get-dispatch-macro-character disp-char sub-char &optional readtable ⇒ function
set-dispatch-macro-character disp-char sub-char new-function &optional readtable ⇒ t
| 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. |
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 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.
(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
The readtable is modified.
For either function, an error is signaled if disp-char is not a dispatching macro character in readtable.
It is necessary to use make-dispatch-macro-character to set up the dispatch character before specifying its sub-characters.