Since my post was mentioned, I thought I’d chime in.

I’ve used both libraries and I’ve found little practical difference between the two. I think porting a codebase from Lwt to Async (and vice versa) is mostly mechanical work.

While I still prefer Async’s interface a little more but I think the two main points in my blog post still stand. If portability and maximum interoperability with the community are important to you then the decision is already made in my eyes.

On March 7, 2016 at 9:26:41 AM, Ashish Agarwal (agarwal1975@gmail.com) wrote:

> 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.

There is Lwt_preemptive.detach and Async's In_thread.run to get around this.

> 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/ .

I'd be wary of drawing conclusions from one blog post and even from opam. I think the answer is: both are used a lot. Also depends on what you mean by "a user". It's not too useful to count Jane Street's packages and one barely used package on opam both as 1. A lot of code is not on opam.

> Is there an existing compatibility library functorized over the intersection of Async and Lwt? That would make being compatible with both much easier.

Most people provide this internally for each of their projects, e.g. Cohttp's IO signature. However, we have quite a few projects that needed this abstraction, so duplicating this code in each repo seemed wrong. Thus we developed future, which was recently released in opam.

On Mon, Mar 7, 2016 at 9:06 AM, Yotam Barnoy <yotambarnoy@gmail.com> wrote:

Is there an existing compatibility library functorized over the intersection of Async and Lwt? That would make being compatible with both much easier.

On Mon, Mar 7, 2016 at 4:08 AM, Simon Cruanes <simon.cruanes.2007@m4x.org> wrote:

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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