> Notice how state was introduced? It made the code easier to read.

That quote shows that the author kinda misses the point here.

    type FibPair = (Int, Int)

    fibSeed :: FibPair
    fibSeed = (0, 1)

    fibNext :: FibPair -> FibPair
    fibNext (p, v) = (v, v + p)

    fibList :: [FibPair]
    fibList = iterate fibNext fibSeed

The above code does exactly the same as his Fibonacci example, and it's written in pure Haskell. I'd argue the above is way more readable.

I get the following output:

    0 1 1 2 3 5 8 13 21 34

With the following main function:

    main :: IO ()
    main = putStrLn . unwords . map (show . fst) . take 10 $ fibList

Which just takes the first element of each generated tuple, maps it to the string representation, and then adds a space between each number.