add BireducibleLaws

laws/src/main/scala/cats/laws/BireducibleLaws.scala

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2015 Typelevel
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package cats
+package laws
+
+import cats.data.Ior
+import cats.kernel.laws.IsEq
+
+trait BireducibleLaws[F[_, _]] extends BifoldableLaws[F] {
+  implicit def F: Bireducible[F]
+
+  def bireduceLeftConsistentWithDefaultImplementation[A, B](
+    fab: F[A, B],
+    ma: (A, A) => A,
+    mb: (B, B) => B
+  ): IsEq[A Ior B] = {
+    val obtained = F.bireduceLeft(fab)(ma, mb)
+    val expected = Bireducible.bireduceLeft(fab)(ma, mb)
+
+    obtained <-> expected
+  }
+
+  def bireduceRightConsistentWithDefaultImplementation[A, B](
+    fab: F[A, B],
+    ma: (A, Eval[A]) => Eval[A],
+    mb: (B, Eval[B]) => Eval[B]
+  ): IsEq[A Ior B] = {
+    val obtained = F.bireduceRight(fab)(ma, mb).value
+    val expected = Bireducible.bireduceRight(fab)(ma, mb).value
+
+    obtained <-> expected
+  }
+
+  def bireduceMapConsistentWithDefaultImplementation[A, B, C](
+    fab: F[A, B],
+    ma: A => C,
+    mb: B => C
+  )(implicit
+    C: Semigroup[C]
+  ): IsEq[C] = {
+    val obtained = F.bireduceMap(fab)(ma, mb)
+    val expected = Bireducible.bireduceMap(fab)(ma, mb)
+
+    obtained <-> expected
+  }
+
+  def bireduceConsistentWithDefaultImplementation[A, B](
+    fab: F[A, B]
+  )(implicit A: Semigroup[A], B: Semigroup[B]): IsEq[A Ior B] = {
+
+    val obtained = F.bireduce(fab)
+    val expected = Bireducible.bireduce(fab)
+
+    obtained <-> expected
+  }
+
+  def bireduceLeftToConsistentWithBireduceRightTo[A, B, C](fab: F[A, B])(
+    ma: A => C,
+    mb: B => C
+  )(
+    mca: (C, A) => C,
+    mcb: (C, B) => C
+  ): IsEq[C] = {
+    val left = F.bireduceLeftTo(fab)(ma, mb)(mca, mcb)
+    val right =
+      F.bireduceRightTo(fab)(
+        a => Eval.now(ma(a)),
+        b => Eval.now(mb(b))
+      )(
+        (a, c) => c.map(mca(_, a)),
+        (b, c) => c.map(mcb(_, b))
+      ).value
+
+    left <-> right
+  }
+}