sml - 访问树中的节点/叶子

Question

我在标准 ML 中做一个家庭作业问题，我们刚刚开始学习，我坚持尝试计算一棵树中叶子的总和。我如何访问这棵树的节点中的元素？

Answer 1

You deconstruct complex data types through pattern matching. Most of the time, you do this in your function arguments. If your function f takes a list as an argument, instead of defining it as

fun f X = ...

you'd say

fun f x::xs = ...

Now, when you pass it a list, it will automatically assign x to the first element, and xs to the remainder.

In your case, it's going to look something like this:

fun sum Node(element,children)::siblings = ...