threading.lisp

(defun ->-helper (forms)
  (if (null forms)
      nil
      (let ((form (first forms))
            (first-form (->-helper (rest forms))))
        (if first-form
            (append (list (first form))
                    (list first-form)
                    (rest form))
            form))))

(defmacro -> (&rest forms)
  (->-helper (reverse forms)))