pub fn emit_map<K, V, M: Map<K, V>>(
    this: &M,
    tag: u32,
    ktag: u32,
    vtag: u32,
    stream: &mut OutputStream,
    kmapper: fn(_: &mut OutputStream, _: u32, _: &K),
    vmapper: fn(_: &mut OutputStream, _: u32, _: &V)
)