(peek coll)
For a list or queue, same as first, for a vector, same as, but much more efficient than, last. If the collection is empty, returns nil.
user=> (def large-vec (vec (range 0 10000)))
#'user/large-vec
user=> (time (last large-vec))
"Elapsed time: 1.279841 msecs"
9999
user=> (time (peek large-vec))
"Elapsed time: 0.049238 msecs"
9999
user=> (peek '(:a :b :c))
:a
user=> (peek [1 2 3 4])
;;=> 4
user=> (peek [])
;;=> nil
user=> (peek '(1 2 3 4))
;;=> 1
user=> (peek '())
;;=> nil
user=> (peek nil)
;;=> nil