Simon Marlow:
On 24 March 2006 12:28, Ross Paterson wrote:
On Fri, Mar 24, 2006 at 11:30:57AM -0000, Simon Marlow wrote:
So I believe the issue is mainly one of perspective. Until I wrote this email I hadn't thought of (4) and my preference was for (2), but now I quite like the idea of (4). We would include concurrency in Haskell', but provide a separate addendum that specifies how imlementations that don't provide concurrency should behave. One advantage of (4) over (3) is that we can unambiguously claim that Haskell' has concurrencey.
And we can unambiguously state that there is only one Haskell' implementation (though a second is on the way).
Sure, concurrency is essential to many applications, and should be precisely specified. But it is also irrelevant to a lot of uses of Haskell (except for ensuring that one's libraries are also usable on concurrent implementations, as JohnM said). A specification of the language without concurrency would be at least as valuable (having more implementations). Perspective, as you say -- most people agree we need both -- but I think you're a bit too negative about the smaller variant.
This is just a difference of opinion, and probably won't be easily resolved. It comes down to whether you think Haskell' should be a language that is wide enough to include such applications as a web server, or whether it has to stop short of including concurrency because it's too hard to implement (and it's not always hard - the YHC guys managed it in a matter of days, but I do realise it would be hard in Hugs).
I think it would be a mistake to relegate concurrency to an addendum; it is a central feature of the language, and in fact is one area where Haskell (strictly speaking GHC) is really beginning to demonstrate significant advantages over other languages. We should make the most of it.
I 100% agree!! Personally, I think, after the FFI, a good story about concurrency and exceptions is what H98 misses most for applications other than variations on the compiler theme. Manuel