On Sun, Nov 30, 2008 at 10:43 AM, Max Rabkin <[EMAIL PROTECTED]> wrote: > On Sun, Nov 30, 2008 at 9:30 AM, Luke Palmer <[EMAIL PROTECTED]> wrote: >> cross :: [a] -> [b] -> [(a,b)] >> >> It's just kind of a pain (you build [(a,(b,(c,d)))] and then flatten >> out the tuples). The applicative notation is a neat little trick >> which does this work for you. > > It seems to me like this would all be easy if (a,b,c,d) was sugar for > (a,(b,(c,d))), and I can't see a disadvantage to that.
This is a tricky and subtle question, actually. It has to do with the lifting of tuples; those two types have different domains. For example, the element in the latter: (1,(2,_|_)) Has no corresponding element in the former (there is (1,2,_|_,_|_), but that corresponds to (1,(2,(_|_,_|_))) ). Now, if tuples in Haskell were unlifted, meaning (_|_,_|_) = _|_, then there would be no issue. But that has far-reaching consequences in the language design, among which the "seq" function would have to be eliminated (many people would not be opposed to this). Also usage of unlifted tuples can cause subtle space leaks. Now, what all this domain theory has to do with practical issues, I'm not sure. But you can't just do a slick replacement, because it changes properties of programs that did not know the difference. Frankly, I would prefer what you propose as well (actually, I would prefer it to mean (a,(b,(c,(d,())))), but it's the same idea). But the change is difficult and requires thought. Luke _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
