You can define an (infinite, FSVO infinite limited by your patience and available RAM) list without defining a new function, just summing itself with the rest of itself: fibs = 0 : 1 : zipWith (+) fibs (tail fibs), and then you can get the first however many you need with take. Once realized it won't have to recompute anything again.

(I did have to crib from a wiki because I couldn't remember if it was just zip or not.)