package main

import "fmt"

type Sequencer interface {
	Next() Sequencer
}

type Elem struct {
	b   int
	res float64
}
type OddElem Elem
type EvenElem Elem

func (o *OddElem) Next() Sequencer {
	b := o.b + 1
	e := &EvenElem{b, o.res - 1.0/float64(b)}
	fmt.Println(e.res)
	return e
}

func (e *EvenElem) Next() Sequencer {
	b := e.b + 1
	o := &OddElem{b, e.res + 1.0/float64(b)}
	fmt.Println(o.res)
	return o
}

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

func main() {
	var s Sequencer
	s = &OddElem{1, 1}
	for i := 0; i < 10; i++ {
		s = s.Next()
	}
}

/*
func main() {
	res := 1.0
	for b := 2; b < 10; b++ {
		if b%2 == 0 {
			res -= 1.0 / float64(b)
		} else {
			res += 1.0 / float64(b)
		}
		fmt.Println(res)
	}
}
*/