gistfile1.go

package main

import "fmt"

type (
	Test1 func() Test2
	Test2 func() Test1
)

func (t Test1) Next() Test2{
	return t()
}

func (t Test2) Next() Test1{
	return t()
}

var (
	Series Test1 = func() (t1 Test2) {
		b, res := 1, 1.
		return Test2(func() (t Test1) {
			b += 1
			res -= 1.0/float64(b)
			fmt.Println(res)		
			return Test1(func() (t Test2) {
				b += 1
				res += 1.0/float64(b)
				fmt.Println(res)
				return t1
			})
		})
	}
)

//1-1/2+1/3-1/4...

func main() {
	Series().Next().Next().Next().Next().Next().Next().Next()
}