Re: [boost] [spirit] semantic action for mismatches?

Subject: Re: [boost] [spirit] semantic action for mismatches?
From: caustik (caustik_at_[hidden])
Date: 2011-01-08 13:16:04

On Sat, Jan 8, 2011 at 10:03 AM, Hartmut Kaiser <hartmut.kaiser_at_[hidden]>wrote:

> > > > I might give that a shot as I can't seem to get local variables to
> > > > solve my problem. I would expect these two commands to have the same
> > > > result (albeit unnecessarily assigning the _a variable, which just
> > > > gets tossed away anyway), but apparently they are not?
> > > >
> > > > r = p[_a = _1]
> > > > r = p
> > >
> > > Automatic attribute propagation from the rhs expression to the lhs
> > > rule is disabled as soon as semantic actions are involved. If you want
> > > to enforce attribute propagation anyways, write:
> > >
> > >    rule<...> r;
> > >    r %= p[...];
> > >
> > > If the rhs has no semantic actions attached, operator=() behaves
> > > exactly like operator%=().
> >
> > That does the trick. Apologies for the previous top-post. I've been out
> of
> > the mailing list game for a while now =)
> >
> > This style ended up working and I can finally move on to other things:
> >
> > r %= p1[_a = _1] >> ('*' | (eps[bind(&class::undo, &instance, _a)] >>
> > !eps))
> > >> p2
>
> FWIW, this should do the same, but simpler:
>
>    r %= p1[_a = _1] >> ('*' | !eps[bind(&class::undo, &instance, _a)]) >>
> p2;
>
>
Ah, I was thinking that ! behaved like this:

(!eps)[action]

as opposed to this:

!(eps[action])