// Boost Lambda Library  ret.hpp -----------------------------------------

// Copyright (C) 1999, 2000 Jaakko Järvi (jaakko.jarvi@cs.utu.fi)

//

// 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)

//

// For more information, see www.boost.org

#ifndef BOOST_LAMBDA_RET_HPP

#define BOOST_LAMBDA_RET_HPP

namespace boost { 

namespace lambda {

  // TODO:

//  Add specializations for function references for ret, protect and unlambda

//  e.g void foo(); unlambda(foo); fails, as it would add a const qualifier

  // for a function type. 

  // on the other hand unlambda(*foo) does work

// -- ret -------------------------

// the explicit return type template 

  // TODO: It'd be nice to make ret a nop for other than lambda functors

  // but causes an ambiguiyty with gcc (not with KCC), check what is the

  // right interpretation.

  //  // ret for others than lambda functors has no effect

  // template <class U, class T>

  // inline const T& ret(const T& t) { return t; }

template<class RET, class Arg>

inline const 

lambda_functor<

  lambda_functor_base<

    explicit_return_type_action<RET>, 

    tuple<lambda_functor<Arg> >

  > 

>

ret(const lambda_functor<Arg>& a1)

{

  return  

    lambda_functor_base<

      explicit_return_type_action<RET>, 

      tuple<lambda_functor<Arg> >

    > 

    (tuple<lambda_functor<Arg> >(a1));

}

// protect ------------------

  // protecting others than lambda functors has no effect

template <class T>

inline const T& protect(const T& t) { return t; }

template<class Arg>

inline const 

lambda_functor<

  lambda_functor_base<

    protect_action, 

    tuple<lambda_functor<Arg> >

  > 

>

protect(const lambda_functor<Arg>& a1)

{

  return 

      lambda_functor_base<

        protect_action, 

        tuple<lambda_functor<Arg> >

      > 

    (tuple<lambda_functor<Arg> >(a1));

}

// -------------------------------------------------------------------

// Hides the lambda functorness of a lambda functor. 

// After this, the functor is immune to argument substitution, etc.

// This can be used, e.g. to make it safe to pass lambda functors as 

// arguments to functions, which might use them as target functions

// note, unlambda and protect are different things. Protect hides the lambda

// functor for one application, unlambda for good.

template <class LambdaFunctor>

class non_lambda_functor

{

  LambdaFunctor lf;

public:

  // This functor defines the result_type typedef.

  // The result type must be deducible without knowing the arguments

  template <class SigArgs> struct sig {

    typedef typename 

      LambdaFunctor::inherited:: 

        template sig<typename SigArgs::tail_type>::type type;

  };

  explicit non_lambda_functor(const LambdaFunctor& a) : lf(a) {}

  typename LambdaFunctor::nullary_return_type  

  operator()() const {

    return lf.template 

      call<typename LambdaFunctor::nullary_return_type>

        (cnull_type(), cnull_type(), cnull_type(), cnull_type()); 

  }

  template<class A>

  typename sig<tuple<const non_lambda_functor, A&> >::type 

  operator()(A& a) const {

    return lf.template call<typename sig<tuple<const non_lambda_functor, A&> >::type >(a, cnull_type(), cnull_type(), cnull_type()); 

  }

  template<class A, class B>

  typename sig<tuple<const non_lambda_functor, A&, B&> >::type 

  operator()(A& a, B& b) const {

    return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&> >::type >(a, b, cnull_type(), cnull_type()); 

  }

  template<class A, class B, class C>

  typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type 

  operator()(A& a, B& b, C& c) const {

    return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type>(a, b, c, cnull_type()); 

  }

};

template <class Arg>

inline const Arg& unlambda(const Arg& a) { return a; }

template <class Arg>

inline const non_lambda_functor<lambda_functor<Arg> > 

unlambda(const lambda_functor<Arg>& a)

{

  return non_lambda_functor<lambda_functor<Arg> >(a);

}

  // Due to a language restriction, lambda functors cannot be made to

  // accept non-const rvalue arguments. Usually iterators do not return 

  // temporaries, but sometimes they do. That's why a workaround is provided.

  // Note, that this potentially breaks const correctness, so be careful!

// any lambda functor can be turned into a const_incorrect_lambda_functor

// The operator() takes arguments as consts and then casts constness

// away. So this breaks const correctness!!! but is a necessary workaround

// in some cases due to language limitations.

