Fix a lot of things and implement gc

src/value.rs

@@ -1,10 +1,11 @@
 use Result;
 use std::convert::TryInto;
+use heap::Heap;
 
-#[derive(Debug, Copy, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum Value {
     Int(i32),
-    HeapRef(usize),
+    HeapRef(Heap),
 }
 
 impl TryInto<i32> for Value {
@@ -22,9 +23,9 @@ impl TryInto<i32> for &Value {
     type Error = &'static str;
 
     fn try_into(self) -> Result<i32> {
-        match self {
-            &Value::Int(a) => Ok(a),
-            &Value::HeapRef(_) => Err("Cannot use HeapRef as i32"),
+        match *self {
+            Value::Int(a) => Ok(a),
+            Value::HeapRef(_) => Err("Cannot use HeapRef as i32"),
         }
     }
 }