鉴于此：
main :: IO ()
main = do
(conf, site, cleanup) <- $(loadSnapTH [| getConf |]
'getActions
["snaplets/heist/templates"])
_ <- try $ httpServe conf site :: IO (Either SomeException ())
cleanup
------------------------------------------------------------------------------
-- | This action loads the config used by this application. The loaded config
-- is returned as the first element of the tuple produced by the loadSnapTH
-- Splice. The type is not solidly fixed, though it must be an IO action that
-- produces the same type as 'getActions' takes. It also must be an instance of
-- Typeable. If the type of this is changed, a full recompile will be needed to
-- pick up the change, even in development mode.
--
-- This action is only run once, regardless of whether development or
-- production mode is in use.
getConf :: IO (Config Snap AppConfig)
getConf = commandLineConfig defaultConfig
------------------------------------------------------------------------------
-- | This function generates the the site handler and cleanup action from the
-- configuration. In production mode, this action is only run once. In
-- development mode, this action is run whenever the application is reloaded.
--
-- Development mode also makes sure that the cleanup actions are run
-- appropriately before shutdown. The cleanup action returned from loadSnapTH
-- should still be used after the server has stopped handling requests, as the
-- cleanup actions are only automatically run when a reload is triggered.
--
-- This sample doesn't actually use the config passed in, but more
-- sophisticated code might.
getActions :: Config Snap AppConfig -> IO (Snap (), IO ())
getActions conf = do
(msgs, site, cleanup) <- runSnaplet
(appEnvironment =<< getOther conf) app
hPutStrLn stderr $ T.unpack msgs
return (site, cleanup)
如果我想添加mongodb数据库功能（this nice example here），我甚至开始？
Snap只有两个例子：