Add cobind to Ephemeral stream & check laws.

possiblywrong · Sep 10, 2013 · d28b5db · d28b5db
1 parent 7b7f9e0
commit d28b5db
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Showing 2 changed files with 33 additions and 1 deletion.
diff --git a/core/src/main/scala/scalaz/EphemeralStream.scala b/core/src/main/scala/scalaz/EphemeralStream.scala
@@ -61,6 +61,14 @@ sealed abstract class EphemeralStream[A] {
     foldLeft(0)(addOne _)
   }
 
+  def tails: EphemeralStream[EphemeralStream[A]] =
+    if (isEmpty) emptyEphemeralStream
+    else cons(this, tail().tails)
+
+  def inits: EphemeralStream[EphemeralStream[A]] =
+    if (isEmpty) emptyEphemeralStream
+    else EphemeralStream[A]() ##:: tail().inits.map(head() ##:: _)
+
   def findM[M[_]: Monad](p: A => M[Boolean]): M[Option[A]] =
     if(isEmpty)
       Monad[M].point(None)
@@ -122,11 +130,30 @@ object EphemeralStream extends EphemeralStreamInstances with EphemeralStreamFunc
       if (b < size) Some((as0(b), b + 1))
       else None)
   }
+
+  class ConsWrap[A](e: => EphemeralStream[A]) {
+    def ##::(h: A): EphemeralStream[A] = cons(h, e)
+  }
+
+  implicit def consWrapper[A](e: => EphemeralStream[A]): ConsWrap[A] =
+    new ConsWrap[A](e)
+
+  object ##:: {
+    def unapply[A](xs: EphemeralStream[A]): Option[(A, EphemeralStream[A])] =
+      if (xs.isEmpty) None
+      else Some((xs.head(), xs.tail()))
+  }
 }
 
 sealed abstract class EphemeralStreamInstances {
   // TODO more instances
-  implicit val ephemeralStreamInstance = new MonadPlus[EphemeralStream] with Zip[EphemeralStream] with Unzip[EphemeralStream] with Traverse[EphemeralStream] {
+  implicit val ephemeralStreamInstance: MonadPlus[EphemeralStream] with Zip[EphemeralStream] with Unzip[EphemeralStream] with Traverse[EphemeralStream] with Cobind[EphemeralStream] = new MonadPlus[EphemeralStream] with Zip[EphemeralStream] with Unzip[EphemeralStream] with Traverse[EphemeralStream] with Cobind[EphemeralStream] {
+    import EphemeralStream._
+    override def cojoin[A](a: EphemeralStream[A]): EphemeralStream[EphemeralStream[A]] = a match {
+      case _ ##:: tl  => if (tl.isEmpty) EphemeralStream(a)
+                         else a ##:: cojoin(tl)
+    }
+    def cobind[A, B](fa: EphemeralStream[A])(f: EphemeralStream[A] => B): EphemeralStream[B] = map(cojoin(fa))(f)
     def plus[A](a: EphemeralStream[A], b: => EphemeralStream[A]) = a ++ b
     def bind[A, B](fa: EphemeralStream[A])(f: A => EphemeralStream[B]) = fa flatMap f
     def point[A](a: => A) = EphemeralStream(a)
@@ -188,6 +215,10 @@ trait EphemeralStreamFunctions {
     case h #:: t  => cons(h, fromStream(t))
   }
 
+  def fromIterable[A](i: Iterable[A]): EphemeralStream[A] =
+    if (i.isEmpty) emptyEphemeralStream
+    else i.head ##:: fromIterable(i.tail)
+
   implicit def toIterable[A](e: EphemeralStream[A]): Iterable[A] = new Iterable[A] {
     def iterator = new Iterator[A] {
       var cur = e

diff --git a/tests/src/test/scala/scalaz/EphemeralStreamTest.scala b/tests/src/test/scala/scalaz/EphemeralStreamTest.scala
@@ -11,6 +11,7 @@ class EphemeralStreamTest extends Spec {
   checkAll(monadPlus.laws[EphemeralStream])
   checkAll(traverse.laws[EphemeralStream])
   checkAll(zip.laws[EphemeralStream])
+  checkAll(cobind.laws[EphemeralStream])
 
   implicit def ephemeralStreamShow[A: Show]: Show[EphemeralStream[A]] =
     Show[List[A]].contramap(_.toList)