java-cons

commit d9fc77bd641ab1815d3421e60797128a6af3c2df
parent 6b05521344b6683cf9af52679f470aea1e258a9e
Author: Oshgnacknak <osh@oshgnacknak.de>
Date:   Fri, 15 Jan 2021 00:36:47 +0100

Add method empty

Diffstat:
M
src/Cons.java
 | 
2
++
M
src/ConsTest.java
 | 
2
++
M
src/Empty.java
 | 
5
+++++
M
src/EmptyTest.java
 | 
5
+++++
M
src/NonEmpty.java
 | 
5
+++++
M
src/NonEmptyTest.java
 | 
5
+++++

6 files changed, 24 insertions(+), 0 deletions(-)
diff --git a/src/Cons.java b/src/Cons.java
@@ -16,6 +16,8 @@ public interface Cons<V> {
 
     <W> W foldr(BiFunction<V, W, W> f, W init);
 
+    boolean empty();
+
     @SafeVarargs
     static <V> Cons<V> of(V... arr) {
         return fromArray(0, arr);
diff --git a/src/ConsTest.java b/src/ConsTest.java
@@ -8,12 +8,14 @@ class ConsTest {
     void testOf() {
         var cons = Cons.of(1, 2, 3, 4);
         assertEquals(3, cons.rest().rest().first());
+        assertFalse(cons.empty());
         assertEquals("(cons 1 (cons 2 (cons 3 (cons 4 empty))))", cons.toString());
     }
 
     @Test
     void testOfNone() {
         var cons = Cons.of();
+        assertTrue(cons.empty());
         assertEquals(new Empty<>(), cons);
         assertEquals("empty", cons.toString());
     }
diff --git a/src/Empty.java b/src/Empty.java
@@ -40,6 +40,11 @@ public class Empty<V> implements Cons<V> {
     }
 
     @Override
+    public boolean empty() {
+        return true;
+    }
+
+    @Override
     public String toString() {
         return "empty";
     }
diff --git a/src/EmptyTest.java b/src/EmptyTest.java
@@ -37,6 +37,11 @@ class EmptyTest {
     }
 
     @Test
+    void testEmpty() {
+        assertTrue(empty.empty());
+    }
+
+    @Test
     void testToString() {
         assertEquals("empty", empty.toString());
     }
diff --git a/src/NonEmpty.java b/src/NonEmpty.java
@@ -49,6 +49,11 @@ public class NonEmpty<V> implements Cons<V> {
     }
 
     @Override
+    public boolean empty() {
+        return false;
+    }
+
+    @Override
     public boolean equals(Object o) {
         if (this == o) return true;
         if (!(o instanceof Cons)) return false;
diff --git a/src/NonEmptyTest.java b/src/NonEmptyTest.java
@@ -56,6 +56,11 @@ class NonEmptyTest {
     }
 
     @Test
+    void testEmpty() {
+        assertFalse(cons.empty());
+    }
+
+    @Test
     void testToString() {
         var expected = "(cons 1 (cons 2 (cons 3 empty)))";
         assertEquals(expected, cons.toString());