Haskell inheritance, data, constructors

Question

So I want to define multiple data classes for my Asteroids game/assignment:

data One = One {oneVelocity :: Velocity, onePosition :: Position, (((other proper         


        

Answer 1

There is no inheritance in Haskell (at least, not the kind you associate with object-oriented classes). You just want composition of data types.

data Particle = Particle { velocity :: Velocity
                         , position :: Position 
                         }

-- Exercise for the reader: research the GHC extension that
-- allows all three of these types to use the same name `p`
-- for the particle field.
data One = One { p1 :: Particle
               , ... }
data Two = Two { p2 :: Particle
               , ... }
data Three = Three { p3 :: Particle
                   , ... }

Or, you can define a type that encapsulates the other properties, and let those be added to different kinds of Particles.

data Properties = One { ... } 
                | Two { ... }
                | Three { ... }

data Particle = Particle { velocity :: Velocity
                         , position :: Position
                         , properties :: Properties
                         } 

(Or see @leftaroundabout's answer, which is a nicer way of handling this approach.)

Answer 2

You should probably use just a single data type for all of these, but parameterised on the specific details:

data MovingObj s = MovingObj
        { velocity :: Velocity
        , position :: Position
        , specifics :: s }

Then you can create e.g. asteroid :: MovingObj AsteroidSpecifics, but you can also write functions that work with any such moving object like

advance :: TimeStep -> MovingObj s -> MovingObj s
advance h (MovingObj v p s) = MovingObj v (p .+^ h*^v) s