Tinker isn't for running full files of code. Instead it's meant to be able to run a few lines at a time to interact with the application without having to spin up a local server.
If your code is a class you want to interact with, include it in your app (e.g. Autoload it in) and in Tinker you can call the class and do what you need there.
tldr:: Tinker is a tool to help interact with the app without needing to spin up a server. It's a simple feature you can use to test a couple of lines you'd normally delete from your project.