[Haskell-cafe] Shortening if-then-else

[Yitzchak Gale]

> Is there a shorter way to write the if-then-else part below?
> 
> --
> tryTakeSeat :: [Word8] -> Word8 -> ScriptState (Maybe Word8)
> tryTakeSeat _ _ =
>     do ...
>        if (cmdType cmd) /= (CmdSitError Server)
>           then return $ Just seat_num
>           else return Nothing
> --

tryTakeSeat _ _ = runMaybeT $ do
       ...
       guard $ cmdType cmd /= CmdSitError Server
       return seat_num

-Yitz