Question

我坐在这上面超过4个小时，不能把头包裹起来。我尝试运行以下代码：

top = 100 :: Int

couplesToOne num
    |num<0            = error "num<0"
    |num==0           = 0
    |num `mod` 2 == 0 = num `div` 2
    |num `mod` 2 == 1 = (num+1) `div` 2
    |otherwise        = error "otherwise"

numInBig n bigSide 
    |(bigSide^2 <= n) = couplesToOne (n-1)  
    |(bigSide^2 >  n) = couplesToOne (n-1) - (couplesToOne (floor(sqrt(bigSide^2 - n))))
    |otherwise        = error "otherwise"

ans = map (numInBig top) [3..((div top 4) + 1)]

我收到以下错误消息：

No instance for (RealFrac Int) arising from a use of `numInBig'
In the first argument of `map', namely `(numInBig top)'
In the expression: map (numInBig top) [3 .. ((div top 4) + 1)]
In an equation for `ans':
    ans = map (numInBig top) [3 .. ((div top 4) + 1)]
    enter code here

我想（可能是？）这是因为“sqrt”返回一个浮点数，但这就是为什么我添加了应该返回积分的地板。

你能帮我吗？

Answer 1

这有效：

top = 100 :: Int

couplesToOne num
    |num<0            = error "num<0"
    |num==0           = 0
    |num `mod` 2 == 0 = num `div` 2
    |num `mod` 2 == 1 = (num+1) `div` 2
    |otherwise        = error "otherwise"

numInBig n bigSide 
    |(bigSide^2 <= n) = couplesToOne (n-1)  
    |(bigSide^2 >  n) = couplesToOne (n-1) - couplesToOne (floor(sqrt(fromIntegral(bigSide^2 - n))))
    |otherwise        = error "otherwise"

ans = map (numInBig top) [3..((div top 4) + 1)]

您需要额外fromIntegral，因为sqrt::Floating a => a -> a未定义Int。

> ans
[50,50,50,50,50,50,50,50,48,47,46,45,44,44,43,43,42,41,41]

为什么我在这里遇到类型错误？

1 个答案: