fig-naive-prime-finder.go

package main

import (
	"fmt"
	"math/rand"
	"time"
)

func main() {
	repeatFn := func(
		done <-chan interface{},
		fn func() interface{},
	) <-chan interface{} {
		valueStream := make(chan interface{})
		go func() {
			defer close(valueStream)
			for {
				select {
				case <-done:
					return
				case valueStream <- fn():
				}
			}
		}()
		return valueStream
	}
	take := func(
		done <-chan interface{},
		valueStream <-chan interface{},
		num int,
	) <-chan interface{} {
		takeStream := make(chan interface{})
		go func() {
			defer close(takeStream)
			for i := 0; i < num; i++ {
				select {
				case <-done:
					return
				case takeStream <- <-valueStream:
				}
			}
		}()
		return takeStream
	}
	toInt := func(done <-chan interface{}, valueStream <-chan interface{}) <-chan int {
		intStream := make(chan int)
		go func() {
			defer close(intStream)
			for v := range valueStream {
				select {
				case <-done:
					return
				case intStream <- v.(int):
				}
			}
		}()
		return intStream
	}
	primeFinder := func(done <-chan interface{}, intStream <-chan int) <-chan interface{} {
		primeStream := make(chan interface{})
		go func() {
			defer close(primeStream)
			for integer := range intStream {
				integer -= 1
				prime := true
				for divisor := integer - 1; divisor > 1; divisor-- {
					if integer%divisor == 0 {
						prime = false
						break
					}
				}

				if prime {
					select {
					case <-done:
						return
					case primeStream <- integer:
					}
				}
			}
		}()
		return primeStream
	}
	rand := func() interface{} { return rand.Intn(50000000) }

	done := make(chan interface{})
	defer close(done)

	start := time.Now()

	randIntStream := toInt(done, repeatFn(done, rand))
	fmt.Println("Primes:")
	for prime := range take(done, primeFinder(done, randIntStream), 10) {
		fmt.Printf("\t%d\n", prime)
	}

	fmt.Printf("Search took: %v", time.Since(start))
}