From 9ed1034a2beaf075a9f46973ff833bda8c67fc64 Mon Sep 17 00:00:00 2001
From: John Ky <john.ky@iohk.io>
Date: Wed, 6 Nov 2024 21:46:47 +1100
Subject: [PATCH] New runErrorMap function

---
 core/HaskellWorks/Polysemy/Error.hs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/core/HaskellWorks/Polysemy/Error.hs b/core/HaskellWorks/Polysemy/Error.hs
index 100cf13..eac37ce 100644
--- a/core/HaskellWorks/Polysemy/Error.hs
+++ b/core/HaskellWorks/Polysemy/Error.hs
@@ -2,6 +2,7 @@ module HaskellWorks.Polysemy.Error
   ( module HaskellWorks.Error,
     trap,
     trap_,
+    runErrorMap,
     embedRunExceptT,
     embedThrowExceptT,
   ) where
@@ -30,6 +31,14 @@ trap_ :: forall e a r. ()
 trap_ h =
   trap (const h)
 
+-- | Run an 'Error' effect and map the error value to a different type.
+runErrorMap :: ()
+  => (e -> d)
+  -> Sem (Error e : r) a
+  -> Sem r (Either d a)
+runErrorMap f =
+  fmap (first f) . runError
+
 embedRunExceptT :: forall e a r m. ()
   => Member (Embed m) r
   => ExceptT e m a