/*=============================================================================

     Adaptable closures

     Phoenix V0.9

     Copyright (c) 2001-2002 Joel de Guzman

     Distributed under the Boost Software License, Version 1.0. (See

     accompanying file LICENSE_1_0.txt or copy at

     http://www.boost.org/LICENSE_1_0.txt)

     URL: http://spirit.sourceforge.net/

 ==============================================================================*/

 #ifndef PHOENIX_CLOSURES_HPP

 #define PHOENIX_CLOSURES_HPP

 ///////////////////////////////////////////////////////////////////////////////

 #include "boost/lambda/core.hpp"

 ///////////////////////////////////////////////////////////////////////////////

 namespace boost {

 namespace lambda {

 ///////////////////////////////////////////////////////////////////////////////

 //

 //  Adaptable closures

 //

 //      The framework will not be complete without some form of closures

 //      support. Closures encapsulate a stack frame where local

 //      variables are created upon entering a function and destructed

 //      upon exiting. Closures provide an environment for local

 //      variables to reside. Closures can hold heterogeneous types.

 //

 //      Phoenix closures are true hardware stack based closures. At the

 //      very least, closures enable true reentrancy in lambda functions.

 //      A closure provides access to a function stack frame where local

 //      variables reside. Modeled after Pascal nested stack frames,

 //      closures can be nested just like nested functions where code in

 //      inner closures may access local variables from in-scope outer

 //      closures (accessing inner scopes from outer scopes is an error

 //      and will cause a run-time assertion failure).

 //

 //      There are three (3) interacting classes:

 //

 //      1) closure:

 //

 //      At the point of declaration, a closure does not yet create a

 //      stack frame nor instantiate any variables. A closure declaration

 //      declares the types and names[note] of the local variables. The

 //      closure class is meant to be subclassed. It is the

 //      responsibility of a closure subclass to supply the names for

 //      each of the local variable in the closure. Example:

 //

 //          struct my_closure : closure<int, string, double> {

 //

 //              member1 num;        // names the 1st (int) local variable

 //              member2 message;    // names the 2nd (string) local variable

 //              member3 real;       // names the 3rd (double) local variable

 //          };

 //

 //          my_closure clos;

 //

 //      Now that we have a closure 'clos', its local variables can be

 //      accessed lazily using the dot notation. Each qualified local

 //      variable can be used just like any primitive actor (see

 //      primitives.hpp). Examples:

 //

 //          clos.num = 30

 //          clos.message = arg1

 //          clos.real = clos.num * 1e6

 //

 //      The examples above are lazily evaluated. As usual, these

 //      expressions return composite actors that will be evaluated

 //      through a second function call invocation (see operators.hpp).

 //      Each of the members (clos.xxx) is an actor. As such, applying

 //      the operator() will reveal its identity:

 //

 //          clos.num() // will return the current value of clos.num

 //

 //      *** [note] Acknowledgement: Juan Carlos Arevalo-Baeza (JCAB)

 //      introduced and initilally implemented the closure member names

 //      that uses the dot notation.

 //

 //      2) closure_member

 //

 //      The named local variables of closure 'clos' above are actually

 //      closure members. The closure_member class is an actor and

 //      conforms to its conceptual interface. member1..memberN are

 //      predefined typedefs that correspond to each of the listed types

 //      in the closure template parameters.

 //

 //      3) closure_frame

 //

 //      When a closure member is finally evaluated, it should refer to

 //      an actual instance of the variable in the hardware stack.

 //      Without doing so, the process is not complete and the evaluated

 //      member will result to an assertion failure. Remember that the

 //      closure is just a declaration. The local variables that a

 //      closure refers to must still be instantiated.

 //

 //      The closure_frame class does the actual instantiation of the

 //      local variables and links these variables with the closure and

 //      all its members. There can be multiple instances of

 //      closure_frames typically situated in the stack inside a

 //      function. Each closure_frame instance initiates a stack frame

 //      with a new set of closure local variables. Example:

 //

 //          void foo()

 //          {

 //              closure_frame<my_closure> frame(clos);

 //              /* do something */

 //          }

 //

 //      where 'clos' is an instance of our closure 'my_closure' above.

