用Java中的Streams实现与Haskell的“或”函数等效的好方法是什么

Question

I'm looking for an equivalent to Haskell's "or" function in Java using Streams.

This version does not return when given an infinite stream:

    public static Boolean or(Stream<Boolean> bs) {
      return bs.reduce(false, (x, y) -> x || y);
    }

This version does not run because the bs stream is used twice:

    public static Boolean or(Stream<Boolean> bs) {
    Optional<Boolean> b0 = bs.findFirst();

    if (b0.isPresent()) {
        return  b0.get() || or(bs.skip(1));
    } else {
        return false;
    }
}

I'm new to Java, so any tips would be greatly appreciated. Thanks.

Answer 1

Just use Stream#anyMatch(...) with a Predicate that returns the value itself.

// assuming there are no null values
boolean or = booleans.anyMatch(b -> b); // will only match if value is true

Similarly to what is described in the Haskell documentation for or that you linked, if the Stream is infinite, it cannot return false . It will continue to consume the Stream if all it sees is false values.

This is a short-circuiting operation. It will (actually, it can, but doesn't have to) return true as soon as it finds a true value.