CLHS: Section 22.1.3.3.2.1

22.1.3.3.2.1 Examples of Effect of Readtable Case on the Lisp Printer

 (defun test-readtable-case-printing ()
   (let ((*readtable* (copy-readtable nil))
         (*print-case* *print-case*))
     (format t "READTABLE-CASE *PRINT-CASE*  Symbol-name  Output~
              ~%--------------------------------------------------~
              ~%")
     (dolist (readtable-case '(:upcase :downcase :preserve :invert))
       (setf (readtable-case *readtable*) readtable-case)
       (dolist (print-case '(:upcase :downcase :capitalize))
         (dolist (symbol '(|ZEBRA| |Zebra| |zebra|))
           (setq *print-case* print-case)
           (format t "~&:~A~15T:~A~29T~A~42T~A"
                   (string-upcase readtable-case)
                   (string-upcase print-case)
                   (symbol-name symbol)
                   (prin1-to-string symbol)))))))

The output from (test-readtable-case-printing) should be as follows:

    READTABLE-CASE *PRINT-CASE*  Symbol-name  Output
    --------------------------------------------------
    :UPCASE        :UPCASE       ZEBRA        ZEBRA
    :UPCASE        :UPCASE       Zebra        |Zebra|
    :UPCASE        :UPCASE       zebra        |zebra|
    :UPCASE        :DOWNCASE     ZEBRA        zebra
    :UPCASE        :DOWNCASE     Zebra        |Zebra|
    :UPCASE        :DOWNCASE     zebra        |zebra|
    :UPCASE        :CAPITALIZE   ZEBRA        Zebra
    :UPCASE        :CAPITALIZE   Zebra        |Zebra|
    :UPCASE        :CAPITALIZE   zebra        |zebra|
    :DOWNCASE      :UPCASE       ZEBRA        |ZEBRA|
    :DOWNCASE      :UPCASE       Zebra        |Zebra|
    :DOWNCASE      :UPCASE       zebra        ZEBRA
    :DOWNCASE      :DOWNCASE     ZEBRA        |ZEBRA|
    :DOWNCASE      :DOWNCASE     Zebra        |Zebra|
    :DOWNCASE      :DOWNCASE     zebra        zebra
    :DOWNCASE      :CAPITALIZE   ZEBRA        |ZEBRA|
    :DOWNCASE      :CAPITALIZE   Zebra        |Zebra|
    :DOWNCASE      :CAPITALIZE   zebra        Zebra
    :PRESERVE      :UPCASE       ZEBRA        ZEBRA
    :PRESERVE      :UPCASE       Zebra        Zebra
    :PRESERVE      :UPCASE       zebra        zebra
    :PRESERVE      :DOWNCASE     ZEBRA        ZEBRA
    :PRESERVE      :DOWNCASE     Zebra        Zebra
    :PRESERVE      :DOWNCASE     zebra        zebra
    :PRESERVE      :CAPITALIZE   ZEBRA        ZEBRA
    :PRESERVE      :CAPITALIZE   Zebra        Zebra
    :PRESERVE      :CAPITALIZE   zebra        zebra
    :INVERT        :UPCASE       ZEBRA        zebra
    :INVERT        :UPCASE       Zebra        Zebra
    :INVERT        :UPCASE       zebra        ZEBRA
    :INVERT        :DOWNCASE     ZEBRA        zebra
    :INVERT        :DOWNCASE     Zebra        Zebra
    :INVERT        :DOWNCASE     zebra        ZEBRA
    :INVERT        :CAPITALIZE   ZEBRA        zebra
    :INVERT        :CAPITALIZE   Zebra        Zebra
    :INVERT        :CAPITALIZE   zebra        ZEBRA