Merge pull request functionaljava#286 from jbgi/first-class-cata

mperry · web-flow · commit d3231b038ddd · 2016-07-01T20:51:11.000+10:00
First class cata for either and option
diff --git a/core/src/main/java/fj/data/Either.java b/core/src/main/java/fj/data/Either.java
@@ -746,6 +746,17 @@ 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> either_(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.
    */
diff --git a/core/src/main/java/fj/data/Option.java b/core/src/main/java/fj/data/Option.java
@@ -688,6 +688,18 @@ public static <T> F<T, Option<T>> fromNull() {
     return Option::fromNull;
   }
 
+  /**
+   * First-class catamorphism for Option: return a function that will performs
+   * a reduction on an optional value using the given arguments.
+   *
+   * @param none The value to return if this optional value has no value.
+   * @param some The function to apply to the value of this optional value.
+   * @return the reducing function.
+   */
+  public static final <A, B> F<Option<A>, B> option_(final B none, final F<A, B> some) {
+    return o -> o.option(none, some);
+  }
+
   /**
    * Joins the given optional value of optional value using a bind operation.
    *
