def _batch_eval(self, exprs, n, extra_constraints=(), solver=None, model_callback=None): 
raise BackendError("<STR_LIT>")<EOL>
Evaluate one or multiple expressions.

:param exprs:               A list of expressions to evaluate.
:param n:                   Number of different solutions to return.
:param extra_constraints:   Extra constraints (as ASTs) to add to the solver for this solve.
:param solver:              A solver object, native to the backend, to assist in the evaluation.
:param model_callback:      a function that will be executed with recovered models (if any)
:return:                    A list of up to n tuples, where each tuple is a solution for all expressions.