Eso VS pfps-shopping-cart

I have a project with purely functional esoteric language interpreters that can do console I/O (link), and I do it by having the interpreter define a function that turns the input string into the output string. To do real-time user interaction I just give it an input 'string' that's built as it's used by reading the console, the interpreter can't tell the difference between that and a fully predefined input.

I was interested in the mixed functional style you could do with Scala, so I decided to make a polyglot esoteric language interpreter where I wrote all the backend stuff functionally. It turned into one of my biggest projects.

Gabriel Volpe has a book that goes over just that using the typelevel stack. I highly recommend it: https://leanpub.com/pfp-scala

The only issue I had was how to put all this knowledge together. For that I bought Practical FP in scala by Gabriel Vlope, it's not for beginners, tho but takes you through a project with the latest typelevel stack. Here's the link. https://leanpub.com/pfp-scala.

This is a really good book https://leanpub.com/pfp-scala

If you want a solid understanding of FP and not just FP in Scala, I highly recommend installing GHCup and working through Haskell Programming From First Principles. Then I would work through Scala With Cats, Essential Effects, and Practical FP in Scala for how all of that maps onto Scala.

Practical FP in Scala

BTW for learning good application structure with Tagless Final I really recommend the book Practical FP in Scala and its work-along example application. That's where I stole the pattern above from.