Question: How to get the length of a list

I want to get the length of a list. Is there any command available for that? For example, I want it return 2 for the list [8374, 32875], since it has two items.

 

I also have another wonder. The answer might be negative, but I just leave here any way. Is it possilbe the pass a proc to another proc as an input parameter? For example have a proc A has a loop in it. And I want certain process B run in it, but without being defined beforehand. In application, I has proc C and D. Every time when I run A, I just need to tell A what B is, in the way that I pass C to B, or D to B. Then I can run A with different function. Thanks!

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