diff --git a/build.sbt b/build.sbt
index 2171c14..71d90d8 100644
--- a/build.sbt
+++ b/build.sbt
@@ -19,6 +19,7 @@ scalacOptions += "-Ypartial-unification"
 
 libraryDependencies ++= Seq(
   "org.typelevel"       %% "cats-core"   % "1.2.0",
+  "org.typelevel"       %% "cats-free"   % "1.2.0",
   "com.chuusai" %% "shapeless" % "2.3.3",
   "org.scalatest" %% "scalatest"   % "3.0.5"  % Test
 )
\ No newline at end of file
diff --git a/src/main/scala/fluence/hackethberlin/DataDef.scala b/src/main/scala/fluence/hackethberlin/DataDef.scala
deleted file mode 100644
index 418fa29..0000000
--- a/src/main/scala/fluence/hackethberlin/DataDef.scala
+++ /dev/null
@@ -1,8 +0,0 @@
-package fluence.hackethberlin
-
-import fluence.hackethberlin.types.DataVyper
-import shapeless.HList
-
-class DataDef[D <: HList](dataDef: D)(implicit dv: DataVyper[D]) {
-  def toVyper: String = dv.toVyperDefinitions(dataDef).mkString("\n")
-}
diff --git a/src/main/scala/fluence/hackethberlin/FuncDef.scala b/src/main/scala/fluence/hackethberlin/FuncDef.scala
index 1c9fb04..c577b9f 100644
--- a/src/main/scala/fluence/hackethberlin/FuncDef.scala
+++ b/src/main/scala/fluence/hackethberlin/FuncDef.scala
@@ -1,19 +1,18 @@
 package fluence.hackethberlin
 
-import fluence.hackethberlin.types.{DataVyper, StructType}
+import fluence.hackethberlin.types.{DataVyper, ProductType}
 import shapeless._
 
-class FuncDef[Args <: HList: DataVyper, Ret <: types.Type](
-  name: String,
-  argsDef: Args,
-  ret: Option[Ret],
-  body: StructType[Args] ⇒ Expr[Ret],
-  decorators: Set[Decorator] = Set.empty
+class FuncDef[Args <: HList, Ret <: types.Type](
+                                                            name: String,
+                                                            argsDef: ProductType[Args],
+                                                            ret: Option[Ret],
+                                                            body: ProductType[Args] ⇒ Expr[Ret],
+                                                            decorators: Set[Decorator] = Set.empty
 ) {
 
   def toVyper: String =
-    s"${decorators.map(_.toVyper).mkString("\n")}\ndef $name(${DataVyper[Args]
-      .mkString(argsDef, ", ")})${ret.fold("")(" -> " + _.toVyper)}:\n${body(new StructType[Args](argsDef)).toVyper(1)};\n"
+    s"${decorators.map(_.toVyper).mkString("\n")}\ndef $name(${argsDef.toArgsVyper})${ret.fold("")(" -> " + _.toVyper)}:\n${body(argsDef).toVyper(1)};\n"
 
   def @:(decorator: Decorator): FuncDef[Args, Ret] =
     new FuncDef[Args, Ret](name, argsDef, ret, body, decorators + decorator)
@@ -25,13 +24,13 @@ object FuncDef {
     name: String,
     argsDef: Args,
     ret: Ret
-  )(body: StructType[Args] ⇒ Expr.Return[Ret]): FuncDef[Args, Ret] =
-    new FuncDef(name, argsDef, Some(ret), body)
+  )(body: ProductType[Args] ⇒ Expr.Return[Ret]): FuncDef[Args, Ret] =
+    new FuncDef(name, ProductType(argsDef), Some(ret), body)
 
   def apply[Args <: HList: DataVyper](
     name: String,
     argsDef: Args
-  )(body: StructType[Args] ⇒ Expr[types.Void]): FuncDef[Args, types.Void] =
-    new FuncDef(name, argsDef, None, body)
+  )(body: ProductType[Args] ⇒ Expr[types.Void]): FuncDef[Args, types.Void] =
+    new FuncDef(name, ProductType(argsDef), None, body)
 
