Template parameters not used in partial specialization when using member typedefine

{ This article is multi-posted to [comp.lang.c++]. -mod/aps }

// Seting up classes for example... Interesting bit is when we try
to
// specialize template class FunctorImpl.
class Nil { };

template<class H, class T>
struct TypeList
{
     typedef H Head;
     typedef T Tail;
};

template
<class T01=Nil, class T02=Nil, class T03=Nil, class T04=Nil, class
T05=Nil,
   //...
   >
struct Seq;

template<class T01>
struct Seq<T01>
{
     typedef TypeList<T01, Nil > Type;
};

// more specializations of Seq, but those are not needed for the
example...

template <typename R, class TList> class FunctorImpl;

// OK, finally the interesting bit. The below will error with:
// error: template parameters not used in partial specialization: ?P1?
//
template <class R, class P1>
class FunctorImpl<R, typename Seq<P1>::Type >
{
public:
     typedef R ResultType;
     typedef P1 Parm1;
     virtual R operator()(Parm1) = 0;
};

// This of course works:
//
template <class R, class P1>
class FunctorImpl<R, TypeList<P1, Nil> >
{
public:
     typedef R ResultType;
     typedef P1 Parm1;
     virtual R operator()(Parm1) = 0;
};

// The motivation for this is I'd like to ultimate (instead of Seq)
// use the Function Signature specialization trick:

template <class Fun> struct Cons;

template <class T1> struct Cons<void (*)(T1)>
{
     typedef TypeList<T1, Nil> Type;
};

template <class T1, class T2>
struct Cons<void (*)(T1, T2)>
{
     typedef TypeList<T1, TypeList<T2, Nil> > Type;
};

//...

#define MakeTL(...) Cons< void (*) (__VA_ARGS__) >::Type

template <class R, class P1>
class FunctorImpl<R, typename MakeTL(P1) >
{
public:
     typedef R ResultType;
     typedef P1 Parm1;
     virtual R operator()(Parm1) = 0;
};

But this fails for the same reason "class FunctorImpl<R, typename
Seq<P1>::Type >" fails.

Is there any way around this? This seems like it should be valid C+
+... but this appears to be compiler independent.

--
      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]