<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def xeval(source, optimize=True):
 """Compiles to native Python bytecode and runs program, returning the topmost value on the stack. Args: optimize: Whether to optimize the code after parsing it. Returns: None: If the stack is empty obj: If the stack contains a single value """

    native = xcompile(source, optimize=optimize)
    return native()