Add unused variable warnings

compiler/build.sbt

@@ -18,6 +18,8 @@ lazy val root = (project in file("."))
     scalacOptions ++= Seq("-feature",
                           "-deprecation",
                           "-unchecked",
+                          //"-Ypatmat-exhaust-depth", "320",
+                          "-Xlint:unused",
                           "-encoding", "utf-8"),
 
     // Main configuration