Add start and end flags.

primes.go

@@ -1,32 +1,35 @@
 package main
 
-import "log"
+import (
+	"flag"
+	"log"
+)
 
-func runCounter(counter chan<- int, prime int) {
+func runCounter(counter chan<- uint, prime uint) {
 	for count := prime * 2; ; count += prime {
 		counter <- count
 	}
 }
 
-func newCounter(prime int) <-chan int {
-	counter := make(chan int)
+func newCounter(prime uint) <-chan uint {
+	counter := make(chan uint)
 	go runCounter(counter, prime)
 	return counter
 }
 
-func stepCounter(h map[int]<-chan int, counter <-chan int) {
+func stepCounter(h map[uint]<-chan uint, counter <-chan uint) {
 	c := <-counter
 	if h[c], counter = counter, h[c]; counter != nil {
 		go stepCounter(h, counter)
 	}
 }
 
-func insertPrime(primes chan<- int, h map[int]<-chan int, gC int) {
+func insertPrime(primes chan<- uint, h map[uint]<-chan uint, gC uint) {
 	primes <- gC
 	stepCounter(h, newCounter(gC))
 }
 
-func primeStep(primes chan<- int, h map[int]<-chan int, gC int) {
+func primeStep(primes chan<- uint, h map[uint]<-chan uint, gC uint) {
 	counter := h[gC]
 	if counter == nil {
 		insertPrime(primes, h, gC)
@@ -36,23 +39,34 @@ func primeStep(primes chan<- int, h map[int]<-chan int, gC int) {
 	}
 }
 
-func primeLoop(primes chan<- int) {
+func primeLoop(primes chan<- uint) {
 	primes <- 2
-	h := make(map[int]<-chan int)
+	h := make(map[uint]<-chan uint)
 	for gC := 3; ; gC += 2 {
-		primeStep(primes, h, gC)
+		primeStep(primes, h, uint(gC))
 	}
 }
 
-func makePrimes() <-chan int {
-	primes := make(chan int)
+func makePrimes() <-chan uint {
+	primes := make(chan uint)
 	go primeLoop(primes)
 	return primes
 }
 
 func main() {
+	var start uint
+	var end uint
+	flag.UintVar(&start, "start", 0, "usage")
+	flag.UintVar(&end, "end", 10, "usage")
+	flag.Parse()
 	primes := makePrimes()
 	for {
-		log.Println(<-primes)
+		prime := <-primes
+		if prime > end {
+			return
+		}
+		if prime >= start {
+			log.Println(prime)
+		}
 	}
 }