In the grandparent comment's link (showing clojure data in haskell): I'm pretty sure that is not how people code in Haskell, its not how the libraries are usually designed etc etc. Using only data is definitely possible in Haskell, but it's not encouraged by default, the core abstractions are used for concretions of information.

In the same way you can do immutable and functional stuff in java, it's not going to mesh with the rest of the ecosystem or language around you.