Finding unique elements of a list

[Thomas Johnsson XA (LN/EAB)]

In other functional languages I've used (Haskell, (Lazy) ML,..), I've often used the following variation of quicksort when representing sets as sorted lists without duplicates:
(This is Erlang syntax, not Haskell..:-)

mkset([M|Xs]) ->
    mkset([X||X<-Xs,X<M])++[M]++mkset([X||X<-Xs,X>M]);
mkset([]) -> 
    [].

Cute, if I may say so myself (:-), but unfortunately O(n^2) when the argument
already is a sorted list :-(

Erlang has lists:usort, which presumably does the same thing,
hopefully more efficiently. (?)

-- Thomas