An Infinite List of Fibonacci Numbers in Ruby

So I was reading through the Haskell Prelude when I stumbled across `scanl’ as a kind of abstraction over `foldl’. I stared, and thought, and stared some more, and couldn’t come up with a use for it; a quick Web search revealed exactly one use: Fibonacci numbers.
(In retrospect: duh.)
So here are all the Fibonacci numbers [...]