If you are interested in a GUI example then you might like the post I wrote just before this one: http://www.haskellforall.com/2014/06/spreadsheet-like-program

If you are interested in a GUI example then you might like the post I wrote just before this one: http://www.haskellforall.com/2014/06/spreadsheet-like-programming-in-haskell.html http://www.haskellforall.com/2014/06/spreadsheet-like-progra... That shows a spreadsheet that you assemble using Applicative and Monoid operations that is built on top of several abstraction layers, and the correctness proof of each layer buulds on the previous proofs.