qsort.hs

qsort :: (Int -> Int -> Bool) -> [Int] -> [Int]
qsort _ [] = []
qsort fn (pivot:elems) =
    let p = filter (fn pivot) elems
        q = filter (not . fn pivot) elems
    in qsort fn p ++ [pivot] ++ qsort fn q


-- qsort (>) [5,2,6,1,87,0,9]
-- [0,1,2,5,6,9,87]

-- qsort (<) [5,2,6,1,87,0,9]
-- [87,9,6,5,2,1,0]