One of the symbols :upcase, :downcase, or :capitalize.
The symbol :upcase.
The value of *print-case* controls the case (upper, lower, or mixed) in which to print any uppercase characters in the names of symbols when vertical-bar syntax is not used.
*print-case* has an effect at all times when the value of *print-escape* is false. *print-case* also has an effect when the value of *print-escape* is true unless inside an escape context (i.e., unless between vertical-bars or after a slash).
(defun test-print-case ()
(dolist (*print-case* '(:upcase :downcase :capitalize))
(format t "~&~S ~S~
⇒ TEST-PC
;; Although the choice of which characters to escape is specified by
;; *PRINT-CASE*, the choice of how to escape those characters
;; (i.e., whether single escapes or multiple escapes are used)
;; is implementation-dependent. The examples here show two of the
;; many valid ways in which escaping might appear.
(test-print-case) ;Implementation A
|> THIS-AND-THAT |And-something-elSE|
|> this-and-that a\n\d-\s\o\m\e\t\h\i\n\g-\e\lse
|> This-And-That A\n\d-\s\o\m\e\t\h\i\n\g-\e\lse
⇒ NIL
(test-print-case) ;Implementation B
|> THIS-AND-THAT |And-something-elSE|
|> this-and-that a|nd-something-el|se
|> This-And-That A|nd-something-el|se
⇒ NIL
read normally converts lowercase characters appearing in symbols to corresponding uppercase characters, so that internally print names normally contain only uppercase characters.
If *print-escape* is true, lowercase characters in the name of a symbol are always printed in lowercase, and are preceded by a single escape character or enclosed by multiple escape characters; uppercase characters in the name of a symbol are printed in upper case, in lower case, or in mixed case so as to capitalize words, according to the value of *print-case*. The convention for what constitutes a "word" is the same as for string-capitalize.