Re: [boost] Re: Automata builder -- interface

From: joel de guzman (isis-tech_at_[hidden])
Date: 2001-05-30 13:02:40

From: "Larry Evans":
> >
> > Aggregates need not store subjects by value. A reference is fine since
we
> > know that the subject has a lifetime equal to or greater than the
aggregate.
> > Rules<> are composed by reference in Spirit. I such cases, the aggregate
> > does not own the subject(s).
>
> This will work for FIRST and NILABLE because they are synthesized
attributes.
> However, FOLLOW requires an inherited attribute, which can be stored as
part
> of some type of smart pointer.

pardon my ignorance, but who owns a follow? Rule?

>
> Also, if references are stored in a rule, then wouldn't this cause a
problem if
> Rule1 references Rule2 and Rule2 references Rule1?  One or the other
> must be created before a reference can be returned to it.  Am I missing
something?
>

I don't know if this applies in the context of the automata builder.
I am speaking just from experience with Spirit. Rules in Spirit,
just like in c++ need to be declared before being used. To allow
cyclic structures typically found in BNF declarations, a rule
may be declared but defined later (forward declared).

Rule<>  a, c;
Rule<>  b = c | a;
a = ...
b = ...

In fact, we can just forward declare all rules.

Rule<> a, b, c;

b = c | a;
a = ...
c = ...

Joel de Guzman