Add "first" and "last" semigroups

puffnfresh · puffnfresh · commit f89381d5aeed · 2016-05-13T11:33:26.000+10:00
diff --git a/core/src/main/java/fj/Semigroup.java b/core/src/main/java/fj/Semigroup.java
@@ -264,6 +264,20 @@ public static <A> Semigroup<A> semigroup(final F2<A, A, A> sum) {
   public static final Semigroup<StringBuilder> stringBuilderSemigroup =
       semigroup((s1, s2) -> new StringBuilder(s1).append(s2));
 
+  /**
+   * A semigroup which always uses the "first" (left-hand side) value.
+   */
+  public static <A> Semigroup<A> firstSemigroup() {
+      return semigroup((a1, a2) -> a1);
+  }
+
+  /**
+   * A semigroup which always uses the "last" (right-hand side) value.
+   */
+  public static <A> Semigroup<A> lastSemigroup() {
+    return semigroup((a1, a2) -> a2);
+  }
+
   /**
    * A semigroup for functions.
    *
