tonymorris · May 31, 2013 11:35 · May 31, 2013
diff --git a/RefactoringPuzzle.scala b/RefactoringPuzzle.scala
@@ -0,0 +1,44 @@
+object RefactorPuzzle {
+  case class IntRdr[+A](read: Int => A) {
+    def map[B](f: A => B): IntRdr[B] = 
+      IntRdr(f compose read)
+
+    def flatMap[B](f: A => IntRdr[B]): IntRdr[B] =
+      IntRdr(n => f(read(n)).read(n))
+  }
+
+  object IntRdr {
+    def apply[A](a: A): IntRdr[A] =
+      IntRdr(_ => a)
+  }
+
+  // Return all the Some values, or None if not all are Some.
+  def runOptions[A](x: List[Option[A]]): Option[List[A]] = 
+    x.foldRight[Option[List[A]]](Option(Nil))((a, b) => a.flatMap(aa => b.map(aa :: _)))
+
+  // Apply an Int to a list of int readers and return the list of return values.
+  def runIntRdrs[A](x: List[IntRdr[A]]): IntRdr[List[A]] = 
+    x.foldRight[IntRdr[List[A]]](IntRdr(Nil))((a, b) => a.flatMap(aa => b.map(aa :: _)))
+
+/*
+
+========================
+ THE REFACTORING PUZZLE
+========================
+
+The two functions `runOptions` and `runIntRdrs` share a lot of duplicated code.
+This is demonstrated below.
+
+How to refactor this code to remove the code duplication?
+
+*/
+
+//-------      -------------      -------      -----------
+//def runOptions[A](x: List[Option[A]]): Option[List[A]] =
+//def runIntRdrs[A](x: List[IntRdr[A]]): IntRdr[List[A]] =
+
+//  ------------      -----------      ------------------------------------------------- 
+//  x.foldRight[Option[List[A]]](Option(Nil))((a, b) => a.flatMap(aa => b.map(aa :: _)))
+//  x.foldRight[IntRdr[List[A]]](IntRdr(Nil))((a, b) => a.flatMap(aa => b.map(aa :: _)))
+
+}