On 04/04/2007 01:14 PM, Eric Niebler wrote:
Larry Evans wrote: [snip]
Proto uses or_ and and_ for alternatives and sequences. It seems that alt_ and seq_ would be closer to the spirit names. Any reason why those names were preferred over alt_ and seq_?
Because for what they do, or_ and and_ are the right names. :-) You realize that these do not create expression templates, right?
Yes, but I guess I need to reread about expression templates.
They are part of proto's meta-grammar facility. If you want to know if an expression type E matches grammar G1 or G2, you use:
proto::matches<E, proto::or_<G1, G2> >
That's a compile-time boolean test. Proto::and_ behaves similarly. Like mpl::or_ and mpl::and_ (and like || and &&) these do short-circuit evaluation.
HTH,
That sort of helps. I guess I was just predisposed to thinking of them as doing something similar to spirit's alternative<L,R> and sequence<L,R> templates; however, I guess not. Maybe my confusion is somehow related to the possiblity of have placeholder's as arguments to the templates. I understand that this is related to proto's ability to do transform of the template expressions, OTOH, spirit doesn't transform templates, only runtime values (via the parse member function). In short, I need to study proto some more :(