[Haskell-beginners] Constructor classes and type classes.

[PATRICK BROWNE]

{-
I am trying to understand constructor classes and their relationship with
ordinary type classes.
I wrote the code below to help me understand the distinction. The code is
only for explanatory purposes, set operations use a tuple syntax.

I use the naming convention of 'typeVar', 'typeCons', and 'dataCons' for
type variables, type constructors, and data constructors respectively.
Question1:
Is my naming convention correct?
I am particularly concerned about SetClass3 where the super class seems to
use a type constructor but the subclass seems to use the same term as a
data constructor.

Q2:
In this case constructor classes and type classes seem to provide similar
functionality.
In general what situation are each best suited?
-}

import Data.List
data SetType typeVar = SetType [typeVar] deriving Show


class SetClass1 typeCons where
  member1 ::   Eq typeVar  =>  (typeVar, typeCons typeVar)  -> Bool
  intersect1 ::  (Eq typeVar,Show typeVar) =>  (typeCons typeVar, typeCons
typeVar) -> typeCons typeVar


class  SetClass2 dataCons typeVar where
  member2 ::  (typeVar, (dataCons typeVar))  -> Bool
  intersect2 :: (dataCons typeVar, dataCons typeVar) -> dataCons typeVar


class SetClass1 typeCons => SetClass3  typeCons dataVariable where
 union3 ::  (Eq dataVariable,Show dataVariable) =>  (typeCons dataVariable,
typeCons dataVariable) -> typeCons dataVariable

instance SetClass1 SetType where
 member1 (x ,(SetType y)) = elem  x y
 intersect1 ((SetType x),(SetType y)) = SetType (intersect x y)

instance SetClass2 SetType Int where
 member2 (x ,SetType y) =   elem  x y
 intersect2 (SetType x,SetType y) = SetType (intersect x y)

instance SetClass3 SetType Int where
 union3 (SetType x,SetType y) = SetType (union x y)


test1a = member1 (1, (SetType [1,2]))
test1b = intersect1 ((SetType [1,3,4]),(SetType [1,2]))
test2a = member2 (1, (SetType [1::Int]))
test2b = intersect2 ((SetType [1::Int]), (SetType [(1::Int)]))
test3a = union3 ((SetType [1::Int,2::Int,3::Int]),(SetType [4::Int,5::Int]))

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