[Haskell-cafe] Language Workbenches - the Haskell solution?

[Yoel Jacobsen]

It seems that Martin Fowler's article "Language Workbenches: The 
killer-App for Domain Specific Languages?" - 
http://www.martinfowler.com/articles/languageWorkbench.html - has 
generated some nice dynamic solution where a configuration file is 
written in the same language as the program. Notable examples are lisp - 
http://lispm.dyndns.org/news?ID=NEWS-2005-07-08-1 and python - 
http://billionairebusinessman.blogspot.com/2005/09/drop-that-schema-and-put-your-hands-in.html

I'm trying to create an _elegant_ solution in Haskell. But I'm stuck. 
Since the native record-like access in Haskell syntax is using labelled 
fields in datatype decleration but the later are strictly compile-time. 
Therefore, if I compile my program and add a field in the configuration 
file (written in Haskell, using, for instance hs-plugins), I'll need to 
recompile the data declaration as well.

Further, what is the type of the parser? Consider the following 
implementation:

source = "#123456789012345678901234567890123456789012345678901234567890\n\
  \SVCLFOWLER         10101MS0120050313.........................\n\
  \SVCLHOHPE          10201DX0320050315........................\n\
  \SVCLTWO           x10301MRP220050329..............................\n\ 
         \USGE10301TWO 
x50214..7050329..............................."

data Configuration = Config String [(String, Int, Int)]

config = [
           Config "SVCL" [("CustomerName", 4, 18),
                          ("CustomerID", 19, 23),
                          ("CallTypeCode", 24, 27),
                          ("DateOfCallString", 28, 35)],

           Config "USGE" [("CustomerID", 4, 8),
                          ("CustomerName", 9, 22),
                          ("Cycle", 30, 30),
                          ("ReadDAte", 31, 36)]]

-- parse takes the configuration, a line from the source string and 
generate a record

parse :: Configuration -> String -> Record


What is the type of Record?

Anyway, any elegant solution or a hint towards one are most welcome.

Thanks,
   Yoel