This seems to be newer...

Although the same approach may be taken, the concept and required understanding is different.

And then you look at all the other languages which don't wrap the list/vector/array/collection with an optional type. So why should haskell? "null" in another languages it not the same as "Maybe" in haskell !!

If the input array is empty or null, return an empty array:

C#/Java: new int[] {} / new int[0];
C++: std::vector<int>();
JavaScript/CoffeeScript/TypeScript/PHP/Haskell: [];
Rust: Vec::<i32>::new();

The input array can be null, ie missing. That'd be Nothing.

Fixed.

Cheers!

Another thing, in the home below the language select, you can choose how the system suggest the next kata to solve, try changing it to rank up instead of fundamentals or whatever option you find suitable to you.

Don't report an issue when there's no need to.
You've been commenting on about half of the 8kyu katas, saying how they are all duplicates. You can't do anything to change that now, as they were made like 3 years ago.
Try doing what Chrono says and do some harder katas, like 3 - 4kyu, instead of complaining how easy 8kyu katas are.

I see you consider a lot of katas lame, why don't you write some yourself then? A lot of katas are similar without being an exact duplicate. They have different authors too, and no, the kata authors don't need to add a notification if some other kata is harder than their own (why should them?). I see you've mostly solved 8 kyu katas (the easiest ones) try some harder katas and see if you can solve them.

that's why i'm reporting an issue

The katas don't directly build on another kata.
The algorithm to provide the katas doesn't know how hard one kata is to another, it only knows what rank it is.

In haskell it's an anti-pattern to represent False by the string "False". Maybe String is the right return type here.

My point is if a kata builds upon (the knowledge gained of) another kata, that the latter one should be offered first by codewars. Or get some notification about it.

Question: “A farm contains chickens and cows. There are x legs and y heads. How many chickens and cows are there?”
Line of tescase: animals 72 200 shouldBe Just (44,28)
Line of code: animals --Code

you have to fill in: animals y x =
for it to make sense

"there are x legs and y heads" --> x first then y
"animals 72 200" --> y first then x

Just because its easy for you, doesn't mean that other people will find it easy.

Lame kata after already solving https://www.codewars.com/kata/beginner-lost-without-a-map