>
> Hello,
>
> I'm trying to find out if it's possible to use Haskell data type
> definition capability to define types and compile defined types into
> other languages, for example into Google's protocol buffers data
> definition language. So basically speaking I'm thinking about using
> Haskell sub-set as a data-definition DSL together with some functions
> which will generate some code based on supplied defined data types. My
> idea is:
>
> data Person = Person {
> id :: Int
> , name :: String
> , email :: Maybe String
> }
> deriving (Show, Data, Typeable)
>
> emit_proto Person 1
>
> where emit_proto is function which will translate Person data type
> definition into Google's proto language (the 1 is index from which start
> to index type's fields) by traversing data type definition and
> translating all its children plus do some header/footer generation etc:
>
> message Person {
> required int32 id = 1;
> required string name = 2;
> optional string email = 3;
> }
>
> I've looked for something like that and found SYB papers which works on
> top of data instance (i.e. actual data, not data type). I also found
> JSON lib which again works on top of data and not data type. I've tried
> to look into Data.Typetable etc, but have not found function which will
> print data type's field name and field type name (although JSON lib
> seems to use field name for JSON generation so I'll need to investigate
> this more). I've tested `typeOf' function and it's quite useful, but its
> limitation is that it's not working on ADT name:
>
> data Color = RED|GREEN|BLUE
>
> *Main> typeOf Color
>
> <interactive>:1:8: Not in scope: data constructor `Color'
>
> *Main> typeOf RED
> Main.Color
>
> and I would need that in order to translate Color defined above into
> enum like:
>
> enum Color {
> RED = 0;
> GREEN = 1;
> BLUE = 2;
> }
>
>
> My question is: do you think I'm looking into good direction (i.e.
> Data/Typeable) or do you think I'll need to use something different for
> data definition DSL (Template Haskell?, or impossible in Haskell so
> write my own language with full parser? etc?)
>
> Thanks for any idea or opinion on this!
> Karel
>
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