Re: [Haskelldb-users] [Haskell-cafe] Request for feedback: HaskellDB + HList

[Justin B. <jgb...@gm...>]

I like the direction you are going. I looked into using HList a year
or so ago and I wasn't quite up to it.  The latest (unreleased)
version of HaskellDB is on patch-tag at
http://patch-tag.com/r/haskelldb/snapshot/current/content/pretty.
Would you mind creating a patch file against that for easier review? I
won't commit it until you say its ready but I'd like to see what
changes you have made.

No announcement has been made but I took over maintainership from
Bjorn a few months ago. I hope to get a 1.0 release of HaskellDB out
this summer, and having something new like this in it would be pretty
sweet.

On Sat, May 16, 2009 at 3:08 PM, Brian Bloniarz <ph...@ho...> wrote:
> Hi,
>
> It's come time to share something that I've been playing around with
> recently:
> a branch of HaskellDB which replaces the home-grown Record code with HList
> records. It's definitely not ready for primetime, but I thought it'd be a
> good
> time to post the code and solicit some feedback from the community.
>
> HaskellDB the concept is very promising, but IMHO the code still falls short
> of that promise. Hopefully this is a small step in the right direction --
> the
> advantages of using HList:
> * Shared implementation of extensible records
> * Additional features from HList
>   * Better error messages for record misuse
>   * "Lacks" predicates
> * Simpler code
>
> As an example of how this can be better, a DB insert looks like so:
>> insert db table $ constantRecord $
>>     film .=. "Munchie" .*.
>>     director .=. Just "Jim Wynorski" .*.
>>     emptyRecord
> The columns need not appear in the same order as in the database. If you
> forget
> a column, you'll get "error: No instance for (Fail (FieldNotFound (Proxy
> Director)))"
> rather than an opaque error. Using the new "insertOpt" function, Maybe
> columns
> will default to Nothing rather than needing to be specified.
>
> The details:
>
> I haven't updated everything, but there's enough to run test/TestCases.hs
> under Postgresql. TestCases is probably the best place to look for examples
> of
> the new syntax for now.
>
> HList had name conflicts with HaskellDB's SQL expression language
> ((.*.), (.++.), etc.) My temporary band-aid is to move the expression
> functions
> to Database.HaskellDB.SqlExpr, and require people to import qualified.
>
> The Attr type is gone, columns labels are untyped now. I also replaced a
> few instances of primitive type-level recursion with HMap/HMapOut. This
> makes
> the code simpler, and the type signatures more complex -- type families
> would
> help a lot here, I think.
>
> Feedback welcome! You can find my darcs tree at:
>
> http://mysite.verizon.net/vzewxzuh/sitebuildercontent/sitebuilderfiles/haskelldb-hlist-20090516.tar.gz
> It also requires minor changes to HList, available at:
>
> http://mysite.verizon.net/vzewxzuh/sitebuildercontent/sitebuilderfiles/hlist-20090516.tar.gz
> I'll talk to the HList people about getting those merged.
>
> Thanks!
>
> Brian Bloniarz
>
>
> ________________________________
> Hotmail® has a new way to see what's up with your friends. Check it out.
> _______________________________________________
> Haskell-Cafe mailing list
> Has...@ha...
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>