Add first class either catamorphism

jbgi · jbgi · commit f040341840ea · 2016-06-22T21:56:05.000+02:00
diff --git a/core/src/main/java/fj/data/Either.java b/core/src/main/java/fj/data/Either.java
@@ -737,6 +737,17 @@ public static <A, B> Either<A, B> right(final B b) {
     return new Right<>(b);
   }
 
+  /**
+   * First class catamorphism for either. Folds over this either breaking into left or right.
+   *
+   * @param left  The function to call if this is left.
+   * @param right The function to call if this is right.
+   * @return The reducing function.
+   */
+  public static <A, B, X> F<Either<A,B>, X> cata(final F<A, X> left, final F<B, X> right) {
+    return e -> e.either(left, right);
+  }
+
   /**
    * @return A function that maps another function across an either's left projection.
    */
