From 0bb09734dbbf37e59a52a440f46b047e44995094 Mon Sep 17 00:00:00 2001
From: Michael Mroz <michael@mroz.io>
Date: Thu, 17 Nov 2022 06:41:14 -0800
Subject: [PATCH] Weaken Either monoid dependencies to only require a semigroup
 on left (#2845)

* Weaken Either monoid dependencies to require only a semigroup on left

* Update API files

Co-authored-by: Michael Mroz <admin@heretic.software>
Co-authored-by: Alejandro Serrano <trupill@gmail.com>
---
 arrow-libs/core/arrow-core/api/arrow-core.api      |  4 ++--
 .../commonMain/kotlin/arrow/typeclasses/Monoid.kt  | 14 +++++++-------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/arrow-libs/core/arrow-core/api/arrow-core.api b/arrow-libs/core/arrow-core/api/arrow-core.api
index ac9aed03e72..d5ffc5138ff 100644
--- a/arrow-libs/core/arrow-core/api/arrow-core.api
+++ b/arrow-libs/core/arrow-core/api/arrow-core.api
@@ -3107,7 +3107,7 @@ public abstract interface class arrow/typeclasses/Monoid : arrow/typeclasses/Sem
 	public abstract fun combineAll (Ljava/util/Collection;)Ljava/lang/Object;
 	public abstract fun combineAll (Ljava/util/List;)Ljava/lang/Object;
 	public static fun constant (Larrow/typeclasses/Monoid;)Larrow/typeclasses/Monoid;
-	public static fun either (Larrow/typeclasses/Monoid;Larrow/typeclasses/Monoid;)Larrow/typeclasses/Monoid;
+	public static fun either (Larrow/typeclasses/Semigroup;Larrow/typeclasses/Monoid;)Larrow/typeclasses/Monoid;
 	public abstract fun empty ()Ljava/lang/Object;
 	public static fun endo ()Larrow/typeclasses/Monoid;
 	public abstract fun fold (Ljava/util/Collection;)Ljava/lang/Object;
@@ -3128,7 +3128,7 @@ public final class arrow/typeclasses/Monoid$Companion {
 	public final fun Long ()Larrow/typeclasses/Monoid;
 	public final fun Short ()Larrow/typeclasses/Monoid;
 	public final fun constant (Larrow/typeclasses/Monoid;)Larrow/typeclasses/Monoid;
-	public final fun either (Larrow/typeclasses/Monoid;Larrow/typeclasses/Monoid;)Larrow/typeclasses/Monoid;
+	public final fun either (Larrow/typeclasses/Semigroup;Larrow/typeclasses/Monoid;)Larrow/typeclasses/Monoid;
 	public final fun endo ()Larrow/typeclasses/Monoid;
 	public final fun list ()Larrow/typeclasses/Monoid;
 	public final fun map (Larrow/typeclasses/Semigroup;)Larrow/typeclasses/Monoid;
diff --git a/arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/typeclasses/Monoid.kt b/arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/typeclasses/Monoid.kt
index 3de4fd8bcfa..6b88f4152c7 100644
--- a/arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/typeclasses/Monoid.kt
+++ b/arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/typeclasses/Monoid.kt
@@ -76,8 +76,8 @@ public interface Monoid<A> : Semigroup<A> {
     public fun string(): Monoid<String> = StringMonoid
 
     @JvmStatic
-    public fun <A, B> either(MA: Monoid<A>, MB: Monoid<B>): Monoid<Either<A, B>> =
-      EitherMonoid(MA, MB)
+    public fun <A, B> either(SGA: Semigroup<A>, MB: Monoid<B>): Monoid<Either<A, B>> =
+      EitherMonoid(SGA, MB)
 
     @JvmStatic
     public fun <A> endo(): Monoid<Endo<A>> =
@@ -191,22 +191,22 @@ public interface Monoid<A> : Semigroup<A> {
     }
 
     private class EitherMonoid<L, R>(
-      private val MOL: Monoid<L>,
+      private val SGOL: Semigroup<L>,
       private val MOR: Monoid<R>
     ) : Monoid<Either<L, R>> {
       override fun empty(): Either<L, R> = Either.Right(MOR.empty())
 
       override fun Either<L, R>.combine(b: Either<L, R>): Either<L, R> =
-        combine(MOL, MOR, b)
+        combine(SGOL, MOR, b)
 
       override fun Collection<Either<L, R>>.fold(): Either<L, R> =
-        fold(either(MOL, MOR))
+        fold(either(SGOL, MOR))
 
       override fun fold(elems: List<Either<L, R>>): Either<L, R> =
-        elems.fold(either(MOL, MOR))
+        elems.fold(either(SGOL, MOR))
 
       override fun Either<L, R>.maybeCombine(b: Either<L, R>?): Either<L, R> =
-        b?.let { combine(MOL, MOR, it) } ?: this
+        b?.let { combine(SGOL, MOR, it) } ?: this
     }
 
     private class PairMonoid<A, B>(