PPP Exercises: Emulating interfaces, modules and imports

Exercise:

1. Write a function 'createIntStack' that takes any implementation 'funStack' of 'FunStack' and returns an implementation of 'IntStack' using 'funStack'.
   

   Let FunStack =
      Tuple
         T (E <:Ok) <:Ok
         new(E <:Ok) :T(E)
         empty(E <:Ok  stack :T(E)) :Bool
         push(E <:Ok  element :E  stack :T(E)) :T(E)
         pop(E <:Ok  stack :T(E)) :T(E)
         top(E <:Ok  stack :T(E)) :E
      end;
   
   Let IntStack =
      Tuple
         T <:Ok
         new() :T
         empty(stack :T) :Bool
         push(element :Int  stack :T) :T
         pop(stack :T) :T
         top(stack :T) :Int
      end;
   

   Test it with
   

   import list;
   
   let listStack :FunStack =
      tuple
         Let T(E <:Ok) <:Ok = list.T(E)
         let new(E <:Ok) :T(E) = list.new( :E)
         let empty(E <:Ok  stack :T(E)) :Bool =
             list.empty(stack)
         let push(E <:Ok  element :E  stack :T(E)) :T(E) =
             list.cons(element stack)
         let pop(E <:Ok  stack :T(E)) :T(E) = 
             list.tail(stack)
         let top(E <:Ok  stack :T(E)) :E = 
             list.head(stack)
      end;
   
   let intStack = createIntStack(listStack);
   

2. Write a curried function 'createGenStack' that takes any implementation 'list' of 'List' and returns a polymorphic function like 'genStack' in the exercise Type operators and genericity that implements a stack using 'list'.
   

   Let GenStack(E <:Ok) <:Ok =
      Tuple
         T <:Ok
         new() :T
         empty(stack :T) :Bool
         push(element :E  stack :T) :T
         pop(stack :T) :T
         top(stack :T) :E
      end;
   

3. Now think about the following questions, taking into account the previous solution:
   • Which TL constructs may realize (or emulate) the concepts of interfaces, modules, and imports without using the keywords "interface", "module", "import", "export"?
   • Which correspondences are there?
   • What happens when a module is linked, e.g. 'import print :Print'?