(let [[a b]
                          (list "a" "b")
                          foo "asdf"]
                      (string/join "_" '(a b foo)))

(let [[a b]
                          (list "a" "b")
                          foo "asdf"]
                      (string/join "_" (list a b foo)))

'(a b foo) is not evaluated

@munichlinux a quote tells Clojure not to evaluate anything in the form that follows

(let [foo "asdf"]
  'foo)
;; => foo

(let [foo "asdf"]
  foo)
;; => "asdf"

@lilactown ah, I got that wrong

Thanks