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set-exclusive-or, nset-exclusive-or [Function]

set-exclusive-or list-1 list-2 &key key test test-not => result-list

nset-exclusive-or list-1 list-2 &key key test test-not => result-list

Arguments and Values::

list-1--a proper list.

list-2--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.

result-list--a list.

Description::

set-exclusive-or returns a list of elements that appear in exactly one of list-1 and list-2.

nset-exclusive-or is the destructive version of set-exclusive-or.

For all possible ordered pairs consisting of one element from list-1 and one element from list-2, the :test or :test-not function is used to determine whether they satisfy the test.

If :key is supplied, it is used to extract the part to be tested from the list-1 or list-2 element. The first argument to the :test or :test-not function is the part of an element of list-1 extracted by the :key function (if supplied); the second argument is the part of an element of list-2 extracted by the :key function (if supplied). If :key is not supplied or nil, the list-1 or list-2 element is used.

The result contains precisely those elements of list-1 and list-2 that appear in no matching pair.

The result list of set-exclusive-or might share storage with one of list-1 or list-2.

Examples::

      (setq lst1 (list 1 "a" "b")
            lst2 (list 1 "A" "b")) =>  (1 "A" "b")
      (set-exclusive-or lst1 lst2) =>  ("b" "A" "b" "a")
      (set-exclusive-or lst1 lst2 :test #'equal) =>  ("A" "a")
      (set-exclusive-or lst1 lst2 :test 'equalp) =>  NIL
      (nset-exclusive-or lst1 lst2) =>  ("a" "b" "A" "b")
      (setq lst1 (list (("a" . "b") ("c" . "d") ("e" . "f"))))
     =>  (("a" . "b") ("c" . "d") ("e" . "f"))
      (setq lst2 (list (("c" . "a") ("e" . "b") ("d" . "a"))))
     =>  (("c" . "a") ("e" . "b") ("d" . "a"))
      (nset-exclusive-or lst1 lst2 :test #'string= :key #'cdr)
     =>  (("c" . "d") ("e" . "f") ("c" . "a") ("d" . "a"))
      lst1 =>  (("a" . "b") ("c" . "d") ("e" . "f"))
      lst2 =>  (("c" . "a") ("d" . "a"))
     

Side Effects::

nset-exclusive-or is permitted to modify any part, car or cdr, of the list structure of list-1 or list-2.

Exceptional Situations::

Should be prepared to signal an error of type type-error if list-1 and list-2 are not proper lists.

See Also::

Compiler Terminology, Traversal Rules and Side Effects

Notes::

The :test-not parameter is deprecated.

Since the nset-exclusive-or side effect is not required, it should not be used in for-effect-only positions in portable code.