go/test/chan/sieve.go

// $G $D/$F.go && $L $F.$A && ./$A.out

// 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.

// This version generates up to 100 and checks the results.
// With a channel, of course.

package main

// Send the sequence 2, 3, 4, ... to channel 'ch'.
func Generate(ch *chan-< int) {
	for i := 2; ; i++ {
		ch -< i  // Send 'i' to channel 'ch'.
	}
}

// Copy the values from channel 'in' to channel 'out',
// removing those divisible by 'prime'.
func Filter(in *chan<- int, out *chan-< int, prime int) {
	for {
		i := <-in  // Receive value of new variable 'i' from 'in'.
		if i % prime != 0 {
			out -< i  // Send 'i' to channel 'out'.
		}
	}
}

// The prime sieve: Daisy-chain Filter processes together.
func Sieve(primes *chan-< int) {
	ch := new(chan int);  // Create a new channel.
	go Generate(ch);  // Start Generate() as a subprocess.
	for {
		prime := <-ch;
		primes -< prime;
		ch1 := new(chan int);
		go Filter(ch, ch1, prime);
		ch = ch1
	}
}

func main() {
	primes := new(chan int);
	go Sieve(primes);
	if <-primes != 2 { panic(2) }
	if <-primes != 3 { panic(3) }
	if <-primes != 5 { panic(5) }
	if <-primes != 7 { panic(7) }
	if <-primes != 11 { panic(11) }
	if <-primes != 13 { panic(13) }
	if <-primes != 17 { panic(17) }
	if <-primes != 19 { panic(19) }
	if <-primes != 23 { panic(23) }
	if <-primes != 29 { panic(29) }
	if <-primes != 31 { panic(31) }
	if <-primes != 37 { panic(37) }
	if <-primes != 41 { panic(41) }
	if <-primes != 43 { panic(43) }
	if <-primes != 47 { panic(47) }
	if <-primes != 53 { panic(53) }
	if <-primes != 59 { panic(59) }
	if <-primes != 61 { panic(61) }
	if <-primes != 67 { panic(67) }
	if <-primes != 71 { panic(71) }
	if <-primes != 73 { panic(73) }
	if <-primes != 79 { panic(79) }
	if <-primes != 83 { panic(83) }
	if <-primes != 89 { panic(89) }
	if <-primes != 97 { panic(97) }
	sys.exit(0);
}