#### 6.1.2.5 Examples of for-as-in-list subclause

    ;; Print every item in a list.
     (loop for item in '(1 2 3) do (print item))
     |>  1
     |>  2
     |>  3
    ⇒  NIL

    ;; Print every other item in a list.
     (loop for item in '(1 2 3 4 5) by #'cddr
           do (print item))
     |>  1
     |>  3
     |>  5
    ⇒  NIL

    ;; Destructure a list, and sum the x values using fixnum arithmetic.
     (loop for (item . x) of-type (t . fixnum) in '((A . 1) (B . 2) (C . 3))
           unless (eq item 'B) sum x)
    ⇒  4