Generally it looks good, at least to an Haskell beginner like me.
I find the use of dropWhile to be a bit confusing. I admit I had to read your comment to understand why you used it.
I think it could also have introduced a bug. What is the expected behaviour for split ',' ",,"?
Your code returns [""] but I would expect ["","",""]. Was your behaviour intended?
This solution fixed the issue.
split :: (Eq a) => a -> [a] -> [[a]]
split _ [] = []
split separator ys = f : (split separator (dropSeparator separator rest))
where (f, rest) = break (== separator) ys
dropSeparator :: Eq a => a -> [a] -> [a]
dropSeparator _ [] = []
dropSeparator separator (x:xs) = if x == separator then xs else x:xs
I prefer using meaningful variable names, such as separator, even if I'm not sure if it is idiomatic Haskell. Ditto for the parentheses and the introduction of the helper function.
