Lennart Augustsson wrote:
I don't think anyone has claimed that any interface can be implemented without globals. Of course some can't (just pick an interface that is the specification of a global variable).
I said in the original challenge even I'd let you (anyone) change the interface if you could provide a sensible explanation of why the new interface was better, safer, more convenient or whatever.
What I (and others) claims is that such interfaces are bad. Using a global variable makes an assumption that there's only ever going to be one of something,
It's not an assumption, any more than I always want 1*N to yield N is an assumption. It's a fundamental property I absolutely want to guarantee. By far the simplest way to do this is simply not to expose a newWhatever constructor in my API. If I expose anything it should be Whatever itself or getWatever, neither of which is possible if Whatever contains MVars, Chans and the like. What's more, there seems to be no good *semantic* reason why this should not be possible. The only objections seem dogmatic to me.
and that's just an inflexible assumption to make. You think global variables are essential, I think they are a sign of bad design. So we have different opinions and neither one of us is going to convince the other.
You might stand some chance of convincing me by showing a better design :-) Dan seems to have had a reasonable go at 1 of them. I'm not sure passes the improved interface test but I'll think about it. But there are quite a few left. There's the Hughes paper too of course, using implicit parameters (a highly dubious language feature IMO). But even if someone does produce an entirely unsafePerformIO hack free set of standard libs, I have to ask why jump through all these hoops? There's no semantic difficulty with the proposed language extension, and it should be very simple to implement (John seems to have done it already). Regards -- Adrian Hey _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
