lazy comparison for equality ?

Hi - I'm a Haskell beginner and I have a problem. Let's have a list which may be normal list list1 = [1,2,3] or a circular list list2 = 1:2:list2 Now I'd like to have a function which tells me whether the given list is circular or not. This doesn't work: circ l = l l circ2 l [] = False circ2 l (_:as) | l==as = True | True = (circ2 l as) It seems that comparison l==as really compares element by element thus falling into an infinite loop. I would need to compare pointers instead of values. Does anybody know how this could be done ? Thanks.