ConnectionIO Final Tagless Example

Foo.scala

import doobie._
import doobie.implicits._

// Something for FunctionK ~>

trait Foo[F[_]]{ 
  def getFoo: F[Bar] 
}

object Foo {
  case class Bar(x: Int)
  object Bar {
     implicit val metaBar: Meta[Bar] = Meta[Int].imap(Bar(_), _.x)
  }
  // For Metadata Testing
  private[Foo] val getBar : Query0[Bar] = sql"SELECT 1".query[Bar]
  
  private def connectIOTrait: Foo[ConnectionIO] = new Foo[ConnectionIO]{
    def getFoo: ConnectionIO[Bar] = getBar.unique
  }
  
  def mapK[F[_], G[_]](foo: Foo[F])(f: F ~> G): Foo[G] = new Foo[G]{
    def getFoo: G[Bar] = f(foo.getFoo)
  }
  def impl[F[_]](t: Transactor[F]): Foo[F] = connectIOTrait.mapK(_.transact(t)) 
}