Re: Late review of Boost.Parser

From: Zach Laine (whatwasthataddress_at_[hidden])
Date: 2024-03-02 03:01:53

On Fri, Mar 1, 2024 at 1:16 PM Дмитрий Архипов via Boost
<boost_at_[hidden]> wrote:
>
> > > Much of the wealth of research into parser combinators wasn't incorporated
> > > into this library. I didn't see in the documentation, for example, an easy
> > > way to "map" one parser's attribute into another. This kind of thing should
> > > be a basis operation provided by the library.
> >
> > Could you explain what you mean by this?  This happens implicitly
> > usually, and you can explicitly do it in semantic actions.  Do you
> > mean something else?
>
> I actually wanted to ask for a similar thing, but then forgot about
> it. Basically, sometimes you have to
> create a rule simply because you want to convert the attribute from
> type A to type B, and you use a
> semantic action. Semantic actions result in parser's attribute
> becoming none. But if instead semantic
> action's result type would be the parser's attribute, then using an
> action would become a mapping operation.
> E.g.
>
> (+bp::digit)[( [](auto& attr){ return std::stol(attr); } )]; //
> mapping string -> long
>
> If the library would also unwrap tuples in attributes, you could even
> do things like
>
> (double_ >> double_)[ std::plus<>() ]

Hopefully I answered this elsewhere in this thread, or partially in
https://github.com/tzlaine/parser/issues/106 .  There's an
implementation for that already, but I'm certain to change it.  As-is,
it's too hard to use, because too often your lambas need constraining.
Anyway, if those two sources don't answer this, just let me know.

Zach