#### 6.1.2.3 Examples of for-as-arithmetic subclause

    ;; Print some numbers.
     (loop for i from 1 to 3
           do (print i))
     |>  1
     |>  2
     |>  3
    ⇒  NIL

    ;; Print every third number.
     (loop for i from 10 downto 1 by 3
           do (print i))
     |>  10
     |>  7
     |>  4
     |>  1
    ⇒  NIL

    ;; Step incrementally from the default starting value.
     (loop for i below 3
           do (print i))
     |>  0
     |>  1
     |>  2
    ⇒  NIL