Merge pull request #9 from bellroy/remove-overlapping-instance

Remove `instance PluckError e (Except e) m`
qfpl · May 6, 2024 · e2dae7f · e2dae7f
2 parents a18cf8d + 0d09d4c
commit e2dae7f
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diff --git a/changelog.md b/changelog.md
@@ -3,6 +3,9 @@
 * Replaced the `HoistError` typeclass, which is about monads, with a
   simpler `PluckError` typeclass that is about extracting errors from
   values.
+* Removed the instance for `Except e`, as it triggers overlapping
+  instance errors when attempting to hoist `ExceptT e m` for unknown
+  monads `m`.
 * Introduced a parallel `Control.Monad.Fail.Hoist` module, for
   hoisting error messages into `MonadFail`.
 

diff --git a/src/Control/Monad/Error/Hoist.hs b/src/Control/Monad/Error/Hoist.hs
@@ -194,7 +194,3 @@ instance Applicative m => PluckError e (Either e) m where
 instance Monad m => PluckError e (ExceptT e m) m where
   pluckError = runExceptT
   foldError f g = either f g <=< runExceptT
-
-instance Applicative m => PluckError e (Except e) m where
-  pluckError = pure . runExcept
-  foldError f g = either f g . runExcept