/*
 * $Id$
 */

/*
 * Copyright (c) 2016 Brook Milligan.
 * 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)
 */

#include <cassert>
#include <boost/proto/core.hpp>
#include <boost/proto/context.hpp>
#include "exp.hpp"

// XXX - suggested addition to Boost.Proto:
//       a metafunction such as here for deducing the type of a proto terminal.
//       This makes specializing on the type of terminal possible (see below).
#include "terminal.hpp"

// XXX - enabling the following yields compilation errors (at least in Boost v1.59)
#define USE_PROTO_CHILD_0_FOR_SPECIALIZING 0

struct placeholder {};

typedef boost::proto::terminal<double>::type real_type;
typedef boost::proto::terminal<placeholder>::type const placeholder_type;

placeholder_type _ = {{}};

class context
{
  typedef context this_context;

#if USE_PROTO_CHILD_0_FOR_SPECIALIZING

public:
  template < typename Expr
	     , typename Tag = typename boost::proto::tag_of<Expr>::type
	     , typename Arg0 = typename boost::proto::result_of::child_c<Expr,0>::type
	     >
  struct eval;

  template < typename Expr, typename Tag, typename Arg0 >
  struct eval
    : boost::proto::context::default_eval< Expr,this_context const >
  {};

  template < typename Expr >
  struct eval< Expr,boost::proto::tag::terminal,placeholder >
  {
    typedef double result_type;

    result_type operator () (Expr&, this_context const& context) const
    { return context.x_; }
  };

#else	 // !USE_PROTO_CHILD_0_FOR_SPECIALIZING
  
  template < typename Expr
	     , typename Arg0 = boost::proto::type_traits::terminal_t<Expr>
	     >
  struct terminal_eval
    : boost::proto::context::default_eval< Expr,this_context const >
  {};

  template < typename Expr >
  struct terminal_eval< Expr,placeholder >
  {
    typedef double result_type;

    result_type operator () (Expr&, this_context const& context) const
    { return context.x_; }
  };
  
public:
  template < typename Expr
	     , long Arity = boost::proto::arity_of<Expr>::value
	     >
  struct eval;

  template < typename Expr, long Arity >
  struct eval
    : boost::proto::context::default_eval< Expr,this_context const >
  {};

  template < typename Expr >
  struct eval< Expr,0 >
    : terminal_eval<Expr>
  {};

#endif  // USE_PROTO_CHILD_0_FOR_SPECIALIZING
  
private:
  double x_ = 2;
};

int main ()
{
  real_type x = { 0 };
  auto f = math::exp(x);
  assert(boost::proto::eval(f,context()) == std::exp(0));

  boost::proto::value(x) = 1;
  assert(boost::proto::eval(f,context()) == std::exp(1));

  auto g = math::exp(_);
  assert(boost::proto::eval(g,context()) == std::exp(2));

  return 0;
}