Chris@16: /*=============================================================================
Chris@16:     Adaptable closures
Chris@16: 
Chris@16:     Phoenix V0.9
Chris@16:     Copyright (c) 2001-2002 Joel de Guzman
Chris@16: 
Chris@16:     Distributed under the Boost Software License, Version 1.0. (See
Chris@16:     accompanying file LICENSE_1_0.txt or copy at
Chris@16:     http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16:     URL: http://spirit.sourceforge.net/
Chris@16: 
Chris@16: ==============================================================================*/
Chris@16: #ifndef PHOENIX_CLOSURES_HPP
Chris@16: #define PHOENIX_CLOSURES_HPP
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: #include "boost/lambda/core.hpp"
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: namespace boost {
Chris@16: namespace lambda {
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: //
Chris@16: //  Adaptable closures
Chris@16: //
Chris@16: //      The framework will not be complete without some form of closures
Chris@16: //      support. Closures encapsulate a stack frame where local
Chris@16: //      variables are created upon entering a function and destructed
Chris@16: //      upon exiting. Closures provide an environment for local
Chris@16: //      variables to reside. Closures can hold heterogeneous types.
Chris@16: //
Chris@16: //      Phoenix closures are true hardware stack based closures. At the
Chris@16: //      very least, closures enable true reentrancy in lambda functions.
Chris@16: //      A closure provides access to a function stack frame where local
Chris@16: //      variables reside. Modeled after Pascal nested stack frames,
Chris@16: //      closures can be nested just like nested functions where code in
Chris@16: //      inner closures may access local variables from in-scope outer
Chris@16: //      closures (accessing inner scopes from outer scopes is an error
Chris@16: //      and will cause a run-time assertion failure).
Chris@16: //
Chris@16: //      There are three (3) interacting classes:
Chris@16: //
Chris@16: //      1) closure:
Chris@16: //
Chris@16: //      At the point of declaration, a closure does not yet create a
Chris@16: //      stack frame nor instantiate any variables. A closure declaration
Chris@16: //      declares the types and names[note] of the local variables. The
Chris@16: //      closure class is meant to be subclassed. It is the
Chris@16: //      responsibility of a closure subclass to supply the names for
Chris@16: //      each of the local variable in the closure. Example:
Chris@16: //
Chris@16: //          struct my_closure : closure<int, string, double> {
Chris@16: //
Chris@16: //              member1 num;        // names the 1st (int) local variable
Chris@16: //              member2 message;    // names the 2nd (string) local variable
Chris@16: //              member3 real;       // names the 3rd (double) local variable
Chris@16: //          };
Chris@16: //
Chris@16: //          my_closure clos;
Chris@16: //
Chris@16: //      Now that we have a closure 'clos', its local variables can be
Chris@16: //      accessed lazily using the dot notation. Each qualified local
Chris@16: //      variable can be used just like any primitive actor (see
Chris@16: //      primitives.hpp). Examples:
Chris@16: //
Chris@16: //          clos.num = 30
Chris@16: //          clos.message = arg1
Chris@16: //          clos.real = clos.num * 1e6
Chris@16: //
Chris@16: //      The examples above are lazily evaluated. As usual, these
Chris@16: //      expressions return composite actors that will be evaluated
Chris@16: //      through a second function call invocation (see operators.hpp).
Chris@16: //      Each of the members (clos.xxx) is an actor. As such, applying
Chris@16: //      the operator() will reveal its identity:
Chris@16: //
Chris@16: //          clos.num() // will return the current value of clos.num
Chris@16: //
Chris@16: //      *** [note] Acknowledgement: Juan Carlos Arevalo-Baeza (JCAB)
Chris@16: //      introduced and initilally implemented the closure member names
Chris@16: //      that uses the dot notation.
