Retrieving Traversed JSON Fields

Question

Given:

import argonaut._
import Argonaut._

def f(c: HCursor): Option[CursorHistory] = 
     (c --\ "foo").hcursor.map(_.history)

scala> val json = Parse.parse("""{"foo" : 42}""")
json: Either[String,argonaut.Json] = Right({"foo":42})

scala> f(json.right.get.hcursor)
res52: Option[argonaut.CursorHistory] = 
    Some(CursorHistory(List(El(CursorOpDownField(foo),true))))

scala> res52.get.toList.head
res53: argonaut.CursorOp = El(CursorOpDownField(foo),true)

How can I get the JSON keys' names, i.e. foo, from the CursorOp in res53?

In other words, given an HCursor, I'd like to know which fields, i.e. List[String], have been traversed.