any::TypeId,

    /// Marks the original type that this box was created from
    inner_type: TypeId,

    ) -> &'a mut Primitive<'a> {

    ) -> &'a mut FreePrimitive<'a> {

/// A VM value not attached to a particular VM instance
#[derive(Debug, Clone)]
#[allow(missing_docs)]
pub enum FreePrimitive<'a> {
    List(FreeListCell<'a>),
    Vector(Vec<FreePrimitive<'a>>),
    Bytevector(Vec<u8>),
    Integer(i64),
    Float(f64),
    String(Rc<str>),
    // As we don't know the target symbol table,
    // externalized symbols are represented by their symbol text
    Symbol(Rc<str>),
    Bool(bool),
    // TODO How can users *extract* what's in a PrimitiveBox.
    // - the type they want to extract as *must* implement Clone to get it out of the box
    Data(Rc<PrimitiveBox>),
}
/// A [`ListCell`] that is not attached to a VM instance
#[derive(Debug, Clone)]
pub enum FreeListCell<'a> {
    /// The empty list
    Null,
    /// A list with a single element
    Leaf(&'a FreePrimitive<'a>),
    /// A pair of list cells
    Cons(&'a FreeListCell<'a>, &'a FreeListCell<'a>),
}