From a14feff1d6833e5a398b2f94d54e695e7a737892 Mon Sep 17 00:00:00 2001
From: "Dr. Carsten Leue" <carsten.leue@de.ibm.com>
Date: Mon, 15 Jan 2024 12:04:55 +0100
Subject: [PATCH] fix: add missing MapLeft

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>
---
 either/either.go                 | 9 +++++----
 ioeither/ioeither.go             | 2 +-
 readereither/generic/reader.go   | 9 +++++++++
 readereither/reader.go           | 9 +++++++++
 readerioeither/generic/reader.go | 9 +++++++++
 readerioeither/reader.go         | 9 +++++++++
 6 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/either/either.go b/either/either.go
index cfe542e..512b33a 100644
--- a/either/either.go
+++ b/either/either.go
@@ -67,16 +67,17 @@ func MapTo[E, A, B any](b B) func(Either[E, A]) Either[E, B] {
 	return F.Bind2nd(MonadMapTo[E, A, B], b)
 }
 
-func MonadMapLeft[E, A, B any](fa Either[E, A], f func(E) B) Either[B, A] {
-	return MonadFold(fa, F.Flow2(f, Left[A, B]), Right[B, A])
+func MonadMapLeft[E1, A, E2 any](fa Either[E1, A], f func(E1) E2) Either[E2, A] {
+	return MonadFold(fa, F.Flow2(f, Left[A, E2]), Right[E2, A])
 }
 
 func Map[E, A, B any](f func(a A) B) func(fa Either[E, A]) Either[E, B] {
 	return Chain(F.Flow2(f, Right[E, B]))
 }
 
-func MapLeft[E, A, B any](f func(E) B) func(fa Either[E, A]) Either[B, A] {
-	return F.Bind2nd(MonadMapLeft[E, A, B], f)
+// MapLeft applies a mapping function to the error channel
+func MapLeft[A, E1, E2 any](f func(E1) E2) func(fa Either[E1, A]) Either[E2, A] {
+	return F.Bind2nd(MonadMapLeft[E1, A, E2], f)
 }
 
 func MonadChain[E, A, B any](fa Either[E, A], f func(a A) Either[E, B]) Either[E, B] {
diff --git a/ioeither/ioeither.go b/ioeither/ioeither.go
index c8e24ce..d32d73e 100644
--- a/ioeither/ioeither.go
+++ b/ioeither/ioeither.go
@@ -175,7 +175,7 @@ func MonadMapLeft[E1, E2, A any](fa IOEither[E1, A], f func(E1) E2) IOEither[E2,
 	return G.MonadMapLeft[IOEither[E1, A], IOEither[E2, A]](fa, f)
 }
 
-func MapLeft[E1, E2, A any](f func(E1) E2) func(IOEither[E1, A]) IOEither[E2, A] {
+func MapLeft[A, E1, E2 any](f func(E1) E2) func(IOEither[E1, A]) IOEither[E2, A] {
 	return G.MapLeft[IOEither[E1, A], IOEither[E2, A]](f)
 }
 
