Quoth Pupeno : | I have this piece of code: What do you think about this? may_ = maybe (return ()) (\ _ -> f) stopDaytimeServer dts = do may_ (killServer (ss dts)) (streamPort dts) may_ (killServer (ds dts)) (dgramPort dts) | PS: I have a worse case: I don't think it will be too much worse. I would not try to combine the struct updates, in the "both" case -- it doesn't buy you anything, and pulls you into duplication you don't want. Donn Cave, donn@drizzle.com | stopDaytimeServer dts = | case dts of | DaytimeServer {streamPort = Just _, dgramPort = Just _} -> do | killServer (ss dts) | killServer (ds dts) | DaytimeServer {streamPort = Just _, dgramPort = Nothing} -> do | killServer (ss dts) | DaytimeServer {streamPort = Nothing, dgramPort = Just _} -> do | killServer (ds dts) | -- | Having a 'DaytimeServer', run it according to its specifications. | runDaytimeServer :: DaytimeServer -> IO DaytimeServer | runDaytimeServer dts = | case dts of | DaytimeServer {streamPort = Just _, dgramPort = Just _} -> do | ss <- runDgramDaytimeServer dts | ds <- runStreamDaytimeServer dts | return dts{ss = ss, ds = ds} | DaytimeServer {streamPort = Just _, dgramPort = Nothing} -> do | ss <- runStreamDaytimeServer dts | return dts{ss = ss} | DaytimeServer {streamPort = Nothing, dgramPort = Just _} -> do | ds <- runDgramDaytimeServer dts | return dts{ds = ds}