Source : Free On-Line Dictionary of Computing

Quicksort
     
        A sorting {algorithm} with O(n log n) average time
        {complexity}.
     
        One element, x of the list to be sorted is chosen and the
        other elements are split into those elements less than x and
        those greater than or equal to x.  These two lists are then
        sorted {recursive}ly using the same algorithm until there is
        only one element in each list, at which point the sublists are
        recursively recombined in order yielding the sorted list.
     
        This can be written in {Haskell}:
     
        	qsort               :: Ord a => [a] -> [a]
        	qsort []             = []
        	qsort (x:xs)         = qsort [ u | u<-xs, u=x ]
     
        [Mark Jones, Gofer prelude.]