@Override
    public boolean isDefinedAt(A x) {
        for (PartialFunction<A, B> pf : pfs) {
            if (pf.isDefinedAt(x)) {
                return true;
            }
        }
        return false;
    }
Work exactly same as scala's PartialFunction.

@param <A> argument type
@param <B> result type
indexr-common/src/main/java/io/indexr/util/function/PartialFunction.java