src/src/Kernel/Containers/promise.hpp

   1
   2 /******************************************************************************
   3 * MODULE     : promise.hpp
   4 * DESCRIPTION: promises
   5 * COPYRIGHT  : (C) 2007  Joris van der Hoeven
   6 *******************************************************************************
   7 * This software falls under the GNU general public license version 3 or later.
   8 * It comes WITHOUT ANY WARRANTY WHATSOEVER. For details, see the file LICENSE
   9 * in the root directory or <http://www.gnu.org/licenses/gpl-3.0.html>.
  10 ******************************************************************************/
  11
  12 #ifndef PROMISE_H
  13 #define PROMISE_H
  14 #include "tree.hpp"
  15
  16 class tree;
  17 template<class T> class promise_rep;
  18 template<class T> class promise;
  19 template<class T> tm_ostream& operator << (tm_ostream& out, promise<T> cmd);
  20 template<class T> bool is_nil (promise<T> l);
  21
  22 template<class T>
  23 class promise_rep: public abstract_struct {
  24 public:
  25   inline promise_rep () {}
  26   inline virtual ~promise_rep () {}
  27   inline virtual tm_ostream& print (tm_ostream& out);
  28   virtual T eval () = 0;
  29 };
  30
  31 template<class T>
  32 class promise {
  33 public:
  34 ABSTRACT_NULL_TEMPLATE(promise,T);
  35   inline T operator () ();
  36   friend tm_ostream& operator << LESSGTR (tm_ostream& out, promise<T> cmd);
  37 };
  38 ABSTRACT_NULL_TEMPLATE_CODE(promise,class,T);
  39
  40 #define TMPL template<class T>
  41 TMPL inline tm_ostream& promise_rep<T>::print (tm_ostream& out) {
  42   return out << "promise"; }
  43 TMPL inline T promise<T>::operator () () {
  44   return rep->eval (); }
  45 TMPL inline bool operator == (promise<T> mw1, promise<T> mw2) {
  46   return mw1.rep == mw2.rep; }
  47 TMPL inline tm_ostream& operator << (tm_ostream& out, promise<T> cmd) {
  48   if (is_nil (cmd)) return out << "(null)"; else return cmd->print(out); }
  49 #undef TMPL
  50
  51 #endif // defined PROMISE_H