Re: Ord methods are surprisingly strict

I figured the biggest wins on lazy <= et al would come from ADTs with two constructors with at least one nullary. Bool, Maybe, and [] all qualify. And generally, with operations that can potentially be lazy in either argument, the convention is that it's in the first argument. Also, there is at least one compelling reason for the comparison operators to be lazy. Take the infinite search monad: newtype Search r a = Search { find :: (a -> r) -> a } It has an Alt instance for finding the better of two results with a given valuation function: instance Ord r => Alt (Search r) where Search ma Search mb = Search $ \p -> let a = ma p b = mb p in if p a >= p b then a else b For Search Bool, which uses a predicate as its valuation function, this means that, if p a is True, it doesn't need to evaluate b or p b at all. On Thu, May 7, 2020, 14:00 David Feuer wrote:

Even aside from the memory leak potential and the performance degradation from allocation, adding extra tests will degrade performance in typical cases for many types. Comparing against minBound/maxBound isn't always free. For a simple Int comparison, that's an extra compare and conditional jump every time. For such a fundamental operation, that's a big ouch!

On Thu, May 7, 2020, 2:53 PM Christopher Allen wrote:

...

If one of my applications develops a memory leak because of this potential change, where should I invoice you for the time wasted tracking down & fixing it? My short-term contract rate is $250/hour but I could be argued down to $200/hour.

On May 7, 2020, at 1:00 PM, Sven Panne wrote:

Am Do., 7. Mai 2020 um 15:26 Uhr schrieb David Feuer < david.feuer@gmail.com>:

...

I believe this is all about strictness analysis. If these were lazy, then users would have to be very careful to force the lazy arguments when they don't need that laziness to avoid building unnecessary thunks.

This argument holds basically for every potentially lazy function, and I fail to see why comparisons should be special, so this is not really convincing. :-) We have easy ways to make things more strict, but not the other way around.

In any case, it has historically been the case that the reference implementations in the Haskell language/library report define the strictness of the defined functions, too. Otherwise things could be very surprising, in both ways (too lazy, too strict). Furthermore, the report is *very* explicit about the derived instances: https://www.haskell.org/onlinereport/haskell2010/haskellch11.html#x18-183000... And (), Bool, ... are defined via deriving: https://www.haskell.org/onlinereport/haskell2010/haskellch9.html#x16-1710009 _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries