[Haskell-cafe] Haskell, Queries and Monad Comprehension

Hi all, is there anybody currently using Haskell to construct or implement a query language? I have read a couple of papers on "Monad Comprehension Calculus" and similar but none using Haskell nor any other existing programming language to build an actual implementation. Most papers give some sort of "Pseudo code", but I couldn't find any meat. Günther