VM closure problem

#[deriving(Show, Clone)]
pub enum Slot {
    Nil,
    Int(i64),
    Float(f64),
    Bool(bool),
    Str(String),
    Key(Keyword),
    Func(uint),
    VFunc(uint),
    Obj(CljObject),
    CType(uint),
    SCC(Closure),
}

macro_rules! execute (
    (using $vm:ident with $args:ident
     $($op:pat as $ty:ty => $code:expr),+) => (

        impl Execute for Instr {
            fn execute(&self, $vm:&mut Vm) -> Instr {
                match self.decode() {
                    $($op => { let $args : $ty = from_instr(self); $code }),+
                }
            }
        }
    )
) 

   vm::GETFREEVAR as OpAD => {
        
        let idx = args.d as uint;
        let dst_idx = args.a as uint;
     
        let freevar = match vm.slots.slot[1].clone()  {
                        SCC(clos) => clos.freevar[idx].clone(),
                        _ => fail!("Not Closure in Slot") 
                      }

        vm.slots.store(dst_idx, freevar);

        vm.fetch_next()
    },