Which easy thing do you think is hard to do in Haskell?

Printing is the classic answer.

Mutable arrays, for the clever people who know how or print.

Also, looking at the article, the cryptic "fix" operator for making a cyclic structure. Elegant, beautiful, efficient, but mysterious.

Perhaps I’m missing something, but printing stuff in Haskell seems pretty simple.

    print “hello world”

As for mutable arrays, is there something wrong with Data.Array.MArray from the array[0] library?

[0]: https://hackage.haskell.org/package/array-0.5.4.0

Here's a cyclic structure. Seems very easy to me. No cryptic operator required!

    let one_zeros = 1 : zero_ones
        zero_ones = 0 : one_zeros

Monadic anamorphisms

Are you suggesting monadic anamorphisms are easy in other languages but hard in Haskell? Could you give an example for comparison?

I was being facetious, you can certainly do stuff like anamorphisms easily in other languages, but the hard work of pulling out and expressing the abstraction is definitely a job for Haskell.

Anyway here's one from Data.Functor.Foldable.Exotic just for fun:

    anaM :: (Corecursive t, Traversable (Base t), Monad m) => (a -> m (Base t a)) -> (a -> m t)
    anaM psi = a where a = (fmap embed . traverse a) <=< psi