Re: [Boost-users] [Spirit] Qi lexeme only taking the first word

Subject: Re: [Boost-users] [Spirit] Qi lexeme only taking the first word
From: Michael Powell (mwpowellhtx_at_[hidden])
Date: 2018-11-08 19:09:01

On Tue, Nov 6, 2018 at 11:46 PM Michael Powell <mwpowellhtx_at_[hidden]> wrote:
>
> On Tue, Nov 6, 2018 at 10:28 PM Gavin Lambert via Boost-users
> <boost-users_at_[hidden]> wrote:
> >
> > On 7/11/2018 15:08, Michael Powell wrote:
> > >> When it matches
> > >>
> > >> id >> *(char_('.') >> id)
> > >>
> > >> this has an attribute of vector<string,vector<tuple<char,std::string>>> or something similar.
> > >
> > > Where are you getting that from? It makes no sense whatsoever given
> > > the struct full_it_t { std::string val; }, which is similarly mapped,
> > > and ruled, etc.
> >
> > This might be wrong, but it's how I read the docs:
> >
> > The output of parsing is a Fusion sequence of the attributes that were
> > parsed.
> >
> > So the output of
> >
> >    id >> *(char_('.') >> id)
> >
> > is something like (but not exactly)
> >
> >    tuple<string>
> >    tuple<string, char, string>
> >    tuple<string, char, string, char, string>
> >    etc
> >
> > string because that's the output attribute declared for id.
> > char because you've used char_ instead of using '.' by itself (otherwise
> > it would just disappear).
> > And the latter two can be repeated zero or more times because you've used *.
> >
> > When you assign this to a rule with %=, it tries to best-fit this
> > against the rule's declared output attribute.
> >
> > full_id_t contains a single string field, so the Fusion adaptation makes
> > it equivalent to tuple<string>, and apparently this results in any
> > additional values being discarded, not in concatenating as you expect.
> >
> > You can probably use an explicit semantic action to build a single
> > string instead of using %=.
> >
> > Or you can make full_id_t contain vector<string> as rmawatson and I
> > previously suggested, which should give you all the values.
> >
> > Another possibility, which I can't test because coliru appears to be
> > grumpy at present, is to try using:
> >
> >    full_id %= as_string[lexeme[id >> *(char_('.') >> id)]];
>
> This approach works for me. And remains true to the AST. +1 Thanks!

Boy, wow... I'll qualify that with this: in "this" case I was able to
persuade Spirit/Fusion to produce what I wanted.

In other cases, not so much. It really, I mean **REALLY**, wants to
produce that std::vector<...>, doesn't it?

It will take a bit of digesting to adjust the AST, etc, to that, but
it's good (no, GREAT) to know about.

> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> > https://lists.boost.org/mailman/listinfo.cgi/boost-users