| The principal thing I push learners towards after Haskell would be things like Coq and Agda. Coq has better learning materials, Agda has Haskell integration. The usual sequence is [1] followed by [2]. Augment with [3] and [4] as needed. One negative thing about Coq/Agda/Idris is they don't have a satisfactory encoding of typeclasses [5]. This is a problem in general with all dependently typed languages. Proof obligations get "churned" by changing code and the only tool to address that is extremely general proof terms combined with proof search. The best proof search is Coq, but the code extraction is heartburn-inducing for Haskell users. Whereas in Haskell, we get extremely lightweight and type-safe code refactoring because of the way in which we leverage typeclasses and parametricity. This turns out to be very valuable as your projects get more serious. That said, still entirely worthwhile to learn Coq or Agda. By the way, this [6] is how I teach Haskell. Working on a book as well. [1]: http://www.cis.upenn.edu/~bcpierce/sf/current/index.html [2]: http://adam.chlipala.net/cpdt/ [3]: http://cheng.staff.shef.ac.uk/proofguide/proofguide.pdf [4]: http://www.amazon.com/How-Prove-It-Structured-Approach/dp/05... [5]: http://wiki.portal.chalmers.se/agda/pmwiki.php?n=ReferenceMa... [6]: https://github.com/bitemyapp/learnhaskell |