DerivativeImpl.scala

def derivativeImpl(c: blackbox.Context)(f: c.Expr[Double => Double]): c.Expr[Double => Double] = {
  import c.universe._

  val Function(List(ValDef(_, name, _, _)), funcBody) = f.tree

  val components = extractComponents(funcBody)(c)
  val transformedComponents =
    components.map(_.derive.toTree(c)).reduce((a, b) => q"$a + $b")

  c.Expr(q"($name: Double) => $transformedComponents")
}