Merge pull request #506 from rintcius/foldable-doc

more examples for Foldable

docs/src/main/tut/foldable.md

@@ -29,11 +29,35 @@ import cats.std.all._
 
 Foldable[List].fold(List("a", "b", "c"))
 Foldable[List].foldMap(List(1, 2, 4))(_.toString)
+Foldable[List].foldK(List(List(1,2,3), List(2,3,4)))
+Foldable[List].reduceLeftToOption(List[Int]())(_.toString)((s,i) => s + i)
+Foldable[List].reduceLeftToOption(List(1,2,3,4))(_.toString)((s,i) => s + i)
+Foldable[List].reduceRightToOption(List(1,2,3,4))(_.toString)((i,s) => Later(s.value + i)).value
+Foldable[List].reduceRightToOption(List[Int]())(_.toString)((i,s) => Later(s.value + i)).value
 Foldable[Set].find(Set(1,2,3))(_ > 2)
 Foldable[Set].exists(Set(1,2,3))(_ > 2)
 Foldable[Set].forall(Set(1,2,3))(_ > 2)
 Foldable[Set].forall(Set(1,2,3))(_ < 4)
 Foldable[Vector].filter_(Vector(1,2,3))(_ < 3)
+Foldable[List].isEmpty(List(1,2))
+Foldable[Option].isEmpty(None)
+Foldable[List].nonEmpty(List(1,2))
+Foldable[Option].toList(Option(1))
+Foldable[Option].toList(None)
+
+def parseInt(s: String): Option[Int] = scala.util.Try(Integer.parseInt(s)).toOption
+
+Foldable[List].traverse_(List("1", "2"))(parseInt)
+Foldable[List].traverse_(List("1", "A"))(parseInt)
+Foldable[List].sequence_(List(Option(1), Option(2)))
+Foldable[List].sequence_(List(Option(1), None))
+Foldable[List].dropWhile_(List[Int](2,4,5,6,7))(_ % 2 == 0)
+Foldable[List].dropWhile_(List[Int](1,2,4,5,6,7))(_ % 2 == 0)
+
+val FoldableListOption = Foldable[List].compose[Option]
+FoldableListOption.fold(List(Option(1), Option(2), Option(3), Option(4)))
+FoldableListOption.fold(List(Option(1), Option(2), Option(3), None))
+FoldableListOption.fold(List(Option("1"), Option("2"), Option("3"), None))
 ```
 
 Hence when defining some new data structure, if we can define a `foldLeft` and