打印出某个Var对象或者special form的文档信息
=> (doc map)
;; prints in console:
-------------------------
clojure.core/map
([f coll] [f c1 c2] [f c1 c2 c3] [f c1 c2 c3 & colls])
Returns a lazy sequence consisting of the result of applying f to the
set of first items of each coll, followed by applying f to the set
of second items in each coll, until any one of the colls is
exhausted. Any remaining items in other colls are ignored. Function
f should accept number-of-colls arguments.
=> (doc clojure.core)
-------------------------
clojure.core
Fundamental library of the Clojure language