I'm trying to learn to write XmlPicklers. I've been trying to follow the tutorial on the HaskelWiki, but it doesn't quite cover an issue I've run into.

http://www.haskell.org/haskellwiki/HXT/Conversion_of_Haskell_data_from/to_XML

I have a ADTs like so:

data Plant = Plant 

    { renewables :: [Renewable]

    , rewewableMonthly :: [RenewableMonthly]

    , waterHeating :: [WaterHeating]

    , hvac :: [HVAC]

    } deriving (Read, Show, Eq)


data Renewable = Renewable 

    { dcRating :: Double -- kW

    , annualTDV :: Double -- CA Energy Comm. TDV

    } deriving (Read, Show, Eq)


data RenewableMonthly = RenewableMonthly

    { month :: Int

    , cost :: Double

    , demand :: Double

    , energy :: Double

    } deriving (Read, Show, Eq)


data WaterHeating = WaterHeating 

    { whName :: String                      -- name for reference purposes.

    , whQuantity :: Int      

...

data HVAC = HVAC 

    { slaStatus :: String                  -- Specific leakage area construction type.

    , newCFM50 :: Double                   -- New building leakage in cubic feet per minute.

    , existCFM50 :: Double

I want to use an XmlPickler to read and write this. The XML looks like this:

<Plant>

  <Renewables DCRating="8.4" AnnualTDV="0" />

  <RenewableMonthly Month="1" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="2" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="3" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="4" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="5" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="6" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="7" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="8" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="9" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="10" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="11" Cost="0" Demand="0" Energy="0" />

  <RenewableMonthly Month="12" Cost="0" Demand="0" Energy="0" />

  <WaterHeating Name="Daikin Altherma HP" Quantity="1" ConstructionStatus="New" EnergyFactor="2.344" SolarFraction="0" ....
  <HVAC SLAStatus="New" NewCFM50="0" ExistCFM50="0" NewSLA="4.9000000953674316" ExistSLA="4.9" DuctStatus="New" ....

    <Zone 
...

Running my code I get an error:

-- (1) readDocument: start processing document "1101_11-001 Walsh.xml" -- (1) getXmlContents: content read and decoded for "file:///fairoaks1/all_proj/1101%20PG&E%20CAHP%2011-12/CRM/EProDataExtractPlanning/XML%20samples/1101_11-001%20Walsh.xml" -- (1) getXmlContents' -- (1) readDocument: "1101_11-001 Walsh.xml" (mime type: "text/xml" ) will be processed -- (1) readDocument: "1101_11-001 Walsh.xml" processed

fatal error: document unpickling failed
xpCheckEmptyContents: unprocessed XML content detected context: element "Plant" contents:

Is it possible to write an XmlPickler for this? Do I need to make Renewable, RenewableMonthly, WaterHeating, and HVAC all the same type with 4 constructors and use xpAlt? Ideas?

Thanks,

Tim