Lumen L5 compatibility helpers. That file should be added on root path of your project... and added to your composer.json

compat_l5.php

<?php

if(!function_exists('config_path'))
{
        /**
        * Return the path to config files
        * @param null $path
        * @return string
        */
        function config_path($path=null)
        {
                return app()->getConfigurationPath(rtrim($path, ".php"));
        }
}

if(!function_exists('public_path'))
{

        /**
        * Return the path to public dir
        * @param null $path
        * @return string
        */
        function public_path($path=null)
        {
                return rtrim(app()->basePath('public/'.$path), '/');
        }
}

if(!function_exists('storage_path'))
{

        /**
        * Return the path to storage dir
        * @param null $path
        * @return string
        */
        function storage_path($path=null)
        {
                return app()->storagePath($path);
        }
}

if(!function_exists('database_path'))
{

        /**
        * Return the path to database dir
        * @param null $path
        * @return string
        */
        function database_path($path=null)
        {
                return app()->databasePath($path);
        }
}

if(!function_exists('resource_path'))
{

        /**
        * Return the path to resource dir
        * @param null $path
        * @return string
        */
        function resource_path($path=null)
        {
                return app()->resourcePath($path);
        }
}

if(!function_exists('lang_path'))
{

        /**
        * Return the path to lang dir
        * @param null $str
        * @return string
        */
        function lang_path($path=null)
        {
                return app()->getLanguagePath($path);
        }
}

if ( ! function_exists('asset'))
{
	/**
	 * Generate an asset path for the application.
	 *
	 * @param  string  $path
	 * @param  bool    $secure
	 * @return string
	 */
	function asset($path, $secure = null)
	{
		return app('url')->asset($path, $secure);
	}
}

if ( ! function_exists('elixir'))
{
    /**
     * Get the path to a versioned Elixir file.
     *
     * @param  string  $file
     * @return string
     */
    function elixir($file)
    {
        static $manifest = null;
        if (is_null($manifest))
        {
            $manifest = json_decode(file_get_contents(public_path().'/build/rev-manifest.json'), true);
        }
        if (isset($manifest[$file]))
        {
            return '/build/'.$manifest[$file];
        }
        throw new InvalidArgumentException("File {$file} not defined in asset manifest.");
    }
}

if ( ! function_exists('auth'))
{
	/**
	 * Get the available auth instance.
	 *
	 * @return \Illuminate\Contracts\Auth\Guard
	 */
	function auth()
	{
		return app('Illuminate\Contracts\Auth\Guard');
	}
}

if ( ! function_exists('bcrypt'))
{
	/**
	 * Hash the given value.
	 *
	 * @param  string  $value
	 * @param  array   $options
	 * @return string
	 */
	function bcrypt($value, $options = array())
	{
		return app('hash')->make($value, $options);
	}
}

if ( ! function_exists('redirect'))
{
	/**
	 * Get an instance of the redirector.
	 *
	 * @param  string|null  $to
	 * @param  int     $status
	 * @param  array   $headers
	 * @param  bool    $secure
	 * @return \Illuminate\Routing\Redirector|\Illuminate\Http\RedirectResponse
	 */
	function redirect($to = null, $status = 302, $headers = array(), $secure = null)
	{
		if (is_null($to)) return app('redirect');
		return app('redirect')->to($to, $status, $headers, $secure);
	}
}

if ( ! function_exists('response'))
{
	/**
	 * Return a new response from the application.
	 *
	 * @param  string  $content
	 * @param  int     $status
	 * @param  array   $headers
	 * @return \Symfony\Component\HttpFoundation\Response|\Illuminate\Contracts\Routing\ResponseFactory
	 */
	function response($content = '', $status = 200, array $headers = array())
	{
		$factory = app('Illuminate\Contracts\Routing\ResponseFactory');
		if (func_num_args() === 0)
		{
			return $factory;
		}
		return $factory->make($content, $status, $headers);
	}
}

if ( ! function_exists('secure_asset'))
{
	/**
	 * Generate an asset path for the application.
	 *
	 * @param  string  $path
	 * @return string
	 */
	function secure_asset($path)
	{
		return asset($path, true);
	}
}

if ( ! function_exists('secure_url'))
{
	/**
	 * Generate a HTTPS url for the application.
	 *
	 * @param  string  $path
	 * @param  mixed   $parameters
	 * @return string
	 */
	function secure_url($path, $parameters = array())
	{
		return url($path, $parameters, true);
	}
}


if ( ! function_exists('session'))
{
	/**
	 * Get / set the specified session value.
	 *
	 * If an array is passed as the key, we will assume you want to set an array of values.
	 *
	 * @param  array|string  $key
	 * @param  mixed  $default
	 * @return mixed
	 */
	function session($key = null, $default = null)
	{
		if (is_null($key)) return app('session');
		if (is_array($key)) return app('session')->put($key);
		return app('session')->get($key, $default);
	}
}


if ( ! function_exists('cookie'))
{
	/**
	 * Create a new cookie instance.
	 *
	 * @param  string  $name
	 * @param  string  $value
	 * @param  int     $minutes
	 * @param  string  $path
	 * @param  string  $domain
	 * @param  bool    $secure
	 * @param  bool    $httpOnly
	 * @return \Symfony\Component\HttpFoundation\Cookie
	 */
	function cookie($name = null, $value = null, $minutes = 0, $path = null, $domain = null, $secure = false, $httpOnly = true)
	{
		$cookie = app('Illuminate\Contracts\Cookie\Factory');
		if (is_null($name))
		{
			return $cookie;
		}
		return $cookie->make($name, $value, $minutes, $path, $domain, $secure, $httpOnly);
	}
}

Hi.
getLanguagePath() is protected (at least in Lumen 5.6). I suggest:

if(!function_exists('lang_path')) 
{
    /**
     * Return the path to lang dir
     * @param null $str
     * @return string
     */
    function lang_path($path = null) {
        return resource_path() . DIRECTORY_SEPARATOR . 'lang' . ($path ? DIRECTORY_SEPARATOR . $path : $path);
    }
}

Can you give directions on how to include this file in composer.json and where to locate the helper file concerning best practices ?
That will be helpful for newbies in lumen.

Thanks for your contribution.

Can you give directions on how to include this file in composer.json and where to locate the helper file concerning best practices ?
That will be helpful for newbies in lumen.

Thanks for your contribution.

This article shows how to do it using composer:
https://laravel-news.com/creating-helpers