Chris@16: //
Chris@16: //      2) closure_member
Chris@16: //
Chris@16: //      The named local variables of closure 'clos' above are actually
Chris@16: //      closure members. The closure_member class is an actor and
Chris@16: //      conforms to its conceptual interface. member1..memberN are
Chris@16: //      predefined typedefs that correspond to each of the listed types
Chris@16: //      in the closure template parameters.
Chris@16: //
Chris@16: //      3) closure_frame
Chris@16: //
Chris@16: //      When a closure member is finally evaluated, it should refer to
Chris@16: //      an actual instance of the variable in the hardware stack.
Chris@16: //      Without doing so, the process is not complete and the evaluated
Chris@16: //      member will result to an assertion failure. Remember that the
Chris@16: //      closure is just a declaration. The local variables that a
Chris@16: //      closure refers to must still be instantiated.
Chris@16: //
Chris@16: //      The closure_frame class does the actual instantiation of the
Chris@16: //      local variables and links these variables with the closure and
Chris@16: //      all its members. There can be multiple instances of
Chris@16: //      closure_frames typically situated in the stack inside a
Chris@16: //      function. Each closure_frame instance initiates a stack frame
Chris@16: //      with a new set of closure local variables. Example:
Chris@16: //
Chris@16: //          void foo()
Chris@16: //          {
Chris@16: //              closure_frame<my_closure> frame(clos);
Chris@16: //              /* do something */
Chris@16: //          }
Chris@16: //
Chris@16: //      where 'clos' is an instance of our closure 'my_closure' above.
Chris@16: //      Take note that the usage above precludes locally declared
Chris@16: //      classes. If my_closure is a locally declared type, we can still
Chris@16: //      use its self_type as a paramater to closure_frame:
Chris@16: //
Chris@16: //          closure_frame<my_closure::self_type> frame(clos);
Chris@16: //
Chris@16: //      Upon instantiation, the closure_frame links the local variables
Chris@16: //      to the closure. The previous link to another closure_frame
Chris@16: //      instance created before is saved. Upon destruction, the
Chris@16: //      closure_frame unlinks itself from the closure and relinks the
Chris@16: //      preceding closure_frame prior to this instance.
Chris@16: //
Chris@16: //      The local variables in the closure 'clos' above is default
Chris@16: //      constructed in the stack inside function 'foo'. Once 'foo' is
Chris@16: //      exited, all of these local variables are destructed. In some
Chris@16: //      cases, default construction is not desirable and we need to
Chris@16: //      initialize the local closure variables with some values. This
Chris@16: //      can be done by passing in the initializers in a compatible
Chris@16: //      tuple. A compatible tuple is one with the same number of
Chris@16: //      elements as the destination and where each element from the
Chris@16: //      destination can be constructed from each corresponding element
Chris@16: //      in the source. Example:
Chris@16: //
Chris@16: //          tuple<int, char const*, int> init(123, "Hello", 1000);
Chris@16: //          closure_frame<my_closure> frame(clos, init);
Chris@16: //
Chris@16: //      Here now, our closure_frame's variables are initialized with
Chris@16: //      int: 123, char const*: "Hello" and int: 1000.
