[core libraries] Re: Removing bitSize

[Edward Kmett]

As ugly as it is, this function is still mentioned in the current Haskell 2010 Report, so users should have some reasonable expectation of finding it.

When there is a new Haskell Report that drops it I'd say that is when we should finish its removal.

-Edward



Sent from my iPhone
> On Feb 4, 2018, at 4:38 PM, Andrew Martin <andrew.thaddeus at gmail.com> wrote:
> 
> I'm in favor of removing it entirely. Making it an alias may help people who want to keep code compatible with base < 4.7, but it could also introduce some confusion. Some thoughts:
> 
> - It doesn't help people who want to write a `Bits` instance for their data type. That will still require CPP.
> - People writing bit-type-polymorphic code will have to upgrade to FiniteBits when using newer base, which will force CPP for compatibility anyway.
> - People writing bit-type monomorphic code don't even need this function, since they can just write out the number of bits (except for with Int and Word, whose sizes vary by platform).
> 
> 
>> On Sun, Feb 4, 2018 at 4:15 PM, David Feuer <david.feuer at gmail.com> wrote:
>> Quite some time has passed since I first raised this question. There
>> doesn't seem to have been much discussion, but we really need to do
>> something! Just leaving bitSize as deprecated seems like the worst
>> option. Does anyone else have anything to add?
>> 
>> On Mon, Jul 10, 2017 at 11:50 PM, David Feuer <david.feuer at gmail.com> wrote:
>> > The long-deprecated bitSize method of the Bits class is slated to be
>> > removed in base-4.11 (GHC 8.4). There is one remaining question:
>> > should we replace it with a *function* by that name with a FiniteBits
>> > constraint? I don't feel very strongly either way, but Ryan Scott
>> > seems in favor and Edward Kmett seems opposed. So it seems best to
>> > bring it to the libraries list and let the CLC make the call. If the
>> > function is added, it would look like this:
>> >
>> > bitSize :: FiniteBits a => a -> Int
>> > bitSize = finiteBitSize
>> >
>> > The biggest downside I see is that we might one day want to reuse the
>> > name for something with a better type, such as
>> >
>> > bitSize :: forall proxy a. FiniteBits a => proxy a -> Int
>> > bitSize _ = finiteBitSize (undefined :: a)
>> >
>> > or
>> >
>> > bitSize :: forall a. FiniteBits a => Tagged a Int
>> > bitSize = Tagged (finiteBitSize (undefined :: a))
>> >
>> > or (with type applications)
>> >
>> > bitSize :: forall a. FiniteBits a => Int
>> > bitSize = finiteBitSize (undefined :: a)
>> >
>> > Thanks,
>> > David Feuer
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> 
> 
> 
> -- 
> -Andrew Thaddeus Martin
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