[Haskell-cafe] Data Type Inheritance ala OO - Inheritence -- howto best in Haskell ?

kaffeepause73 kaffeepause73 at yahoo.de
Thu Jun 16 14:08:33 CEST 2011

Dear all, 

I'm created a timeSignal datatype as container around a "Vector Double" data
type (see simple code below) and subsequently started to instanciate Num &
Eq to be able to perform operations on it. Additionally I want store ifno
like an index, time information and eventually an inheritence log (the log
is not yet in there).  

As I will in the end need up to 10 different datatypes, however using
slightly different content (time signal, single value, distribution, ...) I
ask myself, how I could define a super data-type with sub-data-types to
inherit, but then also overload certain functions (like u would do in OO). 

What is best way in haskell to achieve this ? (I'm unsure wether haskell
classes are what I'm looking for)

Cheers Phil

########## Code below

import qualified Data.Vector.Unboxed as V

data TimeSig = TimeSig Int Double (V.Vector Double) -- signal Index timeStep

getVect :: TimeSig -> (V.Vector Double) 
getVect (TimeSig idx dt vect)= vect

getIdx :: TimeSig -> Int
getIdx (TimeSig idx dt vect) = idx

getdt :: TimeSig -> Double
getdt (TimeSig idx dt vect) = dt

pzipWith :: (Double -> Double -> Double) -> TimeSig -> TimeSig -> TimeSig
pzipWith f p1 p2 =  TimeSig idx dt vect
                vect = V.zipWith f (getVect p1)  (getVect p2) 
                idx = getIdx p1
                dt = getdt p1
pmap :: (Double -> Double) -> TimeSig -> TimeSig
pmap f p = TimeSig (getIdx p) (getdt p) (V.map f (getVect p))

instance Num TimeSig 
      (+) p1 p2 = pzipWith (+) p1 p2
      (-) p1 p2 = pzipWith (-) p1 p2
      negate p1 = pmap negate p1
      abs p1 = pmap abs p1
      (*) p1 p2 = pzipWith (*) p1 p2

instance Eq TimeSig where
            (==) p1 p2 = (==) (getVect p1) (getVect p2)

instance Show TimeSig where  
  show (TimeSig idx dt vect) = "TimeSignal Nr: " ++ show idx ++ "  dt: " ++
show dt ++ " val:" ++ show vect    
main = do 

        let p = TimeSig 5 0.1 (V.fromList [0..10::Double])
        putStrLn (show p)
        putStrLn (show (p+p))

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