2a)
declare proc{NewWrapper ?Wrap ?Unwrap}
           Key={NewName}
        in
           fun{Wrap X}
              fun{$ K} if K==Key
                       then X
                       else raise 'use Unwrap' end
                       end
              end
           end
           fun{Unwrap C}
              try{C Key}
              catch _ then raise error(unwrap(C)) end
              end
           end
        end

declare Queue =
local
   Wrap Unwrap
   {NewWrapper Wrap Unwrap}

   fun {Empty}
      {Wrap nil}
   end

   fun {Enqueue X#Q}
      {Wrap X|{Unwrap Q}}
   end

   fun {Dequeue Q}
      case {Unwrap Q} of
         nil then {Wrap nil}
      [] [X] then {Wrap nil}
      [] (H|T) then {Wrap H|{Unwrap {Dequeue {Wrap T}}}}
      end
   end

   fun {First Q}
      case {Unwrap Q} of
         nil then raise empty(queue: first) end
      [] [X] then {Wrap X}
      [] (_|T) then {Wrap {Unwrap {First {Wrap T}}}}
      end
   end

   fun {IsEmpty Q}
      case {Unwrap Q} of
         nil then true
      [] _ then false
      end
   end

   fun {ToList Q}
      {Unwrap Q}
   end
in
   queue(empty: Empty
         enqueue: Enqueue
         dequeue: Dequeue
         first: First
         isEmpty: IsEmpty
         toList: ToList
        )
end
{Browse {Queue.isEmpty {Queue.enqueue 1#{Queue.empty}}}}
{Browse {Queue.isEmpty {Queue.empty}}}

{Browse {Queue.toList {Queue.dequeue {Queue.enqueue 4#{Queue.enqueue 3#{Queue.enqueue 2#{Queue.enqueue 1#{Queue.empty}}}}}}}}
{Browse {Queue.toList {Queue.first {Queue.enqueue 4#{Queue.enqueue 3#{Queue.enqueue 2#{Queue.enqueue 1#{Queue.empty}}}}}}}}
{Browse {Queue.first {Queue.empty}}}

2B)



declare proc{NewWrapper ?Wrap ?Unwrap}
           Key={NewName}
        in
           fun{Wrap X}
              fun{$ K} if K==Key
                       then X
                       else raise 'use Unwrap' end
                       end
              end
           end
           fun{Unwrap C}
              try{C Key}
              catch _ then raise error(unwrap(C)) end
              end
           end
        end

declare Queue =
local
   Wrap Unwrap
   {NewWrapper Wrap Unwrap}

   fun {Empty}
      ({Wrap nil}#{Wrap nil})
   end

   fun {Enqueue X # (Q1#Q2)}
      case {Unwrap Q1} of
         nil then ({Wrap [X]} # {Wrap X|{Unwrap Q2}})
      []  _ then ( Q1 # {Wrap X|{Unwrap Q2}}) %pjest Q1
      end
   end

   fun {Dequeue Q1#Q2}
      case {Unwrap Q1}#{Unwrap Q2} of
         ([X]#Q2) then ({Dequeue ({Wrap {Reverse Q2}}#{Wrap nil}) })
      [] ((_|T)#Q2) then ({Wrap T}#{Wrap Q2})
      [] _ then ({Wrap nil}#{Wrap nil})
      end
   end

   fun {IsEmpty Q1#Q2}
      case {Unwrap Q1}#{Unwrap Q2} of
         (nil#nil) then true
      [] _ then false
      end
   end

   fun {First Q1#Q2}
      case {Unwrap Q1}#Q2 of
         (nil#_) then raise empty(queue: first) end
      [] ((H|_)#_) then H
      end
   end

   fun {ToList Q1#Q2}
      {Unwrap Q1}#{Unwrap Q2}
   end


in
   queue(empty: Empty
         enqueue: Enqueue
         dequeue: Dequeue
         first: First
         isEmpty: IsEmpty
         toList: ToList
         )
end

{Browse {Queue.toList {Queue.enqueue 3#{Queue.enqueue 2#{Queue.enqueue 1#{Queue.empty}}}}}}

{Browse {Queue.isEmpty {Queue.enqueue 1#{Queue.empty}}}}
{Browse {Queue.isEmpty {Queue.empty}}}

{Browse {Queue.toList {Queue.dequeue {Queue.enqueue 4#{Queue.enqueue 2#{Queue.enqueue 1#{Queue.empty}}}}}}}
{Browse {Queue.first {Queue.enqueue 5#{Queue.enqueue 4#{Queue.enqueue 2#{Queue.enqueue 1#{Queue.empty}}}}}}}
{Browse {Queue.first {Queue.empty}}}