set-exclusive-or, nset-exclusive-or (Function)

Syntax:

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:

Section 3.2.1 (Compiler Terminology), Section 3.6 (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.