readtablep

readtablep Function

Syntax:

readtablep object → generalized-boolean

Arguments and Values:

object—an object.

generalized-boolean—a generalized boolean.

Description:

Returns true if object is of type readtable; otherwise, returns false.

Examples:

 
(readtablep \*readtable\*) → true 
(readtablep (copy-readtable)) → true 
(readtablep ’\*readtable\*) → false 

Notes:

(readtablep object) ≡ (typep object ’readtable)

set-dispatch-macro-character, . . .

^{set-dispatch-macro-character, get-dispatch-macro} character Function

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 
			      #\&#123;(1 2 3 4) → 1 
			      #3\&#123;(0 1 2 3) → 3 
			      #\&#123;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.

Expanded Reference: readtablep

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