-- >>> abs (f root) < 1/100000
-- True
--
+-- >>> import Data.Number.BigFloat
+-- >>> let eps = 1/(10^20) :: BigFloat Prec50
+-- >>> let Just root = newtons_method f f' eps 2
+-- >>> root
+-- 1.13472413840151949260544605450647284028100785303643e0
+-- >>> abs (f root) < eps
+-- True
+--
newtons_method :: (Fractional a, Ord a)
=> (a -> a) -- ^ The function @f@ whose root we seek
-> (a -> a) -- ^ The derivative of @f@