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

    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