Hi,
The code [1] below compiles and runs with GHCi version 7.0.4.
I get one warning and an error message with GHCi version 7.6.1.

1)  Warning -XDatatypeContexts is deprecated. Unless there are propagation effects, this is well explained.

2) foom-1.hs:65:15:
    `quality' is applied to too many type arguments
    In the type `quality entity -> agent -> IO Observation'
    In the class declaration for `OBSERVERS'
Failed, modules loaded: none.

I do not understand the error message from 7.6.1. 
I am not too interested actually fixing it, I just want to understand it.

Thanks,
Pat

[1]The code is from: A Functional Ontology of Observation and Measurement Werner Kuhn

{-# LANGUAGE DatatypeContexts,MultiParamTypeClasses  #-}
module ENDURANTS where
import System.Time
type Id = String
type Position = Integer
type Moisture = Float
type Celsius = String
type Heat =  Float


data WeatherStation = WeatherStation Id Position deriving Show
data Value = Boolean Bool | Count Int | Measure Float | Category String deriving Show
data Observation = Observation Value Position ClockTime deriving Show
data AmountOfAir = AmountOfAir Heat Moisture  deriving Show

muensterAir = AmountOfAir  10.0 70.0

class ENDURANTS endurant where
 
-- must add instances all down the hierarchy for each instance
instance ENDURANTS WeatherStation where
instance ENDURANTS AmountOfAir where

class ENDURANTS physicalEndurant => PHYSICAL_ENDURANTS physicalEndurant where

instance PHYSICAL_ENDURANTS WeatherStation where
instance PHYSICAL_ENDURANTS AmountOfAir where

class PHYSICAL_ENDURANTS  amountOfMatter => AMOUNTS_OF_MATTER amountOfMatter where

instance AMOUNTS_OF_MATTER   WeatherStation where

class PHYSICAL_ENDURANTS physicalObject => PHYSICAL_OBJECTS physicalObject where

instance PHYSICAL_OBJECTS WeatherStation where

class PHYSICAL_OBJECTS apo => APOS apo where
 getPosition :: apo -> Position


instance APOS WeatherStation where
 getPosition (WeatherStation iD pos) = pos + 10
 
-- a data type declaration and data type constructor.
data PHYSICAL_ENDURANTS physicalEndurant => Temperature physicalEndurant = Temperature physicalEndurant deriving Show

-- Qualities the class of all quality types (= properties) is a constructor class
-- its constructors can be applied to endurants, perdurants, qualities or abstracts
class QUALITIES quality entity

instance QUALITIES Temperature AmountOfAir

class (APOS agent, QUALITIES quality entity) => OBSERVERS agent quality entity where
   observe :: quality entity -> agent -> IO Observation
   express :: quality entity -> agent -> Value
   observe quale agent = do
                       clockTime <- getClockTime
                       return (Observation (express quale agent)
                                  (getPosition agent) clockTime)

instance OBSERVERS WeatherStation Temperature AmountOfAir where
  express (Temperature (AmountOfAir heat moisture)) weatherStation =  Measure heat

{-
-- running the following
express (Temperature (AmountOfAir 40 20)) (WeatherStation "rr" 6)
-- Gives
Measure 40.0 Measure 40.0
-- We can get the type: Value
:t express (Temperature (AmountOfAir 40 20)) (WeatherStation "rr" 6)

-}