From 9628bb69c286ebb309bff680196b546e57efaa62 Mon Sep 17 00:00:00 2001
From: Ross Paterson <ross@soi.city.ac.uk>
Date: Sat, 2 Feb 2019 00:45:16 +0000
Subject: [PATCH] backward compatability for MonadFix ListT instance
---
Control/Monad/Trans/List.hs | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/Control/Monad/Trans/List.hs b/Control/Monad/Trans/List.hs
index 3cde4ce..919898e 100644
--- a/Control/Monad/Trans/List.hs
+++ b/Control/Monad/Trans/List.hs
@@ -145,8 +145,8 @@ instance (Monad m) => MonadPlus (ListT m) where
instance (MonadFix m) => MonadFix (ListT m) where
mfix f = ListT $ mfix (runListT . f . head) >>= \ xs -> case xs of
- [] -> pure []
- x:_ -> (x:) <$> (runListT . mfix) ((mapListT . fmap) tail . f)
+ [] -> return []
+ x:_ -> liftM (x:) (runListT (mfix (mapListT (fmap tail) . f)))
{-# INLINE mfix #-}
instance MonadTrans ListT where
--
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