Re: [Caml-list] Monad Library?

[David House <dhouse@janestreet.com>]

The Core library [1] has a good monad library that gets used in
basically every single Jane Street program (and notably inside async).
Among its features are:

* Module types for monads with one or two type parameters

* Functors to make modules satisfying those signatures given just bind + return

* "Infix" submodules which one can locally open ("let open
Option.Monad_infix in") in order to temporarily work inside another
monad -- very useful.

It notably does *not* feature a syntax extension to make monadic
computations look pretty. You must write out the binds and returns
yourself. To be honest, the reason for this is mostly history, but we
actually have some anecdotal evidence now that writing in the explicit
style makes things easier to understand for authors and readers of
code.

[1]: https://bitbucket.org/yminsky/ocaml-core/wiki/Home


On Fri, Nov 23, 2012 at 11:54 AM, Wojciech Meyer
<wojciech.meyer@googlemail.com> wrote:
> On Fri, Nov 23, 2012 at 11:43 AM, Chris Yocum <cyocum@gmail.com> wrote:
>> I was looking into using Monads in my programs but I am slightly at a
>> loss as to what library is in general use.  There is pa_monad but that
>
> pa_monad is really useful and nice, I think the updated library is
> available as pa_monad_custom OPAM package.
>
>> seems to be a ocamlp4 exention and not a library.  There is
>> http://lambda.jimpryor.net/monad_library/ but that doesn't seem to be
>> in opam or in godi so I am unsure as to its status.
>>
>> Does anyone have any suggestion for a well supported monad library for
>> Ocaml?
>
> First I would need to find an answer what do you mean by a monad library.
>
> Monads is a general abstraction with a very simple interface. so they
> don't require library as such.
>
> However I agree it would be good to have some library that provides a
> monadic interface to some common functionality found maybe in std
> libraries, also some way of composing monads would be good having
> monad transformers along. Batteries included offer monadic interface
> to some common data types like list, bool, option.
>
> You could look at Xavier Leroy's lectures here [1] to see the
> excellent examples of using monads in OCaml.
>
> For somewhat advanced type system trickery to use generic interface
> for monads you can look at this excellent post [2].
>
> -Wojciech
>
> [1] http://gallium.inria.fr/~xleroy/mpri/progfunc/monads.2up.pdf
> [2] http://alaska-kamtchatka.blogspot.co.uk/2011/09/higher-order-fun.html
> [3] http://batteries.forge.ocamlcore.org/
>
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