list a ::= Nil a;

type  ::=   EAp (type)
          | ELet (type); 

;; 

listId l1 
   = case l1 of 
        Nil n -> Nil n
     end;

allBinders e = 
   case e of
      EAp x ->   listId (allBinders x);
      ELet y ->  listId (allBinders y)
   end;