Non-numerical use cases for functional programming?

Question

I just finished reading a book on scala. What strikes me is that every single example in the whole book was numerical in some form or another.

Like a lot of programm

Answer 1

Check "Purely functional data structures" (and here's the PhD thesis that inspired the book).

They show how you can create standard data structures in purely functional (no side-effects) languages. You can then use them to program anything.

Disclaimer: I'm pulling an Atwood here, I've barely read a couple of reviews of the book and skimmed over the thesis, it's on my toread list.