[Haskell-cafe] Cmdargs and common flags

[Kevin Quick]

Magnus,

I used the following technique, but it was a couple of iterations of CmdArgs ago:


data UIMode = Normal | Batch | Query deriving (Data,Typeable,Show,Eq)

uimode_arg :: forall t. t -> UIMode
uimode_arg _ = enum Normal
                [ Batch &= flag "B" & text "batch mode (no interaction)" & group grp
                , Query &= flag "Q"
                            & text "query mode (user verification solicited)"
                            & group grp
                ]
     where grp = "Operating Mode"


data Globalargs = CMD1 { ... , uimode :: UIMode , ... }
                 | CMD2 { ... , uimode :: UIMode , ... }


cmd1mode :: Mode Globalargs
cmd1mode = mode $ CMD1 { ... , uimode = uimode_arg "cmd1" }
                   &= text (usage "...")


cmd2mode :: Mode Globalargs
cmd2mode = mode $ CMD1 { ... , uimode = uimode_arg "cmd2" }
                   &= text (usage "...")

modes :: [ Mode Globalargs ]
modes = [ cmd1mode, cmd2mode ]

main  = do cmdArgs progSummary modes
            ...


I've cut and pasted from my usage and perhaps pasted too little, so let me know if the above is unuseably brief.  And again, cmdargs has changed somewhat since this code was written and I haven't tried a recent compilation.

-KQ

P.S.  This often required {-# OPTIONS_GHC -fno-full-laziness -fno-strictness #-} because GHC (6.12? 6.10?) would complain about my uimode_arg type otherwise.


On Thu, 20 Jan 2011 01:48:35 -0700, Magnus Therning <magnus at therning.org> wrote:

> I'm looking for a good way of dealing with common flags in cmdargs.
> Currently what I do requires a bit of repetition that I'd really like
> to get rid of:
>
> 1. Data types
>
>     data Modes = Cmd1 { foo :: String, ... } | Cmd2 { foo :: String, ... }
>
> 2. Mode specifications
>
>     cmd1 = Cmd1 { foo = def &= help "..", ...}
>     cmd2 = Cmd2 { foo = def &= help "..", ...}
>
> I have no idea how to deal with the repetition in the data types, so
> all suggestions are welcome.
>
> For the repetition in the mode specifications I attempted to factor
> the common bits into a "variable":
>
>     flagFoo = "" &= help ".."
>
> but that resulted in only the first command getting the proper
> specification.  I suppose this comes down to the impurity, but how do
> I work around that?  (Especially, are there any good examples of using
> the pure part of the API?)
>
> /M
>


-- 
-KQ