[Caml-list] pa_monad 1.0 - syntax extension for monads

[Jacques Carette]

We are pleased to announce the release of the stable version our syntax
extension for monadic expressions in Ocaml.

All the details can be obtained from
http://www.cas.mcmaster.ca/~carette/pa_monad/ .

Example: A simple but realistic example of the use of a list monad looks
like this

bind
[1; 2; 3]
(fun a -> bind
[3; 4; 5]
(fun b -> return (a + b)))

where we assume the appropriate definitions of the functions "bind" and
"return". With the help of "pa_monad" this can be written as

perform
a <-- [1; 2; 3];
b <-- [3; 4; 5];
return (a + b)

which is much clearer and thus easier to understand and maintain. By the
way, the expression evaluates to [4; 5; 6; 5; 6; 7; 6; 7; 8] the sum of
each pair of values of the input lists.

Highlights:

- Efficient code: The generated code is as efficient as hand-coded.
- Highly flexible: The "bind" and "failwith" functions can be
specified in various ways
(a) Binding with default names:
perform ...
(b) Binding with user-defined names:
perform with my_bind and my_failwith in ...
(c) One-of-a-kind binding:
perform with fun a f -> f a and ... in ...
(d) Module-based binding:
perform with MyMonad in ...
or with OCaml's local modules:
let foo ... =
let module MyMonad = ... in
perform with MyMonad in ...

The package for this extension contains more examples as well as some
self-tests and an extensive README with yet more details (including a
patch to tuareg-mode). In the source code (and the generated ocamldoc
html), one can find amongst other things an informal and formal
description of the grammar of the extension, and a (rewriting) semantics
for the extension.

This code is licensed under the GNU library general public license,
compatible with Ocaml's own license.

All feedback welcome,
Jacques Carette, Lydia E. van Dijk and Oleg Kiselyov

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[Paul Snively]

Jacques, Lydia, and Oleg,

Thanks so much for this! It's almost embarrassing to ask for more,
but I'm going to anyway:

1) It isn't clear how to build a native version of the release,
although the Makefile appears to contemplate doing so.
2) It would be nice if the release were integrated with findlib.
3) It would be nice if Oleg's monadic delimited continuations were
revised to be as nicely supported by pa_monad as the IO, Exception,
and Nondet monads that are included with the distribution are.

I will poke around at all three of these issues myself. In the
meantime, thanks again for a great tool!

Best regards,
Paul

[Jacques Carette]

As requested, pa_monad 1.1 now is integrated with findlib [thanks to
Lydia], and Oleg's delimited continuations are included in the
distribution (and compatible with the extension).

See http://www.cas.mcmaster.ca/~carette/pa_monad for full details.

Jacques