[moving discussion from Haskell list to libraries list]
"S. Alexander Jacobson"
It would be helpful to have an example of using combinators to take a value of type e.g.
import Network.URI import System.Time data Foo = Foo {uri::URI, name::String, stamp::ClockTime}
and produce e.g. a string such as
<? xml version="1.0" ?> <? xml-stylesheet type="text/xsl" href="myStyle.xsl"?> <Foo xmlns:Foo="http://mynamespace" uri="http://someURL" name="blah" stamp="Mon, 11 Oct 2004 09:05:31 -0400"/>
Well, fundamentally, this kind of conversion is dependent not only on the Haskell type defined by your application, but also the way you want to represent it in XML. There are lots of possible choices for the latter. The DRiFT implementation that derives the Haskell2Xml class makes one choice for the type mapping, using nested elements - you have made a rather different choice that uses attributes instead. Neither is more "correct" - it is a stylistic judgement. Although one could perhaps define some kind of meta-language for describing various kinds of HaskellType -> XMLType translation, with an automatic processor to derive a particular translation for the type instances you want today, that is probably overkill. Why not just write the specific mapping by hand in the first place (as you have now done)?
Note, I think I've figured out how to do this using raw types (after modifying to allow PIs in the prolog!), but I assume using the combinators is more correct.
No, the combinators are not "more correct". They are just one possible implementation choice, heavily biased towards XML -> XML transformations. If you are mainly generating documents rather than transforming them, then the combinators might be unhelpful. So just use the raw XML element etc types instead. At least you can re-use the parser, validator, and pretty-printer.
But I actually think the document function should *automatically* implement xmlEscape. Otherwise, it is too easy for the user to produce incorrect documents notwithstanding what the library claims to promise!
Yes, good point.
Will this work to insert a PI before the first element?
No, the CFilter combinators only manipulate the element content, not the DTD or Prolog. (Other XML toolboxes may have made different choices here - I think Uwe Schmidt's HXT allows combinator-processing of the DTD for instance.) Regards, Malcolm