When print returns the output-stream ...

str-print.lisp

(defun pr (obj &optional (str *standard-output*))
  (princ o str)
  str)

;;; ... it becomes possible to chain `pr' expressions together:

;; (pr "!" (pr "world" (pr " " (pr "hello"))))

;;; This means, with a little convenience function (like `format'): 

(defun rp (str obj)
  (pr obj str))

;;; a sequence of objects can be printed as a reduction.

#|
CL-USER> (reduce #'rp '("hello" " " "world" "!") :initial-value *standard-output*)
hello world!
#<SWANK/GRAY::SLIME-OUTPUT-STREAM {10024777B3}>
CL-USER> (reduce #'pr '("hello" " " "world" "!") :initial-value *standard-output* :from-end t)
!world hello
#<SWANK/GRAY::SLIME-OUTPUT-STREAM {10024777B3}>
|#