[fish45]

A common example I use is an Abstract Syntax Tree, which is essentially a mutually recursive polymorphic tree. In Elixir you might model this with a tuple labelled by an atom. With Haskell you'd use ADTs and pattern matching, which are easy to pick up because they're first class in the language but they're still something to learn. In Java, your understanding has to be a bit deeper; you'd have to learn about abstract classes. In C, you'd need to understand forward declaration and tagged unions.

Honestly I can't think of an example of anything which is harder to model in Haskell's type system, but I think the Java and C examples demonstrate that you do have to learn different type systems to model more complex examples.

I totally agree that type systems end up reducing cognitive overhead in the long run though.