[Haskell] Re: understanding HaXml and escaping

[S. Alexander Jacobson]

Followup:

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
same thing...

-Alex-


http://www.thaiopensource.com/relaxng/derivative.html

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)) ]
>
> Regards,
>     Malcolm
>

______________________________________________________________
S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com