[proto] Comma Strangeness
Well, my little lambda-like experimental language is getting rather large. I'm really having fun with it and am close to actually doing something almost useful with it. :) Unfortunately I've run into a problem I can't seem to isolate to a small testcase. I'm doing something like this: proto::display_expr( list [ obj["name1"].attr["a"], obj["name2"].attr["a"], obj["name3"].attr["b"] ] ); Presume I have all of the terminals, members, etc. declared/defined correctly (at least "correctly" as I understand it). display_expr dumps out an expression without any comma operators. It just shows a subscript off "list" with one "index," obj["name3"].attr["b"]. It's the behavior I would expect if the operands of the commas were not protoized expressions, but they _should_ be protoized. The funny thing is, if I write a small testcase just isolating the terminals, members, etc. needed to construct the expression, it works as expected. But in the context of the (much) larger language, it fails. However, the grammar specification shouldn't have any bearing on what display_expr dumps out. So any ideas as to why commas might be gobbled up prematurely? -Dave
I have the following toy program : #include <iostream> #include <boost/proto/proto.hpp> using namespace std; namespace proto=boost::proto; struct list_ {}; struct attr_ {}; struct obj_ {}; template<class E> struct obj_expr; struct obj_domain : proto::domain<proto::pod_generator<obj_expr> > {}; template <class E> struct obj_expr { BOOST_PROTO_BASIC_EXTENDS(E, obj_expr<E>, obj_domain); BOOST_PROTO_EXTENDS_SUBSCRIPT(); BOOST_PROTO_EXTENDS_MEMBERS( ((attr_, attr)) ) }; proto::terminal<list_>::type list; obj_expr<proto::terminal<obj_>::type> obj; int main() { proto::display_expr( list[obj["name1"].attr["a"], obj["name2"].attr["a"], obj["name3"].attr["b"]] ); return 0; } and I do see the expression getting printed out correctly as follows. Do you see something different? subscript( terminal(5list_) , comma( comma( subscript( member( subscript( terminal(4obj_) , terminal(name1) ) , terminal(5attr_) ) , terminal(a) ) , subscript( member( subscript( terminal(4obj_) , terminal(name2) ) , terminal(5attr_) ) , terminal(a) ) ) , subscript( member( subscript( terminal(4obj_) , terminal(name3) ) , terminal(5attr_) ) , terminal(b) ) ) ) Manjunath
On Friday 26 March 2010 20:37:19 Manjunath Kudlur wrote:
and I do see the expression getting printed out correctly as follows. Do you see something different?
As I said, if I make a toy program, it works. Only in the context of the larger language code does it fail. I don't expect anyone to be able to easily reproduce the problem. I'm just looking for ideas of what to try next. -Dave
On 3/26/2010 6:11 PM, David Greene wrote:
The grammar *could* have a bearing on what proto operators are considered, so long as you specified the grammar as the second parameter to proto::domain<>. If your grammar doesn't allow comma, then proto's comma operator is ignored, leaving only C++'s build-in comma. If that's not the problem, you'll have to post a self-contained repro of the problem so we can track it down. -- Eric Niebler BoostPro Computing http://www.boostpro.com
participants (3)
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David Greene -
Eric Niebler -
Manjunath Kudlur