[Haskell-cafe] Re: Strange subtract operator behavior - and lazy naturals
On 2007-10-21, Yitzchak Gale [EMAIL PROTECTED] wrote: I wrote: Yitzchak Gale wrote: So why not make the laziness available also for cases where 1 - 2 == 0 does _not_ do the right thing? data LazyInteger = IntZero | IntSum Bool Integer LazyInteger or data LazyInteger = LazyInteger Bool Nat or whatever. Luke Palmer wrote: data LazyInteger = IntDiff Nat Nat The only value which would diverge when compared to a constant would be infinity - infinity. Hmm. But then you could have integers that are divergent and non-infinite. What do we gain by doing it this way? IntDiff is essentially fail-lazily for (Infinity - Infinity), rather than fail-quickly of the other two. Sometimes fail-lazily is appropriate, sometimes not. I don't think it makes too much difference here though. My actual concern is about having to compute with IntDiff (large) (large + x) many times instead of IntDiff 0 x. I'd rather one of the two above, though I think I'd prefer explicity PosInt and NegInt branches over an inscrutable boolean flag. -- Aaron Denney -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Strange subtract operator behavior - and lazy naturals
David Benbennick [EMAIL PROTECTED] writes: On 10/17/07, John Meacham [EMAIL PROTECTED] wrote: Oops, sorry, the version I posted was an intermediate one that had a different addition algorithm. here is a better one that fixes that issue: Zero + y = y Sum x n1 + y = Sum x (y + n1) note that it alternates the order in the recursive call, interleaving the elements of the two arguments. Thanks. Have you thought at all about how to make maximally lazy Naturals? For example, a data type that can answer True to both genericLength (1:undefined) + genericLength (1:2:3:4:5:6:undefined) (6 :: Nat) genericLength (1:2:3:4:5:6:undefined) + genericLength (1:undefined) (6 :: Nat) Is that a desired feature? It may be desirable, but it's not lambda definable, so you'd have to use concurrency to acheive it. -- Jón Fairbairn [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
