On Mon, Oct 03, 2011 at 09:42:59PM +0800, Magicloud Magiclouds wrote:
Hi, I have a function: post :: (ToJson p, FromJson q) => String -> String -> String -> Map.Map String p -> IO q Now I'd like to call it like: r <- post site token "user.addMedia" (Map.fromList [ ("users", users :: ToJson) , ("medias", medias :: ToJson) ]) So I got the problem. If I used things like "users :: ToJson", then class used as a type error occurred. But if I did not use them, since users and medias were actually different types, then fromList failed, required the type of medias the same with users.
If users and medias are different types, then you cannot put them in the same list. The ToJson class provides a method toJson :: ToJson a => a -> Json so presumably you need to call this method on users and medias, like ... ("users", toJson users) , ("medias", toJson medias) -Brent