Range Over Channels in Mercury

Our first example demonstrates how to iterate over values received from a channel. In Java, we’ll use a BlockingQueue to simulate this behavior.

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

public class RangeOverChannels {
    public static void main(String[] args) throws InterruptedException {
        // We'll iterate over 2 values in the queue.
        BlockingQueue<String> queue = new LinkedBlockingQueue<>(2);
        queue.put("one");
        queue.put("two");

        // This loop iterates over each element as it's received from queue.
        // Because we don't add any more elements after the initial two,
        // the iteration terminates after receiving the 2 elements.
        while (!queue.isEmpty()) {
            String elem = queue.take();
            System.out.println(elem);
        }
    }
}

To run the program:

$ javac RangeOverChannels.java
$ java RangeOverChannels
one
two

This example demonstrates how to iterate over elements in a BlockingQueue, which is similar to ranging over a channel in other languages. In Java, we use a while loop to continue taking elements from the queue until it’s empty.

Note that in Java, we don’t have a direct equivalent to “closing” a channel. Instead, we simply stop adding elements to the queue and process until it’s empty. If you need to signal that no more elements will be added, you might use a separate boolean flag or a poison pill object.

This example also shows that it’s possible to process all elements in a queue even after we’ve stopped adding new ones, similar to receiving remaining values from a closed channel in other languages.