Macro

Macro.scala

import FieldList._
import shapeless.{HList, LabelledGeneric}
import scala.language.experimental.macros
import scala.reflect.macros.blackbox

object Foo {

  def foo_impl[T, L <: HList](c: blackbox.Context)
                                 (t: c.Expr[T])
                                 (gen: c.Expr[LabelledGeneric.Aux[T, L]],
                                  fl: c.Expr[FieldList[L]]): c.Expr[String] = {
    import c.universe._
    reify {
      val sb = new StringBuilder
      val obj = t.splice
      val generic = gen.splice
      val fieldList = fl.splice
      // T.fieldList returns a List[String] of the class' fields. 
      obj.fieldList(generic, fieldList).foldLeft(sb) { case (builder, next) =>
        builder.append(next)
        builder.append(" -> ")
        builder.append() // How to get the value of obj.$next?
      }.toString()
    }
  }

  def foo[T, L <: HList](t: T)(implicit gen: LabelledGeneric.Aux[T, L], fl: FieldList[L]): String = macro foo_impl[T, L]

}