From 27c4ae026054e0b00d63d3134243584b20812b1c Mon Sep 17 00:00:00 2001
From: Pol Dellaiera <pol.dellaiera@protonmail.com>
Date: Tue, 19 Oct 2021 18:06:46 +0200
Subject: [PATCH] Implements `Monoid` interface/typeclass.

---
 src/Typeclass/Monoid.php | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 src/Typeclass/Monoid.php

diff --git a/src/Typeclass/Monoid.php b/src/Typeclass/Monoid.php
new file mode 100644
index 0000000..20bb7f1
--- /dev/null
+++ b/src/Typeclass/Monoid.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Marcosh\LamPHPda\Typeclass;
+
+/**
+ * @psalm-immutable
+ *
+ * @template A
+ */
+interface Monoid extends Semigroup
+{
+    /**
+     * @psalm-pure
+     *
+     * @return Monoid<A>
+     */
+    public static function mempty(): Monoid;
+}