[Haskell-beginners] Unique integers in a list

[Ramesh Kumar]

Hi,

I've just started learning Haskell a couple of weeks ago using Simon Thompson's "Haskell: Craft of Functional Programming".
There is an exercise in chapter 7 of the book which goes something like this:

Define a function of the type:     unique :: [Integer] -> [Integer]
which if given a list of integers, should return a list of those integers which occur only once in the input list.
Example:
   unique [5,2,4,2,3,1,5,2] should result in [4,3,1]


*** The questions assumes we know only of list comprehensions and recursion. 


I am guessing the solution must include something like this:

unique :: [Integer] -> [Integer]
unique xs = [ x | x <- xs, isSingle x ]

My problem is in defining the function 'isSingle'.

I would greatly appreciate any pointers on this.

Many thanks.
Ramesh
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