Add support for json4s ast

build.sbt

@@ -116,13 +116,22 @@ lazy val `circe-json` = { project in file("circe-json") }.dependsOn(core, api).s
   }
 )
 
+lazy val `json4s-json` = { project in file("json4s-json") }.dependsOn(core, api).settings(
+  commonSettings,
+
+  name := "scala-jsonschema-json4s-json",
+
+  libraryDependencies += "org.json4s" %% "json4s-ast" % "3.6.2"
+)
+
 lazy val root = { project in file(".") }.aggregate(
   core,
   macros,
   api,
   `play-json`,
   `circe-json`,
-  `spray-json`).settings(
+  `spray-json`,
+  `json4s-json`).settings(
 
   commonSettings,
 

json4s-json/src/main/scala/com/github/andyglow/jsonschema/AsJson4s.scala

@@ -0,0 +1,26 @@
+package com.github.andyglow.jsonschema
+
+import com.github.andyglow.json.Value._
+import com.github.andyglow.json._
+import json.Schema
+import org.json4s.JsonAST._
+
+object AsJson4s {
+
+  def apply(value: Value): JValue = value match {
+    case `null` => JNull
+    case `true` => JBool(true)
+    case `false` => JBool(false)
+    case num(x) => JDecimal(x)
+    case str(x) => JString(x)
+    case arr(x) => JArray(x.map(AsJson4s.apply).toList)
+    case obj(x) => JObject(x.map { case (k, v) => JField(k, AsJson4s.apply(v)) }.toList)
+  }
+
+  implicit class SchemaOps[T](val x: Schema[T]) extends AnyVal {
+
+    def asJson4s(
+      title: Option[String] = None,
+      description: Option[String] = None): JValue = AsJson4s(AsValue.schema(x, title, description))
+  }
+}

json4s-json/src/test/scala/com/github/andyglow/jsonschema/AsJson4sSpec.scala

@@ -0,0 +1,53 @@
+package com.github.andyglow.jsonschema
+
+import org.scalatest._
+import org.scalatest.Matchers._
+import org.scalatest.prop.TableDrivenPropertyChecks._
+import com.github.andyglow.json.Value._
+import org.json4s.JsonAST._
+
+class AsJson4sSpec extends PropSpec{
+  import AsJson4sSpec._
+
+  private val examples = Table(
+    ("json"                           , "PlayJson"),
+    (`null`                           , JNull),
+    (`true`                           , JBool(true)),
+    (`false`                          , JBool(false)),
+    (str("foo")                       , JString("foo")),
+    (num(4)                           , JDecimal(4)),
+    (num(4.78)                        , JDecimal(4.78)),
+    (arr(1, 2, 3)                     , JArray(List(JDecimal(1), JDecimal(2), JDecimal(3)))),
+    (obj("foo" -> "foo", "bar" -> 15) , JObject("foo" -> JString("foo"), "bar" -> JDecimal(15)))
+  )
+
+  property("Check that AsJson4s translates internal representation of json to json4s Json") {
+    forAll(examples) { (internal, play) => AsJson4s(internal) shouldEqual play }
+  }
+
+  property("Check Schema.asJson4s") {
+    import AsJson4s._
+
+    json.Json.schema[UserProfile].asJson4s() shouldEqual JObject(
+      f"$$schema"             -> JString("http://json-schema.org/draft-04/schema#"),
+      "type"                  -> JString("object"),
+      "additionalProperties"  -> JBool(false),
+      "properties"            -> JObject(
+        "firstName"               -> JObject("type" -> JString("string")),
+        "middleName"              -> JObject("type" -> JString("string")),
+        "lastName"                -> JObject("type" -> JString("string")),
+        "age"                     -> JObject("type" -> JString("integer")),
+        "active"                  -> JObject("type" -> JString("boolean"))),
+      "required"              -> JArray(List(JString("age"), JString("lastName"), JString("firstName"))))
+  }
+}
+
+object AsJson4sSpec {
+
+  case class UserProfile(
+    firstName: String,
+    middleName: Option[String],
+    lastName: String,
+    age: Int,
+    active: Boolean = true)
+}