Merge pull request #20 from benhutchison/master

	 Change type tags to a trait

core/src/main/scala/shapeless/typeoperators.scala

@@ -58,7 +58,7 @@ object TypeOperators {
   type ∀[P[_]] = ¬[∃[({ type λ[X] = ¬[P[X]]})#λ]]
 
   // Tags
-  type Tagged[U] = { type Tag = U }
+  trait Tagged[U]
   type @@[T, U] = T with Tagged[U]
 
   class Tagger[U] {

core/src/test/scala/shapeless/typeoperators.scala

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2011 Miles Sabin
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package shapeless
+
+import TypeOperators._
+
+class TypeOperatorTests {
+  import org.junit.Test
+  import org.junit.Assert._
+
+
+  @Test
+  def testImplicitScopeForTaggedType {
+    val x = tag[ATag](1)
+    val s: String = x
+    assertEquals(ATag.message, s)
+  }
+}
+
+trait ATag
+object ATag {
+
+  val message = "This object has ATag tag type"
+
+  implicit def taggedToString[T](value: T with Tagged[ATag]): String = message
+}