From 1615a4d737fab83138e40bb6ae2ce379b7aaea1e Mon Sep 17 00:00:00 2001
From: Xavier Dectot <xavier@wheredoibegin.fr>
Date: Thu, 20 Mar 2025 18:29:31 +0100
Subject: [PATCH] b

--- a/src/Control/Monad/Unify.hs
+++ b/src/Control/Monad/Unify.hs
@@ -29,6 +29,7 @@ import Data.Monoid
 import Control.Applicative
 import Control.Monad.State
 import Control.Monad.Error.Class
+import Control.Monad (MonadPlus, when)
 
 import Data.HashMap.Strict as M
 import qualified Data.Semigroup as S
@@ -118,7 +119,7 @@ substituteOne u t = Substitution $ M.singleton u t
 -- |
 -- Replace a unification variable with the specified value in the current substitution
 --
-(=:=) :: (Error e, Monad m, MonadError e m, Unifiable m t) => Unknown -> t -> UnifyT t m ()
+(=:=) :: (Monad m, MonadError String m, Unifiable m t) => Unknown -> t -> UnifyT t m ()
 (=:=) u t' = do
   st <- UnifyT get
   let sub = unifyCurrentSubstitution st
@@ -133,10 +134,10 @@ substituteOne u t = Substitution $ M.singleton u t
 -- |
 -- Perform the occurs check, to make sure a unification variable does not occur inside a value
 --
-occursCheck :: (Error e, Monad m, MonadError e m, Partial t) => Unknown -> t -> UnifyT t m ()
+occursCheck :: (Monad m, MonadError String m, Partial t) => Unknown -> t -> UnifyT t m ()
 occursCheck u t =
   case isUnknown t of
-    Nothing -> when (u `elem` unknowns t) $ UnifyT . lift . throwError . strMsg $ "Occurs check fails"
+    Nothing -> when (u `elem` unknowns t) $ UnifyT . lift . throwError $ "Occurs check fails"
     _ -> return ()
 
 -- |
-- 
2.48.1