Infer #implicit #typeclass of input type inside macro #scala2.10

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Macros.scala

import scala.reflect.macros.Context
import language.experimental.macros

trait MyTypeClass[A] {
  def doit(a: A): A
}

object Macros {
  def inferImplicitsImpl[A: c.WeakTypeTag](c: Context): c.Expr[MyTypeClass[A]] = {
    import c.universe._
    // gets type of input type
    val theType = weakTypeOf[A]

    // builds expected implicit MyTypeClass[A]
    val neededImplicitType = appliedType(weakTypeOf[MyTypeClass[_]].typeConstructor, theType :: Nil)

    // searches an implicit in scope
    val neededImplicit = c.inferImplicitValue(neededImplicitType)

    neededImplicit match {
      case EmptyTree => c.abort(c.enclosingPosition, s"No implicit MyTypeClass[${theType}] available.")
      case impl => c.Expr[MyTypeClass[A]](impl)
    }
  }

  def inferImplicits[A] = macro inferImplicitsImpl[A]

}

Test.scala

object Test {
  implicit val myImpl = new MyTypeClass[Long]{
    def doit(a: Long) = a
  }

  val toto = Macros.inferImplicits[Long]
  val tata = Macros.inferImplicits[String]
}

// Launch it in scala macro & get error
<console>:22: error: No implicit MyTypeClass[String] available.
       val tata = Macros.inferImplicits[String]