From 3d5e994c68fe503cdac092e7b676ca281e7b8d50 Mon Sep 17 00:00:00 2001
From: Colin DAMON <cdamon@ippon.fr>
Date: Thu, 13 May 2021 09:40:26 +0200
Subject: [PATCH] Coding monades in Java
---
.gitlab-ci.yml | 1 +
java-monades/.gitlab-ci.yml | 11 +++++
java-monades/pom.xml | 29 +++++++++++++
java-monades/readme.md | 9 ++++
.../src/main/java/fr/ippon/monad/Maybe.java | 35 ++++++++++++++++
.../src/main/java/fr/ippon/monad/State.java | 41 +++++++++++++++++++
.../test/java/fr/ippon/monad/MaybeTest.java | 30 ++++++++++++++
.../test/java/fr/ippon/monad/StateTest.java | 28 +++++++++++++
readme.md | 4 ++
9 files changed, 188 insertions(+)
create mode 100644 java-monades/.gitlab-ci.yml
create mode 100644 java-monades/pom.xml
create mode 100644 java-monades/readme.md
create mode 100644 java-monades/src/main/java/fr/ippon/monad/Maybe.java
create mode 100644 java-monades/src/main/java/fr/ippon/monad/State.java
create mode 100644 java-monades/src/test/java/fr/ippon/monad/MaybeTest.java
create mode 100644 java-monades/src/test/java/fr/ippon/monad/StateTest.java
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a3769253..6be72a49 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -36,3 +36,4 @@ include:
- local: "/mastermind/.gitlab-ci.yml"
- local: "/try-monade/.gitlab-ci.yml"
- local: "/java-puzzles/.gitlab-ci.yml"
+ - local: "/java-monades/.gitlab-ci.yml"
diff --git a/java-monades/.gitlab-ci.yml b/java-monades/.gitlab-ci.yml
new file mode 100644
index 00000000..632450ec
--- /dev/null
+++ b/java-monades/.gitlab-ci.yml
@@ -0,0 +1,11 @@
+package-java-monades:
+ variables:
+ PROJECT_FOLDER: "java-monades"
+ extends: .java
+ only:
+ refs:
+ - master
+ - merge_requests
+ changes:
+ - ".gitlab-common-ci.yml"
+ - "java-monades/**/*"
diff --git a/java-monades/pom.xml b/java-monades/pom.xml
new file mode 100644
index 00000000..9d851f40
--- /dev/null
+++ b/java-monades/pom.xml
@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+ xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+ <modelVersion>4.0.0</modelVersion>
+
+ <parent>
+ <version>1.0.0</version>
+ <groupId>fr.ippon.kata</groupId>
+ <artifactId>java-parent</artifactId>
+ <relativePath>../java-parent</relativePath>
+ </parent>
+
+ <version>1.0.0-SNAPSHOT</version>
+ <artifactId>java-monades</artifactId>
+
+ <name>JavaMonades</name>
+
+ <developers>
+ <developer>
+ <email>gautier.difolco@gmail.com</email>
+ <name>Gautier DI FOLCO</name>
+ </developer>
+ <developer>
+ <email>cdamon@ippon.fr</email>
+ <name>Colin DAMON</name>
+ </developer>
+ </developers>
+</project>
diff --git a/java-monades/readme.md b/java-monades/readme.md
new file mode 100644
index 00000000..55ca076f
--- /dev/null
+++ b/java-monades/readme.md
@@ -0,0 +1,9 @@
+# Java monades
+
+Implémentation de différents types de monades en Java
+
+- **Auteurs** : Gautier DI FOLCO et Colin DAMON
+- **Date** : 13/05/2021
+- **Langage** : Java
+- **Niveau** : Bon Chance
+- **Replay** : [Twitch](https://www.twitch.tv/videos/1020950472)
diff --git a/java-monades/src/main/java/fr/ippon/monad/Maybe.java b/java-monades/src/main/java/fr/ippon/monad/Maybe.java
new file mode 100644
index 00000000..d4ac5234
--- /dev/null
+++ b/java-monades/src/main/java/fr/ippon/monad/Maybe.java
@@ -0,0 +1,35 @@
+package fr.ippon.monad;
+
+import java.util.Optional;
+import java.util.function.Function;
+
+public class Maybe<T> {
+
+ private final Optional<T> value;
+
+ private Maybe(Optional<T> value) {
+ this.value = value;
+ }
+
+ public static <T> Maybe<T> pure(T value) {
+ return new Maybe<>(Optional.of(value));
+ }
+
+ public static <T> Maybe<T> fail() {
+ return new Maybe<>(Optional.empty());
