List
[1 2 3 4] or [1, 2, 3,]

[print] the number items in list or check to see if the list is empty

[1 2 3 4(
|
[list length]
|
[print]

That will give you the list length, but be careful, if you supply [1, 2, 3( as the source message above, the output will be three 1's, as the comma actually delimits multiple messages from within one message object.

Hope that helps.

@palaver Thank you works great!