在haskell中递归期间打印结果 [英] Printing a result during a recursion in haskell

问题描述

  n  - >我开始学习Haskell，并且正在制作一个程序来执行迭代过程。 n / 2（甚至n）
 n  - > 3n + 1（对于奇数n）
  

所以我得到了这么多：`

 链n | n == 0 =错误你在说什么？ 
 | n == 1 =错误Finished
 | rem n 2 == 0 = chain（n`div` 2）
 | rem 2 / = 0 = chain（3 * n + 1）
  

`
这项工作？
但是它只是在幕后进行计算，有没有什么办法让它显示或导出每次迭代时n的结果，直到它达到1，以便我可以在以后找到列表的长度？

在附注中，有没有办法让GHCi开始在特定的文件夹中？（我正在使用windows）

解决方案

您可以让它像这样返回链中的结果列表：

  chain n | n == 0 =错误你在说什么？ 
 | n == 1 = [] 
 | rem n 2 == 0 =（n`div` 2）：chain（n`div` 2）
 |否则=（3 * n + 1）：链（3 * n + 1）
  

会得到如下结果：

  * Main>链3 
 [10,5,16,8,4,2,1] 
 *主要>连锁店7 
 [22,11,34,17,52,26,13,40,20,10,5,16,8,4,2,1] 
  

I am beginning to learn Haskell and am making a program to do the iterative process:

n -> n/2 (for even n)
n -> 3n+1 (for odd n)

So I got this far:`

chain n     | n == 0       = error "What are you on about?"
            | n == 1       = error "Finished"
            | rem n 2 == 0 = chain (n `div` 2) 
            | rem n 2 /= 0 = chain (3 * n + 1)

` Will this work? But it only does the calculations behind the scenes, is there any way to make it display or export as list the result for n on each iteration until it reaches 1 so I can find the length of the list later?

On a side note, is there any way to make GHCi begin in a specific folder ?(I'm using windows)

解决方案

You could have it return a list of the results in the "chain" like this:

chain n     | n == 0       = error "What are you on about?"
            | n == 1       = []
            | rem n 2 == 0 = (n `div` 2) : chain (n `div` 2)
            | otherwise    = (3 * n + 1) : chain (3 * n + 1)

Now you'll get results like these:

*Main> chain 3
[10,5,16,8,4,2,1]
*Main> chain 7
[22,11,34,17,52,26,13,40,20,10,5,16,8,4,2,1]

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