Taylor Series Expansion of e^x

exponentialSeries.hs

-- Power series expansion of the exponential function
-- i.e. e^x = 1 + x + (x^2)/2! + ... (x^n)/n!

-- 'Cute' version
exp :: Double -> Double
exp x = sum $ take 10 $ map go [0..]
  where fac = product . flip take [1..]
        go n = x ^ n / fac n
        
-- Explanatory version
exp' :: Double -> Double
exp' x = sum (take 10 (map go [0..]))

  where fac :: Int -> Double
        fac n = product (take n [1..])

        go :: Int -> Double
        go n = (x ^ n) / (fac n)