Documentation examples for generic instances for `ToJSONKey` fail to compile

[soenkehahn]

The documentation has an example for implementing ToJSONKey for a simple sum type:

data Color = Red | Green | Blue
  deriving (Show, Read, Eq, Ord)

instance ToJSONKey Color where
  toJSONKey = genericToJSONKey defaultJSONKeyOptions

However, when trying this I get two errors:

• No instance for ‘ToJSON Color’
• No instance for ‘Generic Color’

It'd be nice to have the examples compile.

(I was surprised that ToJSON was needed. So I looked at the example to clarify whether I'm really supposed to have that instance or whether I'm just using the library wrong. But since the example doesn't have the ToJSON instance, but also doesn't compile, I'm still not 100% sure.)