compiles instance of Magnify for CPS.RWST if mtl version >= 2.3

ekmett · Mar 14, 2024 · 14e28b1 · 14e28b1
1 parent d4b2062
commit 14e28b1
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Showing 2 changed files with 3 additions and 1 deletion.
diff --git a/lens.cabal b/lens.cabal
@@ -192,7 +192,7 @@ library
     indexed-traversable           >= 0.1      && < 0.2,
     indexed-traversable-instances >= 0.1      && < 0.2,
     kan-extensions                >= 5        && < 6,
-    mtl                           >= 2.3      && < 2.4,
+    mtl                           >= 2.2.1    && < 2.4,
     parallel                      >= 3.2.1.0  && < 3.3,
     profunctors                   >= 5.5.2    && < 6,
     reflection                    >= 2.1      && < 3,

diff --git a/src/Control/Lens/Zoom.hs b/src/Control/Lens/Zoom.hs
@@ -276,9 +276,11 @@ instance (Monad m, Monoid w) => Magnify (Lazy.RWST b w s m) (Lazy.RWST a w s m)
   magnify l (Lazy.RWST m) = Lazy.RWST $ getEffectRWS #. l (EffectRWS #. m)
   {-# INLINE magnify #-}
 
+#if MIN_VERSION_mtl(2,3,0)
 instance (Monad m, Monoid w, MonadReader b (CPS.RWST b w s m)) => Magnify (CPS.RWST b w s m) (CPS.RWST a w s m) b a where
   magnify l m = CPS.rwsT $ getEffectRWS #. l (EffectRWS #. CPS.runRWST m)
   {-# INLINE magnify #-}
+#endif
 
 instance Magnify m n b a => Magnify (IdentityT m) (IdentityT n) b a where
   magnify l (IdentityT m) = IdentityT (magnify l m)