PartialUnification.scala

PartialUnification.scala

// scalacOptions += "-Ypartial-unification"

object Foo {
  trait KVS[F[_], K, V] {
    def put(k: K, v: V): F[Unit]
    def get(k: K): F[Option[V]]
  }

  trait Repository[F[_], Id, A] {
    def query(id: Id): F[Option[A]]
    def store(a: A): F[A]
  }

  def RepositoryKVInterp[F[_], K, V](
    kvs: KVS[F, K, V]
  ) = new Repository[F, K, V] {

    def query(id: K): F[Option[V]] = ???
    def store(r: V): F[V] = ???
  }

  def InMemoryKVSInterpreter[K, V]: KVS[State[Map[K, V], ?], K, V] = new KVS[State[Map[K, V], ?], K, V] {
    type S = Map[K, V]
    def put(k: K, v: V): State[S, Unit] = State.modify(_ + (k -> v))
    def get(k: K): State[S, Option[V]] = State.inspect(s => s.get(k))
  }

  val inMemoryKVSInterp = InMemoryKVSInterpreter[Int, Int]
  val intp = RepositoryKVInterp(inMemoryKVSInterp)
}