如何将函数调用的值存储到变量 [英] How to store value of function call to a variable

问题描述

我有此功能，需要检查数字 [1..n] 和 n 的 gdc 是否为 == 1 然后进行一些计算.所以我被困住了，因为我找不到将n的初始值存储到变量的方法.

I have this function where I need to check if the gdc of the numbers [1..n] and n is == 1 and do some calculations then. So I am stuck because I can't find a way to store the initial value of n to a variable.

例如，如果我用数字7调用该函数是递归操作，则 n 变为 6 然后是 5 等，这样我就可以了"t gdc 正确；例如 1-7 然后 2-7 然后 3 -7 .您知道如何将 n 的值存储到 a 变量吗?

For example, if I call the function with the number 7 its a recursion so n becomes 6 then 5 etc so I can't gdc properly; for example 1-7 then 2 - 7 then 3 -7. Do you know how I can store the value of n to a variable ?

myproduct :: Integer->Integer

myproduct 0 = 1
myproduct n  
  |gcd n (n from first call)  /= 1 = myproduct (n-1) 
  |otherwise = x
  where 
    x = n * myproduct (n - 1)

推荐答案

使用辅助函数(通常称为 go )进行递归，并在最外层调用中使用与在外部调用中不同的变量名.递归调用，如下所示:

Use a helper function (often called go) to do the recursion, and use a different variable name in the outermost call than in the recursive call, like this:

myproduct :: Integer->Integer

myproduct orig_n = go orig_n
  where
    go 0 = 1
    go n
      |gcd n orig_n  /= 1 = go (n-1)
      |otherwise = x
      where
        x = n * go (n - 1)

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