Fixes #407. Add fj.data.Seq.bind(F<A, Seq<B>> f).

drewctaylorgtri · drewctaylorgtri · commit 4377adb82a20 · 2020-07-25T17:04:40.000-04:00
diff --git a/core/src/main/java/fj/data/Seq.java b/core/src/main/java/fj/data/Seq.java
@@ -1,20 +1,15 @@
 package fj.data;
 
 import fj.*;
+import fj.data.List.Buffer;
+import fj.data.fingertrees.*;
+
+import java.util.*;
 
 import static fj.Bottom.error;
 import static fj.Monoid.intAdditionMonoid;
 import static fj.data.fingertrees.FingerTree.measured;
 
-import fj.data.List.Buffer;
-import fj.data.fingertrees.FingerTree;
-import fj.data.fingertrees.MakeTree;
-import fj.data.fingertrees.Measured;
-
-import java.util.AbstractList;
-import java.util.Iterator;
-import java.util.NoSuchElementException;
-
 /**
  * Provides an immutable finite sequence, implemented as a finger tree. This structure gives O(1) access to
  * the head and tail, as well as O(log n) random access and concatenation of sequences.
@@ -396,4 +391,16 @@ public <B> Seq<B> map(F<A, B> f) {
         return new Seq<>(ftree.map(f, Seq.elemMeasured()));
     }
 
+  /**
+   * Bind the given function across this seq.
+   *
+   * @param f   the given function
+   * @param <B> the type of the seq value
+   * @return the seq
+   */
+  public <B> Seq<B> bind(final F<A, Seq<B>> f) {
+    return foldRight(
+        (element, accumulator) -> f.f(element).append(accumulator),
+        empty());
+  }
 }
diff --git a/core/src/test/java/fj/data/SeqTest.java b/core/src/test/java/fj/data/SeqTest.java
@@ -3,11 +3,10 @@
 import fj.P2;
 import org.junit.Test;
 
+import static fj.Function.constant;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.Is.is;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 /**
  * Created by MarkPerry on 16/01/2015.
@@ -46,4 +45,16 @@ public void test() {
         assertThat(p2._2(), is(Seq.empty()));
     }
 
+  @Test
+  public void testBind() {
+    assertEquals(Seq.empty(), Seq.empty().bind(constant(Seq.empty())));
+    assertEquals(Seq.empty(), Seq.empty().bind(constant(Seq.single(0))));
+    assertEquals(Seq.empty(), Seq.empty().bind(constant(Seq.arraySeq(0, 1))));
+    assertEquals(Seq.empty(), Seq.single("zero").bind(constant(Seq.empty())));
+    assertEquals(Seq.single(0), Seq.single("zero").bind(constant(Seq.single(0))));
+    assertEquals(Seq.arraySeq(0, 1), Seq.single("zero").bind(constant(Seq.arraySeq(0, 1))));
+    assertEquals(Seq.empty(), Seq.arraySeq("zero", "one").bind(constant(Seq.empty())));
+    assertEquals(Seq.arraySeq(0, 0), Seq.arraySeq("zero", "one").bind(constant(Seq.single(0))));
+    assertEquals(Seq.arraySeq(0, 1, 0, 1), Seq.arraySeq("zero", "one").bind(constant(Seq.arraySeq(0, 1))));
+  }
 }
