How to use TimedFastLogger with structured logging?

[saurabhnanda]

I'm trying to emit JSON logs from my app using a TimedFastLogger. The function that I want to write, looks something like this:

logStructuredPayload :: FormattedTime -> StructuredPayload -> IO ()

internally this will convert StructuredPayload to an Aeson.Encoding that needs to contain the timestamp within the json log itself. Something like:

{
  "@timestamp": "...",
  "level": "...",
  "sql_count": "...",
  "sql_time": "....",
  "api_count": "...",
  "api_time": "..."
}

However, I'm not sure if something like this is possible, given the type-signature of TimedFastLogger:

type TimedFastLogger = (FormattedTime -> LogStr) -> IO ()

I guess, a related question would be how to actually use LogCallback :: (v -> IO()) -> IO () -> LogType' v? This is the only LogType' which seems to be operating with something other than a LogStr. Is the purpose of LogCallback to be able to log values of type other than LogStr?