Get type of a “singleton type”

Question

We can create a literal types via shapeless:

import shapeless.syntax.singleton._
var x = 42.narrow
// x: Int(42) = 42

But how can I operate wit

Answer 1

1) In Typelevel Scala you can write just

val x: 42 = 42

type Answ = 42

def doSmth(value: 42) = ???

2) In Dotty Scala you can write the same.

3) In Lightbend Scala (i.e. standard Scala) + Shapeless you can write

import shapeless.Witness
import shapeless.syntax.singleton._

val x: Witness.`42`.T = 42.narrow

type Answ = Witness.`42`.T

def doSmth(value: Witness.`42`.T) = ???

In case 1) build.sbt should be

scalaOrganization := "org.typelevel"
scalaVersion := "2.12.3-bin-typelevel-4"
scalacOptions += "-Yliteral-types"

In case 2) build.sbt should be

scalaOrganization := "ch.epfl.lamp"
scalaVersion := "0.3.0-RC2"

and plugins.sbt

addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.1.5")

In case 3) build.sbt should be

scalaOrganization := "org.scala-lang"
scalaVersion := "2.12.3"
libraryDependencies += "com.chuusai" %% "shapeless" % "2.3.2"

4) or you can use Typelevel Scala and Shapeless at the same time.