package main

import "fmt"

type stack struct {
	items []string
}

func (s stack) push(v string) stack {
	s.items = append(s.items, v)
	return s
}

func (s stack) pop() (stack, string) {
	last := len(s.items) - 1
	top := s.items[last]
	s.items = s.items[:last]
	return s, top
}

func (s stack) peek() (string, bool) {
	if len(s.items) == 0 {
		return "", false
	}
	return s.items[len(s.items)-1], true
}

func (s stack) size() int {
	return len(s.items)
}

func main() {
	s := stack{}
	s = s.push("a")
	s = s.push("b")
	s = s.push("c")

	fmt.Println(s.size()) // 3

	top, ok := s.peek()
	fmt.Println(top, ok) // c true

	s, top = s.pop()
	fmt.Println(top) // c

	s, top = s.pop()
	fmt.Println(top) // b

	fmt.Println(s.size()) // 1
}