Test whether a list contains a specific value in Clojure

Question

What is the best way to test whether a list contains a given value in Clojure?

In particular, the behaviour of contains? is currently confusing me:

Answer 1

It is as simple as using a set - similar to maps, you can just drop it in the function position. It evaluates to the value if in the set (which is truthy) or nil (which is falsey):

(#{100 101 102} 101) ; 101
(#{100 101 102} 99) ; nil

If you're checking against a reasonably sized vector/list you won't have until runtime, you can also use the set function:

; (def nums '(100 101 102))
((set nums) 101) ; 101