joerg.rudnick:
Hi Chris,
these are good questions -- actually, you might have mentioned Takusen, too.
Clearly, HDBC is the largest of these projects, and there are lots of things well done there.
Takusen has an interesting approach, and I would like to see a discussion here about the practical outcomes, as I have done no testing yet.
It has been used in production at a number of places, including Galois.
I myself quite a time ago had an opportunity to do a Haskell job with a PostgreSQL backend for a client, where I tried out all three and got hsql running easiest. A maintainer was vacant, so I stepped in happily -- doing refactorings, fixing problems at request, giving advice to people.
I can say that I am quite a little PostgreSQL centric and that I have a GIS project in sight, for which I want to try to adapt hsql.
And you have to be wary about the license of HDBC (LGPL) if you want to use the package in software you redistribute (though this is rarely the case for database apps, I'm guessing). Satisfying the linking requirements with GHC -O2 are non-trivial, even with -dynamic. -- Don