How to do a while loop in LISP

Question

I cannot get a simple while loop to work in lisp!

(loop (while (row >= 0))
      setf(row (- row 1))
      (collect (findIndex row col))

Answer 1

The correct form of the loop is the following:

(loop while (>= row 0) 
  do (setf row (- row 1))           ; or better: do (decf row)
  collect (findIndex row col))

For a detailed description of the loop syntax, see the manual.

Answer 2

If you count down, you don't need WHILE+decrement.

Your loop goes from row - 1 down to -1. We can write it as a FOR loop. Here are two examples:

(loop for row-number from (1- row) downto -1
      collect (find-index row-number col)))

If you want to count down from row to 0 (here using downfrom ... to instead of from ... downto):

(loop for row-number downfrom row to 0
      collect (find-index row-number col)))