Types “哈斯克尔错误”；无法推断因使用..而产生的（整数浮点）；

我是Haskell的新手，正在尝试计算一系列浮点数的标准偏差。Ubuntu 18.04，ghc 8.0.2。我在谷歌上搜索到了以下错误，但仍然不明白“积分浮点”到底是什么

*Main> let z = stdDev 0 1 y x
<interactive>:250:9: error:
• Could not deduce (Integral Float) arising from a use of ‘stdDev’
  from the context: Floating a
    bound by the inferred type of z :: Floating a => [a]
    at <interactive>:250:5-38
• In the expression: stdDev 0 (length (head (x))) y x
  In an equation for ‘z’: z = stdDev 0 (length (head (x))) y x

变量：

*Main> y
[380.0,1.0]
*Main> x
[[600.0,1.0],[400.0,1.0],[170.0,1.0],[430.0,1.0],[300.0,1.0]]

---

我找到了解决办法。我需要指定函数类型并添加“fromIntegral”，而我的一些算法逻辑是错误的

stdDev :: Int -> Float -> [Float] -> [[Float]] -> [Float]
stdDev i l ms xs
    | fromIntegral(i) < length(head(xs)) = sqrt((sumOfMinusMeans i (ms!!i) xs) 
                                               / l): (stdDev (i+1) l ms xs)
    | otherwise                          = []


sumOfMinusMeans :: Int -> Float -> [[Float]] -> Float
sumOfMinusMeans i m (x:xs)
    | xs == []  = (x!!i - m)**2
    | otherwise = (x!!i - m)**2 + (sumOfMinusMeans i m xs)

stdDev:：Int->Float->[Float]->[[Float]]]->[Float]
stdDev i l ms xs
|fromIntegral（i）Float->[[Float]]->Float
平方米（x:xs）
|xs=[]=（x！！i-m）**2
|否则=（x！！i-m）**2+（分钟数之和i m xs）

*Main> y
[380.0,1.0]
*Main> x
[[600.0,1.0],[400.0,1.0],[170.0,1.0],[430.0,1.0],[300.0,1.0]]

stdDev :: Int -> Float -> [Float] -> [[Float]] -> [Float]
stdDev i l ms xs
    | fromIntegral(i) < length(head(xs)) = sqrt((sumOfMinusMeans i (ms!!i) xs) 
                                               / l): (stdDev (i+1) l ms xs)
    | otherwise                          = []


sumOfMinusMeans :: Int -> Float -> [[Float]] -> Float
sumOfMinusMeans i m (x:xs)
    | xs == []  = (x!!i - m)**2
    | otherwise = (x!!i - m)**2 + (sumOfMinusMeans i m xs)