[ferzul]

> Since immutable values can't create cycles, no memory will be leaked.

this is not generally true. in a lazy language, you can certainly say:

    main = mdo
      y <- f x
      x <- g y
      return y

the requirement is simply that you don't inspect the value of x until later (f makes something, y, to use later; when you use y, it inspects x). x and y now have references to each other.

[dependenttypes]

> in a lazy language, you can certainly say:

Not in haskell. Which language do you specifically have in mind?

[tome]

Yes indeed in Haskell. You have enable RecursiveDo for that particular example to work. I'm not sure why ferzul chose a recursive monadic computation when

    let { x = 0:y; y = 0:x } in x

seems to demonstrate the same thing.