Re: [Haskelldb-users] Improving 'project'

[Alain C. <al...@po...>]

Björn Bringert a écrit :
> On Jan 30, 2008, at 19:01 , Justin Bailey wrote:
>
>> All,
>>
>> project doesn't easily let me add a few columns to an existing query
>> (or take a few columns away). Instead, each use of project requires me
>> to build the entire list of columns I'd like to pass on by hand.
>> Before I go further, if there is a way to do that, please let me know.
>
> No, there is no existing way to achieve this. Indeed, it's one of the 
> most common complaints about HaskellDB :-)
>
>
>>  3) If not 2, how can the solution above be better? I'd like to extend
>> it to adding/removing arbitrary columns and  more control over column
>> order.
>
> The best way to do it would be to add powerful record types to Haskell...
>
> You may want to look at HList, http://homepages.cwi.nl/~ralf/HList/ 
> <http://homepages.cwi.nl/%7Eralf/HList/> I'm not sure how much HList 
> can do now, perhaps they have added things since they wrote the paper. 
> There might be some nice record manipulation stuff there that you 
> could use. Porting HaskellDB to use HList instead of its own records 
> would be nice, if the HList code is in good shape. 
>
Hi,

The HList library compiles with ghc-6.8.2, and seems to be maintained. 
Indeed it would be a great idea to use it instead of HaskellDB's own 
heterogeneous list system.

Alain