Comparing type system of Haskell with C#, looking for analogues

Question

I\'m pretty new a Haskell programming. I\'m trying to deal with its classes, data, instances and newtype. Here is what I\'ve understood:

data NewData = Const         


        

Answer 1

To make sum types like

data NewData = Constr1 Int Int | Constr2 String Float

I usually do the following in c#

interface INewDataVisitor {
    R Constr1(Constr1 constructor);
    R Constr2(Constr2 constructor);
}

interface INewData {
    R Accept(INewDataVisitor visitor);
}

class Constr1 : INewData {
    private readonly int _a;
    private readonly int _b;
    Constr1(int a, int b) {
         _a = a;
         _b = b;
    }
    int a {get {return _a;} }
    int b {get {return _b;} }

    R Accept(INewDataVisitor visitor) {
        return visitor.Constr1(this);
    }
}

class Constr2 : INewData {
    private readonly string _a;
    private readonly float _b;
    Constr2(string a, float b) {
         _a = a;
         _b = b;
    }
    string a {get {return _a;} }
    float b {get {return _b;} }

    R Accept(INewDataVisitor visitor) {
        return visitor.Constr2(this);
    }
}

This isn't quite the same in terms of type safety because an INewData can also be null, might never call a method on the visitor and just return default(R), might call the visitor multiple times, or any other silly thing.

A c# interface like

interface SomeInterface {
  public bool method1(List someParam);
 }

Is really more like the following in Haskell:

data SomeInterface t = SomeInterface {
    method1 :: [t] -> bool
}