1 files changed, 11 insertions, 4 deletions

diff --git a/src/Network/KRPC/Method.hs b/src/Network/KRPC/Method.hs
index 2a791924..ad93cb8b 100644
--- a/src/Network/KRPC/Method.hs
+++ b/src/Network/KRPC/Method.hs
@@ -8,11 +8,13 @@
 --   Normally, you don't need to import this module.
 --
 {-# LANGUAGE CPP                        #-}
-{-# LANGUAGE RankNTypes                 #-}
-{-# LANGUAGE MultiParamTypeClasses      #-}
+{-# LANGUAGE DefaultSignatures          #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE MultiParamTypeClasses      #-}
+{-# LANGUAGE RankNTypes                 #-}
 {-# LANGUAGE ScopedTypeVariables        #-}
-{-# LANGUAGE DefaultSignatures          #-}
+{-# LANGUAGE TypeFamilies               #-}
+{-# LANGUAGE FunctionalDependencies #-}
 module Network.KRPC.Method
        ( Method (..)
        , KRPC (..)
@@ -93,7 +95,9 @@ class ( Typeable req, Typeable resp
       , Serialize req, Serialize resp
 #endif
       )
-    => KRPC req resp where
+    => KRPC req resp | req -> resp, resp -> req where
+
+  type Envelope req resp
 
   -- | Method name. Default implementation uses lowercased @req@
   -- datatype name.
@@ -107,3 +111,6 @@ class ( Typeable req, Typeable resp
     where
       hole = error "krpc.method: impossible" :: req
 #endif
+
+  unseal :: Envelope req resp -> Either String req
+  seal :: resp -> Envelope req resp