Question

在GHCiOnline中，let listRestDiv 4 = floor(4/(fromInteger (nextPrimeDiv 4)))确实有效，但一般

let listRestDiv n = floor(n/(fromInteger (nextPrimeDiv n)))

不接受

，其中nextPrimeDiv n由

提供

let nextPrimeDiv n = head [x|x<-[1..n], n `mod` x == 0, x/=1]

然后返回下一个主要除数。

它说：

无法演绎（RealFrac Integer）因使用`floor＆＃39;从上下文（积分b）由推断类型的listRestDiv ::绑定积分b =＆gt;整数 - ＆gt; b在

并在那里结束。我只是不知道这里的类型。提前感谢任何暗示。

Answer 1

收到的实际完整错误消息，提示我们解决此问题。

Prelude> let listRestDiv n = floor(n/(fromInteger (nextPrimeDiv n)))

<interactive>:8:21:
    Could not deduce (RealFrac Integer) arising from a use of `floor'
    from the context (Integral b)
      bound by the inferred type of
               listRestDiv :: Integral b => Integer -> b
      at <interactive>:8:5-59
    Possible fix: add an instance declaration for (RealFrac Integer)
    In the expression: floor (n / (fromInteger (nextPrimeDiv n)))
    In an equation for `listRestDiv':
        listRestDiv n = floor (n / (fromInteger (nextPrimeDiv n)))

<interactive>:8:28:
    Could not deduce (Fractional Integer) arising from a use of `/'
    from the context (Integral b)
      bound by the inferred type of
               listRestDiv :: Integral b => Integer -> b
      at <interactive>:8:5-59
    Possible fix: add an instance declaration for (Fractional Integer)
    In the first argument of `floor', namely
      `(n / (fromInteger (nextPrimeDiv n)))'
    In the expression: floor (n / (fromInteger (nextPrimeDiv n)))
    In an equation for `listRestDiv':
        listRestDiv n = floor (n / (fromInteger (nextPrimeDiv n)))

这里需要注意的重要事项是

    Possible fix: add an instance declaration for (Fractional Integer)
    In the first argument of `floor', namely
      `(n / (fromInteger (nextPrimeDiv n)))'

所以，你所要做的就是，fromInteger也使用n，就像这样

Prelude> let listRestDiv n = floor(fromInteger n/(fromInteger (nextPrimeDiv n)))

缺少某种Haskell类型转换

1 个答案: