go/doc/progs/sieve1.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import "fmt"

// Send the sequence 2, 3, 4, ... to returned channel 
func generate() chan int {
	ch := make(chan int)
	go func(){
		for i := 2; ; i++ {
			ch <- i
		}
	}()
	return ch
}

// Filter out input values divisible by 'prime', send rest to returned channel
func filter(in chan int, prime int) chan int {
	out := make(chan int)
	go func() {
		for {
			if i := <-in; i % prime != 0 {
				out <- i
			}
		}
	}()
	return out
}

func sieve() chan int {
	out := make(chan int)
	go func() {
		ch := generate()
		for {
			prime := <-ch
			out <- prime
			ch = filter(ch, prime)
		}
	}()
	return out
}

func main() {
	primes := sieve()
	for i := 0; i < 100; i++ { // Print the first hundred primes.
		fmt.Println(<-primes)
	}
}