unique elements in a haskell list

Question

okay, this is probably going to be in the prelude, but: is there a standard library function for finding the unique elements in a list? my (re)implementation, for clarification, is:

has :: (Eq a) => [a] -> a -> Bool
has [] _ = False
has (x:xs) a
  | x == a    = True
  | otherwise = has xs a

unique :: (Eq a) => [a] -> [a]
unique [] = []
unique (x:xs)
  | has xs x  = unique xs
  | otherwise = x : unique xs

Answer 1

I searched for (Eq a) => [a] -> [a] on Hoogle.

First result was nub (remove duplicate elements from a list).

Hoogle is awesome.