Chris@16: //
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: 
Chris@16: 
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: //
Chris@16: //  closure_frame class
Chris@16: //
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: template <typename ClosureT>
Chris@16: class closure_frame : public ClosureT::tuple_t {
Chris@16: 
Chris@16: public:
Chris@16: 
Chris@16:     closure_frame(ClosureT& clos)
Chris@16:     : ClosureT::tuple_t(), save(clos.frame), frame(clos.frame)
Chris@16:     { clos.frame = this; }
Chris@16: 
Chris@16:     template <typename TupleT>
Chris@16:     closure_frame(ClosureT& clos, TupleT const& init)
Chris@16:     : ClosureT::tuple_t(init), save(clos.frame), frame(clos.frame)
Chris@16:     { clos.frame = this; }
Chris@16: 
Chris@16:     ~closure_frame()
Chris@16:     { frame = save; }
Chris@16: 
Chris@16: private:
Chris@16: 
Chris@16:     closure_frame(closure_frame const&);            // no copy
Chris@16:     closure_frame& operator=(closure_frame const&); // no assign
Chris@16: 
Chris@16:     closure_frame* save;
Chris@16:     closure_frame*& frame;
Chris@16: };
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: //
Chris@16: //  closure_member class
Chris@16: //
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: template <int N, typename ClosureT>
Chris@16: class closure_member {
Chris@16: 
Chris@16: public:
Chris@16: 
Chris@16:     typedef typename ClosureT::tuple_t tuple_t;
Chris@16: 
Chris@16:     closure_member()
Chris@16:     : frame(ClosureT::closure_frame_ref()) {}
Chris@16: 
Chris@16:     template <typename TupleT>
Chris@16:     struct sig {
Chris@16: 
Chris@16:         typedef typename detail::tuple_element_as_reference<
Chris@16:             N, typename ClosureT::tuple_t
Chris@16:         >::type type;
Chris@16:     };
Chris@16: 
Chris@16:     template <class Ret, class A, class B, class C>
Chris@16:     //    typename detail::tuple_element_as_reference
Chris@16:     //        <N, typename ClosureT::tuple_t>::type
Chris@16:     Ret
Chris@16:     call(A&, B&, C&) const
Chris@16:     {
Chris@16:         assert(frame);
Chris@16:         return boost::tuples::get<N>(*frame);
Chris@16:     }
Chris@16: 
Chris@16: 
Chris@16: private:
Chris@16: 
Chris@16:     typename ClosureT::closure_frame_t*& frame;
Chris@16: };
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: //
Chris@16: //  closure class
Chris@16: //
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: template <
Chris@16:     typename T0 = null_type,
Chris@16:     typename T1 = null_type,
Chris@16:     typename T2 = null_type,
Chris@16:     typename T3 = null_type,
Chris@16:     typename T4 = null_type
Chris@16: >
Chris@16: class closure {
Chris@16: 
Chris@16: public:
Chris@16: 
Chris@16:     typedef tuple<T0, T1, T2, T3, T4> tuple_t;
Chris@16:     typedef closure<T0, T1, T2, T3, T4> self_t;
Chris@16:     typedef closure_frame<self_t> closure_frame_t;
Chris@16: 
Chris@16:                             closure()
Chris@16:                             : frame(0)      { closure_frame_ref(&frame); }
Chris@16:     closure_frame_t&        context()       { assert(frame); return frame; }
Chris@16:     closure_frame_t const&  context() const { assert(frame); return frame; }
Chris@16: 
Chris@16:     typedef lambda_functor<closure_member<0, self_t> > member1;
Chris@16:     typedef lambda_functor<closure_member<1, self_t> > member2;
Chris@16:     typedef lambda_functor<closure_member<2, self_t> > member3;
Chris@16:     typedef lambda_functor<closure_member<3, self_t> > member4;
Chris@16:     typedef lambda_functor<closure_member<4, self_t> > member5;
Chris@16: 
Chris@16: private:
Chris@16: 
Chris@16:     closure(closure const&);            // no copy
Chris@16:     closure& operator=(closure const&); // no assign
Chris@16: 
Chris@16:     template <int N, typename ClosureT>
Chris@16:     friend class closure_member;
Chris@16: 
Chris@16:     template <typename ClosureT>
Chris@16:     friend class closure_frame;
Chris@16: 
Chris@16:     static closure_frame_t*&
Chris@16:     closure_frame_ref(closure_frame_t** frame_ = 0)
Chris@16:     {
Chris@16:         static closure_frame_t** frame = 0;
Chris@16:         if (frame_ != 0)
Chris@16:             frame = frame_;
Chris@16:         return *frame;
Chris@16:     }
Chris@16: 
Chris@16:     closure_frame_t* frame;
Chris@16: };
Chris@16: 
Chris@16: }}
Chris@16:    //  namespace 
Chris@16: 
Chris@16: #endif