ns-aliases

;; clojure.core contains an alias
(ns-aliases 'clojure.core)
;;=> {jio #<Namespace clojure.java.io>}

;; To start with there are no namespace aliases in the user namespace.
(ns-aliases 'user)
;;=> {}

;; ...but we can add an alias to the user namespace.
(alias 'string 'clojure.string) 
(ns-aliases 'user)
;;=> {string #{Namespace clojure.string>}

;; Suppose you want to pass a namespace as an argument...
(ns wip (:require [clojure.string :as string]
                  [clojure.pprint :as pp]))
(defn foo [nspace] nspace)

;; ...pretty easy to do if you use the namespace symbol.
(foo (the-ns 'clojure.string))
;;=> #<Namespace clojure.string>

;; but, a bit of a problem if you want to pass the alias.
(foo (the-ns 'string))
;; java.lang.Exception: No namespace: string found...

;; We can make a function that will serve using ns-aliases.
(defn the-alias [name] (get (ns-aliases *ns*) name))
(the-alias 'string)
;;=> #<Namespace clojure.string>

(foo (the-alias 'string))
;;=> #<Namespace clojure.string>

;; A more direct function can be written.
;; but this uses an undocumented function.
(defn the-alias [alias-name] (.lookupAlias *ns* (symbol alias-name)))
(the-alias "pp")
;;=> #<Namespace clojure.pprint>