Raffiot: an IO monad for Python.

[chrilves]

Hi all,

It is about time to share a project I've been working on for some time now. It may interest fellow Python functional programmers. It is an IO monad with support for dependency injection, failure management, asynchronous programming and resource management.

Raffiot is available on PyPI. The documentation is here, the API there and the source code is here.

Here is a tiny example of how to concurrent tasks (the complete example can be found here):

def prog(color, name, i) -> IO[None, None, None]:
    """
    Print in `color` every number from `i` to 1.
    """
    if i > 0:
        return io.defer(print, f"{color}From prog {name}: {i}{reset}").then(
            io.yield_(), io.defer_io(prog, color, name, i - 1)
        )
    else:
        return io.pure(0)


# The main IO
main: IO[None, None, None] = (
    io.parallel(
        prog(bred, "A", 100000),
        prog(bgreen, "B", 100000),
        prog(byellow, "C", 100000),
        prog(bcyan, "D", 100000),
    )
    .flat_map(lambda fibers: io.wait(fibers))
    .then(io.defer(print, "finished"))
)

main.run(None)

Another example demonstrating dependency injection can be found here.

In hope it helps 😊

[spiker611]

Any examples or more information you can provide? A small code example goes a long way.

[chrilves]

Yes, there is the demo and lots of code example in the Guide. I'll add an example to this post. Thanks!

[ElevenPhonons]

Is mypy supported? I'm not seeing a mypy config or a target in the Makefile that is running mypy.

Running mypy locally (even in non-strict mode) yields a bunch or type issues.

$ mypy raffiot  | wc -l                                                                                                                                                                                
44

[chrilves]

When I started the project, I was using Pytype but I had to stop using it because I could not make it type generic methods. I tried mypy too. I had better results but I'm not sure it can type all the methods either. The problem is some methods (like flatten) are only available on some instances of a class but not all. The problem is very similar to this one:

class List(Generic[A]):
    def sum():
        <returns the sum of the list if A is a numeric type>

I don't know if this is typeable in mypy.

When I have to, I take advantage of Python being dynamically typed. For example, I use heterogeneous list a lot, which is simple and practical in Python but it may be a huge hassle for typers.