char-upcase, char-downcase (Function)

Syntax:

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, Section 13.1.4.3 (Characters With Case), Section 13.1.10 (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.