From: Maurizio Vitale (mav_at_[hidden])
Date: 2007-04-27 05:38:57
Eric Niebler <eric_at_[hidden]> writes:
>> For instance, given the pattern:
>>
>> proto::terminal< number<bounds<run_time,_>,_,_,_,_,_> >
>>
>> how can I refer in the rhs of a transform to:
>
>
> What do you mean by "rhs"?
if you see a transform as pattern -> transformed tree, then pattern would be
the lhs and the transformed tree would be the rhs.
>> a) the entire pattern being matched (e.g. terminal<> or number<>)
>
>
> Transforms are always of the following form:
>
> template<typename Grammar>
> struct some_transform
> : Grammar
> {
> template<typename Expr, typename State, typename Visitor>
> struct apply
> {
> typedef ... type;
> };
>
> template<typename Expr, typename State, typename Visitor>
> static typename apply<Expr, State, Visitor>::type
> call(Expr const &expr, State const &state, Visitor &visitor)
> {
> return ...;
> }
> };
Oh. Yes, makes sense. Now I got it.
What I was trying was to use the default transform proto::always<pattern, replacement>
hoping that somehow I would have gotten mpl::placeholders bound inside replacement.
> There are no mpl placeholders here, and the placeholders are not
> positional like that. You can't say, find me what matched the Nth
> occurance of proto::_. You only get the whole expression that matched.
Would have been nice, though...
>> This is blocking me at the moment, so if anybody has suggestions, they would be very much
>> appreciated.
>
> HTH,
Hugely. Obviously I'll find problems as soon as I start implementing it, but I think
now I've got it.
Thanks again,
Maurizio