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. HTH Jo