member, member-if, member-if-not Function

Syntax

member item list &key key test test-not tail

member-if predicate list &key key tail

member-if-not predicate list &key key tail

Arguments and Values

item — an object.

list — a proper list.

predicate — a designator for a function of one argument that returns a generalized boolean.

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.

tail — a list.

Description

member, member-if, and member-if-not each search list for item or for a top-level element that satisfies the test. The argument to the predicate function is an element of list.

If some element satisfies the test, the tail of list beginning with this element is returned; otherwise nil is returned.

list is searched on the top level only.

Examples
```(member 2 '(1 2 3)) → (2 3)
(member 2 '((1 . 2) (3 . 4)) :test-not #'= :key #'cdr) → ((3 . 4))
(member 'e '(a b c d)) → NIL```
```(member-if #'listp '(a b nil c d)) → (NIL C D)
(member-if #'numberp '(a #\Space 5/3 foo)) → (5/3 FOO)
(member-if-not #'zerop
'(3 6 9 11 . 12)
:key #'(lambda (x) (mod x 3))) → (11 . 12)```
Exceptional Situations

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

`(member 'a '(g (a y) c a d e a f)) → (A D E A F)`
the value returned by member is identical to the portion of the list beginning with `a`. Thus rplaca on the result of member can be used to alter the part of the list where `a` was found (assuming a check has been made that member did not return nil).