ADTs are algebraic data types. They are quite simple, and have nothing to do with the IO type which haskell uses to constrain side effects. An ADT is just a t

ADTs are algebraic data types. They are quite simple, and have nothing to do with the IO type which haskell uses to constrain side effects. An ADT is just a type made up of ORs and ANDs: data Bool = False | True data Tree a = Leaf a | Branch (Tree a) (Tree a)