Faking tail call optimization with concurrency

recursion.go

package main

import "fmt"

func Fact(k float64) float64 {
	if k == 1 {
		return 1
	}
	return k * Fact(k-1)
}

func TailFact(k, prod float64) float64 {
	if k == 1 {
		return prod
	}
	return TailFact(k-1, k*prod)
}

// This is rather sneaky...
func SneakyFact(k float64, prod float64, result chan<- float64) {
	if k == 1 {
		result <- prod
		return
	}
	prod *= k
	go SneakyFact(k-1, prod, result)
	return
}

func main() {

	//fmt.Println(Fact(1000000)) // bad
	//fmt.Println(TailFact(1000000, 1)) // still bad

	ch := make(chan float64, 1)
	SneakyFact(1000000, 1, ch)
	fmt.Println(<-ch)
}