From a0c1c8ac152493ff249d83e5e9fda048b8811549 Mon Sep 17 00:00:00 2001
From: Pierre Thierry <pierre@nothos.net>
Date: Fri, 20 Feb 2026 10:50:46 +0100
Subject: [PATCH] Add failLeft

---
 src/Data/Either/Extra.hs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/Data/Either/Extra.hs b/src/Data/Either/Extra.hs
index ca67f4e..3e7ff7c 100644
--- a/src/Data/Either/Extra.hs
+++ b/src/Data/Either/Extra.hs
@@ -102,3 +102,7 @@ mapLeft f = either (Left . f) Right
 -- > mapRight show (Right True) == Right "True"
 mapRight :: (b -> c) -> Either a b -> Either a c
 mapRight = fmap
+
+-- | Lift an 'Either String' to a 'MonadFail'
+failLeft :: MonadFail m => Either String a -> m a
+failLeft = either fail pure