Re: [boost] Monad (was: Re: [Boost-users] [afio] Formal review of Boost.AFIO)

Subject: Re: [boost] Monad (was: Re: [Boost-users] [afio] Formal review of Boost.AFIO)
From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2015-08-27 02:43:21

On 27 Aug 2015 3:46 am, "Niall Douglas" <s_sourceforge_at_[hidden]> wrote:
>
> On 26 Aug 2015 at 5:57, Glen Fernandes wrote:
>
> > Paul wrote:
> > > these are all *outcomes* - of varying types of varying and unspecified
> > > Thingy.
> >
> > Niall wrote:
> > > I like Boost.Outcome and boost::outcome::basic_outcome<Policy>.
> > > Do these make sense however:
> > > outcome<T>: Can be empty/T/error_code/exception_ptr.
> > > result<T>: Can be empty/T/error_code.
> > > option<T>: Can be empty/T.
> >
> > Isn't "Outcome" no less generic and unspecific as "Result"? All of
> > Boost.Monad, Boost.Outcome, or Boost.Result, seem like terrible names
to me.
>
> Choice between the pan and the fire.
>
> > We already name specific result types for the kind of result they are
(I'm
> > glad boost::optional is not boost::result). Why not name monad types
for the
> > specific kind of monad they are?
> >
> > Unless this "Monad" library isn't about offering a concrete type called
> > "boost::monad" but instead is just a library to enable someone write
their
> > own monad types.
>
> That's exactly what it does. It's a framework for creating bespoke
> future and monad types.

A Boost.Monad library that would provide a monad_adaptor a la
Boost.Iterator could indeed be useful, but that doesn't seem to be the case
here.

>You define your policy implementations
> classes and feed them to basic_monad<Policy> or basic_future<Policy>
> as needed. The library itself provides three monad specialisations
> and six future specialisations by stamping out the nine policies for
> each of those.
>

Unfortunately the documentation for the policy is literally an empty line.
I have looked at the detail/monad_policy.hpp file, but beyond customising
the storage, I can't see any hook to customise the behaviour.

Could you show us a custom policy implementation for a list monad?

-- gpd