[Haskell-cafe] Well typed OS

Vanessa McHale vanessa.mchale at iohk.io
Fri Oct 5 16:08:12 UTC 2018

You'd probably want an ABI for types, no? You'd need a new executable
format (among many other things!).

The question is: would it be worth it? Types are wonderful in Haskell
because they allow us to structure our programs. What would structuring
processes via types accomplish? It would improve the situation with
shell scripting/pipes as you allude, but that's still an immense amount
of effort.

As for effect types - the IO monad in Haskell exists primarily to allow
side effects in a lazy language, so there's no reason I see to keep it
in an operating system.

On 10/05/2018 12:40 AM, Joachim Durchholz wrote:
> Am 05.10.2018 um 06:36 schrieb Yotam Ohad:
>> Hi,
>> In the last couple of days, I've been toying with the thought of an
>> operating system in which programs (or more accurately, any process)
>> has a distinct type which limits
>> its use of the machine. For example, `echo` (String -> String) won't
>> be able to print an output without a second program which would
>> handle changing stdout.
>> I think it could "break down" the IO monad into other structures that
>> are better at specifying what is changing: A file is read / memory
>> written / etc.
>> I do, however, not sure how to incorporate drivers (which handles IO
>> and external devices) into this. Giving them an `IO a` type feels
>> like cheating. I would be much cooler if there was a way
>> to treat them like the `echo` function from earlier.
>> What are your thoughts/suggestions? I'll be happy to hear them.
> An OS needs to work for any programming language, so I'm not sure how
> to get from an IO-based approach to a working OS. Unless you plan to
> write the OS itself in Haskell and make it so that all programs are
> Haskell modules, but that's a huge task.
> The design approach you're after is called "Capabilities". It's not
> ordinarily described as a type system, and I'm not sure whether it's a
> good idea to use static types in the first place because there are
> situations where you want to grant or revoke them dynamically.
> See https://en.wikipedia.org/wiki/Capability-based_security . This
> article also has a link to other security models; capabilities are
> pretty famous, but it's quite possible that a different one would be a
> better fit.
> Jo
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