[Haskell-cafe] Create a list without duplicates from a list with duplicates

[news at lyra.net]

Hallo!

Let's suppose I have a list [a,b,c,d,c,d]. I'd like to write
a function that returns a new list without duplicates (in
the example [a,b,c,d]). How can I do that? What is the most
general way? I'd like to use the same function for a list of
Int or String or some other user defined data type.

Thank for your attention!