trick

primes.go

package main

import (
	"fmt"
	"sync"
)

func piper(left chan int, wg *sync.WaitGroup) {
	forRight := make(chan int, 0)

	wg.Add(1)
	go (func(left, right chan int) {
		defer wg.Done()
		needNewPipe := true

		number := <-left
		fmt.Printf("%d ", number)

		for newNumber := range left {
			if newNumber%number != 0 {
				if needNewPipe {
					needNewPipe = false

					go piper(forRight, wg)
				}

				forRight <- newNumber
			}
		}

		// Notify right piper we are done.
		close(forRight)

	})(left, forRight)
}

func main() {
	var wg sync.WaitGroup

	init := make(chan int, 0)

	go piper(init, &wg)

	for i := 2; i < 1000; i++ {
		init <- i
	}
	close(init)

	wg.Wait()
}