Refactor handling of Ret.

stepper.py

@@ -63,7 +63,11 @@ def terminate(terminator, blocks, stack_frames, ssa_env, global_env, memory):
         else:
             oper_v = eval_oper(oper, ssa_env, global_env)
         if len(stack_frames) == 0:
-            return [], None, [], [], ssa_env, memory, oper_v
+            new_insns = []
+            new_terminator = None
+            new_blocks = {}
+            new_ssa_env = ssa_env
+            new_stack_frames = []
         else:
             new_insns, new_terminator, new_blocks, new_ssa_env = stack_frames[0]
             new_stack_frames = stack_frames[1:]