etaFibs.hs

-- Eta expanded
slow :: Int -> Integer
slow i = (fmap fibs [0 ..] !! i)
  where 
    fibs 0 = 0
    fibs 1 = 1
    fibs n = slow (n-2) + slow (n-1)
    
-- Eta reduced
fast :: Int -> Integer
fast = (fmap fibs [0 ..] !!)
  where 
    fibs 0 = 0
    fibs 1 = 1
    fibs n = fast (n-2) + fast (n-1)