go/test/sieve.go

// $G $F.go && $L $F.$A  # don't run it - goes forever

// 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

// 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() {
  ch := new(chan int);  // Create a new channel.
  go Generate(ch);  // Start Generate() as a subprocess.
  for {
    prime := <ch;
    print prime, "\n";
    ch1 := new(chan int);
    go Filter(ch, ch1, prime);
    ch = ch1
  }
}

func main() {
  Sieve()
}