[Haskell-beginners] XmlPickler on ADT

[Tim Perry]

Hi everyone,

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
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