- Syntax:
-
get-dispatch-macro-character
disp-char sub-char &optional readtable
function
set-dispatch-macro-character
disp-char sub-char new-function &optional readtable
t
- Arguments and Values:
-
disp-char - a character.
sub-char - a character.
readtable - a readtable designator.
The default is the current readtable.
function - a function designator or nil.
new-function - a function designator.
- Description:
-
set-dispatch-macro-character causes new-function to be called
when disp-char followed by sub-char is read.
If sub-char is a lowercase letter,
it is converted to its uppercase equivalent.
It is an error if sub-char is one of the ten decimal digits.
set-dispatch-macro-character installs a new-function to be called
when a particular dispatching macro character pair is read.
New-function is installed as the dispatch function to be
called when readtable is in use and when disp-char is followed by
sub-char.
For more information about how the new-function is invoked,
see Section 2.1.4.4 Macro Characters.
get-dispatch-macro-character retrieves
the dispatch function associated with disp-char and sub-char
in readtable.
get-dispatch-macro-character returns the macro-character function
for sub-char under disp-char, or nil if there is no
function associated with sub-char.
If sub-char is a decimal digit, get-dispatch-macro-character
returns nil.
- Examples:
-
(get-dispatch-macro-character #\# #\{) NIL
(set-dispatch-macro-character #\# #\{ ;dispatch on #{
#'(lambda(s c n)
(let ((list (read s nil (values) t))) ;list is object after #n{
(when (consp list) ;return nth element of list
(unless (and n (< 0 n (length list))) (setq n 0))
(setq list (nth n list)))
list))) T
#{(1 2 3 4) 1
#3{(0 1 2 3) 3
#{123 123
If it is desired that #$foo :
as if it were (dollars foo).
(defun |#-reader| (stream subchar arg)
(declare (ignore subchar arg))
(list 'dollars (read stream t nil t))) |#-reader|
(set-dispatch-macro-character #\# #\$ #'|#$-reader|) T
- See Also:
-
Section 2.1.4.4 Macro Characters
- Side Effects:
-
The readtable is modified.
- Affected By:
-
*readtable*.
- Exceptional Situations:
-
For either function, an error is signaled if disp-char is not
a dispatching macro character in readtable.
- See Also:
-
*readtable*
- Notes:
-
It is necessary
to use make-dispatch-macro-character to set up the
dispatch character before specifying its sub-characters.
- Allegro CL Implementation Details:
-
None.
23 Reader