[Haskell-cafe] understanding HXT's insertChildrenAfter

20 Jul 2009

      Playing on HXT 8.3.0 via cabal on GHC 6.10.2.

While there are plenty of useful examples of extract
data from XML, applying the appropriate API to transform
and/or merging still baffle me. In this case, it
is the insertChildrenAfter,

let's try it with the following example: given 2 files

--- update.xml
<?xml version="1.0" encoding="UTF-8"?>
<update>
     <hot>sky is now orange</hot>
     <hot>fish is fresh</hot>
     <hot>violets are blue</hot>
</update>

--- master.xml
<?xml version="1.0" encoding="UTF-8"?>
<news>
     <page1>
     <hot>sky is blue</hot>
     <hot>roses are red</hot>
     </page1>
     <page2>
     <story>game shipped on sunday</story>
     </page2>
</news>

with the intention of augment the master list with the new items:

import Text.XML.HXT.Arrow
import qualified Text.XML.HXT.DOM as DOM

getMaster =
         readDocument [(a_validate,v_0)] "master.xml"
     >>> removeDocWhiteSpace

getUpdate =
         readDocument [(a_validate,v_0)] "update.xml"
     >>> removeDocWhiteSpace

selectUpdateArea =
         getChildren >>> hasName "news"
     >>> getChildren >>> hasName "page1"

updateContent =
     insertChildrenAfter
         (selectUpdateArea)
         (getUpdate >>> getChildren >>> getChildren)

main =
     do runX (
             getMaster
         >>> updateContent
         >>> putXmlTree "-"
             )

instead the following tree is produced:

---XTag "/"
    |
    +---XTag "hot"
    |   |
    |   +---XText "sky is red"
    |
    +---XTag "hot"
    |   |
    |   +---XText "fish is fresh"
    |
    +---XTag "hot"
    |   |
    |   +---XText "violets are blue"
    |
    +---XTag "news"
        |
        +---XTag "page1"
        |   |
        |   +---XTag "hot"
        |   |   |
        |   |   +---XText "sky is blue"
        |   |
        |   +---XTag "hot"
        |       |
        |       +---XText "roses are red"
        |
        +---XTag "page2"
            |
            +---XTag "story"
                |
                +---XText "game shipped "

Can someone give some examples of how insertChildrenAfter
works?  How about also some general guidelines when comes
to merging/grafting XML documents.

Jake