[Haskell-cafe] Proper way to write this

[Lemmih]

On 12/26/05, Pupeno <pupeno at pupeno.com> wrote:
> I have this piece of code:
>
> 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)
>
> and I don't like it. I don't like the code repeting. It'd look good with Lips'
> "when":
> (define stop-daytime-serve dts
>   (when (stream dts)
>     (kill-server (ss dts)))
>   (when (dgram dts)
>     (kill-server (ds dts))))
>
> Is there a better way to write that on Haskell ?

Yes, there is:
stopDaytimeServer dts =
  do when (isJust (streamPort dts)) $ killServer (ss dts)
     when (isJust (dgramPort dts)) $ killServer (ds dts)

You can do the same thing with 'runDaytimeServer'.

--
Friendly,
  Lemmih