[Haskell-cafe] Re: XML transformation difficulties

Greg Fitzgerald garious at gmail.com
Fri Jul 14 20:54:32 EDT 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 [] "-" >>>
   (putStrLn . show) status
   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':
String -> a

Are Arrows the wrong tool for this job?


On 7/14/06, Greg Fitzgerald <garious at gmail.com> 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
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