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GNU Emacs Lisp Reference Manual

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8.4.3 Property Lists Outside Symbols

These functions are useful for manipulating property lists that are stored in places other than symbols:

Function: plist-get plist property
This returns the value of the property property stored in the property list plist. For example,

 
(plist-get '(foo 4) 'foo)
     => 4

Function: plist-put plist property value
This stores value as the value of the property property in the property list plist. It may modify plist destructively, or it may construct a new list structure without altering the old. The function returns the modified property list, so you can store that back in the place where you got plist. For example,

 
(setq my-plist '(bar t foo 4))
     => (bar t foo 4)
(setq my-plist (plist-put my-plist 'foo 69))
     => (bar t foo 69)
(setq my-plist (plist-put my-plist 'quux '(a)))
     => (bar t foo 69 quux (a))

You could define put in terms of plist-put as follows:

 
(defun put (symbol prop value)
  (setplist symbol
            (plist-put (symbol-plist symbol) prop value)))

Function: plist-member plist property
This returns non-nil if plist contains the given property. Unlike plist-get, this allows you to distinguish between a missing property and a property with the value nil. The value is actually the tail of plist whose car is property.

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  Copyright 2003   by The Free Software Foundation     Updated Jun 2003