
}