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13.2.14 char-upcase, char-downcase [Function]

char-upcase character => corresponding-character

char-downcase character => corresponding-character

Arguments and Values::

character, corresponding-character—a character.

Description::

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.

Examples::
      (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
Exceptional Situations::

Should signal an error of type type-error if character is not a character.

See Also::

upper-case-p , alpha-char-p , Characters With Case, Documentation of Implementation-Defined Scripts

Notes::

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.