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.


object Eval extends App {
 
  def evalWithX(expr: String, a: Double, b: Double)=
    {val x = b; eval(expr)} - {val x = a; eval(expr)}
 
  println(evalWithX("Math.exp(x)", 0.0, 1.0))
 
}