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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/

// See page 218.

// Spinner displays an animation while computing the 45th Fibonacci number.
package main

import (
    "fmt"
    "time"
)

//!+
func main() {
    go spinner(100 * time.Millisecond)
    const n = 45
    fibN := fib(n) // slow
    fmt.Printf("\rFibonacci(%d) = %d\n", n, fibN)
}

func spinner(delay time.Duration) {
    for {
        for _, r := range `-\|/` {
            fmt.Printf("\r%c", r)
            time.Sleep(delay)
        }
    }
}

func fib(x int) int {
    if x < 2 {
        return x
    }
    return fib(x-1) + fib(x-2)
}

//!-