DDC compiler and effects; better than Haskell? (was Re: [Haskell-cafe] unsafeDestructiveAssign?)

Sebastian Sylvan sebastian.sylvan at gmail.com
Sat Aug 15 19:32:30 EDT 2009

On Sun, Aug 16, 2009 at 12:18 AM, John A. De Goes <john at n-brain.net> wrote:

> On Aug 15, 2009, at 4:59 PM, Sebastian Sylvan wrote:
>> Your point about safety in C has no relation to safety in a functional
>> language with a sophisticated effect system.
>> I'm sorry, but I think it does. You're advocating that modifications to
>> mutable state shouldn't have sequential semantics,
> You must think I'm arguing for some kind of low-level analog of C,
> augmented with an effect system. I'm not. You can't do that.

No, I don't. I think you're arguing for making access to mutable state
commutative. Are you not?

> In such conditions, multiple sequential writes can be safely parallelized,
> in addition to a host of other optimizations.

I'm not saying you shouldn't parallelise them in very specific circumstances
*where it's safe*, I'm just saying that you shouldn't assume that it's safe
unless you know it is. If you want to do a transformation that's unsafe in
general, but safe in a specific circumstance, then of course, go ahead!
To my reading it seems like you're arguing that memory/file access should
*always* be considered commutative though, which is what I'm objecting too.

>  I'm pointing out that this is the case today in C on many CPUs and it's a
>> royal pain to work with in practice (causing many almost-impossible-to-debug
>> crashes). I would not want functional languages to adopt something that's
>> proven to be insanity-inducingly difficult to use.
> Please don't ever bring up C again. You can't do anything interesting in C.

I bring up C until you can explain how what you're suggesting is any
different from the current state in C w.r.t. the ordering of memory access.
>From what you've said so far I can't see how it is, and it would be
instructive to look at the problems with the approach you're advocating
since we're dealing with its pitfalls *today* in the real world.

Sebastian Sylvan
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