[Haskell-cafe] Re: XML transformation difficulties

15 Jul 2006

      Adding some code to go along with my last post:

main = do
   [tree]         <- runX (readDocument [(a_validate, "0")] "text.xml")
   [fooDoc] <- runX (constA tree >>> processChildren isFoo)
   [expanded]     <- runX (constA tree >>> processTopDown (expandNode fooDoc
`when` hasName "bar"))
   [status]       <- runX (constA expanded >>> writeDocument [] "-" >>>
getErrStatus)
   (putStrLn . show) status
where
   expandNode :: (ArrowXml a) => XmlTree -> a XmlTree XmlTree
   expandNode :: (ArrowXml a) => XmlTree -> a XmlTree XmlTree
   expandNode foos = this    -- what here???
   isFoo = deep (hasName "foo")

The issue is that in 'expandNode', I have an XmlTree (foos) and an arrow
whose input is the node to be replaced (also an XmlTree), but I need a
String and an arrow whose input is the XmlTree (foos):

expandNode' :: (ArrowXml a) => String -> a XmlTree XmlTree
expandNode' name = processChildren (hasAttrValue "name" name)

Somewhat related, if the output of an arrow is a string, can I get access to
that string without using 'runX':
getAttrValuehttp://www.fh-wedel.de/%7Esi/HXmlToolbox/hdoc_arrow/Text-XML-HXT-Arrow-XmlAr...::
String -> a
XmlTreehttp://www.fh-wedel.de/%7Esi/HXmlToolbox/hdoc_arrow/Text-XML-HXT-DOM-TypeDef...String

Are Arrows the wrong tool for this job?

Thanks,
Greg

On 7/14/06, Greg Fitzgerald  wrote:
...
I'm trying to think of a way to translate this input, to the output below:
Input:
<test>
   <foo name="a">
       <wahoo>A</wahoo>
    </foo>
   <foo name="b">
      <wahoo>B</wahoo>
   </foo>
   <foo name="c">
       <wahoo>C</wahoo>
    </foo>
   <group>
      <bar ref="b"/>
      <bar ref="a"/>
   </group>
</test>
Output:
<test>
   <group>
       <wahoo>B</wahoo>
       <wahoo>A</wahoo>
   </group>
</test>
That is, anywhere there is a 'bar', replace it with the contents of the
'foo' it references.  I'm having a difficult time representing this with
HXT's Arrow API because the value of the 'ref' attribute is the output of an
arrow, but I need it to be just a plain string so that I could use it as an
input parameter to the 'hasAttrValue' function.  A similar problem, using
'processTopDown', once I traverse to a 'bar' node, I need to then traverse
the root again to find the 'foo', but I'm in the context of the 'bar' node,
not the root.
...
My ears are open to solutions with HaXML or Scrap Your XML-plate, or
anything else.
...
Thanks,
Greg