Unused loop variables in Lisp

Question

Sometime, I need to iterate $n$ times where $n$ is the number of elements in a list. Of course, I could write something like:

(loop for i from 0 below (list-length l)
      do something)

But I like to write rather:

(loop for i from 0
      for u in l ; unused 'u' variable
      do something)

where the for u in l part is merely intended to stop the loop after $n$ iterations. But then I don't use the u variable, and the interpreter keeps complaining. Is there some way to handle this style of coding? Should I avoid it and use list-length instead?

Answer 1

(loop for i from 0
      for NIL in l
      do something)

NIL should do it.

The LOOP destructuring pattern can be empty and the rest list elements are ignored. Additionally: In a LOOP destructuring pattern, NIL indicates that the variable is not used.