 }
diff --git a/src/main/scala/fluence/hackethberlin/MakeVyperApp.scala b/src/main/scala/fluence/hackethberlin/MakeVyperApp.scala
index 9e93e15..18724f4 100644
--- a/src/main/scala/fluence/hackethberlin/MakeVyperApp.scala
+++ b/src/main/scala/fluence/hackethberlin/MakeVyperApp.scala
@@ -7,14 +7,14 @@ import syntax.singleton._
 
 object MakeVyperApp extends App {
 
-  val struct = new StructType(
+  val struct = ProductType(
     ('address ->> address) ::
       ('owner ->> address) ::
       ('size ->> uint256) ::
       ('time ->> int128) :: HNil
   )
 
-  val data = new DataDef(
+  val data = ProductType(
     ('address ->> address) ::
       ('owner ->> `public`(address)) ::
       ('holders ->> (address ~>> bool)) ::
@@ -29,7 +29,7 @@ object MakeVyperApp extends App {
     address
   )(args ⇒ args.ref('addr).toReturn)
 
-  val recordStruct = new StructType(
+  val recordStruct = ProductType(
     ('record_address ->> address) :: ('other_some ->> uint256) :: HNil
   )
 
@@ -37,7 +37,7 @@ object MakeVyperApp extends App {
 
   println(recordStruct.toVyper)
 
-  println(data.toVyper)
+  println(data.toDataVyper)
 
   println(func.toVyper)
 
diff --git a/src/main/scala/fluence/hackethberlin/types/ProductType.scala b/src/main/scala/fluence/hackethberlin/types/ProductType.scala
new file mode 100644
index 0000000..eee9829
--- /dev/null
+++ b/src/main/scala/fluence/hackethberlin/types/ProductType.scala
@@ -0,0 +1,32 @@
+package fluence.hackethberlin.types
+
+import fluence.hackethberlin.{Expr, FuncDef}
+import shapeless.{HList, Witness}
+import shapeless.ops.record.Selector
+
+class ProductType[D <: HList](dataDef: D, dv: DataVyper[D]) extends Type {
+
+  def ref[T <: Symbol, V <: Type](k: Witness.Aux[T])(implicit selector : Selector.Aux[D, T, V]): Expr.Ref[V] =
+    Expr.Ref[V](k.value.name)
+
+  // type in type definition somewhere
+  override def toVyper: String =
+    s"{${dv.toVyperDefinitions(dataDef).mkString(", ")}}"
+
+  // contract data definition
+  def toDataVyper: String =
+    dv.toVyperDefinitions(dataDef).mkString("\n")
+
+  // function arguments
+  def toArgsVyper: String =
+    dv.toVyperDefinitions(dataDef).mkString(", ")
+
+  def funcDef[Ret <: Type](name: String, ret: Ret)(body: ProductType[D] ⇒ Expr.Return[Ret]): FuncDef[D, Ret] =
+    new FuncDef[D, Ret](name, this, Some(ret), body)
+
+}
+
+object ProductType {
+  def apply[D <: HList](dataDef: D)(implicit dv: DataVyper[D]): ProductType[D] =
+    new ProductType[D](dataDef, dv)
+}
\ No newline at end of file
diff --git a/src/main/scala/fluence/hackethberlin/types/StructType.scala b/src/main/scala/fluence/hackethberlin/types/StructType.scala
deleted file mode 100644
index d528c46..0000000
--- a/src/main/scala/fluence/hackethberlin/types/StructType.scala
+++ /dev/null
@@ -1,14 +0,0 @@
-package fluence.hackethberlin.types
-
-import fluence.hackethberlin.Expr
-import shapeless.{HList, Witness}
-import shapeless.ops.record.Selector
-
-class StructType[D <: HList](dataDef: D)(implicit dv: DataVyper[D]) extends Type {
-
-  def ref[T <: Symbol, V <: Type](k: Witness.Aux[T])(implicit selector : Selector.Aux[D, T, V]): Expr.Ref[V] =
-    Expr.Ref[V](k.value.name)
-
-  override def toVyper: String =
-    s"{${dv.toVyperDefinitions(dataDef).mkString(", ")}}"
-}