Question

Im doing a homework problem in Standard ML which we just started learning, and im stuck trying to computer the sum of the leafs in a tree. How could i access the elements in the node of this tree?

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 = ...