+ }
+
+ public <U> Maybe<U> map(Function<T, U> mapper) {
+ return new Maybe<>(value.map(mapper));
+ }
+
+ public <U> Maybe<U> bind(Function<T, Maybe<U>> other) {
+ return value.map(other)
+ .orElse(Maybe.fail());
+ }
+
+ @Override
+ public String toString() {
+ return value.toString();
+ }
+}
diff --git a/java-monades/src/main/java/fr/ippon/monad/State.java b/java-monades/src/main/java/fr/ippon/monad/State.java
new file mode 100644
index 00000000..d0117112
--- /dev/null
+++ b/java-monades/src/main/java/fr/ippon/monad/State.java
@@ -0,0 +1,41 @@
+package fr.ippon.monad;
+
+import java.util.function.Function;
+
+public class State<S, T> {
+
+ private final Function<S, Result<S, T>> runner;
+
+ private State(Function<S, Result<S, T>> runner) {
+ this.runner = runner;
+ }
+
+ public static <S, T> State<S, T> pure(T value) {
+ return new State<>(state -> new Result<>(state, value));
+ }
+
+ public static <S> State<S, Void> set(S value) {
+ return new State<>(state -> new Result<>(value, null));
+ }
+
+ public static <S> State<S, S> get() {
+ return new State<>(state -> new Result<>(state, state));
+ }
+
+ public <U> State<S, U> bind(
+ Function<T, State<S, U>> binder) {
+ return new State<>(initial -> {
+ Result<S, T> result = runner.apply(initial);
+
+ return binder.apply(result.result())
+ .run(result.updated());
+ });
+ }
+
+ public Result<S, T> run(S initial) {
+ return runner.apply(initial);
+ }
+
+ public static record Result<S, T> (S updated, T result) {
+ }
+}
diff --git a/java-monades/src/test/java/fr/ippon/monad/MaybeTest.java b/java-monades/src/test/java/fr/ippon/monad/MaybeTest.java
new file mode 100644
index 00000000..56f6dca8
--- /dev/null
+++ b/java-monades/src/test/java/fr/ippon/monad/MaybeTest.java
@@ -0,0 +1,30 @@
+package fr.ippon.monad;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class MaybeTest {
+
+ @Test
+ void shouldMapFromIntegerToString() {
+ assertThat(Maybe.pure(42)
+ .map(String::valueOf)).usingRecursiveComparison()
+ .isEqualTo(Maybe.pure("42"));
+ }
+
+ @Test
+ void shouldNotMapFailedMaybe() {
+ assertThat(Maybe.fail()
+ .map(String::valueOf)).usingRecursiveComparison()
+ .isEqualTo(Maybe.fail());
+ }
+
+ @Test
+ void shouldBindPureToPure() {
+ assertThat(Maybe.pure(42)
+ .bind(value -> Maybe.pure(String.valueOf(value))))
+ .usingRecursiveComparison()
+ .isEqualTo(Maybe.pure("42"));
+ }
+}
diff --git a/java-monades/src/test/java/fr/ippon/monad/StateTest.java b/java-monades/src/test/java/fr/ippon/monad/StateTest.java
new file mode 100644
index 00000000..2854544f
--- /dev/null
+++ b/java-monades/src/test/java/fr/ippon/monad/StateTest.java
@@ -0,0 +1,28 @@
+package fr.ippon.monad;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class StateTest {
+
+ @Test
+ void shouldWriteSyracuseSequence() {
+ State<Integer, Integer> syracuse = intState()
+ .bind((previous) -> {
+ Integer next = previous % 2 == 0 ? previous / 2
+ : previous * 3 + 1;
+
+ return State.set(next)
+ .bind(dummy -> State.pure(next));
+ });
+
+ assertThat(syracuse.run(5))
+ .isEqualTo(new State.Result<>(16, 16));
+ }
+
+ private State<Integer, Integer> intState() {
+ return State.get();
+ }
+
+}
diff --git a/readme.md b/readme.md
index d83bded7..bdbf2f26 100644
--- a/readme.md
+++ b/readme.md
@@ -86,6 +86,10 @@ Un kata de code est un petit exercice pensé pour s'entrainer jusqu'à maitriser
- [Concurrence en Java](/java-concurrence)
- [Try monade](/try-monade)
+### Bon Chance
+
+- [Monades en java](/java-monades)
+
# Discussions et présentations
- [C'est une bonne situation ça techlead ?](https://www.youtube.com/watch?v=9tOoXfOE12o)
--
GitLab