// Note, that this is not a lambda_functor anymore, so it can not be used

// as a sub lambda expression.

template <class LambdaFunctor>

struct const_incorrect_lambda_functor {

  LambdaFunctor lf;

public:

  explicit const_incorrect_lambda_functor(const LambdaFunctor& a) : lf(a) {}

  template <class SigArgs> struct sig {

    typedef typename

      LambdaFunctor::inherited::template 

        sig<typename SigArgs::tail_type>::type type;

  };

  // The nullary case is not needed (no arguments, no parameter type problems)

  template<class A>

  typename sig<tuple<const const_incorrect_lambda_functor, A&> >::type

  operator()(const A& a) const {

    return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&> >::type >(const_cast<A&>(a), cnull_type(), cnull_type(), cnull_type());

  }

  template<class A, class B>

  typename sig<tuple<const const_incorrect_lambda_functor, A&, B&> >::type

  operator()(const A& a, const B& b) const {

    return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&, B&> >::type >(const_cast<A&>(a), const_cast<B&>(b), cnull_type(), cnull_type());

  }

  template<class A, class B, class C>

  typename sig<tuple<const const_incorrect_lambda_functor, A&, B&, C&> >::type

  operator()(const A& a, const B& b, const C& c) const {

    return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&, B&, C&> >::type>(const_cast<A&>(a), const_cast<B&>(b), const_cast<C&>(c), cnull_type());

  }

};

// ------------------------------------------------------------------------

// any lambda functor can be turned into a const_parameter_lambda_functor

// The operator() takes arguments as const.

// This is useful if lambda functors are called with non-const rvalues.

// Note, that this is not a lambda_functor anymore, so it can not be used

// as a sub lambda expression.

template <class LambdaFunctor>

struct const_parameter_lambda_functor {

  LambdaFunctor lf;

public:

  explicit const_parameter_lambda_functor(const LambdaFunctor& a) : lf(a) {}

  template <class SigArgs> struct sig {

    typedef typename

      LambdaFunctor::inherited::template 

        sig<typename SigArgs::tail_type>::type type;

  };

  // The nullary case is not needed: no arguments, no constness problems.

  template<class A>

  typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type

  operator()(const A& a) const {

    return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type >(a, cnull_type(), cnull_type(), cnull_type());

  }

  template<class A, class B>

  typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type

  operator()(const A& a, const B& b) const {

    return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type >(a, b, cnull_type(), cnull_type());

  }

  template<class A, class B, class C>

  typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&, const C&>

>::type

  operator()(const A& a, const B& b, const C& c) const {

    return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&, const C&> >::type>(a, b, c, cnull_type());

  }

};

template <class Arg>

inline const const_incorrect_lambda_functor<lambda_functor<Arg> >

break_const(const lambda_functor<Arg>& lf)

{

  return const_incorrect_lambda_functor<lambda_functor<Arg> >(lf);

}

template <class Arg>

inline const const_parameter_lambda_functor<lambda_functor<Arg> >

const_parameters(const lambda_functor<Arg>& lf)

{

  return const_parameter_lambda_functor<lambda_functor<Arg> >(lf);

}

// make void ------------------------------------------------

// make_void( x ) turns a lambda functor x with some return type y into

// another lambda functor, which has a void return type

// when called, the original return type is discarded

// we use this action. The action class will be called, which means that

// the wrapped lambda functor is evaluated, but we just don't do anything

// with the result.

struct voidifier_action {

  template<class Ret, class A> static void apply(A&) {}

};

template<class Args> struct return_type_N<voidifier_action, Args> {

  typedef void type;

};

template<class Arg1>

inline const 

lambda_functor<

  lambda_functor_base<

    action<1, voidifier_action>,

    tuple<lambda_functor<Arg1> >

  > 

> 

make_void(const lambda_functor<Arg1>& a1) { 

return 

    lambda_functor_base<

      action<1, voidifier_action>,

      tuple<lambda_functor<Arg1> >

    > 

  (tuple<lambda_functor<Arg1> > (a1));

}

// for non-lambda functors, make_void does nothing 

// (the argument gets evaluated immediately)

template<class Arg1>

inline const 

lambda_functor<

  lambda_functor_base<do_nothing_action, null_type> 

> 

make_void(const Arg1& a1) { 

return 

    lambda_functor_base<do_nothing_action, null_type>();

}

// std_functor -----------------------------------------------------

//  The STL uses the result_type typedef as the convention to let binders know

//  the return type of a function object. 

//  LL uses the sig template.

//  To let LL know that the function object has the result_type typedef 

//  defined, it can be wrapped with the std_functor function.

// Just inherit form the template parameter (the standard functor), 

// and provide a sig template. So we have a class which is still the

// same functor + the sig template.

template<class T>

struct result_type_to_sig : public T {

  template<class Args> struct sig { typedef typename T::result_type type; };

  result_type_to_sig(const T& t) : T(t) {}

};

template<class F>

inline result_type_to_sig<F> std_functor(const F& f) { return f; }

} // namespace lambda 

} // namespace boost

#endif