Posts tagged "redis":

Working with Hedis

I'm now writing the second Haskell service using Redis to store data. There are a few packages on Hackage related to Redis but I only found 2 client libraries, redis-io and hedis. I must say I like the API of redis-io better, but it breaks a rule I hold very dear:

Libraries should never log, that's the responsibility of the application.

So, hedis it is. I tried using the API as is, but found it really cumbersome so looked around and after some inspiration from hedis-simple I came up with the following functions.

First a wrapper around a Redis function that put everything into ExceptionT with a function that transforms a reply into an Exception.

lpush :: Exception e => (Reply -> e) -> ByteString -> [ByteString] -> ExceptionT Redis Integer
lpush mapper key element = ExceptionT $ replyToExc <$> R.lpush key element
  where
    replyToExc = first (toException . mapper)

I found wrapping up functions like this is simple, but repetitive.

Finally I need a way to run the whole thing and unwrap it all back to IO:

runRedis :: Connection -> ExceptionT Redis a -> IO (Either SomeException a)
runRedis conn = R.runRedis conn . runExceptionT