functionaljava · mperry · Jun 4, 2015 · Jun 4, 2015
diff --git a/core/src/main/java/fj/Equal.java b/core/src/main/java/fj/Equal.java
@@ -38,6 +38,17 @@ public boolean eq(final A a1, final A a2) {
     return f.f(a1).f(a2);
   }
 
+  /**
+   * Returns <code>true</code> if the two given arguments are not equal, <code>false</code> otherwise.
+   *
+   * @param a1 An object to test for inequality against another.
+   * @param a2 An object to test for inequality against another.
+   * @return <code>true</code> if the two given arguments are not equal, <code>false</code> otherwise.
+   */
+  public boolean notEq(final A a1, final A a2) {
+    return !eq(a1, a2);
+  }
+
   /**
    * First-class equality check.
    *

diff --git a/core/src/main/java/fj/data/List.java b/core/src/main/java/fj/data/List.java
@@ -1301,6 +1301,32 @@ public boolean allEqual(final Equal<A> eq) {
     return isEmpty() || tail().isEmpty() || eq.eq(head(), tail().head()) && tail().allEqual(eq);
   }
 
+  public final boolean isPrefixOf(final Equal<A> eq, final List<A> xs) {
+    final Iterator<A> i = iterator();
+    final Iterator<A> j = xs.iterator();
+
+    while (i.hasNext() && j.hasNext()) {
+      if (!eq.eq(i.next(), j.next())) {
+        return false;
+      }
+    }
+
+    return !i.hasNext();
+  }
+
+  public final boolean isSuffixOf(final Equal<A> eq, final List<A> xs) {
+    final Iterator<A> i = iterator();
+    final Iterator<A> j = xs.drop(xs.length() - length()).iterator();
+
+    while (i.hasNext() && j.hasNext()) {
+      if (!eq.eq(i.next(), j.next())) {
+        return false;
+      }
+    }
+
+    return !i.hasNext();
+  }
+
   /**
    * First-class length.
    *

diff --git a/core/src/test/java/fj/data/properties/ListProperties.java b/core/src/test/java/fj/data/properties/ListProperties.java
@@ -0,0 +1,57 @@
+package fj.data.properties;
+
+import fj.Equal;
+import fj.P;
+import fj.P2;
+import fj.data.List;
+import fj.runner.PropertyTestRunner;
+import fj.test.Gen;
+import fj.test.Property;
+import org.junit.runner.RunWith;
+
+import static fj.test.Arbitrary.*;
+import static fj.test.Property.implies;
+import static fj.test.Property.prop;
+import static fj.test.Property.property;
+import static fj.Equal.intEqual;
+
+/**
+ * Created by Zheka Kozlov on 02.06.2015.
+ */
+@RunWith(PropertyTestRunner.class)
+public class ListProperties {
+
+  public Property isPrefixOf() {
+    final Gen<P2<List<Integer>, Integer>> gen = arbList(arbInteger).gen.bind(list ->
+      Gen.choose(0, list.length()).map(i -> P.p(list, i)));
+
+    return property(arbitrary(gen), pair -> prop(pair._1().take(pair._2()).isPrefixOf(intEqual, pair._1())));
+  }
+
+  public Property isSuffixOf() {
+    final Gen<P2<List<Integer>, Integer>> gen = arbList(arbInteger).gen.bind(list ->
+      Gen.choose(0, list.length()).map(i -> P.p(list, i)));
+
+    return property(arbitrary(gen), pair -> prop(pair._1().drop(pair._2()).isSuffixOf(intEqual, pair._1())));
+  }
+
+  public Property isPrefixOfShorter() {
+    return property(arbList(arbInteger), arbList(arbInteger), (list1, list2) ->
+      implies(list1.length() > list2.length(), () -> prop(!list1.isPrefixOf(intEqual, list2))));
+  }
+
+  public Property isSuffixOfShorter() {
+    return property(arbList(arbInteger), arbList(arbInteger), (list1, list2) ->
+      implies(list1.length() > list2.length(), () -> prop(!list1.isSuffixOf(intEqual, list2))));
+  }
+
+  public Property isPrefixOfDifferentHeads() {
+    return property(arbList(arbInteger), arbList(arbInteger), arbInteger, arbInteger, (list1, list2, h1, h2) ->
+      implies(intEqual.notEq(h1, h2), () -> prop(!list1.cons(h1).isPrefixOf(intEqual, list2.cons(h2)))));
+  }
+
+  public Property isSuffixOfDifferentHeads() {
+    return property(arbList(arbInteger), arbList(arbInteger), arbInteger, arbInteger, (list1, list2, h1, h2) ->
+      implies(intEqual.notEq(h1, h2), () -> prop(!list1.snoc(h1).isSuffixOf(intEqual, list2.snoc(h2)))));
+  }
+}