Question

Is there a function/macro in Clojure to check what namespaces are currently ‘used’? Which one? So I don’t mean ‘what namespace are we currently in’ but for example, I want to find out if ‘clojure.contrib.string’ is currently ‘used’ as in (use 'clojure.contrib.string). I don’t mean ‘required’.

How does one write a function that give true when for example ‘clojure.contrib.string (the name of the namespace provided via a symbol) is used and false otherwise?
(defn ns-used? [name] (…)

Answer 1

all-ns as suggested by kotarak, is close to what you are looking for, but it also gives you all the namespaces that have been required without having been referred.

Otherwise ns-refers gives you a map of all the functions that are referred in the namespace. Similar and possibly also of interest are ns-map and ns-imports which gives you a mapping of all the imported classes or records.

If you want to strictly find all the namespaces from which functions have been referred, you could do something like this:

(defn ns-used? [ns]
  (let [referred-namespaces (set (map (fn [[k v]] (:ns (meta v))) (ns-refers *ns*)))] 
    (contains? referred-namespaces (find-ns ns))))

If you are happy to check if the namespace has been required or used you could do

(defn ns-used-or-required? [ns]
  (contains? (set (all-ns)) (find-ns ns)))

You will have to pass the symbol in quoted:

(ns-used? 'clojure.core)