So I'm trying to define a function in Haskell that if given an integer and a list of integers will give a 'true' or 'false' whether the integer occurs only once or not.

So far I've got:

> 
> let once :: Eq a => a -> [a] -> Bool; once x l =
> 
> 
> 

But I haven't finished writing the code yet. I'm very new to Haskell as you may be able to tell.