Proposal: Move primitive-Data.Primitive.Addr API into base

[David Feuer]

Ptr Word8 is not (just) a pointer to byte-addressable memory. It's
specifically a pointer to something representing an 8-bit unsigned integer.
If you use a Ptr Word8 for the address of a floating point value, then you
are *wrong* (or doing something very weird, anyway). To quote the
documentation,

A value of type Ptr a represents a pointer to an object, or an array of
objects, which may be marshalled to or from Haskell values of type a.

On Thu, Oct 25, 2018, 11:23 PM Carter Schonwald <carter.schonwald at gmail.com>
wrote:

> ... when is a valid pointer not going to point at byte addressable memory
> on memory architectures ghc can support or target?
>
> On Thu, Oct 25, 2018 at 8:27 PM Daniel Cartwright <chessai1996 at gmail.com>
> wrote:
>
>> Now, one could argue that `Ptr ()` isn't a lie, it sort of reads like C's
>> void pointer. But surely something like `Ptr Word8` is a lie, when it is
>> not actually a Ptr to Word8 values.
>>
>> On Thu, Oct 25, 2018 at 8:11 PM Daniel Cartwright <chessai1996 at gmail.com>
>> wrote:
>>
>>> yes, only the type and its instances should be moved as far as i'm aware.
>>>
>>> Also, it's more than just base.
>>>
>>> this Ptr is a lie:
>>> https://hackage.haskell.org/package/ghc-compact-0.1.0.0/docs/GHC-Compact-Serialized.html#t:SerializedCompact
>>> these Ptrs are lies:
>>> https://hackage.haskell.org/package/base-4.12.0.0/docs/GHC-IO-Handle.html
>>> in GHC.Stats, the foreign import "getRTSStats" has `Ptr () -> IO ()`,
>>> this Ptr () is also a lie
>>>
>>> These are just off the top of my head, there are more
>>>
>>>
>>> On Thu, Oct 25, 2018 at 6:46 PM Carter Schonwald <
>>> carter.schonwald at gmail.com> wrote:
>>>
>>>> hrmm, what are the pieces of base that are using Ptr when they really
>>>> should be using Addr? This would help me understand what would be made
>>>> better in base :)
>>>>
>>>> On Thu, Oct 25, 2018 at 6:19 PM David Feuer <david.feuer at gmail.com>
>>>> wrote:
>>>>
>>>>> We shouldn't really need to move anything into base except Addr and
>>>>> its base instances.
>>>>>
>>>>> On Oct 25, 2018 5:59 PM, "Carter Schonwald" <
>>>>> carter.schonwald at gmail.com> wrote:
>>>>>
>>>>> Indeed.  The monad transformer instances for primmonad need to live in
>>>>> primmonad OR transformers to avoid orphans.
>>>>>
>>>>> Either way, unless transformers moves into base (unlikely), no way
>>>>> anything using prim monad will.
>>>>>
>>>>> On Thu, Oct 25, 2018 at 3:34 PM Andrew Martin <
>>>>> andrew.thaddeus at gmail.com> wrote:
>>>>>
>>>>>> I like the idea of moving the type Addr into base. But we cannot move
>>>>>> the entire module since it has functions that talk about PrimMonad, and we
>>>>>> definitely don't want to move that into base.
>>>>>>
>>>>>> On Thu, Oct 25, 2018 at 11:25 AM Daniel Cartwright <
>>>>>> chessai1996 at gmail.com> wrote:
>>>>>>
>>>>>>> Motivation: There are a lot of places in base where 'Ptr a' is used
>>>>>>> in place of 'Addr', because in base there is no 'Addr', only 'Addr#'. The
>>>>>>> problem lies in the fact that many of these uses of 'Ptr a' are lying; the
>>>>>>> 'a' value is meaningless. Authors of functions therein have used things
>>>>>>> like 'Ptr ()', 'Ptr Word8', 'Ptr a', but these types do not mean what they
>>>>>>> say they mean - they're just Addr. There are probably other motivations for
>>>>>>> this that I can't think of off the top of my head right now.
>>>>>>> _______________________________________________
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>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> -Andrew Thaddeus Martin
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>>>>>>
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