From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2008-04-02 05:30:51
On Wed, Apr 2, 2008 at 1:59 AM, shunsuke <pstade.mb_at_[hidden]> wrote:
> Giovanni Piero Deretta wrote:
> >> BTW, Boost.Egg has the potential to implement your compose.
> >>
> >> typedef result_of_lazy<fold>::type fold_;
> >> typedef result_of_lazy<reverse>::type reverse_;
> >> typedef return_of<fold_(reverse_(T_bll_1), T_bll_2, T_bll_3)>::type reverse_fold;
> >>
> >
> > Oh! So Egg has the functionality to make function objects directly
> > usable in lambda expressions (without bind)???
> > i.e.
> >
> > for_each(range_of_ranges, regular(protect(std::cout << accumulate(ll::_1, 0))))
> >
> > does that actually work? (for appropriate definitions of for_each and
> > accumulate, of course).
> > I was going to ask you to provide this functionality in egg (yes, I'm
> > working on a review :) )
>
> Yes. egg::lazy/nestN makes bind/protect deprecated.
> I've noticed that bind/protect is a customization point.
> e.g.
>
> X_lazy<T_boost_bind> bb_lazy; // T_boost_bind represents boost::bind.
> bb_lazy(foo)(::_1, 2);
>
> In fact, implementing T_boost_bind is so difficult that Egg skips it. :-)
>
>
> > BTW, i prefer to spell 'regular(protect(...))' as 'lambda[...]'
>
> What is `regular`? Is it the same as egg::regular?
yes, exactly. I do not have a 'regular' function, I've just used this
name because this is what egg uses.
> BTW, everything must be function-call to support result_of.
What do you mean exactly with "everything must be function call?".
>
>
> > Even if I guarantee that my function objects (in this case fold and
> > reverse) are stateless? Does using the lambda placeholders complicate
> > things?
>
> If fold_ is DefaultConstructible and a default-constructed one is callable,
> it would be:
>
> typedef
> static_< mpl::always<
> return_of<T_regular(fold_(reverse_(T_bll_1), T_bll_2, T_bll_3))>::type
> > >
> reverse_fold;
>
> I tend to hesitate to use result_of/return_of without function-calls.
Again, what do you mean exactly? And why do you esistate? I'm
evaluating egg design, so these answers would be very valuable.
> So your `compose` may be a candidate of yet another lambda framework.
As if there weren't already enough :)
-- gpd