On 10 September 2010 17:53, Jared Jennings
I've tried
data OFXThing = OFX { statement :: OFXThing } | StatementResponse { ... transactions :: [OFXThing] }
but that would let me make trees of things that make no sense in OFX, like a transaction containing a statement.
Using alternative constructors (i.e. sum types) is the right approach to get different "datatypes" in the tree. However you aren't respecting the nesting of the tree here - "OFX" is a level higher in the tree than a statement response and the OFX constructor recurs on itself which looks suspect. I suspect OFX is pathologically huge format and isn't a good starting point for designing syntax trees (the downloadable Spec seemed to be several megabytes zipped). If the DTD is very large you might want to use the untyped tree to extract parts of interest and convert after parsing to a smaller typed tree (with only the syntax you are interested in). By the way, HaXML has has a tool called DTD2HS (I think) that will generate Haskell datatypes from a DTD definition. Best wishes Stephen