在Haskell中计算左手Riemann和

import Numeric.LinearAlgebra
import Numeric.GSL.Integration

-- 定义要积分的函数
f :: Double -> Double
f x = x^2

-- 计算左手Riemann和
leftHandRiemannSum :: Double -> Double -> Int -> Double
leftHandRiemannSum a b n = sum [f (a + i * h) * h | i <- [0..n-1]]
  where h = (b - a) / fromIntegral n

-- 主函数
main :: IO ()
main = do
  let a = 0.0  -- 积分下限
      b = 1.0  -- 积分上限
      n = 100  -- 将曲线分成100个小矩形
  result <- integrateQNG 1e-6 (leftHandRiemannSum a b n) a b
  putStrLn $ "左手Riemann和的近似值为: " ++ show result