[WIP] Implement subroutine opcodes

Author: Giuseppe Cerami

eth/vm/rstack.py

@@ -16,7 +16,6 @@
     ValidationError,
 )
 
-from collections import UserList as rstack
 """
 This module simply implements for the return stack the exact same design used for the data stack.
 As this stack must simply push_int or pop1_int any time a subroutine is accessed or left, only those two functions are provided.
@@ -32,10 +31,10 @@ class RStack():
 
     def __init__(self) -> None:
         values: List[int]
-        self.values = rstack.data
-        self._append = rstack.data.append
-        self._pop_typed = rstack.data.pop
-        self.__len__ = rstack.data.__len__
+        self.values = values
+        self._append = values.append
+        self._pop_typed = values.pop
+        self.__len__ = values.__len__
 
     def push_int(self) -> int:
         if len(self.values) > 1023: