introduce Bireducible

Author: satorg

core/src/main/scala/cats/Bireducible.scala

@@ -0,0 +1,142 @@
+/*
+ * 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
+
+import cats.data.Ior
+
+trait Bireducible[F[_, _]] extends Bifoldable[F] { self =>
+
+  /**
+   * Apply `ma` and `mb` to the "initial elements" of `fab` and combine them with
+   * every other value using the given functions `mca` and `mcb`.
+   */
+  def bireduceLeftTo[A, B, C](fab: F[A, B])(
+    ma: A => C,
+    mb: B => C
+  )(
+    mca: (C, A) => C,
+    mcb: (C, B) => C
+  ): C
+
+  def bireduceRightTo[A, B, C](fab: F[A, B])(
+    ma: A => Eval[C],
+    mb: B => Eval[C]
+  )(
+    mac: (A, Eval[C]) => Eval[C],
+    mbc: (B, Eval[C]) => Eval[C]
+  ): Eval[C]
+
+  def bireduceLeft[A, B](fab: F[A, B])(ma: (A, A) => A, mb: (B, B) => B): A Ior B =
+    bireduceLeftTo(fab)(Ior.left, Ior.right)((c, a) => c.leftMap(ma(a, _)), (c, b) => c.map(mb(b, _)))
+
+  def bireduceRight[A, B](fab: F[A, B])(
+    ma: (A, Eval[A]) => Eval[A],
+    mb: (B, Eval[B]) => Eval[B]
+  ): Eval[A Ior B] =
+    bireduceRightTo(fab)(
+      { a => Eval.now(Ior.left(a)) },
+      { b => Eval.now(Ior.right(b)) }
+    )(
+      { (a, c) =>
+        c.flatMap {
+          _.leftMap { aa =>
+            ma(a, Eval.now(aa))
+          }.fold(
+            aa => aa.map(Ior.left),
+            bb => Eval.now(Ior.right(bb)),
+            (aa, bb) => aa.map(Ior.both(_, bb))
+          )
+        }
+      },
+      { (b, c) =>
+        c.flatMap {
+          _.map { bb =>
+            mb(b, Eval.now(bb))
+          }.fold(
+            aa => Eval.now(Ior.left(aa)),
+            bb => bb.map(Ior.right),
+            (aa, bb) => bb.map(Ior.both(aa, _))
+          )
+        }
+      }
+    )
+
+  /**
+   * Collapse the structure by mapping each element to an element of a type that has a [[cats.Monoid]]
+   */
+  def bireduceMap[A, B, C](fab: F[A, B])(ma: A => C, mb: B => C)(implicit C: Semigroup[C]): C =
+    bireduceLeftTo(fab)(ma, mb)(
+      (c: C, a: A) => C.combine(c, ma(a)),
+      (c: C, b: B) => C.combine(c, mb(b))
+    )
+
+  def bireduce[A, B, C](fab: F[A, B])(implicit A: Semigroup[A], B: Semigroup[B]): A Ior B =
+    bireduceLeft(fab)(A.combine, B.combine)
+
+  def compose[G[_, _]](implicit ev: Bireducible[G]): Bireducible[λ[(α, β) => F[G[α, β], G[α, β]]]] =
+    new ComposedBireducible[F, G] {
+      override val F = self
+      override val G = ev
+    }
+}
+
+object Bireducible {
+
+  /** 
+   * Summon an instance of [[Bireducible]].
+   */
+  @inline def apply[F[_, _]](implicit F: Bireducible[F]): Bireducible[F] = F
+}
+
+private[cats] trait ComposedBireducible[F[_, _], G[_, _]]
+    extends Bireducible[λ[(α, β) => F[G[α, β], G[α, β]]]]
+    with ComposedBifoldable[F, G] {
+
+  implicit def F: Bireducible[F]
+  implicit def G: Bireducible[G]
+
+  override def bireduceLeftTo[A, B, C](fgab: F[G[A, B], G[A, B]])(
+    ma: A => C,
+    mb: B => C
+  )(
+    mca: (C, A) => C,
+    mcb: (C, B) => C
+  ): C = {
+    def bireduceG(gab: G[A, B]): C = G.bireduceLeftTo(gab)(ma, mb)(mca, mcb)
+    def bifoldG(c: C, gab: G[A, B]): C = G.bifoldLeft(gab, c)(mca, mcb)
+
+    F.bireduceLeftTo[G[A, B], G[A, B], C](fgab)(bireduceG, bireduceG)(bifoldG, bifoldG)
+  }
+
+  override def bireduceRightTo[A, B, C](fgab: F[G[A, B], G[A, B]])(
+    ma: A => Eval[C],
+    mb: B => Eval[C]
+  )(
+    mac: (A, Eval[C]) => Eval[C],
+    mbc: (B, Eval[C]) => Eval[C]
+  ): Eval[C] = {
+    def bireduceG(gab: G[A, B]): Eval[C] = G.bireduceRightTo(gab)(ma, mb)(mac, mbc)
+    def bifoldG(gab: G[A, B], c: Eval[C]): Eval[C] = G.bifoldRight(gab, c)(mac, mbc)
+
+    F.bireduceRightTo(fgab)(bireduceG, bireduceG)(bifoldG, bifoldG)
+  }
+}