[Haskell] Re: understanding HaXml and escaping
S. Alexander Jacobson
alex at alexjacobson.com
Thu Oct 28 12:38:34 EDT 2004
You have a Dtd2Haskell tool, but DTDs are very
inexpressive and the result is string based types.
Is there a tool for converting e.g. relaxNG into
haskell types? Then we get direct support for
e.g. doubles or URLs. I know there is a relaxNG
validator written in haskell, but that is not the
On Thu, 28 Oct 2004, Malcolm Wallace wrote:
> "S. Alexander Jacobson" <alex at alexjacobson.com> writes:
> > Is there a good entry point into HaXml?
> > I've now spent some time trying to understand it
> > and feel like I've gotten nowhere.
> It is a large package with many diverse facilities, so I'm not
> surprised. I take it you have read the ICFP'99 paper linked to from
> the HaXml webpage? To give a fuller answer, it would be helpful to
> know more about your specific XML needs.
> > The Haddock documentation enumerates what each
> > function does, but I still don't know how to
> > produce a valid XML document?
> Where does your document come from? Has it been parsed already,
> then manipulated, and you want to spit it out again? Or are you
> trying to generate a fresh document from nothing? Or perhaps you
> have some existing Haskell data-structure you want to convert to XML
> for external representation only?
> > For example, this is obviously the wrong way to
> > go:
> > simp2 = document $ Document (Prolog Nothing  Nothing )  $
> > Elem "root" [("attr",AttValue [Left "v\"al"])]
> > [CString False "<<<<<>>&&&"]
> > Because, it produces the obviously wrong:
> > <root attr="v"al"><<<<<>>&&&</root>
> Ah. Escaping of special characters within text is a separate
> issue. It need only be done once, just before output.
> See Text.XML.HaXml.Escape - specifically you want something like
> simp2 = document $ Document (Prolog Nothing  Nothing )  $
> xmlEscape stdXmlEscaper $
> Elem "root" [("attr",AttValue [Left "v\"al"])]
> [CString False "<<<<<>>&&&"]
> > I assume/hope that the combinators properly
> > encode/escape attribute values and CDATA,
> No, at the moment they don't. You can always do it one-shot at the
> end, as in the example above, although it would probably be better
> from a correctness point of view if the combinators did as you suggest.
> > And once I've done so, is there a way to put PIs
> > in via the combinators
> Currently, there are no combinators specifically for generating PIs
> (simply because no-one has asked for them before), but it would be
> extremely easy to add. For instance:
> mkPI :: String -> String -> CFilter
> mkPI pitarget str = \t-> [ CMisc (PI (pitarget,str)) ]
S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com
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