there's something strange in the neighborhood

.gitignore

*.swp
target/

build.sbt

scalaVersion := "2.11.7"

val circeVersion = "0.3.0"

libraryDependencies ++= Seq(
  "io.circe" %% "circe-core" % circeVersion,
  "io.circe" %% "circe-generic" % circeVersion,
  "io.circe" %% "circe-parser" % circeVersion
)

initialCommands := """
import hangin._
import io.circe._
import io.circe.generic.auto._
"""

main.scala

package hangin

import io.circe._
import io.circe.generic.auto._

object Main {
  def main(argv: Array[String]) {
    implicitly[Decoder[Bar]]
  }
}

model.scala

package hangin

sealed trait Foo {
  def foo: String
}

case class FooInstance(foo: String) extends Foo

case class Bar(baz: Option[Baz])
case class Baz(quux: Quux)
case class Quux(foo: Option[Foo])