the description for this gist

post.scala

object Logo{

  sealed trait Instruction[A]
  ...
  sealed trait PencilInstruction[A]
  ...
  case class Position(x: Double = 0, y: Double = 0, heading: Degree = Degree())
  case class Degree(private val d: Int = 0) {...}

  object dsl {
    class Moves[F[_]](implicit I: Inject[Instruction, F]) {
      def forward(pos: Position, l: Int): Free[F, Position] = Free.inject[Instruction, F](Forward(pos, l))
      def backward(pos: Position, l: Int): Free[F, Position] = Free.inject[Instruction, F](Backward(pos, l))
      def left(pos: Position, degree: Degree): Free[F, Position] = Free.inject[Instruction, F](RotateLeft(pos, degree))
      def right(pos: Position, degree: Degree): Free[F, Position] = Free.inject[Instruction, F](RotateRight(pos, degree))
      def showPosition(pos: Position): Free[F, Unit] = Free.inject[Instruction, F](ShowPosition(pos))
    }

    object Moves {
      implicit def moves[F[_]](implicit I: Inject[Instruction, F]): Moves[F] = new Moves[F]
    }

    class PencilActions[F[_]](implicit I: Inject[PencilInstruction, F]) {
      def pencilUp(pos: Position): Free[F, Unit] = Free.inject[PencilInstruction, F](PencilUp(pos))
      def pencilDown(pos: Position): Free[F, Unit] = Free.inject[PencilInstruction, F](PencilDown(pos))
    }

    object PencilActions {
      implicit def pencilActions[F[_]](implicit I: Inject[PencilInstruction, F]): PencilActions[F] = new PencilActions[F]
    }
  }
}