I have no idea what is heavily optimized about that Haskell code. I am no Haskell expert, but all you did was use an unboxed array. I added one strictness annotation to the "v" parameter on your iter function and it reduced the time from 10 seconds to 1.5 on my laptop.

None of the other code you wrote uses a linked list, so I don't know why you used them for Haskell. You used vector types for most of them (which Haskell has, by the way). Pretty disingenuous.

I admit that the prominent use of lists in newbie Haskell tutorials could have mislead you, but you seem to know the difference in data types since you used vectors everywhere else.