[Tehnix]

    Have you noticed how easy it is to implement circular 
    data structures or random number generators in C? 
    The same is not true for Haskell.

I might be wrong, but, isn't this a circular data structure (or, what they are referring to) http://www.haskell.org/haskellwiki/Tying_the_Knot ?

    In a language like Haskell, where Lists are defined 
    as Nil | Cons a (List a), creating data structures 
    like cyclic or doubly linked lists seems impossible.
    However, this is not the case: laziness allows for 
    such definitions, and the procedure of doing so is 
    called tying the knot.

[quchen]

Yes.

  oneTwo = 1 : 2 : oneTwo

is a circular singly-linked list containing 1 and 2. If you wanted to change the 1 to a 4 though, you would not be able to do so without creating an entire new list. You can use Vector or Array (i.e. fixed-size containers) to make yourself a circular buffer, but the implementation will be very similar to what you would do in C.

[cbsmith]

Wow. That looks hard. I bet you stayed up all night working on that. ;-)

Seriously: sometimes things are hard because you don't know the language all that well. Consider that possibility.

[cbsmith]

Just to be clear: the advice of "consider that possibility" is intended for the author of the article. quchen clearly knows the "easy" way to do this kind of thing with Haskell.