[Haskell-cafe] Elementary HaXml question

Koen.Roelandt at mineco.fgov.be Koen.Roelandt at mineco.fgov.be
Thu Feb 9 10:13:28 EST 2006

> I'm new to Haskell and HaXml and I'm playing around with the latter to 
> clean some (well-formed) 'legacy' html. This works fine except for the 
> following cases. Some of the elements to be cleaned are:
>         <font size="4"><i>Hello World</i></font>
>         <i><font size="4">Hello World</font></i>
> This should become:
>         <h1 class="subtitle">Hello World</h1>
> From what I could gather from the documentation, it should be something 
> like:
> foldXml         (txt ?> keep :>
>                 (attrval("size",AttValue[Left "4"]) `o` tag "font")
>                    /> tag "i" ?> replaceTag "h1"  :> children)

Is the bracketing correct?  I can't remember the precedence of the
operators offhand, but perhaps it should be 

  foldXml         (txt ?> keep :>
                  (((attrval("size",AttValue[Left "4"]) `o` tag "font")
                      /> tag "i") ?> replaceTag "h1"  :> children))

Yes, the braketing is correct since the following code:

        foldXml     (txt ?> keep :>
                        fontSize4 /> tag "em" ?> mkSubtitle             :>

        fontSize4 = (attrval("size",AttValue[Left "4"]) `o` tag "font")
        mkSubtitle = mkElemAttr "h1" [("class", ("subtitle"!))]

now transforms
        <font size="4"><em>Hello World</em></font>


        <h1 class="subtitle"><em><Hello World</em></font>

Which I'm satisfied with (hurray!). The <em> appears because I 'keep' it 
higher in the original switch, the example above is just an extract for 
brevity's sake. 
I still have a problem with the other example:
        <em><font size="4">Hello World</font></em>

I _think_ the line in the .hs file should be:

        tag "em" /> fontSize4 ?> mkSubtitle             :>

Which doesn't work, and I don't know why. If the first example works, 
shouldn't the second, too? I also tried
        tag "em" /> font ?> mkSubtitle          :> 

Which doesn't work either. I transformed it into 

        tag "font" `o` children `o` tag "em" ?> mkSubtitle :>

without avail. Again, any ideas are welcome. (btw: I like HaXml, Malcolm, 
nice work!)


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