Examples of functional programming in very large web applications?

I've been writing object oriented PHP for years, and I'm having trouble wrapping my head around how the equivalent of a large Rails or Symfony project would be structured using functional programming. (To be clear, I've only really played with Racket tutorials so far.) I've seen a few examples of functionally programmed apps, but they're usually not much larger than a small blog. Could anyone recommend large open source project, or point me in the right direction?