Improved interface to UArray

[Carter Schonwald]

Hey Zemyla!
one fuzzy question i have, and perhaps you have a perspective on this,
would/could the PrimMonad machinery in primitive help simplify / clean up
stuff here too?

On Mon, Feb 24, 2020 at 9:46 AM Zemyla <zemyla at gmail.com> wrote:

> It's currently hard to describe that a type should be usable with UArray
> or IOUArray, and almost impossible to describe without QualifiedConstraints
> that it should be usable with STUArray. And it's actually impossible to use
> GeneralizedNewtypeDeriving to derive new instances of IArray or MArray. It
> also means that it's difficult to keep the three sets of instances in sync.
>
> Therefore, there should be (taking inspiration from primitive) a class
> that describes types which can be used in unboxed arrays. It'd be something
> along the lines of:
>
> class Unboxed e where
>   unsafeNewUArray :: Int# -> e -> State# s -> (# State# s,
> MutableByteArray# s #)
>   unsafeNewUArray_ :: Const (Int# -> State# s -> (# State# s,
> MutableByteArray# s #)) e
>   unsafeReadUArray :: MutableByteArray# s -> Int# -> State# s -> (# State#
> s, e #)
>   unsafeWriteUArray :: MutableByteArray# s -> Int# -> e -> State# s ->
> State# s
>   unsafeIndexUArray :: ByteArray# -> Int# -> e
>
> And then the instances for UArray, STUArray, and IOUArray would be:
>
> instance Unboxed e => IArray UArray e where ...
> instance Unboxed e => MArray IOUArray e IO where ...
> instance Unboxed e => MArray (STUArray s) e (ST s) where ...
>
> Incidentally, this also means it'd be less effort to add instances like
> Unboxed CInt, Unboxed a => Unboxed (Complex a), and Unboxed Ordering.
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