Terser syntax for first-class functions needing a context bound

Question

I have the following function that looks up a mathematical operation that can be applied to a Numeric sequence based on a String

def getAction[T : Fractional]( op : String ) : Seq[T] => String =
  op match {
    case "add" => seq => seq.sum.toString
    case "product" => seq => seq.product.toString
    case "mean" => seq => {
      implicit def intToFractional(i : Int) =
        implicitly[Fractional[T]].fromInt(i);
      (seq.sum / seq.length).toString
    }
    case "sqrt" => seq => seq.map(i => math.sqrt(i.toDouble)).toString
  }

That works fine, except I would prefer to specify the type when applying the returned function rather than at the time or retrieval.

i.e. I want

getAction("sqrt")[Double](Seq(4.0))

rather than

getAction[Double]("sqrt")(Seq(4.0))

The only way I have found to do this is by defining a new class/trait with a generic context-bound apply.

abstract class Action {
  def apply[T : Fractional](seq : Seq[T]) : String
}

Edit: Replaced with whole class rather than just the method because compilable solution was wanted.

object Main extends App {
  import scala.math.Fractional
  import Fractional.Implicits._
  import scala.language.implicitConversions

  abstract class Action {
    def apply[T : Fractional](seq : Seq[T]) : String
  }

  def getAction( op : String ) : Action =
  op match {
    case "add" =>
      new Action {
        def apply[T : Fractional](seq : Seq[T]) = seq.sum.toString
      }
    case "product" =>
      new Action {
        def apply[T : Fractional](seq : Seq[T]) = seq.product.toString
      }
    case "mean" =>
      new Action {
        def apply[T : Fractional](seq : Seq[T])= {
          implicit def intToFractional(i : Int) =
            implicitly[Fractional[T]].fromInt(i);

          (seq.sum / seq.length).toString
        }
      }
    case "sqrt" =>
      new Action {
        def apply[T : Fractional](seq : Seq[T]) =
           seq.map(i => math.sqrt(i.toDouble)).toString
      }
  }

  def getAction_v1[T : Fractional]( op : String ) : Seq[T] => String =
    op match {
      case "add" => seq => seq.sum.toString
      case "product" => seq => seq.product.toString
      case "mean" => seq => {
        implicit def intToFractional(i : Int) =
          implicitly[Fractional[T]].fromInt(i);
        (seq.sum / seq.length).toString
        }
      case "sqrt" => seq => seq.map(i => math.sqrt(i.toDouble)).toString
    }
  }

However, this seems messy to be because of all the repeated anonymous class definitions and repeated type signatures. This makes the actual math operations less obvious than the first version.

Is there a better way?

Edit: here is a simple test suite that shows execution of both versions import org.scalatest.FunSuite

import org.scalatest.FunSuite

class Tests extends FunSuite {

  test("v1"){
    val act = Main.getAction_v1[Double]("sqrt")
    assert(act(Seq(4.0)) === "List(2.0)")
  }

  test("v2") {
    val act = Main.getAction("sqrt")
    assert(act[Double](Seq(4.0)) === "List(2.0)")
  }
}

Answer 1

How about not having to specify the type at all?

implicit class SeqWithAction[T:Fractional](seq:Seq[T]) {
  def getAction( op : String ) : String =
    op match {
      case "add" => seq.sum.toString
      case "product" => seq.product.toString
      case "mean" => {
        implicit def intToFractional(i : Int) =
          implicitly[Fractional[T]].fromInt(i);
        (seq.sum / seq.length).toString
      }
      case "sqrt" => seq.map(i => math.sqrt(i.toDouble)).toString
    }
  }     
}
Seq(4.0).getAction("sqrt")