Changing Set to Seq (#42)

* Changing Set to Seq

`Set`'s `headOption` is not well defined, while `Seq`'s `headOption` is.

* Fixed remaining Sets

src/main/scala/shapeless/PolyExercises.scala

@@ -18,30 +18,30 @@ import poly.{~>}
  */
 object PolyExercises extends FlatSpec with Matchers with org.scalaexercises.definitions.Section {
 
-  object choose extends (Set ~> Option) {
-    def apply[T](s: Set[T]) = s.headOption
+  object choose extends (Seq ~> Option) {
+    def apply[T](s: Seq[T]) = s.headOption
   }
 
-  /** `choose` is a function from Sets to Options with no type specific cases
+  /** `choose` is a function from Seqs to Options with no type specific cases
    * {{{
-   * object choose extends (Set ~> Option) {
-   * def apply[T](s : Set[T]) = s.headOption
+   * object choose extends (Seq ~> Option) {
+   * def apply[T](s : Seq[T]) = s.headOption
    * }
    * }}}
    */
   def exerciseChoose(res0: Option[Int], res1: Option[Char]) = {
     import shapeless.poly._
-    // choose is a function from Sets to Options with no type specific cases
+    // choose is a function from Seqs to Options with no type specific cases
 
-    choose(Set(1, 2, 3)) should be(res0)
-    choose(Set('a', 'b', 'c')) should be(res1)
+    choose(Seq(1, 2, 3)) should be(res0)
+    choose(Seq('a', 'b', 'c')) should be(res1)
   }
 
   /** Being polymorphic, they may be passed as arguments to functions or methods and then applied to values of different types
    * within those functions
    */
   def exercisePairApply(res0: Option[Int], res1: Option[Char]) = {
-    def pairApply(f: Set ~> Option) = (f(Set(1, 2, 3)), f(Set('a', 'b', 'c')))
+    def pairApply(f: Seq ~> Option) = (f(Seq(1, 2, 3)), f(Seq('a', 'b', 'c')))
 
     pairApply(choose) should be(res0, res1)
   }
@@ -51,7 +51,7 @@ object PolyExercises extends FlatSpec with Matchers with org.scalaexercises.defi
    * mapped across an ordinary Scala List
    */
   def exerciseMonomorphicChoose(res0: Option[Int], res1: Option[Int]) =
-    (List(Set(1, 3, 5), Set(2, 4, 6)) map choose) should be(List(res0, res1))
+    (List(Seq(1, 3, 5), Seq(2, 4, 6)) map choose) should be(List(res0, res1))
 
   /** However, they are [[http://www.chuusai.com/2012/05/10/shapeless-polymorphic-function-values-2/ more general than natural transformations]] and are able to capture type-specific cases
    * which, as we'll see below, makes them ideal for generic programming,