Wrappers for TupleN, adding a fold.

scala> (1, 2).fold(_ + _)
res1: Int = 3

scala> (1, 2).fold(Tuple2.apply)
res2: (Int, Int) = (1,2)

core/src/main/scala/scalaz/Identity.scala

@@ -154,7 +154,7 @@ sealed trait Identity[A] extends PimpedType[A] {
   /**
    * @return the result of pf(value) if defined, otherwise the the Zero element of type B.
    */
-  def matchOrZero[B: Zero](pf: PartialFunction[A, B]) = ~pf.lift(value)
+  def matchOrZero[B: Zero](pf: PartialFunction[A, B]): B = ~pf.lift(value)
 
   @tailrec
   final def doWhile(f: A => A, p: A => Boolean): A = {

core/src/main/scala/scalaz/Scalaz.scala

@@ -55,6 +55,7 @@ object Scalaz extends ScalazLow
     with    Streams
     with    Strings
     with    Trees
+    with    TupleWs
     with    TreeLocs
     with    Validations
     with    Zeros

project/build/Boilerplate.scala

@@ -0,0 +1,44 @@
+import sbt._
+import xsbt.FileUtilities.write
+
+trait Boilerplate {
+  self: DefaultProject =>
+
+  def srcManagedScala = "src_managed" / "main" / "scala"
+
+  lazy val generateTupleW = {
+    val cleanSrcManaged = cleanTask(srcManagedScala) named ("clean src_managed")
+    task {
+      val arities = 2 to 22
+
+      def writeFileScalazPackage(fileName: String, source: String): Unit = {
+        val file = (srcManagedScala / "scalaz" / fileName).asFile
+        write(file, source)
+      }
+
+      for (arity: Int <- arities) {
+        val tupleWSource: String = {
+          val tparams = (0 until arity).map(n => ('A' + n).toChar).mkString(", ")
+          val params = (1 to arity).map("_" + _).mkString(", ")
+          """|
+          |trait Tuple%dW[%s] extends PimpedType[Tuple%d[%s]] {
+          |  def fold[Z](f: => (%s) => Z): Z = {import value._; f(%s)}
+          |}
+          |
+          |trait Tuple%dWs {
+          |  implicit def ToTuple%dW[%s](t: (%s)): Tuple%dW[%s] = new { val value = t } with Tuple%dW[%s]
+          |}
+          |""".stripMargin.format(arity, tparams, arity, tparams, tparams, params, arity, arity,
+            tparams, tparams, arity, tparams, arity, tparams)
+        }
+
+        val source = "package scalaz\n\n" + tupleWSource
+        writeFileScalazPackage("Tuple%dWs.scala".format(arity), source)
+      }
+
+      val source = "package scalaz\n\n" + "trait TupleWs extends " + arities.map(n => "Tuple%dWs".format(n)).mkString("\n     with ")
+      writeFileScalazPackage("TupleW.scala", source)
+      None
+    } dependsOn (cleanSrcManaged)
+  }
+}

project/build/ScalazProject.scala

@@ -67,7 +67,10 @@ final class ScalazProject(info: ProjectInfo) extends ParentProject(info) with Ov
 
   val parentPath = path _
 
-  class Core(info: ProjectInfo) extends ScalazDefaults(info)
+  class Core(info: ProjectInfo) extends ScalazDefaults(info) with Boilerplate {
+    override def mainSourceRoots = super.mainSourceRoots +++ srcManagedScala##
+    override def compileAction = super.compileAction dependsOn(generateTupleW)
+  }
 
   class Http(info: ProjectInfo) extends ScalazDefaults(info) {
     val servlet = "javax.servlet" % "servlet-api" % "2.5" withSources