Attempting to encode a nested (aka "non-regular", "non-uniform") data type in Rust.

gistfile1.rs

enum Seq<A> {
    Nil,
    Cons{hd: A, tl:~Seq<(A,A)>}
}

impl<A> Seq<A> {
    fn len(&self) -> int {
        match self {
            &Nil => 0,
            &Cons{ hd: x, tl: ref s } => 1 + 2 * s.len()
        }
    }
}

fn main() {
    io::println(fmt!("Hello World"));
}