<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def concretize(x, solver, sym_handler):
 """ For now a lot of naive concretization is done when handling heap metadata to keep things manageable. This idiom showed up a lot as a result, so to reduce code repetition this function uses a callback to handle the one or two operations that varied across invocations. :param x: the item to be concretized :param solver: the solver to evaluate the item with :param sym_handler: the handler to be used when the item may take on more than one value :returns: a concrete value for the item """

    if solver.symbolic(x):
        try:
            return solver.eval_one(x)
        except SimSolverError:
            return sym_handler(x)
    else:
        return solver.eval(x)