How to check if an item returned is a list itself?

问题

Morning -

I'm trying to see if there is a way to check if an item returned from a list is a list itself.

For example

(elt '(a (b c) d) 1)

Is there a way to check that the item returned is a list?

I tried using length,

(length (elt '(a (b c) d) 1))

but if it is given an item that is not a list it throws an error.

In short I'm looking for a way to go through each element of a list and check if it is a list or not.

Thank you

回答1:

the listp tells you that :

(listp (elt '(a (b c) d) 1))

来源：https://stackoverflow.com/questions/12512143/how-to-check-if-an-item-returned-is-a-list-itself