 //      Take note that the usage above precludes locally declared

 //      classes. If my_closure is a locally declared type, we can still

 //      use its self_type as a paramater to closure_frame:

 //

 //          closure_frame<my_closure::self_type> frame(clos);

 //

 //      Upon instantiation, the closure_frame links the local variables

 //      to the closure. The previous link to another closure_frame

 //      instance created before is saved. Upon destruction, the

 //      closure_frame unlinks itself from the closure and relinks the

 //      preceding closure_frame prior to this instance.

 //

 //      The local variables in the closure 'clos' above is default

 //      constructed in the stack inside function 'foo'. Once 'foo' is

 //      exited, all of these local variables are destructed. In some

 //      cases, default construction is not desirable and we need to

 //      initialize the local closure variables with some values. This

 //      can be done by passing in the initializers in a compatible

 //      tuple. A compatible tuple is one with the same number of

 //      elements as the destination and where each element from the

 //      destination can be constructed from each corresponding element

 //      in the source. Example:

 //

 //          tuple<int, char const*, int> init(123, "Hello", 1000);

 //          closure_frame<my_closure> frame(clos, init);

 //

 //      Here now, our closure_frame's variables are initialized with

 //      int: 123, char const*: "Hello" and int: 1000.

 //

 ///////////////////////////////////////////////////////////////////////////////

 ///////////////////////////////////////////////////////////////////////////////

 //

 //  closure_frame class

 //

 ///////////////////////////////////////////////////////////////////////////////

 template <typename ClosureT>

 class closure_frame : public ClosureT::tuple_t {

 public:

     closure_frame(ClosureT& clos)

     : ClosureT::tuple_t(), save(clos.frame), frame(clos.frame)

     { clos.frame = this; }

     template <typename TupleT>

     closure_frame(ClosureT& clos, TupleT const& init)

     : ClosureT::tuple_t(init), save(clos.frame), frame(clos.frame)

     { clos.frame = this; }

     ~closure_frame()

     { frame = save; }

 private:

     closure_frame(closure_frame const&);            // no copy

     closure_frame& operator=(closure_frame const&); // no assign

     closure_frame* save;

     closure_frame*& frame;

 };

 ///////////////////////////////////////////////////////////////////////////////

 //

 //  closure_member class

 //

 ///////////////////////////////////////////////////////////////////////////////

 template <int N, typename ClosureT>

 class closure_member {

 public:

     typedef typename ClosureT::tuple_t tuple_t;

     closure_member()

     : frame(ClosureT::closure_frame_ref()) {}

     template <typename TupleT>

     struct sig {

         typedef typename detail::tuple_element_as_reference<

             N, typename ClosureT::tuple_t

         >::type type;

     };

     template <class Ret, class A, class B, class C>

     //    typename detail::tuple_element_as_reference

     //        <N, typename ClosureT::tuple_t>::type

     Ret

     call(A&, B&, C&) const

     {

         assert(frame);

         return boost::tuples::get<N>(*frame);

     }

 private:

     typename ClosureT::closure_frame_t*& frame;

 };

 ///////////////////////////////////////////////////////////////////////////////

 //

 //  closure class

 //

 ///////////////////////////////////////////////////////////////////////////////

 template <

     typename T0 = null_type,

     typename T1 = null_type,

     typename T2 = null_type,

     typename T3 = null_type,

     typename T4 = null_type

 >

 class closure {

 public:

     typedef tuple<T0, T1, T2, T3, T4> tuple_t;

     typedef closure<T0, T1, T2, T3, T4> self_t;

     typedef closure_frame<self_t> closure_frame_t;

                             closure()

                             : frame(0)      { closure_frame_ref(&frame); }

     closure_frame_t&        context()       { assert(frame); return frame; }

     closure_frame_t const&  context() const { assert(frame); return frame; }

     typedef lambda_functor<closure_member<0, self_t> > member1;

     typedef lambda_functor<closure_member<1, self_t> > member2;

     typedef lambda_functor<closure_member<2, self_t> > member3;

     typedef lambda_functor<closure_member<3, self_t> > member4;

     typedef lambda_functor<closure_member<4, self_t> > member5;

 private:

     closure(closure const&);            // no copy

     closure& operator=(closure const&); // no assign

     template <int N, typename ClosureT>

     friend struct closure_member;

     template <typename ClosureT>

     friend class closure_frame;

     static closure_frame_t*&

     closure_frame_ref(closure_frame_t** frame_ = 0)

     {

         static closure_frame_t** frame = 0;

         if (frame_ != 0)

             frame = frame_;

         return *frame;

     }

     closure_frame_t* frame;

 };

 }}

    //  namespace 

 #endif