Re: [Caml-list] Question about Lwt/Async

[Simon Cruanes <simon.cruanes.2007@m4x.org>]

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Hi,

It seems that Lwt is more popular in the community
outside JaneStreet than Async (if only by looking at its reverse
dependencies on opam.ocaml.org). There has been posts about this, for
instance http://rgrinberg.com/blog/2014/12/11/abandoning-async/ .
However, if you're writing a library, it is good taste (if possible) to
parametrize you code over an "IO" monad that will be easy to instantiate
with either Async or Lwt (or the trivial blocking monad where 'a t = 'a
and (>>=) x f = f x) along with the required IO primitives.

Regarding general utility functions, if they do not perform IO or depend
on (blocking) IO they can be used directly with Async/Lwt (unless they
really take a very long time to complete).

Le Mon, 07 Mar 2016, Malcolm Matalka a écrit :
> Yotam Barnoy <yotambarnoy@gmail.com> writes:
> > Hi all
> >
> > I'm thinking about my next project in OCaml, and I'm wondering how many
> > users of OCaml currently use Lwt or Async regularly.
> >
> > One of the advantages of OCaml over Haskell (which I'm not crazy about) is
> > the fact that you don't have to constantly be stuck inside a monad.
> > However, once you want to use these user-level threading libraries, you're
> > essentially tied to a monad. It also means that the usage of any other
> > monad from Lwt/Async code is out -- OCaml doesn't have the monad
> > transformer infrastructure to layer monads easily as far as I can tell (am
> > I wrong?). I mean, even in Haskell using Monad Transformers is a pain (IMO).
> >
> > Also, what happens to general utility functions that aren't rewritten for
> > Async/Lwt -- as far as I can tell, being in non-monadic code, they will
> > always starve other threads, since they cannot yield to another Async/Lwt
> > thread. Is this perception correct? If so, this seems to imply that you
> > either write your code to cooperate within these frameworks and suffer the
> > monad, or don't, and make it near-impossible for Lwt/Async users to make
> > use of your code.
> >
> > I would like to get an idea of the usage level of these libraries, as well
> > as the burden of writing compatible code, any difficulties etc. Also, I'd
> > like to get a sense of the domains that benefit from these libraries. Some
> > domains (such as gaming) traditionally involve a continuous main loop, and
> > would thus only suffer from the additional overhead of queuing in these
> > libraries.
> >
> > -Yotam
> 
> I mostly use Async.  However, I think most usage of Lwt or Async
> requires doing as little as possible in these frameworks and using them
> to orchestrate other functions.  For example, I usually try to separate
> parsing of a network protocol from the reading and writing of the bytes.
> 
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-- 
Simon Cruanes

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