Private method access instance variable in Haskell

In Haskell, we can access an instance variable inside a private method of a class by passing the instance variable as an argument to the private method.

Consider the following example:

class MyClass a where
  myMethod :: a -> Int
  
  privateMethod :: a -> Int -> Int
  privateMethod obj x = x + myVar
    where myVar = myMethod obj
  
newtype MyType = MyType { myInt :: Int }
instance MyClass MyType where

  myMethod obj = myInt obj

In this example, MyClass is a class with two methods: myMethod and privateMethod. myMethod takes an instance of the class as an argument and returns an Int. privateMethod takes an instance of the class and an Int as arguments, and returns an Int that is the sum of the input Int and an instance variable myVar.

We define an instance MyType of MyClass that has a single instance variable myInt.

We can now use privateMethod to access myVar which is initialized to the value returned by myMethod. For example:

main :: IO ()
main = do
  let obj = MyType 10
  let result = privateMethod obj 5
  print(result) -- outputs 15

Here, we create an instance obj of MyType with myInt equal to 10. We call privateMethod with obj and 5 as arguments, and the result is 15 which is the sum of myInt and 5.