I propose to change it to be member of FiniteBits
I recall, there was a proposal to remove bitSize from Bits, so it's an opportunity to introduce another small, yet breaking change at the same time. Discussion time 2 week. - Oleg _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries |
Although, popCount for Integer/Natural kind of makes sense, as they
aren't infinite list of [Bit]s, but smarter structure. On 30.11.2019 17.17, Oleg Grenrus wrote: > I propose to change it to be member of FiniteBits > > I recall, there was a proposal to remove bitSize from Bits, so it's an > opportunity to introduce another small, yet breaking change at the > same time. > > Discussion time 2 week. > > - Oleg > > _______________________________________________ > Libraries mailing list > [hidden email] > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries |
popCount is a perfectly sensible method for Natural, and it could theoretically become one for Integer as well if we say that, whenever there's an infinite number of 1s and a finite number of 0s, then the result is -(1 + count of 0s), as though it were maxBound :: Word bits in size and merely converted to an Int (a sensible assumption, considering memory limits). The results for types where there can be both infinite 0s and 1s should still be an error. On Sat, Nov 30, 2019, 09:21 Oleg Grenrus <[hidden email]> wrote: Although, popCount for Integer/Natural kind of makes sense, as they _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries |
In reply to this post by Oleg Grenrus
Yeah, I would be really sad if I can't do popCount on Integer. I suppose the issue really is whether you are allowed to have instances of Bits that have values with an infinite number of 1 bits, e.g. the 2-adic numbers. On Sat, Nov 30, 2019, 9:21 AM Oleg Grenrus <[hidden email]> wrote: Although, popCount for Integer/Natural kind of makes sense, as they _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries |
In reply to this post by Oleg Grenrus
I like this idea.
Cheers, Vanessa McHale On 11/30/19 3:17 PM, Oleg Grenrus wrote: > I propose to change it to be member of FiniteBits > > I recall, there was a proposal to remove bitSize from Bits, so it's an > opportunity to introduce another small, yet breaking change at the > same time. > > Discussion time 2 week. > > - Oleg > > _______________________________________________ > Libraries mailing list > [hidden email] > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries |
In reply to this post by Brent Yorgey
Would a Bits instance for 2-adic numbers be useful? Cheers, On 11/30/19 4:23 PM, Brent Yorgey
wrote:
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In reply to this post by Zemyla
A few points: 1. The Bits instance for Integer essentially already behaves as if they are the 2-adic numbers. For example, if you use testBit you can discover that (-2 :: Integer) is treated as if it were an infinite sequence of 1's followed by a single 0. 2. However, because testBit takes an Int index, instances of Bits actually can't have an infinite number of 1 bits---at least not in practice---since you cannot observe anything past the (maxBound :: Int)th bit. 3. Currently, popCount on negative Integer values satisfies popCount (-x) = -(popCount x) which does not seem very well motivated and does not match the way negative values are presented via testBit. I am strongly -1 on moving popCount to FiniteBits. popCount on positive Integers is useful and well-defined. I am mildly +1 on Zemlya's proposal to change the behavior of popCount for negative Integer values, though I am not sure it is really worth the trouble. -Brent On Sat, Nov 30, 2019 at 10:10 AM Zemyla <[hidden email]> wrote:
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I'd refine the documentation of `Bits` class to say that it's a
class for integral types with finite count of bits toggled, i.e.
finite popCount. On 1.12.2019 5.21, Brent Yorgey wrote:
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In reply to this post by Oleg Grenrus
I'm pretty strongly -1 on moving popCount. Both the Natural and the slightly more... interesting... Integer implementations of that method have turned out to be quite useful in practice. -Edward On Sat, Nov 30, 2019 at 7:17 AM Oleg Grenrus <[hidden email]> wrote: I propose to change it to be member of FiniteBits _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries |
In reply to this post by Oleg Grenrus
I'm not averse to the idea of factoring out complementation into a separate class to make the Bits instance for Natural total. It strikes me as a laudable goal and it comes very close to encoding what Stone called a "Generalized Boolean Algebra" in the 30s, which hints to me that we might be onto the right abstraction here. Consider me a weak +1 there. -Edward On Mon, Dec 2, 2019 at 6:01 AM Oleg Grenrus <[hidden email]> wrote:
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I’d wanna first see how that factoring plays out, Strong -1 on dropping pop count instance Curious to poke at / think about the class refactoring. There’s definitely some ways this stuff could be evolved. Just need clarity on the cost vs benefits etc. On Mon, Dec 2, 2019 at 11:48 AM Edward Kmett <[hidden email]> wrote:
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In reply to this post by Edward Kmett-2
I made two MRs for GHC: On 2.12.2019 18.47, Edward Kmett wrote:
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