通过索引变量访问 SML 元组 [英] Accessing SML tuples by Index Variable

问题描述

问题很简单.

如何在 SML 中使用索引变量访问元组?

How to access a tuple by using Index variable in SML?

val index = 5;
val tuple1 = (1,2,3,4,5,6,7,8,9,10);

val correctValue = #index tuple1 ??

我希望有人能够提供帮助.提前致谢！

I hope, somebody would be able to help out. Thanks in advance!

推荐答案

不存在接受整数值和元组并从元组中提取该元素的函数.当然有 #1, #2, ... 函数，但这些函数不接受整数参数.也就是说，函数"的名称是#5，它不是应用于值5 的函数#.因此，您不能用名称 index 代替 5.

There doesn't exist a function which takes an integer value and a tuple, and extracts that element from the tuple. There are of course the #1, #2, ... functions, but these do not take an integer argument. That is, the name of the "function" is #5, it is not the function # applied to the value 5. As such, you cannot substitute the name index instead of the 5.

如果您事先不知道您想要的元素将位于元组中的哪个位置，那么您可能正在以不打算使用它们的方式使用它们.

If you don't know in advance at which place in the tuple the element you want will be at, you're probably using them in a way they're not intended to be used.

您可能需要一个值列表，对于这些值，'a list 类型更自然.然后，您可以使用 List.nth 访问 nth 元素.

You might want a list of values, for which the 'a list type is more natural. You can then access the nth element using List.nth.

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