Simplified Common Lisp reference
Symbol class: Conses, Lists and related functions
Symbol type: function
getfplacekeydefault(optional) => value
Argument description:
place a place with list
key keying value, also know as indicator
default answer when key-value pair is not found, default is NIL

GETF function searches supplied plist for value with matching key. Plist is list of even number of items. Each item pair specifies key and value. I.e. (K1 V1 K2 V2 ...). Return value is either value for first matching key, or specified default. Keys are matched by EQ function, therefore only suitable values are symbols and integers in range between MOST-NEGATIVE-FIXNUM and MOST-POSITIVE-FIXNUM constants. See also SETF, ASSOC and FIND.

(getf '(a b 4 d a x) 'a) => B
(getf '(a b 4 d a x) 'x) => NIL
(getf '(a b 4 d a x) 'x 'not-found) => NOT-FOUND
(getf '(a b 4 d a x) 4 'not-found) => D
Function indexFull documentation for getf (HyperSpec)