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| ANSI Common Lisp 13 Characters 13.2 Dictionary of Characters
13.2.14 char-upcase, char-downcase | Function
  Syntax:
  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, 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. Allegro CL Implementation Details: None.

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