NonEmpty as a pure carrier for Choose.

In keeping with #206, this offers a solo `Carrier` instance for
`NonEmpty` lists over the `Choose` effects. Because `NonEmpty` is now
in `base`, this doesn't add new dependencies, and nicely rounds out
the carrier definition of `[]` for `NonDet` and `Maybe` for `Empty`.

src/Control/Carrier/Class.hs

@@ -12,13 +12,17 @@ import Control.Effect.Reader (Reader(..))
 import Control.Effect.Sum ((:+:)(..))
 import Control.Effect.Writer (Writer(..))
 import Control.Monad ((<=<))
+import Data.List.NonEmpty (NonEmpty)
 
 -- | The class of carriers (results) for algebras (effect handlers) over signatures (effects), whose actions are given by the 'eff' method.
 class (HFunctor sig, Monad m) => Carrier sig m | m -> sig where
   -- | Construct a value in the carrier for an effect signature (typically a sum of a handled effect and any remaining effects).
   eff :: sig m a -> m a
 
 
+instance Carrier Choose NonEmpty where
+  eff (Choose m) = m True <> m False
+
 instance Carrier Empty Maybe where
   eff Empty = Nothing