• adjoin item list &key key test test-not → new-list

• item - an object.
• list - a proper list.
• test - a designator for a function of two arguments that returns a generalized boolean.
• test-not - a designator for a function of two arguments that returns a generalized boolean.
• key - a designator for a function of one argument, or nil.
• new-list - a list.

Tests whether item is the same as an existing element of list. If the item is not an existing element, adjoin adds it to list (as if by cons) and returns the resulting list; otherwise, nothing is added and the original list is returned.

The test, test-not, and key affect how it is determined whether item is the same as an element of list. For details, see {\secref 17.2.1}.

(defparameter *slist* '()) 

→

*SLIST*



(adjoin 'a *slist*) 

→

(A) 



*slist* 

→

NIL 



(setf *slist* (adjoin '(test-item 1) *slist*)) 

→

((TEST-ITEM 1)) 



(adjoin '(test-item 1) *slist*) 

→

((TEST-ITEM 1) (TEST-ITEM 1)) 



(adjoin '(test-item 1) *slist* :test #'equal) 

→

((TEST-ITEM 1)) 



(adjoin '(new-test-item 1) *slist* :key #'cadr) 

→

((TEST-ITEM 1)) 



(adjoin '(new-test-item 1) *slist*) 

→

((NEW-TEST-ITEM 1) (TEST-ITEM 1)) 

None.

None.

Should be prepared to signal an error of type type-error if list is not a proper list.

Macro PUSHNEW, {\secref\TraversalRules}

(adjoin item list :key fn) ≡ (if (member (funcall fn item) list :key fn) list (cons item list))

The :test-not parameter is deprecated.

\issue{MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE} \issue{TEST-NOT-IF-NOT:FLUSH-ALL}