Copy in the <~> combinator from starlight.

src/Facet/REPL.hs

@@ -15,7 +15,7 @@ import           Control.Carrier.Parser.Church
 import           Control.Carrier.Reader
 import           Control.Carrier.Readline.Haskeline
 import           Control.Carrier.State.Church
-import           Control.Effect.Lens (use, (%=), (.=))
+import           Control.Effect.Lens (use, (%=), (.=), (<~))
 import           Control.Effect.Parser.Source (Source(..), sourceFromString)
 import           Control.Lens (Getting, Lens', ix, lens)
 import           Control.Monad.IO.Class
@@ -192,3 +192,9 @@ elab src = runReader (span src) . L.runState env_ . rethrowElabErrors src
 lens ~> act = use lens >>= act
 
 infixr 2 ~>
+
+-- | Compose a lens onto either side of a Kleisli arrow and run it on the 'State'.
+(<~>) :: Has (State s) sig m => Lens' s a -> (a -> m a) -> m ()
+lens <~> act = lens <~ lens ~> act
+
+infixr 2 <~>