Add Resolver module with helpers and exceptions

src/Language/GraphQL/Class.hs

@@ -24,7 +24,7 @@ fromGraphQLToIntegral (Type.Int value) = Just $ fromIntegral value
 fromGraphQLToIntegral (Type.String value) =
     case Text.Read.decimal value of
         Right (converted, "") -> Just converted
-        _ -> Nothing
+        _conversionError -> Nothing
 fromGraphQLToIntegral _ = Nothing
 
 -- | Instances of this typeclass can be converted to GraphQL internal