Travis/service generation (#46)

* higher bound on clock versions

* Added helper module for generated service code

grpc-haskell.cabal

@@ -26,7 +26,7 @@ flag with-examples
 library
   build-depends:
       base ==4.8.*
-    , clock ==0.6.*
+    , clock >=0.6.0 && <=0.7.2
     , bytestring ==0.10.*
     , stm == 2.4.*
     , containers ==0.5.*

src/Network/GRPC/HighLevel/Generated.hs

@@ -0,0 +1,23 @@
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE RankNTypes #-}
+
+module Network.GRPC.HighLevel.Generated where
+
+import Network.GRPC.HighLevel.Server
+import Network.GRPC.LowLevel.Call
+
+-- | Used at the kind level as a parameter to service definitions
+--   generated by the grpc compiler, with the effect of having the
+--   field types reduce to the appropriate types for the method types.
+data GRPCImpl = ServerImpl | ClientImpl
+
+-- | GHC does not let us partially apply a type family. However, we
+--   can define a type to use as an 'interpreter', and then use this
+--   'interpreter' type fully applied to get the same effect.
+type family MkHandler (impl :: GRPCImpl) (methodType :: GRPCMethodType) i o
+
+type instance MkHandler 'ServerImpl 'Normal          i o = ServerHandler       i o
+type instance MkHandler 'ServerImpl 'ClientStreaming i o = ServerReaderHandler i o
+type instance MkHandler 'ServerImpl 'ServerStreaming i o = ServerWriterHandler i o
+type instance MkHandler 'ServerImpl 'BiDiStreaming   i o = ServerRWHandler     i o