Removing bitSize

David Feuer david.feuer at
Sun Feb 4 21:15:08 UTC 2018

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> 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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