Add a Monoid for IO

puffnfresh · puffnfresh · commit e7ed7ec9c55e · 2016-05-13T20:23:54.000+10:00
diff --git a/core/src/main/java/fj/Monoid.java b/core/src/main/java/fj/Monoid.java
@@ -4,6 +4,8 @@
 import static fj.Function.flip;
 import fj.data.Array;
 import fj.data.List;
+import fj.data.IO;
+import fj.data.IOFunctions;
 import fj.data.Natural;
 import fj.data.Option;
 import fj.data.Set;
@@ -384,6 +386,13 @@ public static <A> Monoid<Array<A>> arrayMonoid() {
     return monoid(Semigroup.<A>arraySemigroup(), Array.<A>empty());
   }
 
+  /**
+   * A semigroup for IO values.
+   */
+  public static <A> Monoid<IO<A>> ioMonoid(final Monoid <A> ma) {
+    return monoid(Semigroup.ioSemigroup(ma.semigroup()), IOFunctions.unit(ma.zero()));
+  }
+
   /**
    * A semigroup for the Unit value.
    */
