[Haskell] Re: understanding HaXml and escaping
Malcolm.Wallace at cs.york.ac.uk
Thu Oct 28 11:46:40 EDT 2004
"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
> 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)) ]
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