MEMBER

membership predicate
Major Section:  PROGRAMMING

General Forms:
(member x lst)
(member x lst :test 'eql)   ; same as above (eql as equality test)
(member x lst :test 'eq)    ; same, but eq is equality test
(member x lst :test 'equal) ; same, but equal is equality test

(Member x lst) equals the longest tail of the list lst that begins with x, or else nil if no such tail exists. The optional keyword, :TEST, has no effect logically, but provides the test (default eql) used for comparing x with successive elements of lst.

The guard for a call of member depends on the test. In all cases, the second argument must satisfy true-listp. If the test is eql, then either the first argument must be suitable for eql (see eqlablep) or the second argument must satisfy eqlable-listp. If the test is eq, then either the first argument must be a symbol or the second argument must satisfy symbol-listp.

See equality-variants for a discussion of the relation between member and its variants:

(member-eq x lst) is equivalent to (member x lst :test 'eq);

(member-equal x lst) is equivalent to (member x lst :test 'equal).

In particular, reasoning about any of these primitives reduces to reasoning about the function member-equal.

Member is defined by Common Lisp. See any Common Lisp documentation for more information.