Add law for foldable

typelevel · Oct 29, 2017 · 8745b55 · 8745b55
1 parent 4e6456a
commit 8745b55
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Showing 4 changed files with 8 additions and 4 deletions.
diff --git a/laws/src/main/scala/cats/laws/FoldableLaws.scala b/laws/src/main/scala/cats/laws/FoldableLaws.scala
@@ -141,6 +141,10 @@ trait FoldableLaws[F[_]] {
     F.dropWhile_(fa)(p) <-> F.foldLeft(fa, mutable.ListBuffer.empty[A]) { (buf, a) =>
       if (buf.nonEmpty || !p(a)) buf += a else buf
     }.toList
+
+  def orderedConsistency[A: Eq](x: F[A], y: F[A])(implicit ev: Eq[F[A]]): IsEq[List[A]] =
+    if (x === y) (F.toList(x) <-> F.toList(y))
+    else List.empty[A] <-> List.empty[A]
 }
 
 object FoldableLaws {

diff --git a/laws/src/main/scala/cats/laws/TraverseLaws.scala b/laws/src/main/scala/cats/laws/TraverseLaws.scala
@@ -67,7 +67,7 @@ trait TraverseLaws[F[_]] extends FunctorLaws[F] with FoldableLaws[F] {
     lhs <-> rhs
   }
 
-  def traverseOrderConsistent[A](fa: F[A]) = {
+  def traverseOrderConsistent[A](fa: F[A]): IsEq[Option[A]] = {
     class FirstOption[T](val o: Option[T])
 
     implicit val firstOptionMonoid = new Monoid[FirstOption[A]] {
@@ -84,10 +84,7 @@ trait TraverseLaws[F[_]] extends FunctorLaws[F] with FoldableLaws[F] {
     )(store).getConst.o
 
     first <-> traverseFirst
-
-
   }
-
   def mapWithIndexRef[A, B](fa: F[A], f: (A, Int) => B): IsEq[F[B]] = {
     val lhs = F.mapWithIndex(fa)(f)
     val rhs = F.traverse(fa)(a =>

diff --git a/laws/src/main/scala/cats/laws/discipline/FoldableTests.scala b/laws/src/main/scala/cats/laws/discipline/FoldableTests.scala
@@ -18,6 +18,7 @@ trait FoldableTests[F[_]] extends Laws {
     CogenA: Cogen[A],
     CogenB: Cogen[B],
     EqA: Eq[A],
+    EqFA: Eq[F[A]],
     EqB: Eq[B],
     EqOptionA: Eq[Option[A]]
   ): RuleSet = {
@@ -26,6 +27,7 @@ trait FoldableTests[F[_]] extends Laws {
       parent = None,
       "foldLeft consistent with foldMap" -> forAll(laws.leftFoldConsistentWithFoldMap[A, B] _),
       "foldRight consistent with foldMap" -> forAll(laws.rightFoldConsistentWithFoldMap[A, B] _),
+      "ordered constistency" -> forAll(laws.orderedConsistency[A] _),
       "exists consistent with find" -> forAll(laws.existsConsistentWithFind[A] _),
       "forall consistent with exists" -> forAll(laws.forallConsistentWithExists[A] _),
       "forall true if empty" -> forAll(laws.forallEmpty[A] _),

diff --git a/laws/src/main/scala/cats/laws/discipline/ReducibleTests.scala b/laws/src/main/scala/cats/laws/discipline/ReducibleTests.scala
@@ -21,6 +21,7 @@ trait ReducibleTests[F[_]] extends FoldableTests[F] {
     EqG: Eq[G[Unit]],
     EqA: Eq[A],
     EqB: Eq[B],
+    EqFA: Eq[F[A]],
     EqOptionA: Eq[Option[A]],
     MonoidA: Monoid[A],
     MonoidB: Monoid[B]