//demonstrate mixing is grammars with transforms is
//an instance of blob anti-pattern.
//
#include <boost/mpl/bool.hpp>

using namespace boost;
//The following code is (essentially) from
//  _C++ Template Metaprogramming_
//  section 2.2 "Metafunctions"
//  page 16.
//
template<class UnaryOp1, class UnaryOp2>
struct apply_fg_sep
{
    template<class X>
    struct matches
    : UnaryOp1::template test<X>
    {};
    
    template<class X>
    typename UnaryOp2::template result<X>::type 
    transform(X x)
    {
        UnaryOp2 xfrm;
        return xfrm(x);
    }
};

template<class Blob>
struct apply_fg_blob
{
    typedef typename Blob::unary_op1 unary_op1;
    
    template<class X>
    struct matches
    : unary_op1::template test<X>
    {};
    
    typedef typename Blob::unary_op2 unary_op2;
    
    template<class X>
      typename unary_op2::template result<X>::type
    transform(X x)
    {
        typename Blob::unary_op2 xfrm;
        return xfrm(x);
    }
};


struct grammar_always_true
{
    template<class>
    struct test
    : mpl::true_
    {};
    
};
struct transform_ident
{
    template<class X>
    struct result
    {
        typedef X type;
    };
    
    template<class X>
      typename result<X>::type 
    operator()(X x)
    {
        return x;
    };
    
};

template<class UnaryOp1, class UnaryOp2>
struct blob
{
    typedef UnaryOp1 unary_op1;
    typedef UnaryOp2 unary_op2;
};

#include <iostream>

int main(void)
{
    {
        std::cout<<"sep demo:\n";
        typedef apply_fg_sep<grammar_always_true,transform_ident> gram_xfrm;
        std::cout<<gram_xfrm::matches<int>::value<<"\n";
        std::cout<<gram_xfrm().transform(99)<<"\n";
    }
    {
        std::cout<<"blob demo:\n";
        typedef apply_fg_blob<blob<grammar_always_true,transform_ident> > gram_xfrm;
        std::cout<<gram_xfrm::matches<int>::value<<"\n";
        std::cout<<gram_xfrm().transform(99)<<"\n";
    }
    return 0;
}