Scala algebraic data types

The link is an article that discusses how to implement algebraic data types in Scala. In short, Haskell defines ADTs like this:

data Bool = False | True

In Scala you implement ADTs like this:

sealed abstract class Bool
case object True extends Bool
case object False extends Bool

which lets you do things like this:

val not : Bool => Bool  =  ( b : Bool ) => if( b eq True ) False else True
val and : ( Bool, Bool ) => Bool  =  ( a :Bool, b: Bool ) => if( a eq False ) False else b
val or : ( Bool, Bool ) => Bool  =  ( a :Bool, b: Bool ) => if( a eq True ) True else b
println(  and( or( True, not( True ) ), not( False ) ) )

The article shows another example based on seasons of the year.