Add a few missing instances

src/Language/GraphQL/Class.hs

@@ -5,6 +5,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE TupleSections #-}
+{-# LANGUAGE FlexibleInstances #-}
 
 -- | ToGraphQL and FromGraphQL typeclasses used for user-defined type
 -- conversion.
@@ -101,6 +102,10 @@ class ToGraphQL a
   where
     toGraphQL :: a -> Type.Value
 
+instance ToGraphQL Type.Value
+  where
+    toGraphQL a = a
+
 instance ToGraphQL Text
   where
     toGraphQL = Type.String
@@ -198,12 +203,20 @@ instance ToGraphQL LocalTime
   where
     toGraphQL = iso8601ToGraphQL
 
+instance ToGraphQL a => ToGraphQL (HashMap.HashMap Text a)
+  where
+    toGraphQL = Type.Object . fmap toGraphQL
+
 -- | Instances of this typeclass can be used to convert GraphQL internal
 -- representation to user-defined type.
 class FromGraphQL a
   where
     fromGraphQL :: Type.Value -> Maybe a
 
+instance FromGraphQL Type.Value
+  where
+    fromGraphQL = Just
+
 instance FromGraphQL Text
   where
     fromGraphQL (Type.String value) = Just value
@@ -311,6 +324,11 @@ instance FromGraphQL LocalTime
   where
     fromGraphQL = fromGraphQLToISO8601
 
+instance FromGraphQL a => FromGraphQL (HashMap.HashMap Text a)
+  where
+    fromGraphQL (Type.Object hm) = traverse fromGraphQL hm
+    fromGraphQL _ = Nothing
+
 stringLE :: Name -> Q Exp
 stringLE = litE . stringL . nameBase