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symbol-plist

symbol-plist Accessor

Syntax:

symbol-plist symbol → plist

(setf (symbol-plist symbol**)** new-plist**)**

Arguments and Values:

symbol—a symbol.

plist, new-plist—a property list.

Description:

Accesses the property list of symbol.

Examples:

(setq sym (gensym)) → #:G9723 
(symbol-plist sym) → () 
(setf (get sym ’prop1) ’val1) → VAL1 
(symbol-plist sym) → (PROP1 VAL1) 
(setf (get sym ’prop2) ’val2) → VAL2 
(symbol-plist sym) → (PROP2 VAL2 PROP1 VAL1) 
(setf (symbol-plist sym) (list ’prop3 ’val3)) → (PROP3 VAL3) 
(symbol-plist sym) → (PROP3 VAL3)

Exceptional Situations:

Should signal an error of type type-error if symbol is not a symbol.

See Also:

get, remprop

Notes:

The use of setf should be avoided, since a symbol’s property list is a global resource that can contain information established and depended upon by unrelated programs in the same Lisp image.

symbol-value

Expanded Reference: symbol-plist​

Basic usage​

symbol-plist returns the property list associated with a symbol. A fresh symbol has an empty property list.

(let ((sym (gensym)))
  (symbol-plist sym))
=> NIL

Viewing properties after adding them with get/setf​

Properties are typically added with (setf (get ...)). symbol-plist reveals the underlying list structure.

(let ((sym (make-symbol "EXAMPLE")))
  (setf (get sym 'color) 'red)
  (setf (get sym 'size) 42)
  (symbol-plist sym))
;; => (SIZE 42 COLOR RED)  (order may vary)

Directly setting the property list​

You can replace the entire property list with setf, though this is generally discouraged since property lists are a shared global resource.

(let ((sym (make-symbol "DEMO")))
  (setf (get sym 'a) 1)
  (setf (get sym 'b) 2)
  (format nil "Before: ~S" (symbol-plist sym))
  (setf (symbol-plist sym) '(x 10 y 20))
  (values (get sym 'x) (get sym 'y) (get sym 'a)))
=> 10
=> 20
=> NIL

Property list structure​

The property list is a flat list of alternating indicators and values.

(let ((sym (make-symbol "DATA")))
  (setf (get sym 'name) "Alice")
  (setf (get sym 'age) 30)
  (let ((plist (symbol-plist sym)))
    (values (length plist)
            (evenp (length plist)))))
=> 4
=> T

Empty property list for standard symbols​

Most standard symbols do not have property list entries by default (though implementations may add some).

;; Check the type of what symbol-plist returns
(listp (symbol-plist (make-symbol "FRESH")))
=> T