Q:

What is the value function inside Laravel's Arr.php object? 

with PHP 7.2.10 I am receiving an uncaught error for a function called value() within Arr.php in laravel. 
I have tried searching the PHP.net manual it returns nothing for a function called value. 
For example this function found in https://github.com/illuminate/support/blob/master/Arr.php
what is value function? 
    public static function first($array, callable $callback = null, $default = null)
    {
        if (is_null($callback)) {
            if (empty($array)) {
                return value($default);
            }
            foreach ($array as $item) {
                return $item;
            }
        }
        foreach ($array as $key => $value) {
            if (call_user_func($callback, $value, $key)) {
                return $value;
            }
        }
        return value($default);
    }

A:

In Illuminate/Support/helpers.php, you'll find the definition:
if (!  function_exists('value')) {
    /**
     * Return the default value of the given value. 
     *
     * @param  mixed  $value
     * @return mixed
     */
    function value($value)
    {
        return $value instanceof Closure ?  $value() : $value;
    }
}

In English:  If $value is a closure, or anonymous function, it will be executed and the return value is returned.  For anything else, it will just return the original $value. 