integration.hs

integration :: (Double -> Double) -> Double -> Double -> Double
integration f a b | a == b = 0
                  | otherwise = coeff * dx * ((f begin + f end) / 2 + helper (begin + dx) 0 (numberOfSteps - 1))
    where
        begin = min a b
        end   = max a b
        numberOfSteps = 1000
        coeff = if end == a then (-1) else 1
        dx    = (end - begin) / numberOfSteps
        helper x sum n | n == 0    = sum
                       | otherwise = helper (x + dx) (sum + f x) (n - 1)