Elisp List Contains a Value

Question

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.

Headstock

Answer 1

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).

Aerification

For further details, see gnu.org/software/emacs/emacs-lisp-intro/html_node/… – Kiley

Answer 2

freiksenet's answer is good and idiomatic. If you are using dash.el, you could also call function -contains?, which does exactly the same—checks if some list contains an element:

(-contains? '(1 2 3) 2) ; t

Gruchot

Answer 3

And if you want to find an element by applying a function, there's a seq-find:

(seq-find (lambda (val) (= 3 val))
          '(1 2 3))

Orville