Type family equation violates injectivity?

Fri Jan 4 14:59:22 UTC 2019

For inline-r we have added a revision that sets upper limit, so now hackage
and stackage should both be happy. I'm not sure if any Linux distribution
provides inline-r as a package but that should be normal situation for
them. Next version will either set lower dependency boundary or will keep a
code that will run with both APIs. So from my perspective any solution
(even keeping things as-is) will be ok.

On Fri, Jan 4, 2019, 17:31 Carter Schonwald <carter.schonwald at gmail.com
wrote:

> Hrmmm.  Here’s what I’ll do: I’ll make the same release a minor version
> bump and make the bug fix bump version unbuildable.
>
> Would this help matters ?
>
> On Fri, Jan 4, 2019 at 9:23 AM Carter Schonwald <
> carter.schonwald at gmail.com> wrote:
>
>> Yeah, I later found it impacted one of my own pieces of code too, in that
>> I needed to make still further type families injective.
>>
>> I do think that a lot of vectors current module structure reflects a
>> desire for injectivity coupled with historical a lack of mechanism for
>> guaranteeing it.
>>
>> Mess up on my part for sure.  :)
>>
>> On Fri, Jan 4, 2019 at 8:11 AM Boespflug, Mathieu <m at tweag.io> wrote:
>>
>>> Hi Carter,
>>>
>>> thanks for looking into this. We were initially surprised to see a
>>> breaking change in a point release, but no biggy. It's pretty hard to offer
>>> strong stability guarantees without automated tooling to catch this kind of
>>> thing, and these things happen. We'll patch up HaskellR shortly.
>>>
>>> Best,
>>>
>>>
>>> On Sun, 30 Dec 2018 at 01:06, Carter Schonwald <
>>> carter.schonwald at gmail.com> wrote:
>>>
>>>> To be clear : I’m annoyed with myself that this impacted a package that
>>>> depends on vector, but this does seem to be the case that the newest bug
>>>> fix release for vector actually revealed a broken design for the vector
>>>> instances / data types in the inline-r package.
>>>>
>>>> To;dr — I suggest patching inline-r to remove the s parameter in its
>>>> immutable vector data types
>>>>
>>>> On Sat, Dec 29, 2018 at 6:48 PM Carter Schonwald <
>>>> carter.schonwald at gmail.com> wrote:
>>>>
>>>>> so i took a look .. (also the inline-r devs seem to have done a
>>>>> hackage revision so you wont hit that issue in your current setup if you do
>>>>> a cabal update ..)
>>>>> and it seems like the type definitions in inline-r are kinda bogus
>>>>> and you should get them patched ...
>>>>>
>>>>> the MVector type class, and related type families, all assume your
>>>>> mutable type has the last two arguments as the io/state token and then the
>>>>> element type
>>>>>
>>>>> eg
>>>>> basicLength :: v s a -> Int
>>>>> <http://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Int.html#t:Int>
>>>>>
>>>>>
>>>>> i looked at
>>>>> https://github.com/tweag/HaskellR/blob/1292c8a9562764d34ee4504b54d93248eb7346fe/inline-r/src/Data/Vector/SEXP.hs#L346-L374
>>>>> and
>>>>>
>>>>>
>>>>>
>>>>> as a point of grounding this chat
>>>>> the injective type familly in question is defined by the follwoing
>>>>>
>>>>>
>>>>> --#if MIN_VERSION_base(4,9,0)type family Mutable <http://hackage.haskell.org/package/vector-0.12.0.2/docs/src/Data.Vector.Generic.Base.html#Mutable> (v <http://hackage.haskell.org/package/vector-0.12.0.2/docs/src/Data.Vector.Generic.Base.html#local-6989586621679032525> :: * -> *) = (mv <http://hackage.haskell.org/package/vector-0.12.0.2/docs/src/Data.Vector.Generic.Base.html#local-6989586621679032526> :: * -> * -> *) | mv -> v#elsetype family Mutable (v :: * -> *) :: * -> * -> *#endif
>>>>>
>>>>> anyways, it looks like the Pure / immutable vector data type in
>>>>> inline-r has a spurious state token argument in its definition that
>>>>> shouldn't be there, OR there need to be two "s" params in inline-r instead
>>>>> of the one
>>>>>
>>>>> heres the full code i linked to in question
>>>>>
>>>>>
>>>>> -- | Mutable R vector. Represented in memory with the same header as
>>>>> 'SEXP'
>>>>>
>>>>> -- nodes. The second type parameter is phantom, reflecting at the type
>>>>> level the
>>>>> -- tag of the vector when viewed as a 'SEXP'. The tag of the vector
>>>>> and the
>>>>> -- representation type are related via 'ElemRep'.
>>>>> data MVector s ty a = MVector
>>>>> { mvectorBase :: {-# UNPACK #-} !(SEXP s ty)
>>>>> , mvectorOffset :: {-# UNPACK #-} !Int32
>>>>> , mvectorLength :: {-# UNPACK #-} !Int32
>>>>> }
>>>>> -- | Internal wrapper type for reflection. First type parameter is the
>>>>> reified
>>>>> -- type to reflect.
>>>>> newtype W t ty s a = W { unW :: MVector s ty a }
>>>>> instance (Reifies t (AcquireIO s), VECTOR s ty a) => G.MVector (W t
>>>>> ty) a where
>>>>>
>>>>> data Vector s (ty :: SEXPTYPE) a = Vector
>>>>>     { vectorBase :: {-# UNPACK #-} !(ForeignSEXP ty) , vectorOffset ::
>>>>> {-# UNPACK #-} !Int32 , vectorLength :: {-# UNPACK #-} !Int32
>>>>> }
>>>>>
>>>>>
>>>>> type instance G.Mutable (W t ty s) = Mutable.W t ty
>>>>> Anyways, the fix here is to remove the s param from the Pure version
>>>>> of W and "Sexp Vector"
>>>>>
>>>>>
>>>>>
>>>>> On Sat, Dec 29, 2018 at 6:16 PM Carter Schonwald <
>>>>> carter.schonwald at gmail.com> wrote:
>>>>>
>>>>>> were you using the same version of vector in both setups?
>>>>>>
>>>>>> in the most recent  vector release  we made mutable type family
>>>>>> injective in the vector package for ghc's that support it ...
>>>>>>
>>>>>> On Sat, Dec 29, 2018 at 1:50 PM Dominick Samperi <djsamperi at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> When I use v8.6.3 of GHC under Ubuntu to install the inline-r package
>>>>>>> I get the error "Type family equation violates injectivity
>>>>>>> annotation," and
>>>>>>> a type variable on the LHS cannot be inferred from the RHS, due to
>>>>>>> the lack of injectivity (I suppose).
>>>>>>>
>>>>>>> On the other hand, v8.0.2 of GHC (shipped with Haskell Platform under
>>>>>>> Ubuntu) does not have this problem (it has other problems).
>>>>>>>
>>>>>>> Has something changed in the latest version of the compiler that
>>>>>>> might
>>>>>>> cause this? Possible work-around?
>>>>>>>
>>>>>>> FYI, the line that triggers the error is:
>>>>>>> type instance G.Mutable (W t ty s) = Mutable.W t ty
>>>>>>>
>>>>>>> The variable that cannot be inferred is 's'.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Dominick
>>>>>>> _______________________________________________
>>>>>>> ghc-devs mailing list
>>>>>>> ghc-devs at haskell.org
>>>>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
>>>>>>>
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