Ok, but we're not quite talking about the difference between Haskell and Clojure, for example.

Sure. But it is almost the difference between Haskell and OCaml.

I suppose it's all relative. Given some selection of enabled language extensions, are you still writing Haskell? I think in the minds of most people (at least on this forum) the difference is academic. Whether a given body of work in Haskell looks like Elm, or if it's all GADTs, data kinds, and type families, they'd both be met with "Surely nobody actually uses this in production! This is ivory tower nonsense! I can't read it! It's not practical! I just want to get stuff done!" ad infinitum.