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(elisp)Char-Tables

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Char-Tables
===========

   A char-table is much like a vector, except that it is indexed by
character codes.  Any valid character code, without modifiers, can be
used as an index in a char-table.  You can access a char-table's
elements with `aref' and `aset', as with any array.  In addition, a
char-table can have "extra slots" to hold additional data not
associated with particular character codes.  Char-tables are constants
when evaluated.

   Each char-table has a "subtype" which is a symbol.  The subtype has
two purposes: to distinguish char-tables meant for different uses, and
to control the number of extra slots.  For example, display tables are
char-tables with `display-table' as the subtype, and syntax tables are
char-tables with `syntax-table' as the subtype.  A valid subtype must
have a `char-table-extra-slots' property which is an integer between 0
and 10.  This integer specifies the number of "extra slots" in the
char-table.

   A char-table can have a "parent", which is another char-table.  If
it does, then whenever the char-table specifies `nil' for a particular
character C, it inherits the value specified in the parent.  In other
words, `(aref CHAR-TABLE C)' returns the value from the parent of
CHAR-TABLE if CHAR-TABLE itself specifies `nil'.

   A char-table can also have a "default value".  If so, then `(aref
CHAR-TABLE C)' returns the default value whenever the char-table does
not specify any other non-`nil' value.

 - Function: make-char-table subtype &optional init
     Return a newly created char-table, with subtype SUBTYPE.  Each
     element is initialized to INIT, which defaults to `nil'.  You
     cannot alter the subtype of a char-table after the char-table is
     created.

     There is no argument to specify the length of the char-table,
     because all char-tables have room for any valid character code as
     an index.

 - Function: char-table-p object
     This function returns `t' if OBJECT is a char-table, otherwise
     `nil'.

 - Function: char-table-subtype char-table
     This function returns the subtype symbol of CHAR-TABLE.

 - Function: set-char-table-default char-table new-default
     This function sets the default value of CHAR-TABLE to NEW-DEFAULT.

     There is no special function to access the default value of a
     char-table.  To do that, use `(char-table-range CHAR-TABLE nil)'.

 - Function: char-table-parent char-table
     This function returns the parent of CHAR-TABLE.  The parent is
     always either `nil' or another char-table.

 - Function: set-char-table-parent char-table new-parent
     This function sets the parent of CHAR-TABLE to NEW-PARENT.

 - Function: char-table-extra-slot char-table n
     This function returns the contents of extra slot N of CHAR-TABLE.
     The number of extra slots in a char-table is determined by its
     subtype.

 - Function: set-char-table-extra-slot char-table n value
     This function stores VALUE in extra slot N of CHAR-TABLE.

   A char-table can specify an element value for a single character
code; it can also specify a value for an entire character set.

 - Function: char-table-range char-table range
     This returns the value specified in CHAR-TABLE for a range of
     characters RANGE.  Here are the possibilities for RANGE:

    `nil'
          Refers to the default value.

    CHAR
          Refers to the element for character CHAR (supposing CHAR is a
          valid character code).

    CHARSET
          Refers to the value specified for the whole character set
          CHARSET (Note: Character Sets).

    GENERIC-CHAR
          A generic character stands for a character set; specifying
          the generic character as argument is equivalent to specifying
          the character set name.  Note: Splitting Characters, for a
          description of generic characters.

 - Function: set-char-table-range char-table range value
     This function sets the value in CHAR-TABLE for a range of
     characters RANGE.  Here are the possibilities for RANGE:

    `nil'
          Refers to the default value.

    `t'
          Refers to the whole range of character codes.

    CHAR
          Refers to the element for character CHAR (supposing CHAR is a
          valid character code).

    CHARSET
          Refers to the value specified for the whole character set
          CHARSET (Note: Character Sets).

    GENERIC-CHAR
          A generic character stands for a character set; specifying
          the generic character as argument is equivalent to specifying
          the character set name.  Note: Splitting Characters, for a
          description of generic characters.

 - Function: map-char-table function char-table
     This function calls FUNCTION for each element of CHAR-TABLE.
     FUNCTION is called with two arguments, a key and a value.  The key
     is a possible RANGE argument for `char-table-range'--either a
     valid character or a generic character--and the value is
     `(char-table-range CHAR-TABLE KEY)'.

     Overall, the key-value pairs passed to FUNCTION describe all the
     values stored in CHAR-TABLE.

     The return value is always `nil'; to make this function useful,
     FUNCTION should have side effects.  For example, here is how to
     examine each element of the syntax table:

          (let (accumulator)
            (map-char-table
             #'(lambda (key value)
                 (setq accumulator
                       (cons (list key value) accumulator)))
             (syntax-table))
            accumulator)
          =>
          ((475008 nil) (474880 nil) (474752 nil) (474624 nil)
           ... (5 (3)) (4 (3)) (3 (3)) (2 (3)) (1 (3)) (0 (3)))