I'm not sure how to help you from here without writing it for you - any block of code can be turned into a function to do this. If you're including the file, it doesn't necessarily even need to be a function, unless of course it's a library of functions meant for a variety of purposes, which is usually the concept behind having a seperate file inclusion.

The above link illustrates how to form a user defined function. You place the code inside the function, include the file, and call the function.