Deniz Dogan wrote: > 2009/6/13 Jochem Berndsen <[email protected]>: >> Keith Sheppard wrote: >>> Is there any reason that sum isn't strict? I can't think of any case >>> where that is a good thing. >>> >>> Prelude> sum [0 .. 1000000] >>> *** Exception: stack overflow >> It is useful if the (+) is nonstrict; although I cannot think of any >> useful mathematical structure where (+) would be nonstrict. > > I remember needing a non-strict sum at least once, but I do not > remember the exact application. But imagine having a (very) long list > of numbers and you want to do A if the sum exceeds a small number, > otherwise B. > > if sum [0..100000] > 10 then A else B > > However, this idea didn't work, because of strictness.
You can only do such things if you know that all entries of your list are nonnegative. That requires a custom solution anyway (not to mention the fact that to determine whether x > 10 or not, we need to explicitly compute x). Regards, -- Jochem Berndsen | [email protected] GPG: 0xE6FABFAB _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
