[Haskell-cafe] hxt pickling question

[briand at aracnet.com]

On Thu, 24 Jan 2013 17:05:15 +0100
Erik Hesselink <hesselink at gmail.com> wrote:

> There's showPickled [0] and unpickleDoc [1], maybe those help?
> 

Thank you , they help a lot :-)  I was stuck looking in Text.XML.HXT.Arrow.Pickle for the answer and got lost trying to decipher IOStateArrow s a XmlTree and runX.

It's odd that there does not seem to be a way to use the example so that a tree can be written directly to a file.

  xpickleDocument :: PU a -> SysConfigList -> String -> IOStateArrow s a XmlTreeSource

  store an arbitray value in a persistent XML document 

Except there doesn't seem to be a way to pass that value into xpickleDocument without reading a document first using xunpickleDocument.

Thanks again.

Brian

> Erik
> 
> [0] http://hackage.haskell.org/packages/archive/hxt/latest/doc/html/Text-XML-HXT-Arrow-Pickle-Xml.html#v:showPickled
> [1] http://hackage.haskell.org/packages/archive/hxt/latest/doc/html/Text-XML-HXT-Arrow-Pickle-Xml.html#v:unpickleDoc
> 
> On Thu, Jan 24, 2013 at 4:40 PM,  <briand at aracnet.com> wrote:
> > Hi,
> >
> > Trying to understand how to write a document using a pickler but I can't make sense of the types.
> >
> > From the example:
> >
> >      runX ( xunpickleDocument xpSeason
> >                                [ withValidate no
> >                                , withTrace 1
> >                                , withRemoveWS yes
> >                                , withPreserveComment no
> >                                ] "simple2.xml"
> >              >>>
> >              processSeason
> >              >>>
> >              xpickleDocument   xpSeason
> >                                [ withIndent yes
> >                                ] "new-simple2.xml"
> >            )
> >
> > So all I want to do is pickle a value directly instead of reading the value from a document.  I expected to do something like:
> >
> > runX (someHXTPicklingFunction myValue
> >       >>>
> >       xpickleDocument ...)
> >
> >
> > but I can't seem to figure out what someHXTPicklingFunction should be, it's certainly nothing obvious like pickleDoc, because that generates the wrong value.
> >
> > Seems like I probably have a much more fundamental problem in that I really don't understand how the arrow part of this little example really works, but I was kind of hoping that doing something "simple" like this might shed some light on that.  And then was immediately stuck in type hell.
> >
> >
> > Thanks,
> >
> > Brian
> >
> >
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