<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def eval(self, amplstatements, **kwargs):
 """ Parses AMPL code and evaluates it as a possibly empty sequence of AMPL declarations and statements. As a side effect, it invalidates all entities (as the passed statements can contain any arbitrary command); the lists of entities will be re-populated lazily (at first access) The output of interpreting the statements is passed to the current OutputHandler (see getOutputHandler and setOutputHandler). By default, errors and warnings are printed on stdout. This behavior can be changed reassigning an ErrorHandler using setErrorHandler. Args: amplstatements: A collection of AMPL statements and declarations to be passed to the interpreter. Raises: RuntimeError: if the input is not a complete AMPL statement (e.g. if it does not end with semicolon) or if the underlying interpreter is not running. """

        if self._langext is not None:
            amplstatements = self._langext.translate(amplstatements, **kwargs)
        lock_and_call(
            lambda: self._impl.eval(amplstatements),
            self._lock
        )
        self._errorhandler_wrapper.check()