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extended-char

extended-char Type

Supertypes:

extended-char, character, t

Description:

The type extended-char is equivalent to the type (and character (not base-char)).

Notes:

The type extended-char might have no elements4 in implementations in which all characters are of type base-char.

Expanded Reference: extended-char​

The extended-char type​

extended-char is a type equivalent to (and character (not base-char)). It represents characters that are not base characters. In many implementations where base-char and character are the same type, extended-char has no members.

(subtypep 'extended-char 'character)
=> T
=> T

Testing for extended characters​

Whether any characters are of type extended-char depends on the implementation.

;; In implementations where base-char = character:
(typep #\a 'extended-char)
=> NIL

;; The type might be empty:
(subtypep 'extended-char nil)
;; => implementation-dependent

Exhaustive partition of character​

The types base-char and extended-char form an exhaustive partition of character. Every character is exactly one of these two types.

;; For any character ch, exactly one of these is true:
(let ((ch #\A))
  (or (typep ch 'base-char)
      (typep ch 'extended-char)))
=> T

(let ((ch #\A))
  (and (typep ch 'base-char)
       (typep ch 'extended-char)))
=> NIL

Relationship with strings​

Extended characters cannot be elements of base strings. They require a string type with a broader element type.

;; Base strings only hold base-char elements:
(subtypep 'base-char
          (array-element-type (make-string 1)))
;; => implementation-dependent