Jonathan Petitcolas

Full-Stack Web Developer, Open-Source Contributor, Seasoned Speaker

Fibonacci sequence generator in Go

Published on 18 August 2014

When completing one of the mathematical challenge of Project Euler, I had to compute some Fibonacci numbers. I found, with the help of François Zaninotto, a very elegant way to get the terms of this famous sequence, based on a StackOverflow answer.

As a reminder, the Fibonacci sequence is defined as:

Fibonacci sequence definition

A very naive and simple way to implement it would be the following:

func GetFibonacci(first int, second int, rank int) int {
    if rank == 1 {
        return first

    if rank == 2 {
        return second

    return GetFibonacci(first, second, rank - 1) + GetFibonacci(first, second, rank - 2)

This is just a retranscription of previous formulas. But using Go in this case does not bring anything special. So, here is a more elegant and Go-friendly way, including a generator:

func FibonacciGenerator(first int, second int) chan int {
    c := make(chan int)

    go func() {
        for i, j := first, second ; ; j, i = i + j, j {
            c <- i

    return c

As the initial conditions may vary, we parametrize the first and second Fibonacci terms. Then, we create a new channel containing only integers with the make function. Consider a channel like a FIFO stack: you can insert some values in it with the -> (move towards) operator or consume them with <- (take from). This is the most awesome and damn simple feature of Go language. With channels, you can prevent your code from becoming a callback hell all Node.js developers already experienced.

Then, we declare an anonymous go-routine. A Go routine is simply executed in a separate thread. Just think about it as an asynchronous function. All the Fibonacci logical is located in the for clause, using the possibility to assign several variables with a single = operator. The following line is the key one: we write i value into the channel. Yet, writing into a channel blocks current thread until the value is read. In this case, it simply yield the returned Fibonacci term.

To write a list of 10 first Fibonacci numbers, you can simply use the following code:

import "fmt"

// Generator code

func main() {
    generator := FibonacciGenerator(1, 1)
    for i := 0 ; i < 10 ; i++ {
        fmt.Println(<- generator)

So short but elegant code… The more in Go I develop, the more addicted I become! :)

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