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emacselisp

Elisp List Contains a Value

How do you check, in elisp, if a list contains a value? so the following would return t:

(contains 3 '(1 2 3))

but

(contains 5 '(1 2 3))

would return nil.

Solution

  • The function you need is member

    For example:

    (member 3 '(1 2 3))

    It will return the tail of list whose car is element. While this is not strictly t, any non-nil value is equivalent to true for a boolean operation. Also, member uses equal to test for equality, use memq for stricter equality (using eq).