[Haskell-cafe] extending and reusing cmdargs option specs ?

[Neil Mitchell]

Hi,

You're asking for:
http://code.google.com/p/ndmitchell/issues/detail?id=291 - it's
something I'm already aware of, and what to do at some point.
Unfortunately, it probably won't be anytime in the next few months,
but it will happen eventually.

Thanks, Neil

On Tue, Aug 9, 2011 at 3:08 AM, wren ng thornton <wren at freegeek.org> wrote:
> On 8/8/11 1:59 PM, Simon Michael wrote:
>>
>> And, I may have made things worse for myself in the reuse/avoiding
>> boilerplate department: I'm not sure how to reuse a cmdargs options data
>> structure, extending it with a few more options.
>
> This is a big problem I'm dealing with too lately. In particular, what I
> would like is if cmdargs could do flattening of structures, either
> automatically or with a new annotation combinator. With this it would be
> easy to have a basic FooBar program:
>
>    data FooBar = FooBar
>        { foo :: Foo
>        , bar :: Bar
>        }
>        deriving (Data, Typeable,...)
>
>    getFooBarMode :: IO (Mode (CmdArgs FooBar))
>    getFooBarMode = ...
>
> and then extend it to a FooBarBaz program:
>
>    data FooBarBaz = FooBarBaz
>        { fooBar :: FooBar
>        , baz :: Baz
>        }
>        deriving (Data, Typeable,...)
>
>    getFooBarBazMode :: IO (Mode (CmdArgs FooBarBaz))
>    getFooBarBazMode = ...
>
> The big trick is that I should be able to call getFooBarMode from
> getFooBarBazMode equivalently to if I had defined,
>
>    data FooBarBaz = FooBarBaz
>        { foo :: Foo
>        , bar :: Bar
>        , baz :: Baz
>        }
>        deriving (Data, Typeable,...)
>
> and copied over getFooBarMode inline into getFooBarBazMode. The problem is
> that the bulk of the code is in the Mode-generating functions, and it's also
> the sort of code that's hardest to keep in sync documentation-wise.
>
> I don't mind the extra indirection in the Mode structures since I don't
> actually use them in the program itself; I have an internal configuration
> type that I compile the FooBarBaz down to, so that I can perform additional
> semantic consistency checks before execution, as well as precomputing what
> the commandline arguments dereference into (e.g., functions).
>
>
>> As always, thanks a lot for cmdargs!
>> -Simon
>
> Indeed. Aside from this feature request I've been quite pleased :)
>
> --
> Live well,
> ~wren
>