(first coll)
Returns the first item in the collection. Calls seq on its argument. If coll is nil, returns nil.
(first '(:alpha :bravo :charlie))
;;=> :alpha
;; nil is a valid (but empty) collection.
(first nil)
;;=> nil
;; if collection is empty, returns nil.
(first [])
;;=> nil
=> (first [1 2])
1
=> (first [ [1 2] [3 4] ])
[1 2]