Re: [Boost-users] [Proto] Processing Lists

On Mon, Feb 22, 2010 at 3:29 AM, David Greene wrote:

I want to process a list that looks something like this:

struct List : or_<  comma<    List,    Item  >,  Item

...

{};

But rather than processing each item separately, I want to pass a fusion (or some other) sequence to a semantic action:

when<  List,  SomeAction(...)

...

{};

Ideally the argument to SomeAction would be a fusion sequence but I don't know how to produce one.  This doesn't work:

when<  List,  SomeAction(flatten(_))

...

{};

because flatten is not a transform.  I don't want to use fold_tree because I don't want to actually fold the sequence.  SomeAction is something like this:

struct SomeAction : callable {  template<typename Seq>  void operator()(Seq range) {    typedef ... iterator;

   // Is this legal for fusion sequences?    for(iterator i = begin(range), iend = end(range);         i != iend;         i = next(i)) {        ...    }  } }

Is there a way to do this?

On a related note, I know I can use varag<> to match a function call expression with an arbitrary number of operands and invoke a transform on each operand.  But how would I generate a fusion sequence of all the operands?  In other words, with:

proto::function< X, proto::vararg<Y> >

how do I talk about the vararg<> part in a semantic action?  CalculatorGrammar has a use of vararg but it uses fold<> to process it.  I don't want to fold a sequence, I want to pass it to a transform.

I had something like struct foo_tostr : proto::or_ >, proto::fold > > {}; to convert the operands of a function call expression to a string. I believe proto::_expr is itself a fusion sequence. I could use fusion::at_c<N>(proto::_expr) to access the elements. proto::functional::pop_front(proto::_expr) is like lisp cdr, gives you everything except the first element of the sequence. Manjunath

Thanks!

                                          -Dave _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users