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post.scala

def program(implicit M: Moves[LogoApp], P: PencilActions[LogoApp]): (Position => Free[LogoApp, Unit]) = {
    import M._, P._
    s: Position =>
    for {
      p1 <- forward(s, 10)
      p2 <- right(p1, Degree(90))
      _ <- pencilUp(p2)
      p3 <- forward(p2, 10)
      _ <- pencilDown(p3)
      p4 <- backward(p3, 20)
      _ <- showPosition(p4)
    } yield ()
  }