diff --git a/readereither/generic/reader.go b/readereither/generic/reader.go
index 949317f..9bba54a 100644
--- a/readereither/generic/reader.go
+++ b/readereither/generic/reader.go
@@ -164,3 +164,12 @@ func MonadFlap[GEFAB ~func(E) ET.Either[L, func(A) B], GEB ~func(E) ET.Either[L,
 func Flap[GEFAB ~func(E) ET.Either[L, func(A) B], GEB ~func(E) ET.Either[L, B], L, E, A, B any](a A) func(GEFAB) GEB {
 	return FC.Flap(MonadMap[GEFAB, GEB], a)
 }
+
+func MonadMapLeft[GA1 ~func(C) ET.Either[E1, A], GA2 ~func(C) ET.Either[E2, A], C, E1, E2, A any](fa GA1, f func(E1) E2) GA2 {
+	return eithert.MonadMapLeft(R.MonadMap[GA1, GA2, C, ET.Either[E1, A], ET.Either[E2, A]], fa, f)
+}
+
+// MapLeft applies a mapping function to the error channel
+func MapLeft[GA1 ~func(C) ET.Either[E1, A], GA2 ~func(C) ET.Either[E2, A], C, E1, E2, A any](f func(E1) E2) func(GA1) GA2 {
+	return F.Bind2nd(MonadMapLeft[GA1, GA2, C, E1, E2, A], f)
+}
diff --git a/readereither/reader.go b/readereither/reader.go
index 0c2e56c..2c2cd0c 100644
--- a/readereither/reader.go
+++ b/readereither/reader.go
@@ -151,3 +151,12 @@ func MonadFlap[L, E, A, B any](fab ReaderEither[L, E, func(A) B], a A) ReaderEit
 func Flap[L, E, B, A any](a A) func(ReaderEither[L, E, func(A) B]) ReaderEither[L, E, B] {
 	return G.Flap[ReaderEither[L, E, func(A) B], ReaderEither[L, E, B]](a)
 }
+
+func MonadMapLeft[C, E1, E2, A any](fa ReaderEither[C, E1, A], f func(E1) E2) ReaderEither[C, E2, A] {
+	return G.MonadMapLeft[ReaderEither[C, E1, A], ReaderEither[C, E2, A]](fa, f)
+}
+
+// MapLeft applies a mapping function to the error channel
+func MapLeft[C, E1, E2, A any](f func(E1) E2) func(ReaderEither[C, E1, A]) ReaderEither[C, E2, A] {
+	return G.MapLeft[ReaderEither[C, E1, A], ReaderEither[C, E2, A]](f)
+}
diff --git a/readerioeither/generic/reader.go b/readerioeither/generic/reader.go
index 22dddc8..2b0b88e 100644
--- a/readerioeither/generic/reader.go
+++ b/readerioeither/generic/reader.go
@@ -440,3 +440,12 @@ func MonadFlap[GREAB ~func(R) GEAB, GREB ~func(R) GEB, GEAB ~func() ET.Either[E,
 func Flap[GREAB ~func(R) GEAB, GREB ~func(R) GEB, GEAB ~func() ET.Either[E, func(A) B], GEB ~func() ET.Either[E, B], R, E, B, A any](a A) func(GREAB) GREB {
 	return FC.Flap(MonadMap[GREAB, GREB], a)
 }
+
+func MonadMapLeft[GREA1 ~func(R) GEA1, GREA2 ~func(R) GEA2, GEA1 ~func() ET.Either[E1, A], GEA2 ~func() ET.Either[E2, A], R, E1, E2, A any](fa GREA1, f func(E1) E2) GREA2 {
+	return eithert.MonadMapLeft(G.MonadMap[GREA1, GREA2], fa, f)
+}
+
+// MapLeft applies a mapping function to the error channel
+func MapLeft[GREA1 ~func(R) GEA1, GREA2 ~func(R) GEA2, GEA1 ~func() ET.Either[E1, A], GEA2 ~func() ET.Either[E2, A], R, E1, E2, A any](f func(E1) E2) func(GREA1) GREA2 {
+	return F.Bind2nd(MonadMapLeft[GREA1, GREA2], f)
+}
diff --git a/readerioeither/reader.go b/readerioeither/reader.go
index 4c6b26c..29074b1 100644
--- a/readerioeither/reader.go
+++ b/readerioeither/reader.go
@@ -280,3 +280,12 @@ func MonadFlap[R, E, B, A any](fab ReaderIOEither[R, E, func(A) B], a A) ReaderI
 func Flap[R, E, B, A any](a A) func(ReaderIOEither[R, E, func(A) B]) ReaderIOEither[R, E, B] {
 	return G.Flap[ReaderIOEither[R, E, func(A) B], ReaderIOEither[R, E, B]](a)
 }
+
+func MonadMapLeft[R, E1, E2, A any](fa ReaderIOEither[R, E1, A], f func(E1) E2) ReaderIOEither[R, E2, A] {
+	return G.MonadMapLeft[ReaderIOEither[R, E1, A], ReaderIOEither[R, E2, A]](fa, f)
+}
+
+// MapLeft applies a mapping function to the error channel
+func MapLeft[R, A, E1, E2 any](f func(E1) E2) func(ReaderIOEither[R, E1, A]) ReaderIOEither[R, E2, A] {
+	return G.MapLeft[ReaderIOEither[R, E1, A], ReaderIOEither[R, E2, A]](f)
+}