Add "lift" from Semigroup into an Option Monoid

puffnfresh · puffnfresh · commit 158aabf0d73f · 2016-05-26T16:00:02.000+10:00
diff --git a/core/src/main/java/fj/Semigroup.java b/core/src/main/java/fj/Semigroup.java
@@ -105,6 +105,14 @@ public Semigroup<A> dual() {
     return semigroup(flip(sum));
   }
 
+  /**
+   * Lifts the semigroup to obtain a trivial monoid.
+   */
+  public Monoid<Option<A>> lift() {
+    return Monoid.monoid(a -> b -> Option.liftM2(sum).f(a).f(b).orElse(a).orElse(b), Option.none());
+  }
+
+  /**
    * Constructs a semigroup from the given function.
    *
    * @param sum The function to construct this semigroup with.

Original file line number	Diff line number	Diff line change
`@@ -105,6 +105,14 @@ public Semigroup<A> dual() {`
`105`	`105`	`return semigroup(flip(sum));`
`106`	`106`	`}`
`107`	`107`
	`108`	`+ /**`
	`109`	`+ * Lifts the semigroup to obtain a trivial monoid.`
	`110`	`+ */`
	`111`	`+ public Monoid<Option<A>> lift() {`
	`112`	`+ return Monoid.monoid(a -> b -> Option.liftM2(sum).f(a).f(b).orElse(a).orElse(b), Option.none());`
	`113`	`+ }`
	`114`	`+`
	`115`	`+ /**`
`108`	`116`	`* Constructs a semigroup from the given function.`
`109`	`117`	`*`
`110`	`118`	`* @param sum The function to construct this semigroup with.`