The language is pretty-printed Haskell.
In regular source code, it would look like this:
checklist :: [Int] -> Array Int Boolchecklist xs = accumArray (||) False (0, n) (zip (filter (<= n) xs) (repeat True)) where n = length xscountlist :: [Int] -> Array Int Intcountlist xs = accumArray (+) 0 (0, n) (zip xs (repeat 1))(as ++ bs) \\ cs = (as \\ cs) ++ (bs \\ cs) -- Not actual codeas \\ (bs ++ cs) = (as \\ bs) \\ cs(as \\ bs) \\ cs = (as \\ cs) \\ bs