From 093e35b4c18f92feac9f0ffabf9a3c3e0f83eb76 Mon Sep 17 00:00:00 2001
From: Paul Campbell <pcampbell@kemitix.net>
Date: Mon, 25 Jun 2018 22:39:25 +0100
Subject: [PATCH] Result satisfies the three Monad Laws

---
 README.md                                     |  2 +
 .../java/net/kemitix/mon/result/Success.java  | 11 ++++++
 .../java/net/kemitix/mon/ResultMonadTest.java | 39 +++++++++++++++++++
 3 files changed, 52 insertions(+)
 create mode 100644 src/test/java/net/kemitix/mon/ResultMonadTest.java

diff --git a/README.md b/README.md
index 337b0b2..45c4ec4 100644
--- a/README.md
+++ b/README.md
@@ -101,6 +101,8 @@ class Test {
 
 ### Result
 
+A Monad.
+
 A container for method return values that may raise an Exception. Useful for when a checked exceptions can't be added 
 to the method signature.
 
diff --git a/src/main/java/net/kemitix/mon/result/Success.java b/src/main/java/net/kemitix/mon/result/Success.java
index 830b41e..9093b08 100644
--- a/src/main/java/net/kemitix/mon/result/Success.java
+++ b/src/main/java/net/kemitix/mon/result/Success.java
@@ -24,6 +24,7 @@ package net.kemitix.mon.result;
 import lombok.RequiredArgsConstructor;
 import net.kemitix.mon.maybe.Maybe;
 
+import java.util.Objects;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Predicate;
@@ -76,6 +77,16 @@ class Success<T> implements Result<T> {
         return value;
     }
 
+    @Override
+    public boolean equals(Object other) {
+        return other instanceof Success && Objects.equals(value, ((Success) other).value);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(value);
+    }
+
     @Override
     public String toString() {
         return String.format("Result.Success{value=%s}", value);
diff --git a/src/test/java/net/kemitix/mon/ResultMonadTest.java b/src/test/java/net/kemitix/mon/ResultMonadTest.java
new file mode 100644
index 0000000..8a8470f
--- /dev/null
+++ b/src/test/java/net/kemitix/mon/ResultMonadTest.java
@@ -0,0 +1,39 @@
+package net.kemitix.mon;
+
+import net.kemitix.mon.result.Result;
+import org.assertj.core.api.WithAssertions;
+import org.junit.Test;
+
+import java.util.function.Function;
+
+public class ResultMonadTest implements WithAssertions {
+
+    @Test
+    public void leftIdentity() {
+        //given
+        final int value = 1;
+        final Result<Integer> result = Result.ok(value);
+        final Function<Integer, Result<Integer>> f = i -> Result.ok(i * 2);
+        //then
+        assertThat(result.flatMap(f)).isEqualTo(f.apply(value));
+    }
+
+    @Test
+    public void rightIdentity() {
+        //given
+        final Result<Integer> result = Result.ok(1);
+        //then
+        assertThat(result.flatMap(Result::ok)).isEqualTo(result);
+    }
+
+    @Test
+    public void associativity() {
+        //given
+        final Result<Integer> result = Result.ok(1);
+        final Function<Integer, Result<Integer>> f = i -> Result.ok(i * 2);
+        final Function<Integer, Result<Integer>> g = i -> Result.ok(i + 6);
+        //then
+        assertThat(result.flatMap(f).flatMap(g)).isEqualTo(result.flatMap(x -> f.apply(x).flatMap(g)));
+    }
+
+}