def set_combiner(value, mutator, *args, **kwargs):
    """Expects the output of the source to be a set to which
    the result of each mutator is added.
    """
    value.add(mutator(*args, **kwargs))
    return value
def set_combiner ( value , mutator , * args , ** kwargs ) : value . add ( mutator ( * args , ** kwargs ) ) return value
Expects the output of the source to be a set to which
    the result of each mutator is added.