//Purpose:
//  Prototype how to do:
/*
http://www.boost.org/libs/mpl/doc/refmanual/find-if.html
 */
//  in d.
//References:
//  This code is pretty much modelled after phobos'
//    IndexOf(T, TList...)
//  in:
//    dmd/src/phobos/std/typetuple.d
//  and described here:
//    http://www.digitalmars.com/d/phobos/std_typetuple.html
//
import std.typetuple;
class ParamPack(TList...)
{
    alias TList unpacked;
}
alias ParamPack!() empty_ppack;
template FindIf(alias Predicate, PPack)
{
    static if (PPack.unpacked.length == 0)
      alias PPack result_type;
    else static if (Predicate!(PPack.unpacked[0]).result_value)
	  alias PPack.unpacked[0] result_type;
    else
      alias
		FindIf!(Predicate, ParamPack!(PPack.unpacked[1 .. length])).result_type result_type;
}
class TypePair(First,Second)
{
    alias First first;
    alias Second second;
}
template FirstIs(First)
{
    template Predicate(Pair)
    {
        static if(is(First == Pair.first))
          const bool result_value=true;
        else
          const bool result_value=false;
    }
}

  void
test()
{
    {
        alias ParamPack!
          ( TypePair!(int,float)
          , TypePair!(float,int)
          ) int_float_map;
        alias FindIf!(FirstIs!(float).Predicate,int_float_map).result_type has_float;
        static assert(!is(has_float == empty_ppack));
        alias FindIf!(FirstIs!(int).Predicate,int_float_map).result_type has_int;
        static assert(!is(has_int == empty_ppack));
        alias FindIf!(FirstIs!(char).Predicate,int_float_map).result_type has_char;
        static assert( is(has_char == empty_ppack));
    }
}