[Haskell-cafe] Relational Algebra

Günther Schmidt gue.schmidt at web.de
Thu Oct 15 11:40:13 EDT 2009

Hi Alistair,

> Both of our projects just generate SQL though, AFAIK. Was there
> something else you wanted to generate?

I wish I could provide a clear answer to that myself, truth is I'm not  
certain myself at the moment.

All this is related to a rl problem I have, it concerns the business logic  
of the app I wrote.

I hindsight it occurred to me that the algorithm can be abstractly  
expressed in terms of relational algebra for which I need an EDSL.

One concrete implementation could then be an interpreter / compiler to  
SQL, if I choose to use a database backend, and another implementation  
could be a interpretor to in-memory data structures (maps, whathaveyou),  
or a debugger to see if I have got the abstract algorithm right.

I had made very good experience with HaskellDB, it was a great help, but  
the DSL of HaskellDB immediately translates to SQL, it's hardwired to do  

With the newer techniques for designing EDSLs ("finally tagless" in  
particular), I'm considering to roll one myself, and I suppose I'll also  
need HList to do so too.

Quite a number of people on this list also use Haskell for rl  
applications, so I reason that someone must already have tried something  


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