char-upcase character => corresponding-character
char-downcase character => corresponding-character
character, corresponding-character---a character.
If character is a lowercase character, char-upcase returns the corresponding uppercase character. Otherwise, char-upcase just returns the given character.
If character is an uppercase character, char-downcase returns the corresponding lowercase character. Otherwise, char-downcase just returns the given character.
The result only ever differs from character in its code attribute; all implementation-defined attributes are preserved.
(char-upcase #\a) => #\A
(char-upcase #\A) => #\A
(char-downcase #\a) => #\a
(char-downcase #\A) => #\a
(char-upcase #\9) => #\9
(char-downcase #\9) => #\9
(char-upcase #\@) => #\@
(char-downcase #\@) => #\@
;; Note that this next example might run for a very long time in
;; some implementations if CHAR-CODE-LIMIT happens to be very large
;; for that implementation.
(dotimes (code char-code-limit)
(let ((char (code-char code)))
(when char
(unless (cond ((upper-case-p char) (char= (char-upcase (char-downcase char)) char))
((lower-case-p char) (char= (char-downcase (char-upcase char)) char))
(t (and (char= (char-upcase (char-downcase char)) char)
(char= (char-downcase (char-upcase char)) char))))
(return char)))))
=> NIL
Should signal an error of type type-error if character is not a character.
@xref{upper-case-p; lower-case-p; both-case-p} , section alpha-char-p [Function] , section Characters With Case, section Documentation of Implementation-Defined Scripts
If the corresponding-char is different than character, then both the character and the corresponding-char have case.
Since char-equal ignores the case of the characters it compares, the corresponding-character is always the same as character under char-equal.
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