Unable to build a traversal dynamically with labelled steps

[aSapien]

There is a compilation error when building a traversal dynamically.

In my use case, I need to create a chain of Vertices from a dynamic-length list, and avoid creating existing chains (hence the coalesce steps)

Example:

  private def createChain(pathInGraph: List[String]) = {
    val Property = Key[String]("value")
    val Link = "Link"
    val Label = "PathComponent"

    val start = g.V.hasLabel(Label).property(Property -> pathInGraph.head).fold.coalesce(
      _.unfold[Vertex],
      _.addV(Label).property(Property -> pathInGraph.head)
    )

    pathInGraph.tail.foldLeft(start) {
      case (anchor, pathComponentValue) =>
        val step = StepLabel[Vertex]()

        anchor.as(step).coalesce(
          _.out(Link).hasLabel(Label).property(Property -> pathComponentValue),
          _.addV(Label).property(Property -> pathComponentValue).addE(Link).from(step).inV
        )
    }
  }

However, the above code fails to compile with error:

 error: type mismatch;
 found   : gremlin.scala.GremlinScala[org.apache.tinkerpop.gremlin.structure.Vertex]{type Labels = org.apache.tinkerpop.gremlin.structure.Vertex :: shapeless.HNil}
 required: gremlin.scala.GremlinScala[org.apache.tinkerpop.gremlin.structure.Vertex]{type Labels = shapeless.HNil}
        anchor.as(step).coalesce(
                                ^

If I remove the labelling step .as(label) it compiles, but then I'm unable to create Edges between the dynamically created chain Vertices.

I'm no expert in Shapeless so it's quite difficult for me to debug and come up with a solution.

Any ideas how I can overcome this error?