x
x
x


Do so in a way which:

 does not involve string manipulation of the input source code
 is plausibly extensible to a runtime-chosen set of bindings rather than just x
 does not make x a global variable


or note that these are impossible.



See also

 For more general examples and language-specific details, see Eval.
 Dynamic variable names is a similar task.


(def ^:dynamic x nil)
 
(defn eval-with-x [program a b]
  (- (binding [x b] (eval program))
     (binding [x a] (eval program))))