Add fj.data.Option.sequence(Validation<E, Option<A>>).

drewctaylor · drewctaylor · commit e98db344df30 · 2020-05-20T19:21:02.000-04:00
diff --git a/core/src/main/java/fj/data/Option.java b/core/src/main/java/fj/data/Option.java
@@ -372,11 +372,11 @@ public final <B> Option<P2<A,B>> bindProduct(final Option<B> ob) {
   public final <B, C> Option<P3<A,B,C>> bindProduct(final Option<B> ob, final Option<C> oc) {
     return bind(ob, oc, P.p3());
   }
-  
+
   public final <B, C, D> Option<P4<A,B,C,D>> bindProduct(final Option<B> ob, final Option<C> oc, final Option<D> od) {
     return bind(ob, oc, od, P.p4());
   }
-  
+
   public final <B,C,D,E> Option<P5<A,B,C,D,E>> bindProduct(final Option<B> ob, final Option<C> oc, final Option<D> od,
                                                      final Option<E> oe) {
     return bind(ob, oc, od, oe, P.p5());
@@ -712,7 +712,7 @@ public static <A> Option<A> join(final Option<Option<A>> o) {
   }
 
   /**
-   * Sequence through the option monad.
+   * Sequence a list through the option monad.
    *
    * @param a The list of option to sequence.
    * @return The option of list after sequencing.
@@ -723,6 +723,16 @@ public static <A> Option<List<A>> sequence(final List<Option<A>> a) {
            a.head().bind(aa -> sequence(a.tail()).map(cons_(aa)));
   }
 
+  /**
+   * Sequence a validation through the option monad.
+   *
+   * @param a The validation of option to sequence.
+   * @return The option of validation after sequencing.
+   */
+  public static <E, A> Option<Validation<E, A>> sequence(final Validation<E, Option<A>> a) {
+    return a.traverseOption(identity());
+  }
+
   /**
    * Returns an optional value that has a value of the given argument, if the given predicate holds
    * on that argument, otherwise, returns no value.
diff --git a/core/src/test/java/fj/data/OptionTest.java b/core/src/test/java/fj/data/OptionTest.java
@@ -1,9 +1,15 @@
 package fj.data;
 
-import org.junit.Assert;
 import org.junit.Test;
 
+import static fj.data.List.arrayList;
+import static fj.data.List.nil;
+import static fj.data.Option.none;
+import static fj.data.Option.sequence;
 import static fj.data.Option.some;
+import static fj.data.Validation.fail;
+import static fj.data.Validation.success;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
 /**
@@ -26,4 +32,21 @@ public void traverseList() {
         assertTrue(actual.equals(expected));
     }
 
+    @Test
+    public void sequenceListTest() {
+        assertEquals(some(nil()), sequence(nil()));
+        assertEquals(none(), sequence(arrayList(none())));
+        assertEquals(some(arrayList(1)), sequence(arrayList(some(1))));
+        assertEquals(none(), sequence(arrayList(none(), none())));
+        assertEquals(none(), sequence(arrayList(some(1), none())));
+        assertEquals(none(), sequence(arrayList(none(), some(2))));
+        assertEquals(some(arrayList(1, 2)), sequence(arrayList(some(1), some(2))));
+    }
+
+    @Test
+    public void sequenceValidationTest() {
+        assertEquals(some(fail(1)), sequence(Validation.<Integer, Option<String>>fail(1)));
+        assertEquals(none(), sequence(Validation.<Integer, Option<String>>success(none())));
+        assertEquals(some(success("string")), sequence(Validation.<Integer, Option<String>>success(some("string"))));
+    }
 }
