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
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.
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.
(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"))
nset-exclusive-or is permitted to modify any part, car or cdr, of the list structure of list-1 or list-2.
Should be prepared to signal an error of type type-error if list-1 and list-2 are not proper lists.
section Compiler Terminology,
section Traversal Rules and Side Effects
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.
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