[web-devel] Database connection laziness (yesod)

Another lazy question:

fun :: Int -> Int

foo a = runReader ask (fun a)

bar a = runReader (return 3) (fun a)

foo causes (fun a) to be evaluated but bar doesn't. Is the same true for database connections? Are they created lazily? I ask because it would be neat to be able to write:

runDB $ getFromCache cache key

where getFromCache queries the DB only on a cache miss, and have a connection created only in the case of a cache miss. I have tried test this myself, but I can't get ghci to cooperate and load yesod from source. Cheers, J