[PHP] Print fibonacci sequence using recursion

Fibonacci sequence is a infinite series of numbers where each item is the sum of the two preceding ones, starting from 0 and 1.
I have written 2 examples
The first function returns a Fibonacci sequence, stopping when we reach given upper limit:

<?php
$upper_limit = 4000000;

echo implode(', ', fibonacci($upper_limit));

function fibonacci(int $max, array $buffer=[]) : array
{
        // if we have no buffer we initialize it with 0 and 1
        if (empty($buffer)) {
            $buffer = [0, 1];
        }
       
        // we get current index
        $index = count($buffer) - 1;
       
        // calculate next number
        $next = $buffer[$index] + $buffer[$index-1];
       
        //if we reached upper limit we return the array containing the sequence
        if($max < $next) {
            return $buffer;
        }

        // (otherwise)
        // we put new item in array
        $buffer[] = $next;
       
        // we run again the function with the new buffer
        return fibonacci($max, $buffer);
}

The second one prints N numbers of the sequence.

<?php

$n = 50;

echo implode(', ', fibonacci($n));

function fibonacci(int $n, array $buffer=[]) : array
{
        // edge cases
        if($n==0) return [];
        if($n==1) return [0];

        // if we have no buffer we initialize it with 0 and 1
        if (empty($buffer)) {
            $buffer = [0, 1];
        }
       
        // we get current index
        $index = count($buffer) - 1;
       
        // calculate next number
        $next = $buffer[$index] + $buffer[$index-1];
       
        // if we have N numbers
        if($n === ($index+1)) {
            return $buffer;
        }

        // (otherwise)
        // we put new item in array
        $buffer[] = $next;
       
        // we run again the function with the new buffer
        return fibonacci($n, $buffer);
}

capaio

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