undefined constant PASSWORD_ARGON2I Laravel

I have been having difficulty using the new password hashing laravel just introduce (argon) in laravel. I got this error message

Use of undefined constant PASSWORD_ARGON2I - assumed 'PASSWORD_ARGON2I' 
(this will throw an Error in a future version of PHP) 
{"exception":"[object] (ErrorException(code: 0): 
Use of undefined constant PASSWORD_ARGON2I - 
assumed 'PASSWORD_ARGON2I' (this will throw an Error 
in a future version of PHP)

And my type of php version is what argon recommended, am working from a mac system

PHP 7.2.0 (cli) (built: Dec 11 2017 16:00:14) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2017 Zend Technologies

Please help

via Chebli Mohamed