(defn foo [a context]
  (-> a
      inc
      (#(bar % context))))

(defn bar [a context]
  (cond (= context 1) (* a 2)
        (= context 2) (/ a 2)))

(ns main)

(defn foo [a]
  (-> inc
      ('bar (ns-map *ns*))))

(ns context-1
  (use main))

(defn bar [a]
  (* a 2))

(ns context-2
  (use main))

(defn bar [a]
  (/ a 2))

(defn context-1-foo [a]
  (let [base-ns *ns*]
    (in-ns 'context-1)
    (let [result (foo a)]
      (in-ns (ns-name base-ns))
      result)))